clippy_utils/ty/

mod.rs

//! Util methods for [`rustc_middle::ty`]

#![allow(clippy::module_name_repetitions)]

use core::ops::ControlFlow;
use rustc_abi::VariantIdx;
use rustc_ast::ast::Mutability;
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_hir as hir;
use rustc_hir::def::{CtorKind, CtorOf, DefKind, Res};
use rustc_hir::def_id::DefId;
use rustc_hir::{Expr, FnDecl, LangItem, find_attr};
use rustc_hir_analysis::lower_ty;
use rustc_infer::infer::TyCtxtInferExt;
use rustc_lint::LateContext;
use rustc_middle::mir::ConstValue;
use rustc_middle::mir::interpret::Scalar;
use rustc_middle::traits::EvaluationResult;
use rustc_middle::ty::adjustment::{Adjust, Adjustment, DerefAdjustKind};
use rustc_middle::ty::layout::ValidityRequirement;
use rustc_middle::ty::{
    self, AdtDef, AliasTy, AssocItem, AssocTag, Binder, BoundRegion, BoundVarIndexKind, FnSig, GenericArg,
    GenericArgKind, GenericArgsRef, IntTy, Region, RegionKind, TraitRef, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable,
    TypeVisitableExt, TypeVisitor, UintTy, Unnormalized, Upcast, VariantDef, VariantDiscr,
};
use rustc_span::symbol::Ident;
use rustc_span::{DUMMY_SP, Span, Symbol};
use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _;
use rustc_trait_selection::traits::query::normalize::QueryNormalizeExt;
use rustc_trait_selection::traits::{Obligation, ObligationCause};
use std::collections::hash_map::Entry;
use std::{debug_assert_matches, iter, mem};

use crate::paths::{PathNS, lookup_path_str};
use crate::res::{MaybeDef, MaybeQPath};
use crate::sym;

mod type_certainty;
pub use type_certainty::expr_type_is_certain;

/// Lower a [`hir::Ty`] to a [`rustc_middle::ty::Ty`].
pub fn ty_from_hir_ty<'tcx>(cx: &LateContext<'tcx>, hir_ty: &hir::Ty<'tcx>) -> Ty<'tcx> {
    cx.maybe_typeck_results()
        .filter(|results| results.hir_owner == hir_ty.hir_id.owner)
        .and_then(|results| results.node_type_opt(hir_ty.hir_id))
        .unwrap_or_else(|| lower_ty(cx.tcx, hir_ty))
}

/// Checks if the given type implements copy.
pub fn is_copy<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
    cx.type_is_copy_modulo_regions(ty)
}

/// This checks whether a given type is known to implement Debug.
pub fn has_debug_impl<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
    cx.tcx
        .get_diagnostic_item(sym::Debug)
        .is_some_and(|debug| implements_trait(cx, ty, debug, &[]))
}

/// Checks whether a type can be partially moved.
pub fn can_partially_move_ty<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
    if has_drop(cx, ty) || is_copy(cx, ty) {
        return false;
    }
    match ty.kind() {
        ty::Param(_) => false,
        ty::Adt(def, subs) => def
            .all_fields()
            .any(|f| !is_copy(cx, f.ty(cx.tcx, subs).skip_norm_wip())),
        _ => true,
    }
}

/// Walks into `ty` and returns `true` if any inner type is an instance of the given adt
/// constructor.
pub fn contains_adt_constructor<'tcx>(ty: Ty<'tcx>, adt: AdtDef<'tcx>) -> bool {
    ty.walk().any(|inner| match inner.kind() {
        GenericArgKind::Type(inner_ty) => inner_ty.ty_adt_def() == Some(adt),
        GenericArgKind::Lifetime(_) | GenericArgKind::Const(_) => false,
    })
}

/// Walks into `ty` and returns `true` if any inner type is an instance of the given type, or adt
/// constructor of the same type.
///
/// This method also recurses into opaque type predicates, so call it with `impl Trait<U>` and `U`
/// will also return `true`.
pub fn contains_ty_adt_constructor_opaque<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, needle: Ty<'tcx>) -> bool {
    fn contains_ty_adt_constructor_opaque_inner<'tcx>(
        cx: &LateContext<'tcx>,
        ty: Ty<'tcx>,
        needle: Ty<'tcx>,
        seen: &mut FxHashSet<DefId>,
    ) -> bool {
        ty.walk().any(|inner| match inner.kind() {
            GenericArgKind::Type(inner_ty) => {
                if inner_ty == needle {
                    return true;
                }

                if inner_ty.ty_adt_def() == needle.ty_adt_def() {
                    return true;
                }

                if let ty::Alias(AliasTy {
                    kind: ty::Opaque { def_id },
                    ..
                }) = *inner_ty.kind()
                {
                    if !seen.insert(def_id) {
                        return false;
                    }

                    for (predicate, _span) in cx
                        .tcx
                        .explicit_item_self_bounds(def_id)
                        .iter_identity_copied()
                        .map(Unnormalized::skip_norm_wip)
                    {
                        match predicate.kind().skip_binder() {
                            // For `impl Trait<U>`, it will register a predicate of `T: Trait<U>`, so we go through
                            // and check substitutions to find `U`.
                            ty::ClauseKind::Trait(trait_predicate)
                                if trait_predicate
                                    .trait_ref
                                    .args
                                    .types()
                                    .skip(1) // Skip the implicit `Self` generic parameter
                                    .any(|ty| contains_ty_adt_constructor_opaque_inner(cx, ty, needle, seen)) =>
                            {
                                return true;
                            },
                            // For `impl Trait<Assoc=U>`, it will register a predicate of `<T as Trait>::Assoc = U`,
                            // so we check the term for `U`.
                            ty::ClauseKind::Projection(projection_predicate) => {
                                if let ty::TermKind::Ty(ty) = projection_predicate.term.kind()
                                    && contains_ty_adt_constructor_opaque_inner(cx, ty, needle, seen)
                                {
                                    return true;
                                }
                            },
                            _ => (),
                        }
                    }
                }

                false
            },
            GenericArgKind::Lifetime(_) | GenericArgKind::Const(_) => false,
        })
    }

