clippy_utils/

lib.rs

#![cfg_attr(bootstrap, feature(unwrap_infallible))]
#![feature(deref_patterns)]
#![feature(macro_metavar_expr)]
#![feature(rustc_private)]
#![recursion_limit = "512"]
#![expect(clippy::missing_errors_doc, clippy::missing_panics_doc, clippy::must_use_candidate)]
#![warn(
    rust_2018_idioms,
    trivial_casts,
    trivial_numeric_casts,
    unused_lifetimes,
    unused_qualifications,
    rustc::internal
)]

// FIXME: switch to something more ergonomic here, once available.
// (Currently there is no way to opt into sysroot crates without `extern crate`.)
extern crate rustc_abi;
extern crate rustc_ast;
extern crate rustc_attr_ir;
extern crate rustc_attr_parsing;
extern crate rustc_const_eval;
extern crate rustc_data_structures;
#[expect(
    unused_extern_crates,
    reason = "The `rustc_driver` crate seems to be required in order to use the `rust_ast` crate."
)]
extern crate rustc_driver;
extern crate rustc_errors;
extern crate rustc_hir;
extern crate rustc_hir_analysis;
extern crate rustc_hir_typeck;
extern crate rustc_index;
extern crate rustc_infer;
extern crate rustc_lexer;
extern crate rustc_lint;
extern crate rustc_middle;
extern crate rustc_mir_dataflow;
extern crate rustc_session;
extern crate rustc_span;
extern crate rustc_trait_selection;

pub mod ast_utils;
#[deny(missing_docs)]
pub mod attrs;
mod check_proc_macro;
pub mod comparisons;
pub mod consts;
pub mod diagnostics;
pub mod eager_or_lazy;
pub mod higher;
mod hir_utils;
pub mod macros;
pub mod mir;
pub mod msrvs;
pub mod numeric_literal;
pub mod paths;
pub mod qualify_min_const_fn;
pub mod res;
pub mod source;
pub mod str_utils;
pub mod sugg;
pub mod sym;
pub mod ty;
pub mod usage;
pub mod visitors;

pub use self::attrs::*;
pub use self::check_proc_macro::{is_from_proc_macro, is_span_if, is_span_match};
pub use self::hir_utils::{
    HirEqInterExpr, SpanlessEq, SpanlessHash, both, count_eq, eq_expr_value, has_ambiguous_literal_in_expr, hash_expr,
    hash_stmt, is_bool, over,
};

use core::mem;
use core::ops::ControlFlow;
use std::collections::hash_map::Entry;
use std::iter::{once, repeat_n, zip};
use std::sync::{Mutex, OnceLock};

use itertools::Itertools as _;
use rustc_abi::Integer;
use rustc_ast::ast::{self, LitKind, RangeLimits};
use rustc_ast::{LitIntType, join_path_syms};
use rustc_attr_ir::lang_items::LangItem;
use rustc_attr_ir::lang_items::LangItem::{OptionNone, OptionSome, ResultErr, ResultOk};
use rustc_attr_ir::{CfgEntry, find_attr};
use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::indexmap;
use rustc_data_structures::packed::Pu128;
use rustc_data_structures::unhash::UnindexMap;
use rustc_hir::def::{DefKind, Res};
use rustc_hir::def_id::{DefId, LocalDefId, LocalModId};
use rustc_hir::definitions::{DefPath, DefPathData};
use rustc_hir::intravisit::{Visitor, walk_expr};
use rustc_hir::{
    self as hir, AnonConst, Arm, BindingMode, Block, BlockCheckMode, Body, ByRef, CRATE_HIR_ID, Closure, ConstArg,
    ConstArgKind, CoroutineDesugaring, CoroutineKind, CoroutineSource, Destination, Expr, ExprField, ExprKind,
    FieldDef, FnDecl, FnRetTy, GenericArg, GenericArgs, HirId, HirIdMap, HirIdSet, Impl, ImplItem, ImplItemKind, Item,
    ItemKind, LetStmt, MatchSource, Mutability, Node, OwnerId, OwnerNode, Param, Pat, PatExpr, PatExprKind, PatKind,
    Path, PathSegment, QPath, Stmt, StmtKind, TraitFn, TraitItem, TraitItemKind, TraitRef, TyKind, UnOp, Variant, def,
};
use rustc_lexer::{FrontmatterAllowed, TokenKind, tokenize};
use rustc_lint::{LateContext, Level, Lint, LintContext as _};
use rustc_middle::hir::nested_filter;
use rustc_middle::hir::place::PlaceBase;
use rustc_middle::mir::{AggregateKind, Operand, RETURN_PLACE, Rvalue, StatementKind, TerminatorKind};
use rustc_middle::ty::adjustment::{Adjust, Adjustment, AutoBorrow, DerefAdjustKind, PointerCoercion};
use rustc_middle::ty::layout::IntegerExt as _;
use rustc_middle::ty::{
    self as rustc_ty, Binder, BorrowKind, ClosureKind, EarlyBinder, GenericArgKind, GenericArgsRef, IntTy, Ty, TyCtxt,
    TypeFlags, TypeVisitableExt as _, TypeckResults, UintTy, UpvarCapture,
};
use rustc_session::config::Input;
use rustc_span::hygiene::{ExpnKind, MacroKind};
use rustc_span::source_map::SourceMap;
use rustc_span::symbol::{Ident, Symbol, kw};
use rustc_span::{InnerSpan, Span, SyntaxContext};
use source::{SpanExt as _, walk_span_to_context};
use visitors::{Visitable, for_each_unconsumed_temporary};

use crate::ast_utils::unordered_over;
use crate::higher::Range;
use crate::msrvs::Msrv;
use crate::res::{MaybeDef as _, MaybeResPath as _};
use crate::source::HasSourceMap;
use crate::ty::{adt_and_variant_of_res, can_partially_move_ty, expr_sig, is_copy, is_recursively_primitive_type};
use crate::visitors::for_each_expr_without_closures;

/// Methods on `Vec` that also exists on slices.
pub const VEC_METHODS_SHADOWING_SLICE_METHODS: [Symbol; 3] = [sym::as_ptr, sym::is_empty, sym::len];

#[macro_export]
macro_rules! extract_msrv_attr {
    () => {
        fn check_attributes(&mut self, cx: &rustc_lint::EarlyContext<'_>, attrs: &[rustc_ast::ast::Attribute]) {
            let sess = rustc_lint::LintContext::sess(cx);
            self.msrv.check_attributes(attrs);
        }

        fn check_attributes_post(&mut self, cx: &rustc_lint::EarlyContext<'_>, attrs: &[rustc_ast::ast::Attribute]) {
            let sess = rustc_lint::LintContext::sess(cx);
            self.msrv.check_attributes_post(attrs);
        }
    };
}

/// If the given expression is a local binding, find the initializer expression.
/// If that initializer expression is another local binding, find its initializer again.
///
/// This process repeats as long as possible (but usually no more than once). Initializer
/// expressions with adjustments are ignored. If this is not desired, use [`find_binding_init`]
/// instead.
///
/// Examples:
/// ```no_run
/// let abc = 1;
/// //        ^ output
/// let def = abc;
/// dbg!(def);
/// //   ^^^ input
///
/// // or...
/// let abc = 1;
/// let def = abc + 2;
/// //        ^^^^^^^ output
/// dbg!(def);
/// //   ^^^ input
/// ```
pub fn expr_or_init<'a, 'b, 'tcx: 'b>(cx: &LateContext<'tcx>, mut expr: &'a Expr<'b>) -> &'a Expr<'b> {
    while let Some(init) = expr
        .res_local_id()
        .and_then(|id| find_binding_init(cx, id))
        .filter(|init| cx.typeck_results().expr_adjustments(init).is_empty())
    {
        expr = init;
    }
    expr
}

/// Finds the initializer expression for a local binding. Returns `None` if the binding is mutable.
///
/// By only considering immutable bindings, we guarantee that the returned expression represents the
/// value of the binding wherever it is referenced.
///
/// Example: For `let x = 1`, if the `HirId` of `x` is provided, the `Expr` `1` is returned.
/// Note: If you have an expression that references a binding `x`, use `path_to_local` to get the
/// canonical binding `HirId`.
pub fn find_binding_init<'tcx>(cx: &LateContext<'tcx>, hir_id: HirId) -> Option<&'tcx Expr<'tcx>> {
    if let Node::Pat(pat) = cx.tcx.hir_node(hir_id)
        && matches!(pat.kind, PatKind::Binding(BindingMode::NONE, ..))
        && let Node::LetStmt(local) = cx.tcx.parent_hir_node(hir_id)
    {
        return local.init;
    }
    None
}

/// Checks if the given local has an initializer or is from something other than a `let` statement
///
/// e.g. returns true for `x` in `fn f(x: usize) { .. }` and `let x = 1;` but false for `let x;`
pub fn local_is_initialized(cx: &LateContext<'_>, local: HirId) -> bool {
    for (_, node) in cx.tcx.hir_parent_iter(local) {
        match node {
            Node::Pat(..) | Node::PatField(..) => {},
            Node::LetStmt(let_stmt) => return let_stmt.init.is_some(),
            _ => return true,
        }
    }

    false
}

/// Checks if we are currently in a const context (e.g. `const fn`, `static`/`const` initializer).
///
/// The current context is determined based on the current body which is set before calling a lint's
/// entry point (any function on `LateLintPass`). If you need to check in a different context use
/// `tcx.hir_is_inside_const_context(_)`.
///
/// Do not call this unless the `LateContext` has an enclosing body. For release build this case
/// will safely return `false`, but debug builds will ICE. Note that `check_expr`, `check_block`,
/// `check_pat` and a few other entry points will always have an enclosing body. Some entry points
/// like `check_path` or `check_ty` may or may not have one.
pub fn is_in_const_context(cx: &LateContext<'_>) -> bool {
    debug_assert!(cx.enclosing_body.is_some(), "`LateContext` has no enclosing body");
    cx.enclosing_body.is_some_and(|id| {
        cx.tcx
            .hir_body_const_context(cx.tcx.hir_body_owner_def_id(id))
            .is_some()
    })
}

/// Returns `true` if the given `HirId` is inside an always constant context.
///
/// This context includes:
///  * const/static items
///  * const blocks (or inline consts)
///  * associated constants
pub fn is_inside_always_const_context(tcx: TyCtxt<'_>, hir_id: HirId) -> bool {
    use rustc_hir::ConstContext::{Const, ConstFn, Static};
    let Some(ctx) = tcx.hir_body_const_context(tcx.hir_enclosing_body_owner(hir_id)) else {
        return false;
    };
    match ctx {
        ConstFn => false,
        Static(_)
        | Const {
            allow_const_fn_promotion: _,
        } => true,
    }
}

/// Checks if `{ctor_call_id}(...)` is `{enum_item}::{variant_name}(...)`.
pub fn is_enum_variant_ctor(
    cx: &LateContext<'_>,
    enum_item: Symbol,
    variant_name: Symbol,
    ctor_call_id: DefId,
) -> bool {
    let Some(enum_def_id) = cx.tcx.get_diagnostic_item(enum_item) else {
        return false;
    };

    let variants = cx.tcx.adt_def(enum_def_id).variants().iter();
    variants
        .filter(|variant| variant.name == variant_name)
        .filter_map(|variant| variant.ctor.as_ref())
        .any(|(_, ctor_def_id)| *ctor_def_id == ctor_call_id)
}

/// Checks if the `DefId` matches the given diagnostic item or it's constructor.
pub fn is_diagnostic_item_or_ctor(cx: &LateContext<'_>, did: DefId, item: Symbol) -> bool {
    let did = match cx.tcx.def_kind(did) {
        DefKind::Ctor(..) => cx.tcx.parent(did),
        // Constructors for types in external crates seem to have `DefKind::Variant`
        DefKind::Variant => match cx.tcx.opt_parent(did) {
            Some(did) if matches!(cx.tcx.def_kind(did), DefKind::Variant) => did,
            _ => did,
        },
        _ => did,
    };

    cx.tcx.is_diagnostic_item(item, did)
}

/// Checks if the `DefId` matches the given `LangItem` or it's constructor.
pub fn is_lang_item_or_ctor(cx: &LateContext<'_>, did: DefId, item: LangItem) -> bool {
    let did = match cx.tcx.def_kind(did) {
        DefKind::Ctor(..) => cx.tcx.parent(did),
        // Constructors for types in external crates seem to have `DefKind::Variant`
        DefKind::Variant => match cx.tcx.opt_parent(did) {
            Some(did) if matches!(cx.tcx.def_kind(did), DefKind::Variant) => did,
            _ => did,
        },
        _ => did,
    };

    cx.tcx.lang_items().get(item) == Some(did)
}

/// Checks is `expr` is `None`
pub fn is_none_expr(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
    expr.basic_res().ctor_parent(cx).is_lang_item(cx, OptionNone)
}

/// If `expr` is `Some(inner)`, returns `inner`
pub fn as_some_expr<'tcx>(cx: &LateContext<'_>, expr: &'tcx Expr<'tcx>) -> Option<&'tcx Expr<'tcx>> {
    if let ExprKind::Call(e, [arg]) = expr.kind
        && e.basic_res().ctor_parent(cx).is_lang_item(cx, OptionSome)
    {
        Some(arg)
    } else {
        None
    }
}

/// Check if the given `Expr` is an empty block (i.e. `{}`) or not.
pub fn is_empty_block(expr: &Expr<'_>) -> bool {
    matches!(
        expr.kind,
        ExprKind::Block(
            Block {
                stmts: [],
                expr: None,
                ..
            },
            _,
        )
    )
}

/// Checks if `expr` is an empty block or an empty tuple.
pub fn is_unit_expr(expr: &Expr<'_>) -> bool {
    matches!(
        expr.kind,
        ExprKind::Block(
            Block {
                stmts: [],
                expr: None,
                ..
            },
            _
        ) | ExprKind::Tup([])
    )
}

/// Checks if given pattern is a wildcard (`_`)
pub fn is_wild(pat: &Pat<'_>) -> bool {
    matches!(pat.kind, PatKind::Wild)
}

/// If `pat` is:
/// - `Some(inner)`, returns `inner`
///    - it will _usually_ contain just one element, but could have two, given patterns like `Some(inner, ..)` or
///      `Some(.., inner)`
/// - `Some`, returns `[]`
/// - otherwise, returns `None`
pub fn as_some_pattern<'a, 'hir>(cx: &LateContext<'_>, pat: &'a Pat<'hir>) -> Option<&'a [Pat<'hir>]> {
    if let PatKind::TupleStruct(ref qpath, inner, _) = pat.kind
        && cx
            .qpath_res(qpath, pat.hir_id)
            .ctor_parent(cx)
            .is_lang_item(cx, OptionSome)
    {
        Some(inner)
    } else {
        None
    }
}

/// Checks if the `pat` is `None`.
pub fn is_none_pattern(cx: &LateContext<'_>, pat: &Pat<'_>) -> bool {
    matches!(pat.kind,
        PatKind::Expr(PatExpr { kind: PatExprKind::Path(qpath), .. })
            if cx.qpath_res(qpath, pat.hir_id).ctor_parent(cx).is_lang_item(cx, OptionNone))
}

/// Checks if `arm` has the form `None => None`.
pub fn is_none_arm(cx: &LateContext<'_>, arm: &Arm<'_>) -> bool {
    is_none_pattern(cx, arm.pat)
        && matches!(
            peel_blocks(arm.body).kind,
            ExprKind::Path(qpath)
            if cx.qpath_res(&qpath, arm.body.hir_id).ctor_parent(cx).is_lang_item(cx, OptionNone)
        )
}

/// Checks if the given `QPath` belongs to a type alias.
pub fn is_ty_alias(qpath: &QPath<'_>) -> bool {
    match *qpath {
        QPath::Resolved(_, path) => matches!(path.res, Res::Def(DefKind::TyAlias | DefKind::AssocTy, ..)),
        QPath::TypeRelative(ty, _) if let TyKind::Path(qpath) = ty.kind => is_ty_alias(&qpath),
        QPath::TypeRelative(..) => false,
    }
}

/// Checks if the `def_id` belongs to a function that is part of a trait impl.
pub fn is_def_id_trait_method(cx: &LateContext<'_>, def_id: LocalDefId) -> bool {
    if let Node::Item(item) = cx.tcx.parent_hir_node(cx.tcx.local_def_id_to_hir_id(def_id))
        && let ItemKind::Impl(imp) = item.kind
    {
        imp.of_trait.is_some()
    } else {
        false
    }
}

pub fn last_path_segment<'tcx>(path: &QPath<'tcx>) -> &'tcx PathSegment<'tcx> {
    match *path {
        QPath::Resolved(_, path) => path.segments.last().expect("A path must have at least one segment"),
        QPath::TypeRelative(_, seg) => seg,
    }
}

pub fn qpath_generic_tys<'tcx>(qpath: &QPath<'tcx>) -> impl Iterator<Item = &'tcx hir::Ty<'tcx>> {
    last_path_segment(qpath)
        .args
        .map_or(&[][..], |a| a.args)
        .iter()
        .filter_map(|a| match a {
            GenericArg::Type(ty) => Some(ty.as_unambig_ty()),
            _ => None,
        })
}