    // A hash set to ensure that the same opaque type (`impl Trait` in RPIT or TAIT) is not
    // visited twice.
    let mut seen = FxHashSet::default();
    contains_ty_adt_constructor_opaque_inner(cx, ty, needle, &mut seen)
}

/// Resolves `<T as Iterator>::Item` for `T`
/// Do not invoke without first verifying that the type implements `Iterator`
pub fn get_iterator_item_ty<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
    cx.tcx
        .get_diagnostic_item(sym::Iterator)
        .and_then(|iter_did| cx.get_associated_type(ty, iter_did, sym::Item))
}

/// Returns true if `ty` is a type on which calling `Clone` through a function instead of
/// as a method, such as `Arc::clone()` is considered idiomatic.
///
/// Lints should avoid suggesting to replace instances of `ty::Clone()` by `.clone()` for objects
/// of those types.
pub fn should_call_clone_as_function(cx: &LateContext<'_>, ty: Ty<'_>) -> bool {
    matches!(
        ty.opt_diag_name(cx),
        Some(sym::Arc | sym::ArcWeak | sym::Rc | sym::RcWeak)
    )
}

/// If `ty` is known to have a `iter` or `iter_mut` method, returns a symbol representing the type.
pub fn has_iter_method(cx: &LateContext<'_>, probably_ref_ty: Ty<'_>) -> Option<Symbol> {
    // FIXME: instead of this hard-coded list, we should check if `<adt>::iter`
    // exists and has the desired signature. Unfortunately FnCtxt is not exported
    // so we can't use its `lookup_method` method.
    let into_iter_collections: &[Symbol] = &[
        sym::Vec,
        sym::Option,
        sym::Result,
        sym::BTreeMap,
        sym::BTreeSet,
        sym::VecDeque,
        sym::LinkedList,
        sym::BinaryHeap,
        sym::HashSet,
        sym::HashMap,
        sym::PathBuf,
        sym::Path,
        sym::MpscReceiver,
        sym::MpmcReceiver,
    ];

    let ty_to_check = match probably_ref_ty.kind() {
        ty::Ref(_, ty_to_check, _) => *ty_to_check,
        _ => probably_ref_ty,
    };

    let def_id = match ty_to_check.kind() {
        ty::Array(..) => return Some(sym::array),
        ty::Slice(..) => return Some(sym::slice),
        ty::Adt(adt, _) => adt.did(),
        _ => return None,
    };

    for &name in into_iter_collections {
        if cx.tcx.is_diagnostic_item(name, def_id) {
            return Some(cx.tcx.item_name(def_id));
        }
    }
    None
}

/// Checks whether a type implements a trait.
/// The function returns false in case the type contains an inference variable.
///
/// See [Common tools for writing lints] for an example how to use this function and other options.
///
/// [Common tools for writing lints]: https://github.com/rust-lang/rust-clippy/blob/master/book/src/development/common_tools_writing_lints.md#checking-if-a-type-implements-a-specific-trait
pub fn implements_trait<'tcx>(
    cx: &LateContext<'tcx>,
    ty: Ty<'tcx>,
    trait_id: DefId,
    args: &[GenericArg<'tcx>],
) -> bool {
    implements_trait_with_env_from_iter(
        cx.tcx,
        cx.typing_env(),
        ty,
        trait_id,
        None,
        args.iter().map(|&x| Some(x)),
    )
}

/// Same as `implements_trait` but allows using a `ParamEnv` different from the lint context.
///
/// The `callee_id` argument is used to determine whether this is a function call in a `const fn`
/// environment, used for checking const traits.
pub fn implements_trait_with_env<'tcx>(
    tcx: TyCtxt<'tcx>,
    typing_env: ty::TypingEnv<'tcx>,
    ty: Ty<'tcx>,
    trait_id: DefId,
    callee_id: Option<DefId>,
    args: &[GenericArg<'tcx>],
) -> bool {
    implements_trait_with_env_from_iter(tcx, typing_env, ty, trait_id, callee_id, args.iter().map(|&x| Some(x)))
}

/// Same as `implements_trait_from_env` but takes the arguments as an iterator.
pub fn implements_trait_with_env_from_iter<'tcx>(
    tcx: TyCtxt<'tcx>,
    typing_env: ty::TypingEnv<'tcx>,
    ty: Ty<'tcx>,
    trait_id: DefId,
    callee_id: Option<DefId>,
    args: impl IntoIterator<Item = impl Into<Option<GenericArg<'tcx>>>>,
) -> bool {
    // Clippy shouldn't have infer types
    assert!(!ty.has_infer());

    // If a `callee_id` is passed, then we assert that it is a body owner
    // through calling `body_owner_kind`, which would panic if the callee
    // does not have a body.
    if let Some(callee_id) = callee_id {
        let _ = tcx.hir_body_owner_kind(callee_id);
    }

    let ty = tcx.erase_and_anonymize_regions(ty);
    if ty.has_escaping_bound_vars() {
        return false;
    }

    let (infcx, param_env) = tcx.infer_ctxt().build_with_typing_env(typing_env);
    let args = args
        .into_iter()
        .map(|arg| arg.into().unwrap_or_else(|| infcx.next_ty_var(DUMMY_SP).into()))
        .collect::<Vec<_>>();

    let trait_ref = TraitRef::new(tcx, trait_id, [GenericArg::from(ty)].into_iter().chain(args));

    debug_assert_matches!(
        tcx.def_kind(trait_id),
        DefKind::Trait | DefKind::TraitAlias,
        "`DefId` must belong to a trait or trait alias"
    );
    #[cfg(debug_assertions)]
    assert_generic_args_match(tcx, trait_id, trait_ref.args);

    let obligation = Obligation {
        cause: ObligationCause::dummy(),
        param_env,
        recursion_depth: 0,
        predicate: trait_ref.upcast(tcx),
    };
    infcx
        .evaluate_obligation(&obligation)
        .is_ok_and(EvaluationResult::must_apply_modulo_regions)
}

/// Checks whether this type implements `Drop`.
pub fn has_drop<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
    match ty.ty_adt_def() {
        Some(def) => def.has_dtor(cx.tcx),
        None => false,
    }
}

// Returns whether the `ty` has `#[must_use]` attribute. If `ty` is a `Result`/`ControlFlow`
// whose `Err`/`Break` payload is an uninhabited type, the `Ok`/`Continue` payload type
// will be used instead. See <https://github.com/rust-lang/rust/pull/148214>.
pub fn is_must_use_ty<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
    match ty.kind() {
        ty::Adt(adt, args) => match cx.tcx.get_diagnostic_name(adt.did()) {
            Some(sym::Result) if args.type_at(1).is_privately_uninhabited(cx.tcx, cx.typing_env()) => {
                is_must_use_ty(cx, args.type_at(0))
            },
            Some(sym::ControlFlow) if args.type_at(0).is_privately_uninhabited(cx.tcx, cx.typing_env()) => {
                is_must_use_ty(cx, args.type_at(1))
            },
            _ => find_attr!(cx.tcx, adt.did(), MustUse { .. }),
        },
        ty::Foreign(did) => find_attr!(cx.tcx, *did, MustUse { .. }),
        ty::Slice(ty) | ty::Array(ty, _) | ty::RawPtr(ty, _) | ty::Ref(_, ty, _) => {
            // for the Array case we don't need to care for the len == 0 case
            // because we don't want to lint functions returning empty arrays
            is_must_use_ty(cx, *ty)
        },
        ty::Tuple(args) => args.iter().any(|ty| is_must_use_ty(cx, ty)),
        ty::Alias(AliasTy {
            kind: ty::Opaque { def_id },
            ..
        }) => {
            for (predicate, _) in cx.tcx.explicit_item_self_bounds(*def_id).skip_binder() {
                if let ty::ClauseKind::Trait(trait_predicate) = predicate.kind().skip_binder()
                    && find_attr!(cx.tcx, trait_predicate.trait_ref.def_id, MustUse { .. })
                {
                    return true;
                }
            }
            false
        },
        ty::Dynamic(binder, _) => {
            for predicate in *binder {
                if let ty::ExistentialPredicate::Trait(ref trait_ref) = predicate.skip_binder()
                    && find_attr!(cx.tcx, trait_ref.def_id, MustUse { .. })
                {
                    return true;
                }
            }
            false
        },
        _ => false,
    }
}

/// Returns `true` if the given type is a non aggregate primitive (a `bool` or `char`, any
/// integer or floating-point number type).
///
/// For checking aggregation of primitive types (e.g. tuples and slices of primitive type) see
/// `is_recursively_primitive_type`
pub fn is_non_aggregate_primitive_type(ty: Ty<'_>) -> bool {
    matches!(ty.kind(), ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Float(_))
}

/// Returns `true` if the given type is a primitive (a `bool` or `char`, any integer or
/// floating-point number type, a `str`, or an array, slice, or tuple of those types).
pub fn is_recursively_primitive_type(ty: Ty<'_>) -> bool {
    match *ty.kind() {
        ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Str => true,
        ty::Ref(_, inner, _) if inner.is_str() => true,
        ty::Array(inner_type, _) | ty::Slice(inner_type) => is_recursively_primitive_type(inner_type),
        ty::Tuple(inner_types) => inner_types.iter().all(is_recursively_primitive_type),
        _ => false,
    }
}

/// Return `true` if the passed `typ` is `isize` or `usize`.
pub fn is_isize_or_usize(typ: Ty<'_>) -> bool {
    matches!(typ.kind(), ty::Int(IntTy::Isize) | ty::Uint(UintTy::Usize))
}

/// Checks if the drop order for a type matters.
///
/// Some std types implement drop solely to deallocate memory. For these types, and composites
/// containing them, changing the drop order won't result in any observable side effects.
pub fn needs_ordered_drop<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
    fn needs_ordered_drop_inner<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, seen: &mut FxHashSet<Ty<'tcx>>) -> bool {
        if !seen.insert(ty) {
            return false;
        }
        if !ty.has_significant_drop(cx.tcx, cx.typing_env()) {
            false
        }
        // Check for std types which implement drop, but only for memory allocation.
        else if ty.is_lang_item(cx, LangItem::OwnedBox)
            || matches!(
                ty.opt_diag_name(cx),
                Some(sym::HashSet | sym::Rc | sym::Arc | sym::cstring_type | sym::RcWeak | sym::ArcWeak)
            )
        {
            // Check all of the generic arguments.
            if let ty::Adt(_, subs) = ty.kind() {
                subs.types().any(|ty| needs_ordered_drop_inner(cx, ty, seen))
            } else {
                true
            }
        } else if !cx
            .tcx
            .lang_items()
            .drop_trait()
            .is_some_and(|id| implements_trait(cx, ty, id, &[]))
        {
            // This type doesn't implement drop, so no side effects here.
            // Check if any component type has any.
            match ty.kind() {
                ty::Tuple(fields) => fields.iter().any(|ty| needs_ordered_drop_inner(cx, ty, seen)),
                ty::Array(ty, _) => needs_ordered_drop_inner(cx, *ty, seen),
                ty::Adt(adt, subs) => adt
                    .all_fields()
                    .map(|f| f.ty(cx.tcx, subs).skip_norm_wip())
                    .any(|ty| needs_ordered_drop_inner(cx, ty, seen)),
                _ => true,
            }
        } else {
            true
        }
    }

    needs_ordered_drop_inner(cx, ty, &mut FxHashSet::default())
}

/// Returns `true` if `ty` denotes an `unsafe fn`.
pub fn is_unsafe_fn<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
    ty.is_fn() && ty.fn_sig(cx.tcx).safety().is_unsafe()
}