/// If the expression is a path to a local (with optional projections),
/// returns the canonical `HirId` of the local.
///
/// For example, `x.field[0].field2` would return the `HirId` of `x`.
pub fn path_to_local_with_projections(expr: &Expr<'_>) -> Option<HirId> {
    match expr.kind {
        ExprKind::Field(recv, _) | ExprKind::Index(recv, _, _) => path_to_local_with_projections(recv),
        ExprKind::Path(QPath::Resolved(
            _,
            Path {
                res: Res::Local(local), ..
            },
        )) => Some(*local),
        _ => None,
    }
}

/// Gets the `hir::TraitRef` of the trait the given method is implemented for.
///
/// Use this if you want to find the `TraitRef` of the `Add` trait in this example:
///
/// ```no_run
/// struct Point(isize, isize);
///
/// impl std::ops::Add for Point {
///     type Output = Self;
///
///     fn add(self, other: Self) -> Self {
///         Point(0, 0)
///     }
/// }
/// ```
pub fn trait_ref_of_method<'tcx>(cx: &LateContext<'tcx>, owner: OwnerId) -> Option<&'tcx TraitRef<'tcx>> {
    if let Node::Item(item) = cx.tcx.hir_node(cx.tcx.hir_owner_parent(owner))
        && let ItemKind::Impl(impl_) = &item.kind
        && let Some(of_trait) = impl_.of_trait
    {
        return Some(&of_trait.trait_ref);
    }
    None
}

/// This method will return tuple of projection stack and root of the expression,
/// used in `can_mut_borrow_both`.
///
/// For example, if `e` represents the `v[0].a.b[x]`
/// this method will return a tuple, composed of a `Vec`
/// containing the `Expr`s for `v[0], v[0].a, v[0].a.b, v[0].a.b[x]`
/// and an `Expr` for root of them, `v`
fn projection_stack<'a, 'hir>(
    mut e: &'a Expr<'hir>,
    ctxt: SyntaxContext,
) -> Option<(Vec<&'a Expr<'hir>>, &'a Expr<'hir>)> {
    let mut result = vec![];
    let root = loop {
        match e.kind {
            ExprKind::Index(ep, _, _) | ExprKind::Field(ep, _) if e.span.ctxt() == ctxt => {
                result.push(e);
                e = ep;
            },
            ExprKind::Index(..) | ExprKind::Field(..) => return None,
            _ => break e,
        }
    };
    result.reverse();
    Some((result, root))
}

/// Gets the mutability of the custom deref adjustment, if any.
pub fn expr_custom_deref_adjustment(cx: &LateContext<'_>, e: &Expr<'_>) -> Option<Mutability> {
    cx.typeck_results()
        .expr_adjustments(e)
        .iter()
        .find_map(|a| match a.kind {
            Adjust::Deref(DerefAdjustKind::Overloaded(d)) => Some(Some(d.mutbl)),
            Adjust::Deref(DerefAdjustKind::Builtin) => None,
            _ => Some(None),
        })
        .and_then(|x| x)
}

/// Checks if two expressions can be mutably borrowed simultaneously
/// and they aren't dependent on borrowing same thing twice
pub fn can_mut_borrow_both(cx: &LateContext<'_>, ctxt: SyntaxContext, e1: &Expr<'_>, e2: &Expr<'_>) -> bool {
    let Some((s1, r1)) = projection_stack(e1, ctxt) else {
        return false;
    };
    let Some((s2, r2)) = projection_stack(e2, ctxt) else {
        return false;
    };
    if !eq_expr_value(cx, ctxt, r1, r2) {
        return true;
    }
    if expr_custom_deref_adjustment(cx, r1).is_some() || expr_custom_deref_adjustment(cx, r2).is_some() {
        return false;
    }

    for (x1, x2) in zip(&s1, &s2) {
        if expr_custom_deref_adjustment(cx, x1).is_some() || expr_custom_deref_adjustment(cx, x2).is_some() {
            return false;
        }

        match (&x1.kind, &x2.kind) {
            (ExprKind::Field(_, i1), ExprKind::Field(_, i2)) => {
                if i1 != i2 {
                    return true;
                }
            },
            _ => return false,
        }
    }
    false
}

/// Returns true if the `def_id` associated with the `path` is recognized as a "default-equivalent"
/// constructor from the std library
fn is_default_equivalent_ctor(cx: &LateContext<'_>, def_id: DefId, path: &QPath<'_>) -> bool {
    let std_types_symbols = &[
        sym::Vec,
        sym::VecDeque,
        sym::LinkedList,
        sym::HashMap,
        sym::BTreeMap,
        sym::HashSet,
        sym::BTreeSet,
        sym::BinaryHeap,
    ];

    if let QPath::TypeRelative(_, method) = path
        && method.ident.name == sym::new
        && let Some(impl_did) = cx.tcx.impl_of_assoc(def_id)
        && let Some(adt) = cx
            .tcx
            .type_of(impl_did)
            .instantiate_identity()
            .skip_norm_wip()
            .ty_adt_def()
    {
        return Some(adt.did()) == cx.tcx.lang_items().string()
            || (cx.tcx.get_diagnostic_name(adt.did())).is_some_and(|adt_name| std_types_symbols.contains(&adt_name));
    }
    false
}

/// Returns true if the expr is equal to `Default::default` when evaluated.
pub fn is_default_equivalent_call(
    cx: &LateContext<'_>,
    repl_func: &Expr<'_>,
    whole_call_expr: Option<&Expr<'_>>,
) -> bool {
    if let ExprKind::Path(ref repl_func_qpath) = repl_func.kind
        && let Some(repl_def) = cx.qpath_res(repl_func_qpath, repl_func.hir_id).opt_def(cx)
        && (repl_def.assoc_fn_parent(cx).is_diag_item(cx, sym::Default)
            || is_default_equivalent_ctor(cx, repl_def.1, repl_func_qpath))
    {
        return true;
    }

    // Get the type of the whole method call expression, find the exact method definition, look at
    // its body and check if it is similar to the corresponding `Default::default()` body.
    let Some(e) = whole_call_expr else { return false };
    let Some(default_fn_def_id) = cx.tcx.get_diagnostic_item(sym::default_fn) else {
        return false;
    };
    let Some(ty) = cx.tcx.typeck(e.hir_id.owner.def_id).expr_ty_adjusted_opt(e) else {
        return false;
    };
    let args = rustc_ty::GenericArgs::for_item(cx.tcx, default_fn_def_id, |param, _| {
        if let rustc_ty::GenericParamDefKind::Lifetime = param.kind {
            cx.tcx.lifetimes.re_erased.into()
        } else if param.index == 0 && param.name == kw::SelfUpper {
            ty.into()
        } else {
            param.to_error(cx.tcx)
        }
    });
    let instance = rustc_ty::Instance::try_resolve(cx.tcx, cx.typing_env(), default_fn_def_id, args);

    let Ok(Some(instance)) = instance else { return false };
    if let rustc_ty::InstanceKind::Item(def) = instance.def
        && !cx.tcx.is_mir_available(def)
    {
        return false;
    }
    let ExprKind::Path(ref repl_func_qpath) = repl_func.kind else {
        return false;
    };
    let Some(repl_def_id) = cx.qpath_res(repl_func_qpath, repl_func.hir_id).opt_def_id() else {
        return false;
    };

    // Get the MIR Body for the `<Ty as Default>::default()` function.
    // If it is a value or call (either fn or ctor), we compare its `DefId` against the one for the
    // resolution of the expression we had in the path. This lets us identify, for example, that
    // the body of `<Vec<T> as Default>::default()` is a `Vec::new()`, and the field was being
    // initialized to `Vec::new()` as well.
    let body = cx.tcx.instance_mir(instance.def);
    for block_data in body.basic_blocks.iter() {
        if block_data.statements.len() == 1
            && let StatementKind::Assign(assign) = &block_data.statements[0].kind
            && assign.0.local == RETURN_PLACE
            && let Rvalue::Aggregate(kind, _places) = &assign.1
            && let AggregateKind::Adt(did, variant_index, _, _, _) = **kind
            && let def = cx.tcx.adt_def(did)
            && let variant = &def.variant(variant_index)
            && variant.fields.is_empty()
            && let Some((_, did)) = variant.ctor
            && did == repl_def_id
        {
            return true;
        } else if block_data.statements.is_empty()
            && let Some(term) = &block_data.terminator
        {
            match &term.kind {
                TerminatorKind::Call {
                    func: Operand::Constant(c),
                    ..
                } if let rustc_ty::FnDef(did, _args) = c.ty().kind()
                    && *did == repl_def_id =>
                {
                    return true;
                },
                TerminatorKind::TailCall {
                    func: Operand::Constant(c),
                    ..
                } if let rustc_ty::FnDef(did, _args) = c.ty().kind()
                    && *did == repl_def_id =>
                {
                    return true;
                },
                _ => {},
            }
        }
    }
    false
}

/// Returns true if the expr is equal to `Default::default()` of its type when evaluated.
///
/// It doesn't cover all cases, like struct literals, but it is a close approximation.
pub fn is_default_equivalent(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
    match &e.kind {
        ExprKind::Lit(lit) => match lit.node {
            LitKind::Bool(false) | LitKind::Int(Pu128(0), _) => true,
            LitKind::Str(s, _) => s.is_empty(),
            _ => false,
        },
        ExprKind::Tup(items) | ExprKind::Array(items) => items.iter().all(|x| is_default_equivalent(cx, x)),
        ExprKind::Repeat(x, len) => {
            if let ConstArgKind::Anon(anon_const) = len.kind
                && let ExprKind::Lit(const_lit) = cx.tcx.hir_body(anon_const.body).value.kind
                && let LitKind::Int(v, _) = const_lit.node
                && v <= 32
                && is_default_equivalent(cx, x)
            {
                true
            } else {
                false
            }
        },
        ExprKind::Call(repl_func, []) => is_default_equivalent_call(cx, repl_func, Some(e)),
        ExprKind::Call(from_func, [arg]) => is_default_equivalent_from(cx, from_func, arg),
        ExprKind::Path(qpath) => cx
            .qpath_res(qpath, e.hir_id)
            .ctor_parent(cx)
            .is_lang_item(cx, OptionNone),
        ExprKind::AddrOf(rustc_hir::BorrowKind::Ref, _, expr) => matches!(expr.kind, ExprKind::Array([])),
        ExprKind::Block(Block { stmts: [], expr, .. }, _) => expr.is_some_and(|e| is_default_equivalent(cx, e)),
        _ => false,
    }
}

fn is_default_equivalent_from(cx: &LateContext<'_>, from_func: &Expr<'_>, arg: &Expr<'_>) -> bool {
    if let ExprKind::Path(QPath::TypeRelative(ty, seg)) = from_func.kind
        && seg.ident.name == sym::from
    {
        match arg.kind {
            ExprKind::Lit(hir::Lit {
                node: LitKind::Str(sym, _),
                ..
            }) => return sym.is_empty() && ty.basic_res().is_lang_item(cx, LangItem::String),
            ExprKind::Array([]) => return ty.basic_res().is_diag_item(cx, sym::Vec),
            ExprKind::Repeat(_, len) => {
                if let ConstArgKind::Anon(anon_const) = len.kind
                    && let ExprKind::Lit(const_lit) = cx.tcx.hir_body(anon_const.body).value.kind
                    && let LitKind::Int(v, _) = const_lit.node
                {
                    return v == 0 && ty.basic_res().is_diag_item(cx, sym::Vec);
                }
            },
            _ => (),
        }
    }
    false
}

/// Checks if the top level expression can be moved into a closure as is.
/// Currently checks for:
/// * Break/Continue outside the given loop HIR ids.
/// * Yield/Return statements.
/// * Inline assembly.
/// * Usages of a field of a local where the type of the local can be partially moved.
///
/// For example, given the following function:
///
/// ```no_run
/// fn f<'a>(iter: &mut impl Iterator<Item = (usize, &'a mut String)>) {
///     for item in iter {
///         let s = item.1;
///         if item.0 > 10 {
///             continue;
///         } else {
///             s.clear();
///         }
///     }
/// }
/// ```
///
/// When called on the expression `item.0` this will return false unless the local `item` is in the
/// `ignore_locals` set. The type `(usize, &mut String)` can have the second element moved, so it
/// isn't always safe to move into a closure when only a single field is needed.
///
/// When called on the `continue` expression this will return false unless the outer loop expression
/// is in the `loop_ids` set.
///
/// Note that this check is not recursive, so passing the `if` expression will always return true
/// even though sub-expressions might return false.
pub fn can_move_expr_to_closure_no_visit<'tcx>(
    cx: &LateContext<'tcx>,
    expr: &'tcx Expr<'_>,
    loop_ids: &[HirId],
    ignore_locals: &HirIdSet,
) -> bool {
    match expr.kind {
        ExprKind::Break(Destination { target_id: Ok(id), .. }, _)
        | ExprKind::Continue(Destination { target_id: Ok(id), .. })
            if loop_ids.contains(&id) =>
        {
            true
        },
        ExprKind::Break(..)
        | ExprKind::Continue(_)
        | ExprKind::Ret(_)
        | ExprKind::Yield(..)
        | ExprKind::InlineAsm(_) => false,
        // Accessing a field of a local value can only be done if the type isn't
        // partially moved.
        ExprKind::Field(
            &Expr {
                hir_id,
                kind:
                    ExprKind::Path(QPath::Resolved(
                        _,
                        Path {
                            res: Res::Local(local_id),
                            ..
                        },
                    )),
                ..
            },
            _,
        ) if !ignore_locals.contains(local_id) && can_partially_move_ty(cx, cx.typeck_results().node_type(hir_id)) => {
            // TODO: check if the local has been partially moved. Assume it has for now.
            false
        },
        _ => true,
    }
}

/// How a local is captured by a closure
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum CaptureKind {
    Value,
    Use,
    Ref(Mutability),
}
impl CaptureKind {
    pub fn is_imm_ref(self) -> bool {
        self == Self::Ref(Mutability::Not)
    }
}
impl std::ops::BitOr for CaptureKind {
    type Output = Self;
    fn bitor(self, rhs: Self) -> Self::Output {
        match (self, rhs) {
            (CaptureKind::Value, _) | (_, CaptureKind::Value) => CaptureKind::Value,
            (CaptureKind::Use, _) | (_, CaptureKind::Use) => CaptureKind::Use,
            (CaptureKind::Ref(Mutability::Mut), CaptureKind::Ref(_))
            | (CaptureKind::Ref(_), CaptureKind::Ref(Mutability::Mut)) => CaptureKind::Ref(Mutability::Mut),
            (CaptureKind::Ref(Mutability::Not), CaptureKind::Ref(Mutability::Not)) => CaptureKind::Ref(Mutability::Not),
        }
    }
}
impl std::ops::BitOrAssign for CaptureKind {
    fn bitor_assign(&mut self, rhs: Self) {
        *self = *self | rhs;
    }
}

/// Given an expression referencing a local, determines how it would be captured in a closure.
///
/// Note as this will walk up to parent expressions until the capture can be determined it should
/// only be used while making a closure somewhere a value is consumed. e.g. a block, match arm, or
/// function argument (other than a receiver).
pub fn capture_local_usage(cx: &LateContext<'_>, e: &Expr<'_>) -> CaptureKind {
    fn pat_capture_kind(cx: &LateContext<'_>, pat: &Pat<'_>) -> CaptureKind {
        let mut capture = CaptureKind::Ref(Mutability::Not);
        pat.each_binding_or_first(&mut |_, id, span, _| match cx
            .typeck_results()
            .extract_binding_mode(cx.sess(), id, span)
            .0
        {
            ByRef::No if !is_copy(cx, cx.typeck_results().node_type(id)) => {
                capture = CaptureKind::Value;
            },
            ByRef::Yes(_, Mutability::Mut) if capture != CaptureKind::Value => {
                capture = CaptureKind::Ref(Mutability::Mut);
            },
            _ => (),
        });
        capture
    }

    debug_assert!(matches!(
        e.kind,
        ExprKind::Path(QPath::Resolved(None, Path { res: Res::Local(_), .. }))
    ));

    let mut capture = CaptureKind::Value;
    let mut capture_expr_ty = e;

    for (parent, child_id) in hir_parent_with_src_iter(cx.tcx, e.hir_id) {
        if let [
            Adjustment {
                kind: Adjust::Deref(_) | Adjust::Borrow(AutoBorrow::Ref(..)),
                target,
            },
            ref adjust @ ..,
        ] = *cx
            .typeck_results()
            .adjustments()
            .get(child_id)
            .map_or(&[][..], |x| &**x)
            && let rustc_ty::RawPtr(_, mutability) | rustc_ty::Ref(_, _, mutability) =
                *adjust.last().map_or(target, |a| a.target).kind()
        {
            return CaptureKind::Ref(mutability);
        }

        match parent {
            Node::Expr(e) => match e.kind {
                ExprKind::AddrOf(_, mutability, _) => return CaptureKind::Ref(mutability),
                ExprKind::Index(..) | ExprKind::Unary(UnOp::Deref, _) => capture = CaptureKind::Ref(Mutability::Not),
                ExprKind::Assign(lhs, ..) | ExprKind::AssignOp(_, lhs, _) if lhs.hir_id == child_id => {
                    return CaptureKind::Ref(Mutability::Mut);
                },
                ExprKind::Field(..) => {
                    if capture == CaptureKind::Value {
                        capture_expr_ty = e;
                    }
                },
                ExprKind::Let(let_expr) => {
                    let mutability = match pat_capture_kind(cx, let_expr.pat) {
                        CaptureKind::Value | CaptureKind::Use => Mutability::Not,
                        CaptureKind::Ref(m) => m,
                    };
                    return CaptureKind::Ref(mutability);
                },
                ExprKind::Match(_, arms, _) => {
                    let mut mutability = Mutability::Not;
                    for capture in arms.iter().map(|arm| pat_capture_kind(cx, arm.pat)) {
                        match capture {
                            CaptureKind::Value | CaptureKind::Use => break,
                            CaptureKind::Ref(Mutability::Mut) => mutability = Mutability::Mut,
                            CaptureKind::Ref(Mutability::Not) => (),
                        }
                    }
                    return CaptureKind::Ref(mutability);
                },
                _ => break,
            },
            Node::LetStmt(l) => match pat_capture_kind(cx, l.pat) {
                CaptureKind::Value | CaptureKind::Use => break,
                capture @ CaptureKind::Ref(_) => return capture,
            },
            _ => break,
        }
    }

    if capture == CaptureKind::Value && is_copy(cx, cx.typeck_results().expr_ty(capture_expr_ty)) {
        // Copy types are never automatically captured by value.
        CaptureKind::Ref(Mutability::Not)
    } else {
        capture
    }
}