/// Peels off all references on the type. Returns the underlying type, the number of references
/// removed, and, if there were any such references, whether the pointer is ultimately mutable or
/// not.
pub fn peel_and_count_ty_refs(mut ty: Ty<'_>) -> (Ty<'_>, usize, Option<Mutability>) {
    let mut count = 0;
    let mut mutbl = None;
    while let ty::Ref(_, dest_ty, m) = ty.kind() {
        ty = *dest_ty;
        count += 1;
        mutbl.replace(mutbl.map_or(*m, |mutbl: Mutability| mutbl.min(*m)));
    }
    (ty, count, mutbl)
}

/// Peels off `n` references on the type. Returns the underlying type and, if any references
/// were removed, whether the pointer is ultimately mutable or not.
pub fn peel_n_ty_refs(mut ty: Ty<'_>, n: usize) -> (Ty<'_>, Option<Mutability>) {
    let mut mutbl = None;
    for _ in 0..n {
        if let ty::Ref(_, dest_ty, m) = ty.kind() {
            ty = *dest_ty;
            mutbl.replace(mutbl.map_or(*m, |mutbl: Mutability| mutbl.min(*m)));
        } else {
            break;
        }
    }
    (ty, mutbl)
}

/// Checks whether `a` and `b` are same types having same `Const` generic args, but ignores
/// lifetimes.
///
/// For example, the function would return `true` for
/// - `u32` and `u32`
/// - `[u8; N]` and `[u8; M]`, if `N=M`
/// - `Option<T>` and `Option<U>`, if `same_type_modulo_regions(T, U)` holds
/// - `&'a str` and `&'b str`
///
/// and `false` for:
/// - `Result<u32, String>` and `Result<usize, String>`
pub fn same_type_modulo_regions<'tcx>(a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
    match (&a.kind(), &b.kind()) {
        (&ty::Adt(did_a, args_a), &ty::Adt(did_b, args_b)) => {
            if did_a != did_b {
                return false;
            }

            iter::zip(*args_a, *args_b).all(|(arg_a, arg_b)| match (arg_a.kind(), arg_b.kind()) {
                (GenericArgKind::Const(inner_a), GenericArgKind::Const(inner_b)) => inner_a == inner_b,
                (GenericArgKind::Type(type_a), GenericArgKind::Type(type_b)) => {
                    same_type_modulo_regions(type_a, type_b)
                },
                _ => true,
            })
        },
        _ => a == b,
    }
}

/// Checks if a given type looks safe to be uninitialized.
pub fn is_uninit_value_valid_for_ty<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
    let typing_env = cx.typing_env().with_post_analysis_normalized(cx.tcx);
    cx.tcx
        .check_validity_requirement((ValidityRequirement::Uninit, typing_env.as_query_input(ty)))
        .unwrap_or_else(|_| is_uninit_value_valid_for_ty_fallback(cx, ty))
}

/// A fallback for polymorphic types, which are not supported by `check_validity_requirement`.
fn is_uninit_value_valid_for_ty_fallback<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
    match *ty.kind() {
        // The array length may be polymorphic, let's try the inner type.
        ty::Array(component, _) => is_uninit_value_valid_for_ty(cx, component),
        // Peek through tuples and try their fallbacks.
        ty::Tuple(types) => types.iter().all(|ty| is_uninit_value_valid_for_ty(cx, ty)),
        // Unions are always fine right now.
        // This includes MaybeUninit, the main way people use uninitialized memory.
        ty::Adt(adt, _) if adt.is_union() => true,
        // Types (e.g. `UnsafeCell<MaybeUninit<T>>`) that recursively contain only types that can be uninit
        // can themselves be uninit too.
        // This purposefully ignores enums as they may have a discriminant that can't be uninit.
        ty::Adt(adt, args) if adt.is_struct() => adt
            .all_fields()
            .all(|field| is_uninit_value_valid_for_ty(cx, field.ty(cx.tcx, args).skip_norm_wip())),
        // For the rest, conservatively assume that they cannot be uninit.
        _ => false,
    }
}

/// Gets an iterator over all predicates which apply to the given item.
pub fn all_predicates_of(tcx: TyCtxt<'_>, id: DefId) -> impl Iterator<Item = &(ty::Clause<'_>, Span)> {
    let mut next_id = Some(id);
    iter::from_fn(move || {
        next_id.take().map(|id| {
            let preds = tcx.predicates_of(id);
            next_id = preds.parent;
            preds.predicates.iter()
        })
    })
    .flatten()
}

/// A signature for a function like type.
#[derive(Clone, Copy, Debug)]
pub enum ExprFnSig<'tcx> {
    Sig(Binder<'tcx, FnSig<'tcx>>, Option<DefId>),
    Closure(Option<&'tcx FnDecl<'tcx>>, Binder<'tcx, FnSig<'tcx>>),
    Trait(Binder<'tcx, Ty<'tcx>>, Option<Binder<'tcx, Ty<'tcx>>>, Option<DefId>),
}
impl<'tcx> ExprFnSig<'tcx> {
    /// Gets the argument type at the given offset. This will return `None` when the index is out of
    /// bounds only for variadic functions, otherwise this will panic.
    pub fn input(self, i: usize) -> Option<Binder<'tcx, Ty<'tcx>>> {
        match self {
            Self::Sig(sig, _) => {
                if sig.c_variadic() {
                    sig.inputs().map_bound(|inputs| inputs.get(i).copied()).transpose()
                } else {
                    Some(sig.input(i))
                }
            },
            Self::Closure(_, sig) => Some(sig.input(0).map_bound(|ty| ty.tuple_fields()[i])),
            Self::Trait(inputs, _, _) => Some(inputs.map_bound(|ty| ty.tuple_fields()[i])),
        }
    }

    /// Gets the argument type at the given offset. For closures this will also get the type as
    /// written. This will return `None` when the index is out of bounds only for variadic
    /// functions, otherwise this will panic.
    pub fn input_with_hir(self, i: usize) -> Option<(Option<&'tcx hir::Ty<'tcx>>, Binder<'tcx, Ty<'tcx>>)> {
        match self {
            Self::Sig(sig, _) => {
                if sig.c_variadic() {
                    sig.inputs()
                        .map_bound(|inputs| inputs.get(i).copied())
                        .transpose()
                        .map(|arg| (None, arg))
                } else {
                    Some((None, sig.input(i)))
                }
            },
            Self::Closure(decl, sig) => Some((
                decl.and_then(|decl| decl.inputs.get(i)),
                sig.input(0).map_bound(|ty| ty.tuple_fields()[i]),
            )),
            Self::Trait(inputs, _, _) => Some((None, inputs.map_bound(|ty| ty.tuple_fields()[i]))),
        }
    }

    /// Gets the result type, if one could be found. Note that the result type of a trait may not be
    /// specified.
    pub fn output(self) -> Option<Binder<'tcx, Ty<'tcx>>> {
        match self {
            Self::Sig(sig, _) | Self::Closure(_, sig) => Some(sig.output()),
            Self::Trait(_, output, _) => output,
        }
    }

    pub fn predicates_id(&self) -> Option<DefId> {
        if let ExprFnSig::Sig(_, id) | ExprFnSig::Trait(_, _, id) = *self {
            id
        } else {
            None
        }
    }
}

/// If the expression is function like, get the signature for it.
pub fn expr_sig<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>) -> Option<ExprFnSig<'tcx>> {
    if let Res::Def(DefKind::Fn | DefKind::Ctor(_, CtorKind::Fn) | DefKind::AssocFn, id) = expr.res(cx) {
        Some(ExprFnSig::Sig(
            cx.tcx.fn_sig(id).instantiate_identity().skip_norm_wip(),
            Some(id),
        ))
    } else {
        ty_sig(cx, cx.typeck_results().expr_ty_adjusted(expr).peel_refs())
    }
}

/// If the type is function like, get the signature for it.
pub fn ty_sig<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<ExprFnSig<'tcx>> {
    if let Some(boxed_ty) = ty.boxed_ty() {
        return ty_sig(cx, boxed_ty);
    }
    match *ty.kind() {
        ty::Closure(id, subs) => {
            let decl = id
                .as_local()
                .and_then(|id| cx.tcx.hir_fn_decl_by_hir_id(cx.tcx.local_def_id_to_hir_id(id)));
            Some(ExprFnSig::Closure(decl, subs.as_closure().sig()))
        },
        ty::FnDef(id, subs) => Some(ExprFnSig::Sig(
            cx.tcx.fn_sig(id).instantiate(cx.tcx, subs).skip_norm_wip(),
            Some(id),
        )),
        ty::Alias(AliasTy {
            kind: ty::Opaque { def_id },
            args,
            ..
        }) => sig_from_bounds(
            cx,
            ty,
            cx.tcx
                .item_self_bounds(def_id)
                .iter_instantiated(cx.tcx, args)
                .map(Unnormalized::skip_norm_wip),
            cx.tcx.opt_parent(def_id),
        ),
        ty::FnPtr(sig_tys, hdr) => Some(ExprFnSig::Sig(sig_tys.with(hdr), None)),
        ty::Dynamic(bounds, _) => {
            let lang_items = cx.tcx.lang_items();
            match bounds.principal() {
                Some(bound)
                    if Some(bound.def_id()) == lang_items.fn_trait()
                        || Some(bound.def_id()) == lang_items.fn_once_trait()
                        || Some(bound.def_id()) == lang_items.fn_mut_trait() =>
                {
                    let output = bounds
                        .projection_bounds()
                        .find(|p| lang_items.fn_once_output().is_some_and(|id| id == p.item_def_id()))
                        .map(|p| p.map_bound(|p| p.term.expect_type()));
                    Some(ExprFnSig::Trait(bound.map_bound(|b| b.args.type_at(0)), output, None))
                },
                _ => None,
            }
        },
        ty::Alias(
            proj @ AliasTy {
                kind: ty::Projection { .. },
                ..
            },
        ) => match cx
            .tcx
            .try_normalize_erasing_regions(cx.typing_env(), Unnormalized::new_wip(ty))
        {
            Ok(normalized_ty) if normalized_ty != ty => ty_sig(cx, normalized_ty),
            _ => sig_for_projection(cx, proj).or_else(|| sig_from_bounds(cx, ty, cx.param_env.caller_bounds(), None)),
        },
        ty::Param(_) => sig_from_bounds(cx, ty, cx.param_env.caller_bounds(), None),
        _ => None,
    }
}

fn sig_from_bounds<'tcx>(
    cx: &LateContext<'tcx>,
    ty: Ty<'tcx>,
    predicates: impl IntoIterator<Item = ty::Clause<'tcx>>,
    predicates_id: Option<DefId>,
) -> Option<ExprFnSig<'tcx>> {
    let mut inputs = None;
    let mut output = None;
    let lang_items = cx.tcx.lang_items();

    for pred in predicates {
        match pred.kind().skip_binder() {
            ty::ClauseKind::Trait(p)
                if (lang_items.fn_trait() == Some(p.def_id())
                    || lang_items.fn_mut_trait() == Some(p.def_id())
                    || lang_items.fn_once_trait() == Some(p.def_id()))
                    && p.self_ty() == ty =>
            {
                let i = pred.kind().rebind(p.trait_ref.args.type_at(1));
                if inputs.is_some_and(|inputs| i != inputs) {
                    // Multiple different fn trait impls. Is this even allowed?
                    return None;
                }
                inputs = Some(i);
            },
            ty::ClauseKind::Projection(p)
                if Some(p.projection_term.def_id()) == lang_items.fn_once_output()
                    && p.projection_term.self_ty() == ty =>
            {
                if output.is_some() {
                    // Multiple different fn trait impls. Is this even allowed?
                    return None;
                }
                output = Some(pred.kind().rebind(p.term.expect_type()));
            },
            _ => (),
        }
    }