/// Checks if the expression can be moved into a closure as is. This will return a list of captures
/// if so, otherwise, `None`.
pub fn can_move_expr_to_closure<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<HirIdMap<CaptureKind>> {
    struct V<'cx, 'tcx> {
        cx: &'cx LateContext<'tcx>,
        // Stack of potential break targets contained in the expression.
        loops: Vec<HirId>,
        /// Local variables created in the expression. These don't need to be captured.
        locals: HirIdSet,
        /// Whether this expression can be turned into a closure.
        allow_closure: bool,
        /// Locals which need to be captured, and whether they need to be by value, reference, or
        /// mutable reference.
        captures: HirIdMap<CaptureKind>,
    }
    impl<'tcx> Visitor<'tcx> for V<'_, 'tcx> {
        fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
            if !self.allow_closure {
                return;
            }

            match e.kind {
                ExprKind::Path(QPath::Resolved(None, &Path { res: Res::Local(l), .. })) => {
                    if !self.locals.contains(&l) {
                        let cap = capture_local_usage(self.cx, e);
                        self.captures.entry(l).and_modify(|e| *e |= cap).or_insert(cap);
                    }
                },
                ExprKind::Closure(closure) => {
                    for capture in self.cx.typeck_results().closure_min_captures_flattened(closure.def_id) {
                        let local_id = match capture.place.base {
                            PlaceBase::Local(id) => id,
                            PlaceBase::Upvar(var) => var.var_path.hir_id,
                            _ => continue,
                        };
                        if !self.locals.contains(&local_id) {
                            let capture = match capture.info.capture_kind {
                                UpvarCapture::ByValue => CaptureKind::Value,
                                UpvarCapture::ByUse => CaptureKind::Use,
                                UpvarCapture::ByRef(kind) => match kind {
                                    BorrowKind::Immutable => CaptureKind::Ref(Mutability::Not),
                                    BorrowKind::UniqueImmutable | BorrowKind::Mutable => {
                                        CaptureKind::Ref(Mutability::Mut)
                                    },
                                },
                            };
                            self.captures
                                .entry(local_id)
                                .and_modify(|e| *e |= capture)
                                .or_insert(capture);
                        }
                    }
                },
                ExprKind::Loop(b, ..) => {
                    self.loops.push(e.hir_id);
                    self.visit_block(b);
                    self.loops.pop();
                },
                _ => {
                    self.allow_closure &= can_move_expr_to_closure_no_visit(self.cx, e, &self.loops, &self.locals);
                    walk_expr(self, e);
                },
            }
        }

        fn visit_pat(&mut self, p: &'tcx Pat<'tcx>) {
            p.each_binding_or_first(&mut |_, id, _, _| {
                self.locals.insert(id);
            });
        }
    }

    let mut v = V {
        cx,
        loops: Vec::new(),
        locals: HirIdSet::default(),
        allow_closure: true,
        captures: HirIdMap::default(),
    };
    v.visit_expr(expr);
    v.allow_closure.then_some(v.captures)
}

/// Arguments of a method: the receiver and all the additional arguments.
pub type MethodArguments<'tcx> = Vec<(&'tcx Expr<'tcx>, &'tcx [Expr<'tcx>])>;

/// Returns the method names and argument list of nested method call expressions that make up
/// `expr`. method/span lists are sorted with the most recent call first.
pub fn method_calls<'tcx>(expr: &'tcx Expr<'tcx>, max_depth: usize) -> (Vec<Symbol>, MethodArguments<'tcx>, Vec<Span>) {
    let mut method_names = Vec::with_capacity(max_depth);
    let mut arg_lists = Vec::with_capacity(max_depth);
    let mut spans = Vec::with_capacity(max_depth);

    let mut current = expr;
    for _ in 0..max_depth {
        if let ExprKind::MethodCall(path, receiver, args, _) = &current.kind {
            if receiver.span.from_expansion() || args.iter().any(|e| e.span.from_expansion()) {
                break;
            }
            method_names.push(path.ident.name);
            arg_lists.push((*receiver, &**args));
            spans.push(path.ident.span);
            current = receiver;
        } else {
            break;
        }
    }

    (method_names, arg_lists, spans)
}

/// Matches an `Expr` against a chain of methods, and return the matched `Expr`s.
///
/// For example, if `expr` represents the `.baz()` in `foo.bar().baz()`,
/// `method_chain_args(expr, &[sym::bar, sym::baz])` will return a `Vec`
/// containing the `Expr`s for
/// `.bar()` and `.baz()`
pub fn method_chain_args<'a>(expr: &'a Expr<'_>, methods: &[Symbol]) -> Option<Vec<(&'a Expr<'a>, &'a [Expr<'a>])>> {
    let mut current = expr;
    let mut matched = Vec::with_capacity(methods.len());
    for method_name in methods.iter().rev() {
        // method chains are stored last -> first
        if let ExprKind::MethodCall(path, receiver, args, _) = current.kind {
            if path.ident.name == *method_name {
                if receiver.span.from_expansion() || args.iter().any(|e| e.span.from_expansion()) {
                    return None;
                }
                matched.push((receiver, args)); // build up `matched` backwards
                current = receiver; // go to parent expression
            } else {
                return None;
            }
        } else {
            return None;
        }
    }
    // Reverse `matched` so that it is in the same order as `methods`.
    matched.reverse();
    Some(matched)
}

/// Returns `true` if the provided `def_id` is an entrypoint to a program.
pub fn is_entrypoint_fn(cx: &LateContext<'_>, def_id: DefId) -> bool {
    cx.tcx
        .entry_fn(())
        .is_some_and(|(entry_fn_def_id, _)| def_id == entry_fn_def_id)
}

/// Returns `true` if the expression is in the program's `#[panic_handler]`.
pub fn is_in_panic_handler(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
    let parent = cx.tcx.hir_get_parent_item(e.hir_id);
    Some(parent.to_def_id()) == cx.tcx.lang_items().panic_impl()
}

/// Gets the name of the item the expression is in, if available.
pub fn parent_item_name(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<Symbol> {
    let parent_id = cx.tcx.hir_get_parent_item(expr.hir_id).def_id;
    match cx.tcx.hir_node_by_def_id(parent_id) {
        Node::Item(item) => item.kind.ident().map(|ident| ident.name),
        Node::TraitItem(TraitItem { ident, .. }) | Node::ImplItem(ImplItem { ident, .. }) => Some(ident.name),
        _ => None,
    }
}

pub struct ContainsName<'a, 'tcx> {
    pub cx: &'a LateContext<'tcx>,
    pub name: Symbol,
}

impl<'tcx> Visitor<'tcx> for ContainsName<'_, 'tcx> {
    type Result = ControlFlow<()>;
    type NestedFilter = nested_filter::OnlyBodies;

    fn visit_name(&mut self, name: Symbol) -> Self::Result {
        if self.name == name {
            ControlFlow::Break(())
        } else {
            ControlFlow::Continue(())
        }
    }

    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
        self.cx.tcx
    }
}

/// Checks if an `Expr` contains a certain name.
pub fn contains_name<'tcx>(name: Symbol, expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) -> bool {
    let mut cn = ContainsName { cx, name };
    cn.visit_expr(expr).is_break()
}

/// Returns `true` if `expr` contains a return expression
pub fn contains_return<'tcx>(expr: impl Visitable<'tcx>) -> bool {
    for_each_expr_without_closures(expr, |e| {
        if matches!(e.kind, ExprKind::Ret(..)) {
            ControlFlow::Break(())
        } else {
            ControlFlow::Continue(())
        }
    })
    .is_some()
}

/// Gets the parent expression, if any –- this is useful to constrain a lint.
pub fn get_parent_expr<'tcx>(cx: &LateContext<'tcx>, e: &Expr<'_>) -> Option<&'tcx Expr<'tcx>> {
    get_parent_expr_for_hir(cx, e.hir_id)
}

/// This retrieves the parent for the given `HirId` if it's an expression. This is useful for
/// constraint lints
pub fn get_parent_expr_for_hir<'tcx>(cx: &LateContext<'tcx>, hir_id: HirId) -> Option<&'tcx Expr<'tcx>> {
    match cx.tcx.parent_hir_node(hir_id) {
        Node::Expr(parent) => Some(parent),
        _ => None,
    }
}

/// Gets the enclosing block, if any.
pub fn get_enclosing_block<'tcx>(cx: &LateContext<'tcx>, hir_id: HirId) -> Option<&'tcx Block<'tcx>> {
    let enclosing_node = cx
        .tcx
        .hir_get_enclosing_scope(hir_id)
        .map(|enclosing_id| cx.tcx.hir_node(enclosing_id));
    enclosing_node.and_then(|node| match node {
        Node::Block(block) => Some(block),
        Node::Item(&Item {
            kind: ItemKind::Fn { body: eid, .. },
            ..
        })
        | Node::ImplItem(&ImplItem {
            kind: ImplItemKind::Fn(_, eid),
            ..
        })
        | Node::TraitItem(&TraitItem {
            kind: TraitItemKind::Fn(_, TraitFn::Provided(eid)),
            ..
        }) => match cx.tcx.hir_body(eid).value.kind {
            ExprKind::Block(block, _) => Some(block),
            _ => None,
        },
        _ => None,
    })
}

/// Returns the [`Closure`] enclosing `hir_id`, if any.
pub fn get_enclosing_closure<'tcx>(cx: &LateContext<'tcx>, hir_id: HirId) -> Option<&'tcx Closure<'tcx>> {
    cx.tcx.hir_parent_iter(hir_id).find_map(|(_, node)| {
        if let Node::Expr(expr) = node
            && let ExprKind::Closure(closure) = expr.kind
        {
            Some(closure)
        } else {
            None
        }
    })
}

/// Checks whether a local identified by `local_id` is captured as an upvar by the given `closure`.
pub fn is_upvar_in_closure(cx: &LateContext<'_>, closure: &Closure<'_>, local_id: HirId) -> bool {
    cx.typeck_results()
        .closure_min_captures
        .get(&closure.def_id)
        .is_some_and(|x| x.contains_key(&local_id))
}

/// Gets the loop or closure enclosing the given expression, if any.
pub fn get_enclosing_loop_or_multi_call_closure<'tcx>(
    cx: &LateContext<'tcx>,
    expr: &Expr<'_>,
) -> Option<&'tcx Expr<'tcx>> {
    for (_, node) in cx.tcx.hir_parent_iter(expr.hir_id) {
        match node {
            Node::Expr(e) => match e.kind {
                ExprKind::Closure { .. }
                    if let rustc_ty::Closure(_, subs) = cx.typeck_results().expr_ty(e).kind()
                        && subs.as_closure().kind() == ClosureKind::FnOnce => {},

                // Note: A closure's kind is determined by how it's used, not it's captures.
                ExprKind::Closure { .. } | ExprKind::Loop(..) => return Some(e),
                _ => (),
            },
            Node::Stmt(_) | Node::Block(_) | Node::LetStmt(_) | Node::Arm(_) | Node::ExprField(_) => (),
            _ => break,
        }
    }
    None
}

/// Gets the parent node if it's an impl block.
pub fn get_parent_as_impl(tcx: TyCtxt<'_>, id: HirId) -> Option<&Impl<'_>> {
    match tcx.hir_parent_iter(id).next() {
        Some((
            _,
            Node::Item(Item {
                kind: ItemKind::Impl(imp),
                ..
            }),
        )) => Some(imp),
        _ => None,
    }
}

/// Removes blocks around an expression, only if the block contains just one expression
/// and no statements. Unsafe blocks are not removed.
///
/// Examples:
///  * `{}`               -> `{}`
///  * `{ x }`            -> `x`
///  * `{{ x }}`          -> `x`
///  * `{ x; }`           -> `{ x; }`
///  * `{ x; y }`         -> `{ x; y }`
///  * `{ unsafe { x } }` -> `unsafe { x }`
pub fn peel_blocks<'a>(mut expr: &'a Expr<'a>) -> &'a Expr<'a> {
    while let ExprKind::Block(
        Block {
            stmts: [],
            expr: Some(inner),
            rules: BlockCheckMode::DefaultBlock,
            ..
        },
        _,
    ) = expr.kind
    {
        expr = inner;
    }
    expr
}

/// Removes blocks around an expression, only if the block contains just one expression
/// or just one expression statement with a semicolon. Unsafe blocks are not removed.
///
/// Examples:
///  * `{}`               -> `{}`
///  * `{ x }`            -> `x`
///  * `{ x; }`           -> `x`
///  * `{{ x; }}`         -> `x`
///  * `{ x; y }`         -> `{ x; y }`
///  * `{ unsafe { x } }` -> `unsafe { x }`
pub fn peel_blocks_with_stmt<'a>(mut expr: &'a Expr<'a>) -> &'a Expr<'a> {
    while let ExprKind::Block(
        Block {
            stmts: [],
            expr: Some(inner),
            rules: BlockCheckMode::DefaultBlock,
            ..
        }
        | Block {
            stmts:
                [
                    Stmt {
                        kind: StmtKind::Expr(inner) | StmtKind::Semi(inner),
                        ..
                    },
                ],
            expr: None,
            rules: BlockCheckMode::DefaultBlock,
            ..
        },
        _,
    ) = expr.kind
    {
        expr = inner;
    }
    expr
}

/// Checks if the given expression is the else clause of either an `if` or `if let` expression.
pub fn is_else_clause(tcx: TyCtxt<'_>, expr: &Expr<'_>) -> bool {
    let mut iter = tcx.hir_parent_iter(expr.hir_id);
    match iter.next() {
        Some((
            _,
            Node::Expr(Expr {
                kind: ExprKind::If(_, _, Some(else_expr)),
                ..
            }),
        )) => else_expr.hir_id == expr.hir_id,
        _ => false,
    }
}

/// Checks if the given expression is a part of `let else`
/// returns `true` for both the `init` and the `else` part
pub fn is_inside_let_else(tcx: TyCtxt<'_>, expr: &Expr<'_>) -> bool {
    hir_parent_with_src_iter(tcx, expr.hir_id).any(|(node, child_id)| {
        matches!(
            node,
            Node::LetStmt(LetStmt {
                init: Some(init),
                els: Some(els),
                ..
            })
            if init.hir_id == child_id || els.hir_id == child_id
        )
    })
}

/// Checks if the given expression is the else clause of a `let else` expression
pub fn is_else_clause_in_let_else(tcx: TyCtxt<'_>, expr: &Expr<'_>) -> bool {
    hir_parent_with_src_iter(tcx, expr.hir_id).any(|(node, child_id)| {
        matches!(
            node,
            Node::LetStmt(LetStmt { els: Some(els), .. })
            if els.hir_id == child_id
        )
    })
}

/// Checks whether the given `Expr` is a range over the entire container.
pub fn is_full_collection_range(cx: &LateContext<'_>, container: Option<HirId>, expr: &Expr<'_>) -> bool {
    if let Some(Range { start, end, ty, .. }) = Range::hir(cx, expr) {
        start.is_none_or(|start| is_integer_literal(start, 0))
            && end.is_none_or(|end| {
                if ty.limits() == RangeLimits::HalfOpen
                    && let Some(container) = container
                    && let ExprKind::MethodCall(seg, recv, [], _) = end.kind
                {
                    seg.ident.name == sym::len && recv.res_local_id() == Some(container)
                } else {
                    false
                }
            })
    } else {
        false
    }
}

/// Checks whether the given expression is a constant literal of the given value.
pub fn is_integer_literal(expr: &Expr<'_>, value: u128) -> bool {
    if let ExprKind::Lit(spanned) = expr.kind
        && let LitKind::Int(v, _) = spanned.node
    {
        return v == value;
    }
    false
}

/// Checks whether the given expression is an untyped integer literal.
pub fn is_integer_literal_untyped(expr: &Expr<'_>) -> bool {
    if let ExprKind::Lit(spanned) = expr.kind
        && let LitKind::Int(_, suffix) = spanned.node
    {
        return suffix == LitIntType::Unsuffixed;
    }

    false
}

/// Checks whether the given expression is a constant literal of the given value.
pub fn is_float_literal(expr: &Expr<'_>, value: f64) -> bool {
    if let ExprKind::Lit(spanned) = expr.kind
        && let LitKind::Float(v, _) = spanned.node
    {
        v.as_str().parse() == Ok(value)
    } else {
        false
    }
}