    inputs.map(|ty| ExprFnSig::Trait(ty, output, predicates_id))
}

fn sig_for_projection<'tcx>(cx: &LateContext<'tcx>, ty: AliasTy<'tcx>) -> Option<ExprFnSig<'tcx>> {
    let mut inputs = None;
    let mut output = None;
    let lang_items = cx.tcx.lang_items();

    for (pred, _) in cx
        .tcx
        .explicit_item_bounds(ty.kind.def_id())
        .iter_instantiated_copied(cx.tcx, ty.args)
        .map(Unnormalized::skip_norm_wip)
    {
        match pred.kind().skip_binder() {
            ty::ClauseKind::Trait(p)
                if (lang_items.fn_trait() == Some(p.def_id())
                    || lang_items.fn_mut_trait() == Some(p.def_id())
                    || lang_items.fn_once_trait() == Some(p.def_id())) =>
            {
                let i = pred.kind().rebind(p.trait_ref.args.type_at(1));

                if inputs.is_some_and(|inputs| inputs != i) {
                    // Multiple different fn trait impls. Is this even allowed?
                    return None;
                }
                inputs = Some(i);
            },
            ty::ClauseKind::Projection(p) if Some(p.projection_term.def_id()) == lang_items.fn_once_output() => {
                if output.is_some() {
                    // Multiple different fn trait impls. Is this even allowed?
                    return None;
                }
                output = pred.kind().rebind(p.term.as_type()).transpose();
            },
            _ => (),
        }
    }

    inputs.map(|ty| ExprFnSig::Trait(ty, output, None))
}

#[derive(Clone, Copy)]
pub enum EnumValue {
    Unsigned(u128),
    Signed(i128),
}
impl core::ops::Add<u32> for EnumValue {
    type Output = Self;
    fn add(self, n: u32) -> Self::Output {
        match self {
            Self::Unsigned(x) => Self::Unsigned(x + u128::from(n)),
            Self::Signed(x) => Self::Signed(x + i128::from(n)),
        }
    }
}

/// Attempts to read the given constant as though it were an enum value.
pub fn read_explicit_enum_value(tcx: TyCtxt<'_>, id: DefId) -> Option<EnumValue> {
    if let Ok(ConstValue::Scalar(Scalar::Int(value))) = tcx.const_eval_poly(id) {
        match tcx.type_of(id).instantiate_identity().skip_norm_wip().kind() {
            ty::Int(_) => Some(EnumValue::Signed(value.to_int(value.size()))),
            ty::Uint(_) => Some(EnumValue::Unsigned(value.to_uint(value.size()))),
            _ => None,
        }
    } else {
        None
    }
}

/// Gets the value of the given variant.
pub fn get_discriminant_value(tcx: TyCtxt<'_>, adt: AdtDef<'_>, i: VariantIdx) -> EnumValue {
    let variant = &adt.variant(i);
    match variant.discr {
        VariantDiscr::Explicit(id) => read_explicit_enum_value(tcx, id).unwrap(),
        VariantDiscr::Relative(x) => match adt.variant((i.as_usize() - x as usize).into()).discr {
            VariantDiscr::Explicit(id) => read_explicit_enum_value(tcx, id).unwrap() + x,
            VariantDiscr::Relative(_) => EnumValue::Unsigned(x.into()),
        },
    }
}

/// Check if the given type is either `core::ffi::c_void`, `std::os::raw::c_void`, or one of the
/// platform specific `libc::<platform>::c_void` types in libc.
pub fn is_c_void(cx: &LateContext<'_>, ty: Ty<'_>) -> bool {
    if let ty::Adt(adt, _) = ty.kind()
        && let &[krate, .., name] = &*cx.get_def_path(adt.did())
        && let sym::libc | sym::core | sym::std = krate
        && name == sym::c_void
    {
        true
    } else {
        false
    }
}

pub fn for_each_top_level_late_bound_region<'cx, B>(
    ty: Ty<'cx>,
    f: impl FnMut(BoundRegion<'cx>) -> ControlFlow<B>,
) -> ControlFlow<B> {
    struct V<F> {
        index: u32,
        f: F,
    }
    impl<'tcx, B, F: FnMut(BoundRegion<'tcx>) -> ControlFlow<B>> TypeVisitor<TyCtxt<'tcx>> for V<F> {
        type Result = ControlFlow<B>;
        fn visit_region(&mut self, r: Region<'tcx>) -> Self::Result {
            if let RegionKind::ReBound(BoundVarIndexKind::Bound(idx), bound) = r.kind()
                && idx.as_u32() == self.index
            {
                (self.f)(bound)
            } else {
                ControlFlow::Continue(())
            }
        }
        fn visit_binder<T: TypeVisitable<TyCtxt<'tcx>>>(&mut self, t: &Binder<'tcx, T>) -> Self::Result {
            self.index += 1;
            let res = t.super_visit_with(self);
            self.index -= 1;
            res
        }
    }
    ty.visit_with(&mut V { index: 0, f })
}

pub struct AdtVariantInfo {
    pub ind: usize,
    pub size: u64,

    /// (ind, size)
    pub fields_size: Vec<(usize, u64)>,
}

impl AdtVariantInfo {
    /// Returns ADT variants ordered by size
    pub fn new<'tcx>(cx: &LateContext<'tcx>, adt: AdtDef<'tcx>, subst: GenericArgsRef<'tcx>) -> Vec<Self> {
        let mut variants_size = adt
            .variants()
            .iter()
            .enumerate()
            .map(|(i, variant)| {
                let mut fields_size = variant
                    .fields
                    .iter()
                    .enumerate()
                    .map(|(i, f)| (i, approx_ty_size(cx, f.ty(cx.tcx, subst).skip_norm_wip())))
                    .collect::<Vec<_>>();
                fields_size.sort_by_key(|(_, a_size)| *a_size);