/// Returns `true` if the given `Expr` has been coerced before.
///
/// Examples of coercions can be found in the Nomicon at
/// <https://doc.rust-lang.org/nomicon/coercions.html>.
///
/// See `rustc_middle::ty::adjustment::Adjustment` and `rustc_hir_analysis::check::coercion` for
/// more information on adjustments and coercions.
pub fn is_adjusted(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
    cx.typeck_results().adjustments().get(e.hir_id).is_some()
}

/// Returns the pre-expansion span if this comes from an expansion of the
/// macro `name`.
/// See also [`is_direct_expn_of`].
#[must_use]
pub fn is_expn_of(mut span: Span, name: Symbol) -> Option<Span> {
    loop {
        if span.from_expansion() {
            let data = span.ctxt().outer_expn_data();
            let new_span = data.call_site;

            if let ExpnKind::Macro(MacroKind::Bang, mac_name) = data.kind
                && mac_name == name
            {
                return Some(new_span);
            }

            span = new_span;
        } else {
            return None;
        }
    }
}

/// Returns the pre-expansion span if the span directly comes from an expansion
/// of the macro `name`.
/// The difference with [`is_expn_of`] is that in
/// ```no_run
/// # macro_rules! foo { ($name:tt!$args:tt) => { $name!$args } }
/// # macro_rules! bar { ($e:expr) => { $e } }
/// foo!(bar!(42));
/// ```
/// `42` is considered expanded from `foo!` and `bar!` by `is_expn_of` but only
/// from `bar!` by `is_direct_expn_of`.
#[must_use]
pub fn is_direct_expn_of(span: Span, name: Symbol) -> Option<Span> {
    if span.from_expansion() {
        let data = span.ctxt().outer_expn_data();
        let new_span = data.call_site;

        if let ExpnKind::Macro(MacroKind::Bang, mac_name) = data.kind
            && mac_name == name
        {
            return Some(new_span);
        }
    }

    None
}

/// Convenience function to get the return type of a function.
pub fn return_ty<'tcx>(cx: &LateContext<'tcx>, fn_def_id: OwnerId) -> Ty<'tcx> {
    let ret_ty = cx.tcx.fn_sig(fn_def_id).instantiate_identity().skip_norm_wip().output();
    cx.tcx.instantiate_bound_regions_with_erased(ret_ty)
}

/// Convenience function to get the nth argument type of a function.
pub fn nth_arg<'tcx>(cx: &LateContext<'tcx>, fn_def_id: OwnerId, nth: usize) -> Ty<'tcx> {
    let arg = cx
        .tcx
        .fn_sig(fn_def_id)
        .instantiate_identity()
        .skip_norm_wip()
        .input(nth);
    cx.tcx.instantiate_bound_regions_with_erased(arg)
}

/// Checks if an expression is constructing a tuple-like enum variant or struct
pub fn is_ctor_or_promotable_const_function(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
    if let ExprKind::Call(fun, _) = expr.kind
        && let ExprKind::Path(ref qp) = fun.kind
    {
        let res = cx.qpath_res(qp, fun.hir_id);
        return match res {
            Res::Def(DefKind::Variant | DefKind::Ctor(..), ..) => true,
            Res::Def(_, def_id) => cx.tcx.is_promotable_const_fn(def_id),
            _ => false,
        };
    }
    false
}

/// Returns `true` if a pattern is refutable.
// TODO: should be implemented using rustc/mir_build/thir machinery
pub fn is_refutable(cx: &LateContext<'_>, pat: &Pat<'_>) -> bool {
    fn is_qpath_refutable(cx: &LateContext<'_>, qpath: &QPath<'_>, id: HirId) -> bool {
        !matches!(
            cx.qpath_res(qpath, id),
            Res::Def(DefKind::Struct, ..) | Res::Def(DefKind::Ctor(def::CtorOf::Struct, _), _)
        )
    }

    fn are_refutable<'a, I: IntoIterator<Item = &'a Pat<'a>>>(cx: &LateContext<'_>, i: I) -> bool {
        i.into_iter().any(|pat| is_refutable(cx, pat))
    }

    match pat.kind {
        PatKind::Missing => unreachable!(),
        PatKind::Wild | PatKind::Never => false, // If `!` typechecked then the type is empty, so not refutable.
        PatKind::Binding(_, _, _, pat) => pat.is_some_and(|pat| is_refutable(cx, pat)),
        PatKind::Ref(pat, _, _) => is_refutable(cx, pat),
        PatKind::Expr(PatExpr {
            kind: PatExprKind::Path(qpath),
            hir_id,
            ..
        }) => is_qpath_refutable(cx, qpath, *hir_id),
        PatKind::Or(pats) => {
            // TODO: should be the honest check, that pats is exhaustive set
            are_refutable(cx, pats)
        },
        PatKind::Tuple(pats, _) => are_refutable(cx, pats),
        PatKind::Struct(ref qpath, fields, _) => {
            is_qpath_refutable(cx, qpath, pat.hir_id) || are_refutable(cx, fields.iter().map(|field| field.pat))
        },
        PatKind::TupleStruct(ref qpath, pats, _) => {
            is_qpath_refutable(cx, qpath, pat.hir_id) || are_refutable(cx, pats)
        },
        PatKind::Slice(head, middle, tail) => {
            match &cx.typeck_results().node_type(pat.hir_id).kind() {
                rustc_ty::Slice(..) => {
                    // [..] is the only irrefutable slice pattern.
                    !head.is_empty() || middle.is_none() || !tail.is_empty()
                },
                rustc_ty::Array(..) => are_refutable(cx, head.iter().chain(middle).chain(tail.iter())),
                _ => {
                    // unreachable!()
                    true
                },
            }
        },
        PatKind::Expr(..) | PatKind::Range(..) | PatKind::Err(_) | PatKind::Deref(_) | PatKind::Guard(..) => true,
    }
}

/// If the pattern is an `or` pattern, call the function once for each sub pattern. Otherwise, call
/// the function once on the given pattern.
pub fn recurse_or_patterns<'tcx, F: FnMut(&'tcx Pat<'tcx>)>(pat: &'tcx Pat<'tcx>, mut f: F) {
    if let PatKind::Or(pats) = pat.kind {
        pats.iter().for_each(f);
    } else {
        f(pat);
    }
}

pub fn is_self(slf: &Param<'_>) -> bool {
    if let PatKind::Binding(.., name, _) = slf.pat.kind {
        name.name == kw::SelfLower
    } else {
        false
    }
}

pub fn is_self_ty(slf: &hir::Ty<'_>) -> bool {
    if let TyKind::Path(QPath::Resolved(None, path)) = slf.kind
        && let Res::SelfTyParam { .. } | Res::SelfTyAlias { .. } = path.res
    {
        return true;
    }
    false
}

pub fn iter_input_pats<'tcx>(decl: &FnDecl<'_>, body: &'tcx Body<'_>) -> impl Iterator<Item = &'tcx Param<'tcx>> {
    (0..decl.inputs.len()).map(move |i| &body.params[i])
}

/// Checks if a given expression is a match expression expanded from the `?`
/// operator or the `try` macro.
pub fn is_try<'tcx>(cx: &LateContext<'_>, expr: &'tcx Expr<'tcx>) -> Option<&'tcx Expr<'tcx>> {
    fn is_ok(cx: &LateContext<'_>, arm: &Arm<'_>) -> bool {
        if let PatKind::TupleStruct(ref path, pat, ddpos) = arm.pat.kind
            && ddpos.as_opt_usize().is_none()
            && cx
                .qpath_res(path, arm.pat.hir_id)
                .ctor_parent(cx)
                .is_lang_item(cx, ResultOk)
            && let PatKind::Binding(_, hir_id, _, None) = pat[0].kind
            && arm.body.res_local_id() == Some(hir_id)
        {
            return true;
        }
        false
    }

    fn is_err(cx: &LateContext<'_>, arm: &Arm<'_>) -> bool {
        if let PatKind::TupleStruct(ref path, _, _) = arm.pat.kind {
            cx.qpath_res(path, arm.pat.hir_id)
                .ctor_parent(cx)
                .is_lang_item(cx, ResultErr)
        } else {
            false
        }
    }

    if let ExprKind::Match(_, arms, ref source) = expr.kind {
        // desugared from a `?` operator
        if let MatchSource::TryDesugar(_) = *source {
            return Some(expr);
        }

        if arms.len() == 2
            && arms[0].guard.is_none()
            && arms[1].guard.is_none()
            && ((is_ok(cx, &arms[0]) && is_err(cx, &arms[1])) || (is_ok(cx, &arms[1]) && is_err(cx, &arms[0])))
        {
            return Some(expr);
        }
    }

    None
}

/// Returns `true` if the lint is `#[allow]`ed or `#[expect]`ed at any of the `ids`, fulfilling all
/// of the expectations in `ids`
///
/// This should only be used when the lint would otherwise be emitted, for a way to check if a lint
/// is allowed early to skip work see [`is_lint_allowed`]
///
/// To emit at a lint at a different context than the one current see
/// [`span_lint_hir`](diagnostics::span_lint_hir) or
/// [`span_lint_hir_and_then`](diagnostics::span_lint_hir_and_then)
pub fn fulfill_or_allowed(cx: &LateContext<'_>, lint: &'static Lint, ids: impl IntoIterator<Item = HirId>) -> bool {
    let mut suppress_lint = false;

    for id in ids {
        let level_spec = cx.tcx.lint_level_spec_at_node(lint, id);
        if let Some(expectation) = level_spec.lint_id() {
            cx.fulfill_expectation(expectation);
        }

        match level_spec.level() {
            Level::Allow | Level::Expect => suppress_lint = true,
            Level::Warn | Level::ForceWarn | Level::Deny | Level::Forbid => {},
        }
    }

    suppress_lint
}

/// Returns `true` if the lint is allowed in the current context. This is useful for
/// skipping long running code when it's unnecessary
///
/// This function should check the lint level for the same node, that the lint will
/// be emitted at. If the information is buffered to be emitted at a later point, please
/// make sure to use `span_lint_hir` functions to emit the lint. This ensures that
/// expectations at the checked nodes will be fulfilled.
pub fn is_lint_allowed(cx: &LateContext<'_>, lint: &'static Lint, id: HirId) -> bool {
    cx.tcx.lint_level_spec_at_node(lint, id).is_allow()
}

pub fn strip_pat_refs<'hir>(mut pat: &'hir Pat<'hir>) -> &'hir Pat<'hir> {
    while let PatKind::Ref(subpat, _, _) = pat.kind {
        pat = subpat;
    }
    pat
}

pub fn int_bits(tcx: TyCtxt<'_>, ity: IntTy) -> u64 {
    Integer::from_int_ty(&tcx, ity).size().bits()
}

#[expect(clippy::cast_possible_wrap)]
/// Turn a constant int byte representation into an i128
pub fn sext(tcx: TyCtxt<'_>, u: u128, ity: IntTy) -> i128 {
    let amt = 128 - int_bits(tcx, ity);
    ((u as i128) << amt) >> amt
}

#[expect(clippy::cast_sign_loss)]
/// clip unused bytes
pub fn unsext(tcx: TyCtxt<'_>, u: i128, ity: IntTy) -> u128 {
    let amt = 128 - int_bits(tcx, ity);
    ((u as u128) << amt) >> amt
}

/// clip unused bytes
pub fn clip(tcx: TyCtxt<'_>, u: u128, ity: UintTy) -> u128 {
    let bits = Integer::from_uint_ty(&tcx, ity).size().bits();
    let amt = 128 - bits;
    (u << amt) >> amt
}

pub fn has_repr_attr(cx: &LateContext<'_>, hir_id: HirId) -> bool {
    find_attr!(cx.tcx, hir_id, Repr { .. })
}

/// Checks if the given HIR node is inside an `impl` block with the `automatically_derived`
/// attribute.
pub fn in_automatically_derived(tcx: TyCtxt<'_>, id: HirId) -> bool {
    tcx.hir_parent_owner_iter(id)
        .filter(|(_, node)| matches!(node, OwnerNode::Item(item) if matches!(item.kind, ItemKind::Impl(_))))
        .any(|(id, _)| find_attr!(tcx, id.def_id, AutomaticallyDerived))
}

/// Functions marked with these attributes must have an exact signature.
pub fn requires_exact_signature(attrs: &[rustc_attr_ir::Attribute]) -> bool {
    find_attr!(attrs, ProcMacro | ProcMacroAttribute | ProcMacroDerive { .. })
}

/// Checks if the given `DefId` matches the `libc` item.
pub fn match_libc_symbol(cx: &LateContext<'_>, did: DefId, name: Symbol) -> bool {
    // libc is meant to be used as a flat list of names, but they're all actually defined in
    // different modules based on the target platform. Ignore everything but crate name and the
    // item name.
    cx.tcx.crate_name(did.krate) == sym::libc && cx.tcx.def_path_str(did).ends_with(name.as_str())
}

/// Returns the list of condition expressions and the list of blocks in a
/// sequence of `if/else`.
/// E.g., this returns `([a, b], [c, d, e])` for the expression
/// `if a { c } else if b { d } else { e }`.
pub fn if_sequence<'tcx>(mut expr: &'tcx Expr<'tcx>) -> (Vec<&'tcx Expr<'tcx>>, Vec<&'tcx Block<'tcx>>) {
    let mut conds = Vec::new();
    let mut blocks: Vec<&Block<'_>> = Vec::new();

    while let Some(higher::IfOrIfLet { cond, then, r#else }) = higher::IfOrIfLet::hir(expr) {
        conds.push(cond);
        if let ExprKind::Block(block, _) = then.kind {
            blocks.push(block);
        } else {
            panic!("ExprKind::If node is not an ExprKind::Block");
        }

        if let Some(else_expr) = r#else {
            expr = else_expr;
        } else {
            break;
        }
    }

    // final `else {..}`
    if !blocks.is_empty()
        && let ExprKind::Block(block, _) = expr.kind
    {
        blocks.push(block);
    }

    (conds, blocks)
}

/// Peels away all the compiler generated code surrounding the body of an async closure.
pub fn get_async_closure_expr<'tcx>(tcx: TyCtxt<'tcx>, expr: &Expr<'_>) -> Option<&'tcx Expr<'tcx>> {
    if let ExprKind::Closure(&Closure {
        body,
        kind: hir::ClosureKind::Coroutine(CoroutineKind::Desugared(CoroutineDesugaring::Async, _)),
        ..
    }) = expr.kind
        && let ExprKind::Block(
            Block {
                expr:
                    Some(Expr {
                        kind: ExprKind::DropTemps(inner_expr),
                        ..
                    }),
                ..
            },
            _,
        ) = tcx.hir_body(body).value.kind
    {
        Some(inner_expr)
    } else {
        None
    }
}

/// Peels away all the compiler generated code surrounding the body of an async function,
pub fn get_async_fn_body<'tcx>(tcx: TyCtxt<'tcx>, body: &Body<'_>) -> Option<&'tcx Expr<'tcx>> {
    get_async_closure_expr(tcx, body.value)
}

// check if expr is calling method or function with #[must_use] attribute
pub fn is_must_use_func_call(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
    let did = match expr.kind {
        ExprKind::Call(path, _) => {
            if let ExprKind::Path(ref qpath) = path.kind
                && let Res::Def(_, did) = cx.qpath_res(qpath, path.hir_id)
            {
                Some(did)
            } else {
                None
            }
        },
        ExprKind::MethodCall(..) => cx.typeck_results().type_dependent_def_id(expr.hir_id),
        _ => None,
    };

    did.is_some_and(|did| find_attr!(cx.tcx, did, MustUse { .. }))
}

/// Checks if a function's body represents the identity function. Looks for bodies of the form:
/// * `|x| x`
/// * `|x| return x`
/// * `|x| { return x }`
/// * `|x| { return x; }`
/// * `|(x, y)| (x, y)`
/// * `|[x, y]| [x, y]`
/// * `|Foo(bar, baz)| Foo(bar, baz)`
/// * `|Foo { bar, baz }| Foo { bar, baz }`
/// * `|x| { let y = x; ...; let z = y; z }`
/// * `|x| { let y = x; ...; let z = y; return z }`
///
/// Consider calling [`is_expr_untyped_identity_function`] or [`is_expr_identity_function`] instead.
fn is_body_identity_function<'hir>(cx: &LateContext<'_>, func: &Body<'hir>) -> bool {
    let [param] = func.params else {
        return false;
    };

    let mut param_pat = param.pat;

    // Given a sequence of `Stmt`s of the form `let p = e` where `e` is an expr identical to the
    // current `param_pat`, advance the current `param_pat` to `p`.
    //
    // Note: This is similar to `clippy_utils::get_last_chain_binding_hir_id`, but it works
    // directly over a `Pattern` rather than a `HirId`. And it checks for compatibility via
    // `is_expr_identity_of_pat` rather than `HirId` equality
    let mut advance_param_pat_over_stmts = |stmts: &[Stmt<'hir>]| {
        for stmt in stmts {
            if let StmtKind::Let(local) = stmt.kind
                && let Some(init) = local.init
                && is_expr_identity_of_pat(cx, param_pat, init, true)
            {
                param_pat = local.pat;
            } else {
                return false;
            }
        }

        true
    };

    let mut expr = func.value;
    loop {
        match expr.kind {
            ExprKind::Block(
                &Block {
                    stmts: [],
                    expr: Some(e),
                    ..
                },
                _,
            )
            | ExprKind::Ret(Some(e)) => expr = e,
            ExprKind::Block(
                &Block {
                    stmts: [stmt],
                    expr: None,
                    ..
                },
                _,
            ) => {
                if let StmtKind::Semi(e) | StmtKind::Expr(e) = stmt.kind
                    && let ExprKind::Ret(Some(ret_val)) = e.kind
                {
                    expr = ret_val;
                } else {
                    return false;
                }
            },
            ExprKind::Block(
                &Block {
                    stmts, expr: Some(e), ..
                },
                _,
            ) => {
                if !advance_param_pat_over_stmts(stmts) {
                    return false;
                }

                expr = e;
            },
            ExprKind::Block(&Block { stmts, expr: None, .. }, _) => {
                if let Some((last_stmt, stmts)) = stmts.split_last()
                    && advance_param_pat_over_stmts(stmts)
                    && let StmtKind::Semi(e) | StmtKind::Expr(e) = last_stmt.kind
                    && let ExprKind::Ret(Some(ret_val)) = e.kind
                {
                    expr = ret_val;
                } else {
                    return false;
                }
            },
            _ => return is_expr_identity_of_pat(cx, param_pat, expr, true),
        }
    }
}

/// Checks if the given expression is an identity representation of the given pattern:
/// * `x` is the identity representation of `x`
/// * `(x, y)` is the identity representation of `(x, y)`
/// * `[x, y]` is the identity representation of `[x, y]`
/// * `Foo(bar, baz)` is the identity representation of `Foo(bar, baz)`
/// * `Foo { bar, baz }` is the identity representation of `Foo { bar, baz }`
///
/// Note that `by_hir` is used to determine bindings are checked by their `HirId` or by their name.
/// This can be useful when checking patterns in `let` bindings or `match` arms.
pub fn is_expr_identity_of_pat(cx: &LateContext<'_>, pat: &Pat<'_>, expr: &Expr<'_>, by_hir: bool) -> bool {
    if cx
        .typeck_results()
        .pat_binding_modes()
        .get(pat.hir_id)
        .is_some_and(|mode| matches!(mode.0, ByRef::Yes(..)))
    {
        // If the parameter is `(x, y)` of type `&(T, T)`, or `[x, y]` of type `&[T; 2]`, then
        // due to match ergonomics, the inner patterns become references. Don't consider this
        // the identity function as that changes types.
        return false;
    }

    // NOTE: we're inside a (function) body, so this won't ICE
    let qpath_res = |qpath, hir| cx.typeck_results().qpath_res(qpath, hir);

    match (pat.kind, expr.kind) {
        (PatKind::Binding(_, id, _, _), _) if by_hir => {
            expr.res_local_id() == Some(id) && cx.typeck_results().expr_adjustments(expr).is_empty()
        },
        (PatKind::Binding(_, _, ident, _), ExprKind::Path(QPath::Resolved(_, path))) => {
            matches!(path.segments, [ segment] if segment.ident.name == ident.name)
        },
        (PatKind::Tuple(pats, dotdot), ExprKind::Tup(tup))
            if dotdot.as_opt_usize().is_none() && pats.len() == tup.len() =>
        {
            over(pats, tup, |pat, expr| is_expr_identity_of_pat(cx, pat, expr, by_hir))
        },
        (PatKind::Slice(before, None, after), ExprKind::Array(arr)) if before.len() + after.len() == arr.len() => {
            zip(before.iter().chain(after), arr).all(|(pat, expr)| is_expr_identity_of_pat(cx, pat, expr, by_hir))
        },
        (PatKind::TupleStruct(pat_ident, field_pats, dotdot), ExprKind::Call(ident, fields))
            if dotdot.as_opt_usize().is_none() && field_pats.len() == fields.len() =>
        {
            // check ident
            if let ExprKind::Path(ident) = &ident.kind
                && qpath_res(&pat_ident, pat.hir_id) == qpath_res(ident, expr.hir_id)
                // check fields
                && over(field_pats, fields, |pat, expr| is_expr_identity_of_pat(cx, pat, expr,by_hir))
            {
                true
            } else {
                false
            }
        },
        (PatKind::Struct(pat_ident, field_pats, None), ExprKind::Struct(ident, fields, hir::StructTailExpr::None))
            if field_pats.len() == fields.len() =>
        {
            // check ident
            qpath_res(&pat_ident, pat.hir_id) == qpath_res(ident, expr.hir_id)
                // check fields
                && unordered_over(field_pats, fields, |field_pat, field| {
                    field_pat.ident == field.ident && is_expr_identity_of_pat(cx, field_pat.pat, field.expr, by_hir)
                })
        },
        _ => false,
    }
}

/// This is the same as [`is_expr_identity_function`], but does not consider closures
/// with type annotations for its bindings (or similar) as identity functions:
/// * `|x: u8| x`
/// * `std::convert::identity::<u8>`
pub fn is_expr_untyped_identity_function(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
    match expr.kind {
        ExprKind::Closure(&Closure { body, fn_decl, .. })
            if fn_decl.inputs.iter().all(|ty| matches!(ty.kind, TyKind::Infer(()))) =>
        {
            is_body_identity_function(cx, cx.tcx.hir_body(body))
        },
        ExprKind::Path(QPath::Resolved(_, path))
            if path.segments.iter().all(|seg| seg.infer_args)
                && let Some(did) = path.res.opt_def_id() =>
        {
            cx.tcx.is_diagnostic_item(sym::convert_identity, did)
        },
        _ => false,
    }
}

/// Checks if an expression represents the identity function
/// Only examines closures and `std::convert::identity`
///
/// NOTE: If you want to use this function to find out if a closure is unnecessary, you likely want
/// to call [`is_expr_untyped_identity_function`] instead, which makes sure that the closure doesn't
/// have type annotations. This is important because removing a closure with bindings can
/// remove type information that helped type inference before, which can then lead to compile
/// errors.
pub fn is_expr_identity_function(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
    match expr.kind {
        ExprKind::Closure(&Closure { body, .. }) => is_body_identity_function(cx, cx.tcx.hir_body(body)),
        _ => expr.basic_res().is_diag_item(cx, sym::convert_identity),
    }
}

/// Gets the node where an expression is either used, or it's type is unified with another branch.
/// Returns both the node and the `HirId` of the closest child node.
pub fn get_expr_use_or_unification_node<'tcx>(tcx: TyCtxt<'tcx>, expr: &Expr<'_>) -> Option<(Node<'tcx>, HirId)> {
    for (node, child_id) in hir_parent_with_src_iter(tcx, expr.hir_id) {
        match node {
            Node::Block(_) => {},
            Node::Arm(arm) if arm.body.hir_id == child_id => {},
            Node::Expr(expr) => match expr.kind {
                ExprKind::Block(..) | ExprKind::DropTemps(_) => {},
                ExprKind::Match(_, [arm], _) if arm.hir_id == child_id => {},
                ExprKind::If(_, then_expr, None) if then_expr.hir_id == child_id => return None,
                _ => return Some((Node::Expr(expr), child_id)),
            },
            node => return Some((node, child_id)),
        }
    }
    None
}

/// Checks if the result of an expression is used, or it's type is unified with another branch.
pub fn is_expr_used_or_unified(tcx: TyCtxt<'_>, expr: &Expr<'_>) -> bool {
    !matches!(
        get_expr_use_or_unification_node(tcx, expr),
        None | Some((
            Node::Stmt(Stmt {
                kind: StmtKind::Expr(_)
                    | StmtKind::Semi(_)
                    | StmtKind::Let(LetStmt {
                        pat: Pat {
                            kind: PatKind::Wild,
                            ..
                        },
                        ..
                    }),
                ..
            }),
            _
        ))
    )
}

/// Checks if the expression is the final expression returned from a block.
pub fn is_expr_final_block_expr(tcx: TyCtxt<'_>, expr: &Expr<'_>) -> bool {
    matches!(tcx.parent_hir_node(expr.hir_id), Node::Block(..))
}

/// Checks if the expression is a temporary value.
// This logic is the same as the one used in rustc's `check_named_place_expr function`.
// https://github.com/rust-lang/rust/blob/3ed2a10d173d6c2e0232776af338ca7d080b1cd4/compiler/rustc_hir_typeck/src/expr.rs#L482-L499
pub fn is_expr_temporary_value(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
    !expr.is_place_expr(|base| {
        cx.typeck_results()
            .adjustments()
            .get(base.hir_id)
            .is_some_and(|x| x.iter().any(|adj| matches!(adj.kind, Adjust::Deref(_))))
    })
}

pub fn std_or_core(cx: &LateContext<'_>) -> Option<&'static str> {
    if is_no_core_crate(cx) {
        None
    } else if is_no_std_crate(cx) {
        Some("core")
    } else {
        Some("std")
    }
}

pub fn is_no_std_crate(cx: &LateContext<'_>) -> bool {
    find_attr!(cx.tcx, crate, NoStd)
}

pub fn is_no_core_crate(cx: &LateContext<'_>) -> bool {
    find_attr!(cx.tcx, crate, NoCore)
}

/// Check if parent of a hir node is a trait implementation block.
/// For example, `f` in
/// ```no_run
/// # struct S;
/// # trait Trait { fn f(); }
/// impl Trait for S {
///     fn f() {}
/// }
/// ```
pub fn is_trait_impl_item(cx: &LateContext<'_>, hir_id: HirId) -> bool {
    if let Node::Item(item) = cx.tcx.parent_hir_node(hir_id) {
        matches!(item.kind, ItemKind::Impl(Impl { of_trait: Some(_), .. }))
    } else {
        false
    }
}

/// Check if it's even possible to satisfy the `where` clause for the item.
///
/// `trivial_bounds` feature allows functions with unsatisfiable bounds, for example:
///
/// ```ignore
/// fn foo() where i32: Iterator {
///     for _ in 2i32 {}
/// }
/// ```
pub fn fn_has_unsatisfiable_clauses(cx: &LateContext<'_>, did: DefId) -> bool {
    use rustc_trait_selection::traits;
    let clauses = cx
        .tcx
        .clauses_of(did)
        .clauses
        .iter()
        .filter_map(|(p, _)| if p.is_global() { Some(*p) } else { None });
    traits::impossible_clauses(cx.tcx, traits::elaborate(cx.tcx, clauses).collect::<Vec<_>>())
}

/// Returns the `DefId` of the callee if the given expression is a function or method call.
pub fn fn_def_id(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<DefId> {
    fn_def_id_with_node_args(cx, expr).map(|(did, _)| did)
}

/// Returns the `DefId` of the callee if the given expression is a function or method call,
/// as well as its node args.
pub fn fn_def_id_with_node_args<'tcx>(
    cx: &LateContext<'tcx>,
    expr: &Expr<'_>,
) -> Option<(DefId, GenericArgsRef<'tcx>)> {
    let typeck = cx.typeck_results();
    match &expr.kind {
        ExprKind::MethodCall(..) => Some((
            typeck.type_dependent_def_id(expr.hir_id)?,
            typeck.node_args(expr.hir_id),
        )),
        ExprKind::Call(
            Expr {
                kind: ExprKind::Path(qpath),
                hir_id: path_hir_id,
                ..
            },
            ..,
        ) => {
            // Only return Fn-like DefIds, not the DefIds of statics/consts/etc that contain or
            // deref to fn pointers, dyn Fn, impl Fn - #8850
            if let Res::Def(DefKind::Fn | DefKind::Ctor(..) | DefKind::AssocFn, id) =
                typeck.qpath_res(qpath, *path_hir_id)
            {
                Some((id, typeck.node_args(*path_hir_id)))
            } else {
                None
            }
        },
        _ => None,
    }
}

/// Returns `Option<String>` where String is a textual representation of the type encapsulated in
/// the slice iff the given expression is a slice of primitives.
///
/// (As defined in the `is_recursively_primitive_type` function.) Returns `None` otherwise.
pub fn is_slice_of_primitives(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<String> {
    let expr_type = cx.typeck_results().expr_ty_adjusted(expr);
    let expr_kind = expr_type.kind();
    let is_primitive = match expr_kind {
        rustc_ty::Slice(element_type) => is_recursively_primitive_type(*element_type),
        rustc_ty::Ref(_, inner_ty, _) if matches!(inner_ty.kind(), &rustc_ty::Slice(_)) => {
            if let rustc_ty::Slice(element_type) = inner_ty.kind() {
                is_recursively_primitive_type(*element_type)
            } else {
                unreachable!()
            }
        },
        _ => false,
    };

    if is_primitive {
        // if we have wrappers like Array, Slice or Tuple, print these
        // and get the type enclosed in the slice ref
        match expr_type.peel_refs().walk().nth(1).unwrap().expect_ty().kind() {
            rustc_ty::Slice(..) => return Some("slice".into()),
            rustc_ty::Array(..) => return Some("array".into()),
            rustc_ty::Tuple(..) => return Some("tuple".into()),
            _ => {
                // is_recursively_primitive_type() should have taken care
                // of the rest and we can rely on the type that is found
                let refs_peeled = expr_type.peel_refs();
                return Some(refs_peeled.walk().last().unwrap().to_string());
            },
        }
    }
    None
}

/// Returns a list of groups where elements in each group are equal according to `eq`
///
/// - Within each group the elements are sorted by the order they appear in `exprs`
/// - The groups themselves are sorted by their first element's appearence in `exprs`
///
/// Given functions `eq` and `hash` such that `eq(a, b) == true`
/// implies `hash(a) == hash(b)`
pub fn search_same<T, Hash, Eq>(exprs: &[T], mut hash: Hash, mut eq: Eq) -> Vec<Vec<&T>>
where
    Hash: FnMut(&T) -> u64,
    Eq: FnMut(&T, &T) -> bool,
{
    match exprs {
        [a, b] if eq(a, b) => return vec![vec![a, b]],
        _ if exprs.len() <= 2 => return vec![],
        _ => {},
    }

    let mut buckets: UnindexMap<u64, Vec<Vec<&T>>> = UnindexMap::default();

    for expr in exprs {
        match buckets.entry(hash(expr)) {
            indexmap::map::Entry::Occupied(mut o) => {
                let bucket = o.get_mut();
                match bucket.iter_mut().find(|group| eq(expr, group[0])) {
                    Some(group) => group.push(expr),
                    None => bucket.push(vec![expr]),
                }
            },
            indexmap::map::Entry::Vacant(v) => {
                v.insert(vec![vec![expr]]);
            },
        }
    }

    buckets
        .into_values()
        .flatten()
        .filter(|group| group.len() > 1)
        .collect()
}

/// Peels off all references on the pattern. Returns the underlying pattern and the number of
/// references removed.
pub fn peel_hir_pat_refs<'a>(pat: &'a Pat<'a>) -> (&'a Pat<'a>, usize) {
    fn peel<'a>(pat: &'a Pat<'a>, count: usize) -> (&'a Pat<'a>, usize) {
        if let PatKind::Ref(pat, _, _) = pat.kind {
            peel(pat, count + 1)
        } else {
            (pat, count)
        }
    }
    peel(pat, 0)
}

/// Peels of expressions while the given closure returns `Some`.
pub fn peel_hir_expr_while<'tcx>(
    mut expr: &'tcx Expr<'tcx>,
    mut f: impl FnMut(&'tcx Expr<'tcx>) -> Option<&'tcx Expr<'tcx>>,
) -> &'tcx Expr<'tcx> {
    while let Some(e) = f(expr) {
        expr = e;
    }
    expr
}

/// Peels off up to the given number of references on the expression. Returns the underlying
/// expression and the number of references removed.
pub fn peel_n_hir_expr_refs<'a>(expr: &'a Expr<'a>, count: usize) -> (&'a Expr<'a>, usize) {
    let mut remaining = count;
    let e = peel_hir_expr_while(expr, |e| match e.kind {
        ExprKind::AddrOf(ast::BorrowKind::Ref, _, e) if remaining != 0 => {
            remaining -= 1;
            Some(e)
        },
        _ => None,
    });
    (e, count - remaining)
}

/// Peels off all unary operators of an expression. Returns the underlying expression and the number
/// of operators removed.
pub fn peel_hir_expr_unary<'a>(expr: &'a Expr<'a>) -> (&'a Expr<'a>, usize) {
    let mut count: usize = 0;
    let mut curr_expr = expr;
    while let ExprKind::Unary(_, local_expr) = curr_expr.kind {
        count = count.wrapping_add(1);
        curr_expr = local_expr;
    }
    (curr_expr, count)
}

/// Peels off all references on the expression. Returns the underlying expression and the number of
/// references removed.
pub fn peel_hir_expr_refs<'a>(expr: &'a Expr<'a>) -> (&'a Expr<'a>, usize) {
    let mut count = 0;
    let e = peel_hir_expr_while(expr, |e| match e.kind {
        ExprKind::AddrOf(ast::BorrowKind::Ref, _, e) => {
            count += 1;
            Some(e)
        },
        _ => None,
    });
    (e, count)
}

/// Peels off all references on the type. Returns the underlying type and the number of references
/// removed.
pub fn peel_hir_ty_refs<'a>(mut ty: &'a hir::Ty<'a>) -> (&'a hir::Ty<'a>, usize) {
    let mut count = 0;
    loop {
        match &ty.kind {
            TyKind::Ref(_, inner_ty, _) => {
                ty = inner_ty;
                count += 1;
            },
            _ => break (ty, count),
        }
    }
}