                Self {
                    ind: i,
                    size: fields_size.iter().map(|(_, size)| size).sum(),
                    fields_size,
                }
            })
            .collect::<Vec<_>>();
        variants_size.sort_by_key(|b| std::cmp::Reverse(b.size));
        variants_size
    }
}

/// Gets the struct or enum variant from the given `Res`
pub fn adt_and_variant_of_res<'tcx>(cx: &LateContext<'tcx>, res: Res) -> Option<(AdtDef<'tcx>, &'tcx VariantDef)> {
    match res {
        Res::Def(DefKind::Struct, id) => {
            let adt = cx.tcx.adt_def(id);
            Some((adt, adt.non_enum_variant()))
        },
        Res::Def(DefKind::Variant, id) => {
            let adt = cx.tcx.adt_def(cx.tcx.parent(id));
            Some((adt, adt.variant_with_id(id)))
        },
        Res::Def(DefKind::Ctor(CtorOf::Struct, _), id) => {
            let adt = cx.tcx.adt_def(cx.tcx.parent(id));
            Some((adt, adt.non_enum_variant()))
        },
        Res::Def(DefKind::Ctor(CtorOf::Variant, _), id) => {
            let var_id = cx.tcx.parent(id);
            let adt = cx.tcx.adt_def(cx.tcx.parent(var_id));
            Some((adt, adt.variant_with_id(var_id)))
        },
        Res::SelfCtor(id) => {
            let adt = cx
                .tcx
                .type_of(id)
                .instantiate_identity()
                .skip_norm_wip()
                .ty_adt_def()
                .unwrap();
            Some((adt, adt.non_enum_variant()))
        },
        _ => None,
    }
}

/// Comes up with an "at least" guesstimate for the type's size, not taking into
/// account the layout of type parameters.
pub fn approx_ty_size<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> u64 {
    use rustc_middle::ty::layout::LayoutOf;
    match (cx.layout_of(ty).map(|layout| layout.size.bytes()), ty.kind()) {
        (Ok(size), _) => size,
        (Err(_), ty::Tuple(list)) => list.iter().map(|t| approx_ty_size(cx, t)).sum(),
        (Err(_), ty::Array(t, n)) => n.try_to_target_usize(cx.tcx).unwrap_or_default() * approx_ty_size(cx, *t),
        (Err(_), ty::Adt(def, subst)) if def.is_struct() => def
            .variants()
            .iter()
            .map(|v| {
                v.fields
                    .iter()
                    .map(|field| approx_ty_size(cx, field.ty(cx.tcx, subst).skip_norm_wip()))
                    .sum::<u64>()
            })
            .sum(),
        (Err(_), ty::Adt(def, subst)) if def.is_enum() => def
            .variants()
            .iter()
            .map(|v| {
                v.fields
                    .iter()
                    .map(|field| approx_ty_size(cx, field.ty(cx.tcx, subst).skip_norm_wip()))
                    .sum::<u64>()
            })
            .max()
            .unwrap_or_default(),
        (Err(_), ty::Adt(def, subst)) if def.is_union() => def
            .variants()
            .iter()
            .map(|v| {
                v.fields
                    .iter()
                    .map(|field| approx_ty_size(cx, field.ty(cx.tcx, subst).skip_norm_wip()))
                    .max()
                    .unwrap_or_default()
            })
            .max()
            .unwrap_or_default(),
        (Err(_), _) => 0,
    }
}

#[cfg(debug_assertions)]
/// Asserts that the given arguments match the generic parameters of the given item.
fn assert_generic_args_match<'tcx>(tcx: TyCtxt<'tcx>, did: DefId, args: &[GenericArg<'tcx>]) {
    use itertools::Itertools;
    let g = tcx.generics_of(did);
    let parent = g.parent.map(|did| tcx.generics_of(did));
    let count = g.parent_count + g.own_params.len();
    let params = parent
        .map_or([].as_slice(), |p| p.own_params.as_slice())
        .iter()
        .chain(&g.own_params)
        .map(|x| &x.kind);

    assert!(
        count == args.len(),
        "wrong number of arguments for `{did:?}`: expected `{count}`, found {}\n\
            note: the expected arguments are: `[{}]`\n\
            the given arguments are: `{args:#?}`",
        args.len(),
        params.clone().map(ty::GenericParamDefKind::descr).format(", "),
    );

    if let Some((idx, (param, arg))) =
        params
            .clone()
            .zip(args.iter().map(|&x| x.kind()))
            .enumerate()
            .find(|(_, (param, arg))| match (param, arg) {
                (ty::GenericParamDefKind::Lifetime, GenericArgKind::Lifetime(_))
                | (ty::GenericParamDefKind::Type { .. }, GenericArgKind::Type(_))
                | (ty::GenericParamDefKind::Const { .. }, GenericArgKind::Const(_)) => false,
                (
                    ty::GenericParamDefKind::Lifetime
                    | ty::GenericParamDefKind::Type { .. }
                    | ty::GenericParamDefKind::Const { .. },
                    _,
                ) => true,
            })
    {
        panic!(
            "incorrect argument for `{did:?}` at index `{idx}`: expected a {}, found `{arg:?}`\n\
                note: the expected arguments are `[{}]`\n\
                the given arguments are `{args:#?}`",
            param.descr(),
            params.clone().map(ty::GenericParamDefKind::descr).format(", "),
        );
    }
}

/// Returns whether `ty` is never-like; i.e., `!` (never) or an enum with zero variants.
pub fn is_never_like(ty: Ty<'_>) -> bool {
    ty.is_never() || (ty.is_enum() && ty.ty_adt_def().is_some_and(|def| def.variants().is_empty()))
}