/// Returns the base type for HIR references and pointers.
pub fn peel_hir_ty_refs_and_ptrs<'tcx>(ty: &'tcx hir::Ty<'tcx>) -> &'tcx hir::Ty<'tcx> {
    match &ty.kind {
        TyKind::Ptr(inner_ty, _) | TyKind::Ref(_, inner_ty, _) => peel_hir_ty_refs_and_ptrs(inner_ty),
        _ => ty,
    }
}

/// Removes `AddrOf` operators (`&`) or deref operators (`*`), but only if a reference type is
/// dereferenced. An overloaded deref such as `Vec` to slice would not be removed.
pub fn peel_ref_operators<'hir>(cx: &LateContext<'_>, mut expr: &'hir Expr<'hir>) -> &'hir Expr<'hir> {
    loop {
        match expr.kind {
            ExprKind::AddrOf(_, _, e) => expr = e,
            ExprKind::Unary(UnOp::Deref, e) if cx.typeck_results().expr_ty(e).is_ref() => expr = e,
            _ => break,
        }
    }
    expr
}

/// Returns a `Vec` of `Expr`s containing `AddrOf` operators (`&`) or deref operators (`*`) of a
/// given expression.
pub fn get_ref_operators<'hir>(cx: &LateContext<'_>, expr: &'hir Expr<'hir>) -> Vec<&'hir Expr<'hir>> {
    let mut operators = Vec::new();
    peel_hir_expr_while(expr, |expr| match expr.kind {
        ExprKind::AddrOf(_, _, e) => {
            operators.push(expr);
            Some(e)
        },
        ExprKind::Unary(UnOp::Deref, e) if cx.typeck_results().expr_ty(e).is_ref() => {
            operators.push(expr);
            Some(e)
        },
        _ => None,
    });
    operators
}

pub fn is_hir_ty_cfg_dependant(cx: &LateContext<'_>, ty: &hir::Ty<'_>) -> bool {
    if let TyKind::Path(QPath::Resolved(_, path)) = ty.kind
        && let Res::Def(_, def_id) = path.res
    {
        return find_attr!(cx.tcx, def_id, CfgTrace(..) | CfgAttrTrace(..));
    }
    false
}

static TEST_ITEM_NAMES_CACHE: OnceLock<Mutex<FxHashMap<LocalModId, Vec<Symbol>>>> = OnceLock::new();

/// Returns the names of the test items in the given module.
/// The names are sorted using the default `Symbol` ordering.
fn test_item_names(tcx: TyCtxt<'_>, module: LocalModId) -> Vec<Symbol> {
    let cache = TEST_ITEM_NAMES_CACHE.get_or_init(|| Mutex::new(FxHashMap::default()));
    let mut map = cache.lock().unwrap();
    match map.entry(module) {
        Entry::Occupied(entry) => entry.get().clone(),
        Entry::Vacant(entry) => {
            let mut names = Vec::new();
            for id in tcx.hir_module_free_items(module) {
                if matches!(tcx.def_kind(id.owner_id), DefKind::Static { .. })
                    && let item = tcx.hir_item(id)
                    && let ItemKind::Static(_mut, ident, ty, _body) = item.kind
                    && let TyKind::Path(QPath::Resolved(_, path)) = ty.kind
                    // We could also check for the type name `test::TestDescAndFn`
                    && let Res::Def(DefKind::Struct, _) = path.res
                    && find_attr!(tcx, item.hir_id(), RustcTestMarker(..))
                {
                    names.push(ident.name);
                }
            }
            names.sort_unstable();
            entry.insert(names).clone()
        },
    }
}

/// Checks if the function containing the given `HirId` is a `#[test]` function
///
/// Note: Add `//@compile-flags: --test` to UI tests with a `#[test]` function
pub fn is_in_test_function(tcx: TyCtxt<'_>, id: HirId) -> bool {
    let names = test_item_names(tcx, tcx.parent_module(id));
    // Without `--test` there are no test items, so the parent walk can never match.
    if names.is_empty() {
        return false;
    }
    once((id, tcx.hir_node(id)))
        .chain(tcx.hir_parent_iter(id))
        // Since you can nest functions we need to collect all until we leave
        // function scope
        .any(|(_id, node)| {
            if let Node::Item(item) = node
                && let ItemKind::Fn { ident, .. } = item.kind
            {
                // Note that we have sorted the item names in the visitor,
                // so the binary_search gets the same as `contains`, but faster.
                return names.binary_search(&ident.name).is_ok();
            }
            false
        })
}

/// Checks if `fn_def_id` has a `#[test]` attribute applied
///
/// This only checks directly applied attributes. To see if a node has a parent function marked with
/// `#[test]` use [`is_in_test_function`].
///
/// Note: Add `//@compile-flags: --test` to UI tests with a `#[test]` function
pub fn is_test_function(tcx: TyCtxt<'_>, fn_def_id: LocalDefId) -> bool {
    let id = tcx.local_def_id_to_hir_id(fn_def_id);
    if let Node::Item(item) = tcx.hir_node(id)
        && let ItemKind::Fn { ident, .. } = item.kind
    {
        test_item_names(tcx, tcx.parent_module(id))
            .binary_search(&ident.name)
            .is_ok()
    } else {
        false
    }
}

/// Checks if `id` has a `#[cfg(test)]` attribute applied
///
/// This only checks directly applied attributes, to see if a node is inside a `#[cfg(test)]` parent
/// use [`is_in_cfg_test`]
pub fn is_cfg_test(tcx: TyCtxt<'_>, id: HirId) -> bool {
    if let Some(cfgs) = find_attr!(tcx, id, CfgTrace(cfgs) => cfgs)
        && cfgs
            .iter()
            .any(|(cfg, _)| matches!(cfg, CfgEntry::NameValue { name: sym::test, .. }))
    {
        true
    } else {
        false
    }
}

/// Checks if any parent node of `HirId` has `#[cfg(test)]` attribute applied
pub fn is_in_cfg_test(tcx: TyCtxt<'_>, id: HirId) -> bool {
    tcx.hir_parent_id_iter(id).any(|parent_id| is_cfg_test(tcx, parent_id))
}

/// Checks if the node is in a `#[test]` function or has any parent node marked `#[cfg(test)]`
pub fn is_in_test(tcx: TyCtxt<'_>, hir_id: HirId) -> bool {
    is_in_test_function(tcx, hir_id) || is_in_cfg_test(tcx, hir_id) || is_in_integration_test_file(tcx)
}

/// Check if the node is in an integration test file (i.e. under `tests/`).
fn is_in_integration_test_file(tcx: TyCtxt<'_>) -> bool {
    if let Input::File(ref path) = tcx.sess.io.input
        && !tcx.sess.opts.unstable_opts.ui_testing
    {
        path.starts_with("tests")
    } else {
        false
    }
}

/// Checks if the item of any of its parents has `#[cfg(...)]` attribute applied.
pub fn inherits_cfg(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
    find_attr!(tcx, def_id, CfgTrace(..))
        || find_attr!(
            tcx.hir_parent_id_iter(tcx.local_def_id_to_hir_id(def_id))
                .flat_map(|parent_id| tcx.hir_attrs(parent_id)),
            CfgTrace(..)
        )
}

/// A type definition as it would be viewed from within a function.
#[derive(Clone, Copy)]
pub enum DefinedTy<'tcx> {
    // Used for locals and closures defined within the function.
    Hir(&'tcx hir::Ty<'tcx>),
    /// Used for function signatures, and constant and static values. The type is
    /// in the context of its definition site. We also track the `def_id` of its
    /// definition site.
    ///
    /// WARNING: As the `ty` is in the scope of the definition, not of the function
    /// using it, you must be very careful with how you use it. Using it in the wrong
    /// scope easily results in ICEs.
    Mir {
        def_site_def_id: Option<DefId>,
        ty: Binder<'tcx, Ty<'tcx>>,
    },
}

/// The location that recives the value of an expression.
pub struct ExprUseSite<'tcx> {
    /// The parent node which consumes the value.
    pub node: Node<'tcx>,
    /// The ID of the immediate child of the use node.
    pub child_id: HirId,
    /// Any adjustments applied to the type.
    pub adjustments: &'tcx [Adjustment<'tcx>],
    /// Whether the type must unify with another code path.
    pub is_ty_unified: bool,
    /// Whether the value will be moved before it's used.
    pub moved_before_use: bool,
    /// Whether the use site has the same `SyntaxContext` as the value.
    pub same_ctxt: bool,
}
impl<'tcx> ExprUseSite<'tcx> {
    pub fn use_node(&self, cx: &LateContext<'tcx>) -> ExprUseNode<'tcx> {
        match self.node {
            Node::LetStmt(l) => ExprUseNode::LetStmt(l),
            Node::ExprField(field) => ExprUseNode::Field(field),

            Node::Item(&Item {
                kind: ItemKind::Static(..) | ItemKind::Const(..),
                owner_id,
                ..
            })
            | Node::TraitItem(&TraitItem {
                kind: TraitItemKind::Const(..),
                owner_id,
                ..
            })
            | Node::ImplItem(&ImplItem {
                kind: ImplItemKind::Const(..),
                owner_id,
                ..
            }) => ExprUseNode::ConstStatic(owner_id),

            Node::Item(&Item {
                kind: ItemKind::Fn { .. },
                owner_id,
                ..
            })
            | Node::TraitItem(&TraitItem {
                kind: TraitItemKind::Fn(..),
                owner_id,
                ..
            })
            | Node::ImplItem(&ImplItem {
                kind: ImplItemKind::Fn(..),
                owner_id,
                ..
            }) => ExprUseNode::Return(owner_id),

            Node::Expr(use_expr) => match use_expr.kind {
                ExprKind::Ret(_) => ExprUseNode::Return(OwnerId {
                    def_id: cx.tcx.hir_body_owner_def_id(cx.enclosing_body.unwrap()),
                }),

                ExprKind::Closure(closure) => ExprUseNode::Return(OwnerId { def_id: closure.def_id }),
                ExprKind::Call(func, args) => match args.iter().position(|arg| arg.hir_id == self.child_id) {
                    Some(i) => ExprUseNode::FnArg(func, i),
                    None => ExprUseNode::Callee,
                },
                ExprKind::MethodCall(name, _, args, _) => ExprUseNode::MethodArg(
                    use_expr.hir_id,
                    name.args,
                    args.iter()
                        .position(|arg| arg.hir_id == self.child_id)
                        .map_or(0, |i| i + 1),
                ),
                ExprKind::Field(_, name) => ExprUseNode::FieldAccess(name),
                ExprKind::AddrOf(kind, mutbl, _) => ExprUseNode::AddrOf(kind, mutbl),
                _ => ExprUseNode::Other,
            },
            _ => ExprUseNode::Other,
        }
    }
}

/// The node which consumes a value.
pub enum ExprUseNode<'tcx> {
    /// Assignment to, or initializer for, a local
    LetStmt(&'tcx LetStmt<'tcx>),
    /// Initializer for a const or static item.
    ConstStatic(OwnerId),
    /// Implicit or explicit return from a function.
    Return(OwnerId),
    /// Initialization of a struct field.
    Field(&'tcx ExprField<'tcx>),
    /// An argument to a function.
    FnArg(&'tcx Expr<'tcx>, usize),
    /// An argument to a method.
    MethodArg(HirId, Option<&'tcx GenericArgs<'tcx>>, usize),
    /// The callee of a function call.
    Callee,
    /// Access of a field.
    FieldAccess(Ident),
    /// Borrow expression.
    AddrOf(ast::BorrowKind, Mutability),
    Other,
}
impl<'tcx> ExprUseNode<'tcx> {
    /// Checks if the value is returned from the function.
    pub fn is_return(&self) -> bool {
        matches!(self, Self::Return(_))
    }

    /// Checks if the value is used as a method call receiver.
    pub fn is_recv(&self) -> bool {
        matches!(self, Self::MethodArg(_, _, 0))
    }

    /// Gets the needed type as it's defined without any type inference.
    pub fn defined_ty(&self, cx: &LateContext<'tcx>) -> Option<DefinedTy<'tcx>> {
        match *self {
            Self::LetStmt(LetStmt { ty: Some(ty), .. }) => Some(DefinedTy::Hir(ty)),
            Self::ConstStatic(id) => Some(DefinedTy::Mir {
                def_site_def_id: Some(id.def_id.to_def_id()),
                ty: Binder::dummy(cx.tcx.type_of(id).instantiate_identity().skip_norm_wip()),
            }),
            Self::Return(id) => {
                if let Node::Expr(Expr {
                    kind: ExprKind::Closure(c),
                    ..
                }) = cx.tcx.hir_node_by_def_id(id.def_id)
                {
                    match c.fn_decl.output {
                        FnRetTy::DefaultReturn(_) => None,
                        FnRetTy::Return(ty) => Some(DefinedTy::Hir(ty)),
                    }
                } else {
                    let ty = cx.tcx.fn_sig(id).instantiate_identity().skip_norm_wip().output();
                    Some(DefinedTy::Mir {
                        def_site_def_id: Some(id.def_id.to_def_id()),
                        ty,
                    })
                }
            },
            Self::Field(field) => match get_parent_expr_for_hir(cx, field.hir_id) {
                Some(Expr {
                    hir_id,
                    kind: ExprKind::Struct(path, ..),
                    ..
                }) => adt_and_variant_of_res(cx, cx.qpath_res(path, *hir_id))
                    .and_then(|(adt, variant)| {
                        variant
                            .fields
                            .iter()
                            .find(|f| f.name == field.ident.name)
                            .map(|f| (adt, f))
                    })
                    .map(|(adt, field_def)| DefinedTy::Mir {
                        def_site_def_id: Some(adt.did()),
                        ty: Binder::dummy(cx.tcx.type_of(field_def.did).instantiate_identity().skip_norm_wip()),
                    }),
                _ => None,
            },
            Self::FnArg(callee, i) => {
                let sig = expr_sig(cx, callee)?;
                let (hir_ty, ty) = sig.input_with_hir(i)?;
                Some(match hir_ty {
                    Some(hir_ty) => DefinedTy::Hir(hir_ty),
                    None => DefinedTy::Mir {
                        def_site_def_id: sig.predicates_id(),
                        ty,
                    },
                })
            },
            Self::MethodArg(id, _, i) => {
                let id = cx.typeck_results().type_dependent_def_id(id)?;
                let sig = cx.tcx.fn_sig(id).skip_binder();
                Some(DefinedTy::Mir {
                    def_site_def_id: Some(id),
                    ty: sig.input(i),
                })
            },
            Self::LetStmt(_) | Self::FieldAccess(..) | Self::Callee | Self::Other | Self::AddrOf(..) => None,
        }
    }
}

struct ReplacingFilterMap<I, F>(I, F);
impl<I, F, U> Iterator for ReplacingFilterMap<I, F>
where
    I: Iterator,
    F: FnMut(&mut I, I::Item) -> Option<U>,
{
    type Item = U;
    fn next(&mut self) -> Option<U> {
        while let Some(x) = self.0.next() {
            if let Some(x) = (self.1)(&mut self.0, x) {
                return Some(x);
            }
        }
        None
    }
}

/// Returns an iterator which walks successive value using parent nodes skipping any node
/// which simply moves a value.
#[expect(clippy::too_many_lines)]
pub fn expr_use_sites<'tcx>(
    tcx: TyCtxt<'tcx>,
    typeck: &'tcx TypeckResults<'tcx>,
    mut ctxt: SyntaxContext,
    e: &'tcx Expr<'tcx>,
) -> impl Iterator<Item = ExprUseSite<'tcx>> {
    let mut adjustments: &[_] = typeck.expr_adjustments(e);
    let mut is_ty_unified = false;
    let mut moved_before_use = false;
    let mut same_ctxt = true;
    ReplacingFilterMap(
        hir_parent_with_src_iter(tcx, e.hir_id),
        move |iter: &mut _, (parent, child_id)| {
            let parent_ctxt;
            let mut parent_adjustments: &[_] = &[];
            match parent {
                Node::Expr(parent_expr) => {
                    parent_ctxt = parent_expr.span.ctxt();
                    same_ctxt &= parent_ctxt == ctxt;
                    parent_adjustments = typeck.expr_adjustments(parent_expr);
                    match parent_expr.kind {
                        ExprKind::Match(scrutinee, arms, _) if scrutinee.hir_id != child_id => {
                            is_ty_unified |= arms.len() != 1;
                            moved_before_use = true;
                            if adjustments.is_empty() {
                                adjustments = parent_adjustments;
                            }
                            return None;
                        },
                        ExprKind::If(cond, _, else_) if cond.hir_id != child_id => {
                            is_ty_unified |= else_.is_some();
                            moved_before_use = true;
                            if adjustments.is_empty() {
                                adjustments = parent_adjustments;
                            }
                            return None;
                        },
                        ExprKind::Break(Destination { target_id: Ok(id), .. }, _) => {
                            is_ty_unified = true;
                            moved_before_use = true;
                            *iter = hir_parent_with_src_iter(tcx, id);
                            if adjustments.is_empty() {
                                adjustments = parent_adjustments;
                            }
                            return None;
                        },
                        ExprKind::Block(b, _) => {
                            is_ty_unified |= b.targeted_by_break;
                            moved_before_use = true;
                            if adjustments.is_empty() {
                                adjustments = parent_adjustments;
                            }
                            return None;
                        },
                        ExprKind::DropTemps(_) | ExprKind::Type(..) => {
                            if adjustments.is_empty() {
                                adjustments = parent_adjustments;
                            }
                            return None;
                        },
                        _ => {},
                    }
                },
                Node::Arm(arm) => {
                    parent_ctxt = arm.span.ctxt();
                    same_ctxt &= parent_ctxt == ctxt;
                    if arm.body.hir_id == child_id {
                        return None;
                    }
                },
                Node::Block(b) => {
                    same_ctxt &= b.span.ctxt() == ctxt;
                    return None;
                },
                Node::ConstBlock(_) => parent_ctxt = ctxt,
                Node::ExprField(&ExprField { span, .. }) => {
                    parent_ctxt = span.ctxt();
                    same_ctxt &= parent_ctxt == ctxt;
                },
                Node::AnonConst(&AnonConst { span, .. })
                | Node::ConstArg(&ConstArg { span, .. })
                | Node::Field(&FieldDef { span, .. })
                | Node::ImplItem(&ImplItem { span, .. })
                | Node::Item(&Item { span, .. })
                | Node::LetStmt(&LetStmt { span, .. })
                | Node::Stmt(&Stmt { span, .. })
                | Node::TraitItem(&TraitItem { span, .. })
                | Node::Variant(&Variant { span, .. }) => {
                    parent_ctxt = span.ctxt();
                    same_ctxt &= parent_ctxt == ctxt;
                    *iter = hir_parent_with_src_iter(tcx, CRATE_HIR_ID);
                },
                Node::AssocItemConstraint(_)
                | Node::ConstArgExprField(_)
                | Node::Crate(_)
                | Node::Ctor(_)
                | Node::Err(_)
                | Node::ForeignItem(_)
                | Node::GenericParam(_)
                | Node::Infer(_)
                | Node::Lifetime(_)
                | Node::OpaqueTy(_)
                | Node::Param(_)
                | Node::Pat(_)
                | Node::PatExpr(_)
                | Node::PatField(_)
                | Node::PathSegment(_)
                | Node::PreciseCapturingNonLifetimeArg(_)
                | Node::Synthetic
                | Node::TraitRef(_)
                | Node::Ty(_)
                | Node::TyPat(_)
                | Node::NestedUseTree(_)
                | Node::WherePredicate(_)
                | Node::TestBinderForall(_)
                | Node::TestBinderExists(_)
                | Node::TestBinderBoundTypeConstraint(_) => {
                    // This shouldn't be possible to hit; the inner iterator should have
                    // been moved to the end before we hit any of these nodes.
                    debug_assert!(false, "found {parent:?} which is after the final use node");
                    return None;
                },
            }

            ctxt = parent_ctxt;
            Some(ExprUseSite {
                node: parent,
                child_id,
                adjustments: mem::replace(&mut adjustments, parent_adjustments),
                is_ty_unified: mem::replace(&mut is_ty_unified, false),
                moved_before_use: mem::replace(&mut moved_before_use, false),
                same_ctxt: mem::replace(&mut same_ctxt, true),
            })
        },
    )
}

pub fn get_expr_use_site<'tcx>(
    tcx: TyCtxt<'tcx>,
    typeck: &'tcx TypeckResults<'tcx>,
    ctxt: SyntaxContext,
    e: &'tcx Expr<'tcx>,
) -> ExprUseSite<'tcx> {
    // The value in `unwrap_or` doesn't actually matter; an expression always
    // has a use site.
    expr_use_sites(tcx, typeck, ctxt, e).next().unwrap_or_else(|| {
        debug_assert!(false, "failed to find a use site for expr {e:?}");
        ExprUseSite {
            node: Node::Synthetic, // The crate root would also work.
            child_id: CRATE_HIR_ID,
            adjustments: &[],
            is_ty_unified: false,
            moved_before_use: false,
            same_ctxt: false,
        }
    })
}

/// Tokenizes the input while keeping the text associated with each token.
pub fn tokenize_with_text(s: &str) -> impl Iterator<Item = (TokenKind, &str, InnerSpan)> {
    let mut pos = 0;
    tokenize(s, FrontmatterAllowed::No).map(move |t| {
        let end = pos + t.len;
        let range = pos as usize..end as usize;
        let inner = InnerSpan::new(range.start, range.end);
        pos = end;
        (t.kind, s.get(range).unwrap_or_default(), inner)
    })
}

/// Checks whether a given span has any comment token
/// This checks for all types of comment: line "//", block "/**", doc "///" "//!"
pub fn span_contains_comment<'sm>(sm: impl HasSourceMap<'sm>, span: Span) -> bool {
    span.check_text(sm, |snippet| {
        tokenize(snippet, FrontmatterAllowed::No).any(|token| {
            matches!(
                token.kind,
                TokenKind::BlockComment { .. } | TokenKind::LineComment { .. }
            )
        })
    })
}

/// Checks whether a given span has any significant token. A significant token is a non-whitespace
/// token, including comments unless `skip_comments` is set.
/// This is useful to determine if there are any actual code tokens in the span that are omitted in
/// the late pass, such as platform-specific code.
pub fn span_contains_non_whitespace<'sm>(sm: impl HasSourceMap<'sm>, span: Span, skip_comments: bool) -> bool {
    span.check_text(sm, |snippet| {
        tokenize_with_text(snippet).any(|(token, _, _)| match token {
            TokenKind::Whitespace => false,
            TokenKind::BlockComment { .. } | TokenKind::LineComment { .. } => !skip_comments,
            _ => true,
        })
    })
}

/// Returns all the comments a given span contains
///
/// Comments are returned wrapped with their relevant delimiters
pub fn span_extract_comment<'sm>(sm: impl HasSourceMap<'sm>, span: Span) -> String {
    span_extract_comments(sm, span).join("\n")
}

/// Returns all the comments a given span contains.
///
/// Comments are returned wrapped with their relevant delimiters.
pub fn span_extract_comments<'sm>(sm: impl HasSourceMap<'sm>, span: Span) -> Vec<String> {
    span.with_source_text(sm, |snippet| {
        tokenize_with_text(snippet)
            .filter(|(t, ..)| matches!(t, TokenKind::BlockComment { .. } | TokenKind::LineComment { .. }))
            .map(|(_, s, _)| s.to_string())
            .collect::<Vec<_>>()
    })
    .unwrap_or_default()
}

pub fn span_find_starting_semi(sm: &SourceMap, span: Span) -> Span {
    sm.span_take_while(span, |&ch| ch == ' ' || ch == ';')
}

/// Returns whether the given let pattern and else body can be turned into the `?` operator
///
/// For this example:
/// ```ignore
/// let FooBar { a, b } = if let Some(a) = ex { a } else { return None };
/// ```
/// We get as parameters:
/// ```ignore
/// pat: Some(a)
/// else_body: return None
/// ```
///
/// And for this example:
/// ```ignore
/// let Some(FooBar { a, b }) = ex else { return None };
/// ```
/// We get as parameters:
/// ```ignore
/// pat: Some(FooBar { a, b })
/// else_body: return None
/// ```
///
/// We output `Some(a)` in the first instance, and `Some(FooBar { a, b })` in the second, because
/// the `?` operator is applicable here. Callers have to check whether we are in a constant or not.
pub fn pat_and_expr_can_be_question_mark<'a, 'hir>(
    cx: &LateContext<'_>,
    pat: &'a Pat<'hir>,
    else_body: &Expr<'_>,
) -> Option<&'a Pat<'hir>> {
    if let Some([inner_pat]) = as_some_pattern(cx, pat)
        && !is_refutable(cx, inner_pat)
        && let else_body = peel_blocks(else_body)
        && let ExprKind::Ret(Some(ret_val)) = else_body.kind
        && let ExprKind::Path(ret_path) = ret_val.kind
        && cx
            .qpath_res(&ret_path, ret_val.hir_id)
            .ctor_parent(cx)
            .is_lang_item(cx, OptionNone)
    {
        Some(inner_pat)
    } else {
        None
    }
}

macro_rules! op_utils {
    ($($name:ident $assign:ident)*) => {
        /// Binary operation traits like `LangItem::Add`
        pub static BINOP_TRAITS: &[LangItem] = &[$(LangItem::$name,)*];

        /// Operator-Assign traits like `LangItem::AddAssign`
        pub static OP_ASSIGN_TRAITS: &[LangItem] = &[$(LangItem::$assign,)*];

        /// Converts `BinOpKind::Add` to `(LangItem::Add, LangItem::AddAssign)`, for example
        pub fn binop_traits(kind: hir::BinOpKind) -> Option<(LangItem, LangItem)> {
            match kind {
                $(hir::BinOpKind::$name => Some((LangItem::$name, LangItem::$assign)),)*
                _ => None,
            }
        }
    };
}

op_utils! {
    Add    AddAssign
    Sub    SubAssign
    Mul    MulAssign
    Div    DivAssign
    Rem    RemAssign
    BitXor BitXorAssign
    BitAnd BitAndAssign
    BitOr  BitOrAssign
    Shl    ShlAssign
    Shr    ShrAssign
}

/// Returns `true` if the pattern is a `PatWild`, or is an ident prefixed with `_`
/// that is not locally used.
pub fn pat_is_wild<'tcx>(cx: &LateContext<'tcx>, pat: &'tcx PatKind<'_>, body: impl Visitable<'tcx>) -> bool {
    match *pat {
        PatKind::Wild => true,
        PatKind::Binding(_, id, ident, None) if ident.as_str().starts_with('_') => {
            !visitors::is_local_used(cx, body, id)
        },
        _ => false,
    }
}

#[derive(Clone, Copy)]
pub enum RequiresSemi {
    Yes,
    No,
}
impl RequiresSemi {
    pub fn requires_semi(self) -> bool {
        matches!(self, Self::Yes)
    }
}

/// Check if the expression return `!`, a type coerced from `!`, or could return `!` if the final
/// expression were turned into a statement.
#[expect(clippy::too_many_lines)]
pub fn is_never_expr<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) -> Option<RequiresSemi> {
    struct BreakTarget {
        id: HirId,
        unused: bool,
    }

    struct V<'cx, 'tcx> {
        cx: &'cx LateContext<'tcx>,
        break_targets: Vec<BreakTarget>,
        break_targets_for_result_ty: u32,
        in_final_expr: bool,
        requires_semi: bool,
        is_never: bool,
    }

    impl V<'_, '_> {
        fn push_break_target(&mut self, id: HirId) {
            self.break_targets.push(BreakTarget { id, unused: true });
            self.break_targets_for_result_ty += u32::from(self.in_final_expr);
        }
    }

    impl<'tcx> Visitor<'tcx> for V<'_, 'tcx> {
        fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
            // Note: Part of the complexity here comes from the fact that
            // coercions are applied to the innermost expression.
            // e.g. In `let x: u32 = { break () };` the never-to-any coercion
            // is applied to the break expression. This means we can't just
            // check the block's type as it will be `u32` despite the fact
            // that the block always diverges.

            // The rest of the complexity comes from checking blocks which
            // syntactically return a value, but will always diverge before
            // reaching that point.
            // e.g. In `let x = { foo(panic!()) };` the block's type will be the
            // return type of `foo` even though it will never actually run. This
            // can be trivially fixed by adding a semicolon after the call, but
            // we must first detect that a semicolon is needed to make that
            // suggestion.

            if self.is_never && self.break_targets.is_empty() {
                if self.in_final_expr && !self.requires_semi {
                    // This expression won't ever run, but we still need to check
                    // if it can affect the type of the final expression.
                    match e.kind {
                        ExprKind::DropTemps(e) => self.visit_expr(e),
                        ExprKind::If(_, then, Some(else_)) => {
                            self.visit_expr(then);
                            self.visit_expr(else_);
                        },
                        ExprKind::Match(_, arms, _) => {
                            for arm in arms {
                                self.visit_expr(arm.body);
                            }
                        },
                        ExprKind::Loop(b, ..) => {
                            self.push_break_target(e.hir_id);
                            self.in_final_expr = false;
                            self.visit_block(b);
                            self.break_targets.pop();
                        },
                        ExprKind::Block(b, _) => {
                            if b.targeted_by_break {
                                self.push_break_target(b.hir_id);
                                self.visit_block(b);
                                self.break_targets.pop();
                            } else {
                                self.visit_block(b);
                            }
                        },
                        _ => {
                            self.requires_semi = !self.cx.typeck_results().expr_ty(e).is_never();
                        },
                    }
                }
                return;
            }
            match e.kind {
                ExprKind::DropTemps(e) => self.visit_expr(e),
                ExprKind::Ret(None) | ExprKind::Continue(_) => self.is_never = true,
                ExprKind::Ret(Some(e)) | ExprKind::Become(e) => {
                    self.in_final_expr = false;
                    self.visit_expr(e);
                    self.is_never = true;
                },
                ExprKind::Break(dest, e) => {
                    if let Some(e) = e {
                        self.in_final_expr = false;
                        self.visit_expr(e);
                    }
                    if let Ok(id) = dest.target_id
                        && let Some((i, target)) = self
                            .break_targets
                            .iter_mut()
                            .enumerate()
                            .find(|(_, target)| target.id == id)
                    {
                        target.unused &= self.is_never;
                        if i < self.break_targets_for_result_ty as usize {
                            self.requires_semi = true;
                        }
                    }
                    self.is_never = true;
                },
                ExprKind::If(cond, then, else_) => {
                    let in_final_expr = mem::replace(&mut self.in_final_expr, false);
                    self.visit_expr(cond);
                    self.in_final_expr = in_final_expr;

                    if self.is_never {
                        self.visit_expr(then);
                        if let Some(else_) = else_ {
                            self.visit_expr(else_);
                        }
                    } else {
                        self.visit_expr(then);
                        let is_never = mem::replace(&mut self.is_never, false);
                        if let Some(else_) = else_ {
                            self.visit_expr(else_);
                            self.is_never &= is_never;
                        }
                    }
                },
                ExprKind::Match(scrutinee, arms, _) => {
                    let in_final_expr = mem::replace(&mut self.in_final_expr, false);
                    self.visit_expr(scrutinee);
                    self.in_final_expr = in_final_expr;

                    if self.is_never {
                        for arm in arms {
                            self.visit_arm(arm);
                        }
                    } else {
                        let mut is_never = true;
                        for arm in arms {
                            self.is_never = false;
                            if let Some(guard) = arm.guard {
                                let in_final_expr = mem::replace(&mut self.in_final_expr, false);
                                self.visit_expr(guard);
                                self.in_final_expr = in_final_expr;
                                // The compiler doesn't consider diverging guards as causing the arm
                                // to diverge.
                                self.is_never = false;
                            }
                            self.visit_expr(arm.body);
                            is_never &= self.is_never;
                        }
                        self.is_never = is_never;
                    }
                },
                ExprKind::Loop(b, _, _, _) => {
                    self.push_break_target(e.hir_id);
                    self.in_final_expr = false;
                    self.visit_block(b);
                    self.is_never = self.break_targets.pop().unwrap().unused;
                },
                ExprKind::Block(b, _) => {
                    if b.targeted_by_break {
                        self.push_break_target(b.hir_id);
                        self.visit_block(b);
                        self.is_never &= self.break_targets.pop().unwrap().unused;
                    } else {
                        self.visit_block(b);
                    }
                },
                _ => {
                    self.in_final_expr = false;
                    walk_expr(self, e);
                    self.is_never |= self.cx.typeck_results().expr_ty(e).is_never();
                },
            }
        }

        fn visit_block(&mut self, b: &'tcx Block<'_>) {
            let in_final_expr = mem::replace(&mut self.in_final_expr, false);
            for s in b.stmts {
                self.visit_stmt(s);
            }
            self.in_final_expr = in_final_expr;
            if let Some(e) = b.expr {
                self.visit_expr(e);
            }
        }

        fn visit_local(&mut self, l: &'tcx LetStmt<'_>) {
            if let Some(e) = l.init {
                self.visit_expr(e);
            }
            if let Some(else_) = l.els {
                let is_never = self.is_never;
                self.visit_block(else_);
                self.is_never = is_never;
            }
        }

        fn visit_arm(&mut self, arm: &Arm<'tcx>) {
            if let Some(guard) = arm.guard {
                let in_final_expr = mem::replace(&mut self.in_final_expr, false);
                self.visit_expr(guard);
                self.in_final_expr = in_final_expr;
            }
            self.visit_expr(arm.body);
        }
    }

    if cx.typeck_results().expr_ty(e).is_never() {
        Some(RequiresSemi::No)
    } else if let ExprKind::Block(b, _) = e.kind
        && !b.targeted_by_break
        && b.expr.is_none()
    {
        // If a block diverges without a final expression then it's type is `!`.
        None
    } else {
        let mut v = V {
            cx,
            break_targets: Vec::new(),
            break_targets_for_result_ty: 0,
            in_final_expr: true,
            requires_semi: false,
            is_never: false,
        };
        v.visit_expr(e);
        v.is_never
            .then_some(if v.requires_semi && matches!(e.kind, ExprKind::Block(..)) {
                RequiresSemi::Yes
            } else {
                RequiresSemi::No
            })
    }
}

/// Produces a path from a local caller to the type of the called method. Suitable for user
/// output/suggestions.
///
/// Returned path can be either absolute (for methods defined non-locally), or relative (for local
/// methods).
pub fn get_path_from_caller_to_method_type<'tcx>(
    tcx: TyCtxt<'tcx>,
    from: LocalDefId,
    method: DefId,
    args: GenericArgsRef<'tcx>,
) -> String {
    let assoc_item = tcx.associated_item(method);
    let def_id = assoc_item.container_id(tcx);
    match assoc_item.container {
        rustc_ty::AssocContainer::Trait => get_path_to_callee(tcx, from, def_id),
        rustc_ty::AssocContainer::InherentImpl | rustc_ty::AssocContainer::TraitImpl(_) => {
            let ty = tcx.type_of(def_id).instantiate_identity().skip_norm_wip();
            get_path_to_ty(tcx, from, ty, args)
        },
    }
}

fn get_path_to_ty<'tcx>(tcx: TyCtxt<'tcx>, from: LocalDefId, ty: Ty<'tcx>, args: GenericArgsRef<'tcx>) -> String {
    match ty.kind() {
        rustc_ty::Adt(adt, _) => get_path_to_callee(tcx, from, adt.did()),
        // TODO these types need to be recursively resolved as well
        rustc_ty::Array(..)
        | rustc_ty::Dynamic(..)
        | rustc_ty::Never
        | rustc_ty::RawPtr(_, _)
        | rustc_ty::Ref(..)
        | rustc_ty::Slice(_)
        | rustc_ty::Tuple(_) => format!(
            "<{}>",
            EarlyBinder::bind(tcx, ty).instantiate(tcx, args).skip_norm_wip()
        ),
        _ => ty.to_string(),
    }
}

/// Produce a path from some local caller to the callee. Suitable for user output/suggestions.
fn get_path_to_callee(tcx: TyCtxt<'_>, from: LocalDefId, callee: DefId) -> String {
    // only search for a relative path if the call is fully local
    if callee.is_local() {
        let callee_path = tcx.def_path(callee);
        let caller_path = tcx.def_path(from.to_def_id());
        maybe_get_relative_path(&caller_path, &callee_path, 2)
    } else {
        tcx.def_path_str(callee)
    }
}

/// Tries to produce a relative path from `from` to `to`; if such a path would contain more than
/// `max_super` `super` items, produces an absolute path instead. Both `from` and `to` should be in
/// the local crate.
///
/// Suitable for user output/suggestions.
///
/// This ignores use items, and assumes that the target path is visible from the source
/// path (which _should_ be a reasonable assumption since we in order to be able to use an object of
/// certain type T, T is required to be visible).
///
/// TODO make use of `use` items. Maybe we should have something more sophisticated like
/// rust-analyzer does? <https://docs.rs/ra_ap_hir_def/0.0.169/src/ra_ap_hir_def/find_path.rs.html#19-27>
fn maybe_get_relative_path(from: &DefPath, to: &DefPath, max_super: usize) -> String {
    use itertools::EitherOrBoth::{Both, Left, Right};

    // 1. skip the segments common for both paths (regardless of their type)
    let unique_parts = to
        .data
        .iter()
        .zip_longest(from.data.iter())
        .skip_while(|el| matches!(el, Both(l, r) if l == r))
        .map(|el| match el {
            Both(l, r) => Both(l.data, r.data),
            Left(l) => Left(l.data),
            Right(r) => Right(r.data),
        });

    // 2. for the remaining segments, construct relative path using only mod names and `super`
    let mut go_up_by = 0;
    let mut path = Vec::new();
    for el in unique_parts {
        match el {
            Both(l, r) => {
                // consider:
                // a::b::sym:: ::    refers to
                // c::d::e  ::f::sym
                // result should be super::super::c::d::e::f
                //
                // alternatively:
                // a::b::c  ::d::sym refers to
                // e::f::sym:: ::
                // result should be super::super::super::super::e::f
                if let DefPathData::TypeNs(sym) = l {
                    path.push(sym);
                }
                if let DefPathData::TypeNs(_) = r {
                    go_up_by += 1;
                }
            },
            // consider:
            // a::b::sym:: ::    refers to
            // c::d::e  ::f::sym
            // when looking at `f`
            Left(DefPathData::TypeNs(sym)) => path.push(sym),
            // consider:
            // a::b::c  ::d::sym refers to
            // e::f::sym:: ::
            // when looking at `d`
            Right(DefPathData::TypeNs(_)) => go_up_by += 1,
            _ => {},
        }
    }

    if go_up_by > max_super {
        // `super` chain would be too long, just use the absolute path instead
        join_path_syms(once(kw::Crate).chain(to.data.iter().filter_map(|el| {
            if let DefPathData::TypeNs(sym) = el.data {
                Some(sym)
            } else {
                None
            }
        })))
    } else if go_up_by == 0 && path.is_empty() {
        String::from("Self")
    } else {
        join_path_syms(repeat_n(kw::Super, go_up_by).chain(path))
    }
}

/// Returns true if the specified `HirId` is the top-level expression of a statement or the only
/// expression in a block.
pub fn is_parent_stmt(cx: &LateContext<'_>, id: HirId) -> bool {
    matches!(
        cx.tcx.parent_hir_node(id),
        Node::Stmt(..) | Node::Block(Block { stmts: [], .. })
    )
}

/// Returns true if the given `expr` is a block or resembled as a block,
/// such as `if`, `loop`, `match` expressions etc.
pub fn is_block_like(expr: &Expr<'_>) -> bool {
    matches!(
        expr.kind,
        ExprKind::Block(..) | ExprKind::ConstBlock(..) | ExprKind::If(..) | ExprKind::Loop(..) | ExprKind::Match(..)
    )
}

/// Returns true if the given `expr` is binary expression that needs to be wrapped in parentheses.
pub fn binary_expr_needs_parentheses(expr: &Expr<'_>) -> bool {
    fn contains_block(expr: &Expr<'_>, is_operand: bool) -> bool {
        match expr.kind {
            ExprKind::Binary(_, lhs, _) | ExprKind::Cast(lhs, _) => contains_block(lhs, true),
            _ if is_block_like(expr) => is_operand,
            _ => false,
        }
    }

    contains_block(expr, false)
}

/// Returns true if the specified expression is in a receiver position.
pub fn is_receiver_of_method_call(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
    if let Some(parent_expr) = get_parent_expr(cx, expr)
        && let ExprKind::MethodCall(_, receiver, ..) = parent_expr.kind
        && receiver.hir_id == expr.hir_id
    {
        return true;
    }
    false
}

/// Returns true if `expr` creates any temporary whose type references a non-static lifetime and has
/// a significant drop and does not consume it.
pub fn leaks_droppable_temporary_with_limited_lifetime<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool {
    for_each_unconsumed_temporary(cx, expr, |temporary_ty| {
        if temporary_ty.has_significant_drop(cx.tcx, cx.typing_env())
            && temporary_ty
                .walk()
                .any(|arg| matches!(arg.kind(), GenericArgKind::Lifetime(re) if !re.is_static()))
        {
            ControlFlow::Break(())
        } else {
            ControlFlow::Continue(())
        }
    })
    .is_break()
}

/// Returns true if `expr` creates any temporary that has a significant drop and does not consume
/// it.
pub fn leaks_droppable_temporary<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool {
    for_each_unconsumed_temporary(cx, expr, |temporary_ty| {
        if temporary_ty.has_significant_drop(cx.tcx, cx.typing_env()) {
            ControlFlow::Break(())
        } else {
            ControlFlow::Continue(())
        }
    })
    .is_break()
}

/// Returns true if the specified `expr` requires coercion,
/// meaning that it either has a coercion or propagates a coercion from one of its sub expressions.
///
/// Similar to [`is_adjusted`], this not only checks if an expression's type was adjusted,
/// but also going through extra steps to see if it fits the description of [coercion sites].
///
/// You should used this when you want to avoid suggesting replacing an expression that is currently
/// a coercion site or coercion propagating expression with one that is not.
///
/// [coercion sites]: https://doc.rust-lang.org/stable/reference/type-coercions.html#coercion-sites
pub fn expr_requires_coercion<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) -> bool {
    let expr_ty_is_adjusted = cx
        .typeck_results()
        .expr_adjustments(expr)
        .iter()
        // ignore `NeverToAny` adjustments, such as `panic!` call.
        .any(|adj| !matches!(adj.kind, Adjust::NeverToAny));
    if expr_ty_is_adjusted {
        return true;
    }

    // Identify coercion sites and recursively check if those sites
    // actually have type adjustments.
    match expr.kind {
        ExprKind::Call(_, args) | ExprKind::MethodCall(_, _, args, _) if let Some(def_id) = fn_def_id(cx, expr) => {
            let fn_sig = cx.tcx.fn_sig(def_id).instantiate_identity().skip_norm_wip();

            if !fn_sig.output().skip_binder().has_type_flags(TypeFlags::HAS_TY_PARAM) {
                return false;
            }

            let self_arg_count = usize::from(matches!(expr.kind, ExprKind::MethodCall(..)));
            let mut args_with_ty_param = {
                fn_sig
                    .inputs()
                    .skip_binder()
                    .iter()
                    .skip(self_arg_count)
                    .zip(args)
                    .filter_map(|(arg_ty, arg)| {
                        if arg_ty.has_type_flags(TypeFlags::HAS_TY_PARAM) {
                            Some(arg)
                        } else {
                            None
                        }
                    })
            };
            args_with_ty_param.any(|arg| expr_requires_coercion(cx, arg))
        },
        // Struct/union initialization.
        ExprKind::Struct(qpath, _, _) => {
            let res = cx.typeck_results().qpath_res(qpath, expr.hir_id);
            if let Some((_, v_def)) = adt_and_variant_of_res(cx, res) {
                let rustc_ty::Adt(_, generic_args) = cx.typeck_results().expr_ty_adjusted(expr).kind() else {
                    // This should never happen, but when it does, not linting is the better option.
                    return true;
                };
                v_def
                    .fields
                    .iter()
                    .any(|field| field.ty(cx.tcx, generic_args).has_type_flags(TypeFlags::HAS_TY_PARAM))
            } else {
                false
            }
        },
        // Function results, including the final line of a block or a `return` expression.
        ExprKind::Block(
            &Block {
                expr: Some(ret_expr), ..
            },
            _,
        )
        | ExprKind::Ret(Some(ret_expr)) => expr_requires_coercion(cx, ret_expr),

        // ===== Coercion-propagation expressions =====
        ExprKind::Array(elems) | ExprKind::Tup(elems) => elems.iter().any(|elem| expr_requires_coercion(cx, elem)),
        // Array but with repeating syntax.
        ExprKind::Repeat(rep_elem, _) => expr_requires_coercion(cx, rep_elem),
        // Others that may contain coercion sites.
        ExprKind::If(_, then, maybe_else) => {
            expr_requires_coercion(cx, then) || maybe_else.is_some_and(|e| expr_requires_coercion(cx, e))
        },
        ExprKind::Match(_, arms, _) => arms
            .iter()
            .map(|arm| arm.body)
            .any(|body| expr_requires_coercion(cx, body)),
        _ => false,
    }
}

/// Returns `true` if `expr` designates a mutable static, a mutable local binding, or an expression
/// that can be owned.
pub fn is_mutable(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
    if let Some(hir_id) = expr.res_local_id()
        && let Node::Pat(pat) = cx.tcx.hir_node(hir_id)
    {
        matches!(pat.kind, PatKind::Binding(BindingMode::MUT, ..))
    } else if let ExprKind::Path(p) = &expr.kind
        && let Some(mutability) = cx
            .qpath_res(p, expr.hir_id)
            .opt_def_id()
            .and_then(|id| cx.tcx.static_mutability(id))
    {
        mutability == Mutability::Mut
    } else if let ExprKind::Field(parent, _) = expr.kind {
        is_mutable(cx, parent)
    } else {
        true
    }
}

/// Peel `Option<…>` from `hir_ty` as long as the HIR name is `Option` and it corresponds to the
/// `core::Option<_>` type.
pub fn peel_hir_ty_options<'tcx>(cx: &LateContext<'tcx>, mut hir_ty: &'tcx hir::Ty<'tcx>) -> &'tcx hir::Ty<'tcx> {
    let Some(option_def_id) = cx.tcx.get_diagnostic_item(sym::Option) else {
        return hir_ty;
    };
    while let TyKind::Path(QPath::Resolved(None, path)) = hir_ty.kind
        && let Some(segment) = path.segments.last()
        && segment.ident.name == sym::Option
        && let Res::Def(DefKind::Enum, def_id) = segment.res
        && def_id == option_def_id
        && let [GenericArg::Type(arg_ty)] = segment.args().args
    {
        hir_ty = arg_ty.as_unambig_ty();
    }
    hir_ty
}

/// If `expr` is a desugared `.await`, return the original expression if it does not come from a
/// macro expansion.
pub fn desugar_await<'tcx>(expr: &'tcx Expr<'_>) -> Option<&'tcx Expr<'tcx>> {
    if let ExprKind::Match(match_value, _, MatchSource::AwaitDesugar) = expr.kind
        && let ExprKind::Call(_, [into_future_arg]) = match_value.kind
        && let ctxt = expr.span.ctxt()
        && for_each_expr_without_closures(into_future_arg, |e| {
            walk_span_to_context(e.span, ctxt).map_or(ControlFlow::Break(()), |_| ControlFlow::Continue(()))
        })
        .is_none()
    {
        Some(into_future_arg)
    } else {
        None
    }
}

/// Checks if the given expression is a call to `Default::default()`.
pub fn is_expr_default<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool {
    if let ExprKind::Call(fn_expr, []) = &expr.kind
        && let ExprKind::Path(qpath) = &fn_expr.kind
        && let Res::Def(_, def_id) = cx.qpath_res(qpath, fn_expr.hir_id)
    {
        cx.tcx.is_diagnostic_item(sym::default_fn, def_id)
    } else {
        false
    }
}

/// Checks if `expr` may be directly used as the return value of its enclosing body.
/// The following cases are covered:
/// - `expr` as the last expression of the body, or of a block that can be used as the return value
/// - `return expr`
/// - then or else part of a `if` in return position
/// - arm body of a `match` in a return position
/// - `break expr` or `break 'label expr` if the loop or block being exited is used as a return value
///
/// Contrary to [`TyCtxt::hir_get_fn_id_for_return_block()`], if `expr` is part of a
/// larger expression, for example a field expression of a `struct`, it will not be
/// considered as matching the condition and will return `false`.
///
/// Also, even if `expr` is assigned to a variable which is later returned, this function
/// will still return `false` because `expr` is not used *directly* as the return value
/// as it goes through the intermediate variable.
pub fn potential_return_of_enclosing_body(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
    let enclosing_body_owner = cx
        .tcx
        .local_def_id_to_hir_id(cx.tcx.hir_enclosing_body_owner(expr.hir_id));
    let mut prev_id = expr.hir_id;
    let mut skip_until_id = None;
    for (hir_id, node) in cx.tcx.hir_parent_iter(expr.hir_id) {
        if hir_id == enclosing_body_owner {
            return true;
        }
        if let Some(id) = skip_until_id {
            prev_id = hir_id;
            if id == hir_id {
                skip_until_id = None;
            }
            continue;
        }
        match node {
            Node::Block(Block { expr, .. }) if expr.is_some_and(|expr| expr.hir_id == prev_id) => {},
            Node::Arm(arm) if arm.body.hir_id == prev_id => {},
            Node::Expr(expr) => match expr.kind {
                ExprKind::Ret(_) => return true,
                ExprKind::If(_, then, opt_else)
                    if then.hir_id == prev_id || opt_else.is_some_and(|els| els.hir_id == prev_id) => {},
                ExprKind::Match(_, arms, _) if arms.iter().any(|arm| arm.hir_id == prev_id) => {},
                ExprKind::Block(block, _) if block.hir_id == prev_id => {},
                ExprKind::Break(
                    Destination {
                        target_id: Ok(target_id),
                        ..
                    },
                    _,
                ) => skip_until_id = Some(target_id),
                _ => break,
            },
            _ => break,
        }
        prev_id = hir_id;
    }

    // `expr` is used as part of "something" and is not returned directly from its
    // enclosing body.
    false
}

/// Checks if the expression has adjustments that require coercion, for example: dereferencing with
/// overloaded deref, coercing pointers and `dyn` objects.
pub fn expr_adjustment_requires_coercion(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
    cx.typeck_results().expr_adjustments(expr).iter().any(|adj| {
        matches!(
            adj.kind,
            Adjust::Deref(DerefAdjustKind::Overloaded(_))
                | Adjust::Pointer(PointerCoercion::Unsize)
                | Adjust::NeverToAny
        )
    })
}

/// Checks if the expression is an async block (i.e., `async { ... }`).
pub fn is_expr_async_block(expr: &Expr<'_>) -> bool {
    matches!(
        expr.kind,
        ExprKind::Closure(Closure {
            kind: hir::ClosureKind::Coroutine(CoroutineKind::Desugared(
                CoroutineDesugaring::Async,
                CoroutineSource::Block
            )),
            ..
        })
    )
}

/// Checks if the chosen edition and `msrv` allows using `if let` chains.
pub fn can_use_if_let_chains(cx: &LateContext<'_>, msrv: Msrv) -> bool {
    cx.tcx.sess.edition().at_least_rust_2024() && msrv.meets(cx, msrvs::LET_CHAINS)
}

/// Returns an iterator over successive parent nodes paired with the ID of the node which
/// immediatly preceeded them.
#[inline]
pub fn hir_parent_with_src_iter(tcx: TyCtxt<'_>, mut id: HirId) -> impl Iterator<Item = (Node<'_>, HirId)> {
    tcx.hir_parent_id_iter(id)
        .map(move |parent| (tcx.hir_node(parent), mem::replace(&mut id, parent)))
}