/// Makes the projection type for the named associated type in the given impl or trait impl.
///
/// This function is for associated types which are "known" to exist, and as such, will only return
/// `None` when debug assertions are disabled in order to prevent ICE's. With debug assertions
/// enabled this will check that the named associated type exists, the correct number of
/// arguments are given, and that the correct kinds of arguments are given (lifetime,
/// constant or type). This will not check if type normalization would succeed.
pub fn make_projection<'tcx>(
    tcx: TyCtxt<'tcx>,
    container_id: DefId,
    assoc_ty: Symbol,
    args: impl IntoIterator<Item = impl Into<GenericArg<'tcx>>>,
) -> Option<AliasTy<'tcx>> {
    fn helper<'tcx>(
        tcx: TyCtxt<'tcx>,
        container_id: DefId,
        assoc_ty: Symbol,
        args: GenericArgsRef<'tcx>,
    ) -> Option<AliasTy<'tcx>> {
        let Some(assoc_item) = tcx.associated_items(container_id).find_by_ident_and_kind(
            tcx,
            Ident::with_dummy_span(assoc_ty),
            AssocTag::Type,
            container_id,
        ) else {
            debug_assert!(false, "type `{assoc_ty}` not found in `{container_id:?}`");
            return None;
        };
        #[cfg(debug_assertions)]
        assert_generic_args_match(tcx, assoc_item.def_id, args);

        Some(AliasTy::new_from_args(
            tcx,
            ty::AliasTyKind::new_from_def_id(tcx, assoc_item.def_id),
            args,
        ))
    }
    helper(
        tcx,
        container_id,
        assoc_ty,
        tcx.mk_args_from_iter(args.into_iter().map(Into::into)),
    )
}

/// Normalizes the named associated type in the given impl or trait impl.
///
/// This function is for associated types which are "known" to be valid with the given
/// arguments, and as such, will only return `None` when debug assertions are disabled in order
/// to prevent ICE's. With debug assertions enabled this will check that type normalization
/// succeeds as well as everything checked by `make_projection`.
pub fn make_normalized_projection<'tcx>(
    tcx: TyCtxt<'tcx>,
    typing_env: ty::TypingEnv<'tcx>,
    container_id: DefId,
    assoc_ty: Symbol,
    args: impl IntoIterator<Item = impl Into<GenericArg<'tcx>>>,
) -> Option<Ty<'tcx>> {
    fn helper<'tcx>(tcx: TyCtxt<'tcx>, typing_env: ty::TypingEnv<'tcx>, ty: AliasTy<'tcx>) -> Option<Ty<'tcx>> {
        #[cfg(debug_assertions)]
        if let Some((i, arg)) = ty
            .args
            .iter()
            .enumerate()
            .find(|(_, arg)| arg.has_escaping_bound_vars())
        {
            debug_assert!(
                false,
                "args contain late-bound region at index `{i}` which can't be normalized.\n\
                    use `TyCtxt::instantiate_bound_regions_with_erased`\n\
                    note: arg is `{arg:#?}`",
            );
            return None;
        }
        match tcx.try_normalize_erasing_regions(
            typing_env,
            Unnormalized::new_wip(Ty::new_projection_from_args(tcx, ty.kind.def_id(), ty.args)),
        ) {
            Ok(ty) => Some(ty),
            Err(e) => {
                debug_assert!(false, "failed to normalize type `{ty}`: {e:#?}");
                None
            },
        }
    }
    helper(tcx, typing_env, make_projection(tcx, container_id, assoc_ty, args)?)
}

/// Helper to check if given type has inner mutability such as [`std::cell::Cell`] or
/// [`std::cell::RefCell`].
#[derive(Default, Debug)]
pub struct InteriorMut<'tcx> {
    ignored_def_ids: FxHashSet<DefId>,
    ignore_pointers: bool,
    tys: FxHashMap<Ty<'tcx>, Option<&'tcx ty::List<Ty<'tcx>>>>,
}

impl<'tcx> InteriorMut<'tcx> {
    pub fn new(tcx: TyCtxt<'tcx>, ignore_interior_mutability: &[String]) -> Self {
        let ignored_def_ids = ignore_interior_mutability
            .iter()
            .flat_map(|ignored_ty| lookup_path_str(tcx, PathNS::Type, ignored_ty))
            .collect();

        Self {
            ignored_def_ids,
            ..Self::default()
        }
    }

    pub fn without_pointers(tcx: TyCtxt<'tcx>, ignore_interior_mutability: &[String]) -> Self {
        Self {
            ignore_pointers: true,
            ..Self::new(tcx, ignore_interior_mutability)
        }
    }

    /// Check if given type has interior mutability such as [`std::cell::Cell`] or
    /// [`std::cell::RefCell`] etc. and if it does, returns a chain of types that causes
    /// this type to be interior mutable.  False negatives may be expected for infinitely recursive
    /// types, and `None` will be returned there.
    pub fn interior_mut_ty_chain(&mut self, cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<&'tcx ty::List<Ty<'tcx>>> {
        self.interior_mut_ty_chain_inner(cx, ty, 0)
    }

    fn interior_mut_ty_chain_inner(
        &mut self,
        cx: &LateContext<'tcx>,
        ty: Ty<'tcx>,
        depth: usize,
    ) -> Option<&'tcx ty::List<Ty<'tcx>>> {
        if !cx.tcx.recursion_limit().value_within_limit(depth) {
            return None;
        }

        match self.tys.entry(ty) {
            Entry::Occupied(o) => return *o.get(),
            // Temporarily insert a `None` to break cycles
            Entry::Vacant(v) => v.insert(None),
        };
        let depth = depth + 1;

        let chain = match *ty.kind() {
            ty::RawPtr(inner_ty, _) if !self.ignore_pointers => self.interior_mut_ty_chain_inner(cx, inner_ty, depth),
            ty::Ref(_, inner_ty, _) | ty::Slice(inner_ty) => self.interior_mut_ty_chain_inner(cx, inner_ty, depth),
            ty::Array(inner_ty, size) if size.try_to_target_usize(cx.tcx) != Some(0) => {
                self.interior_mut_ty_chain_inner(cx, inner_ty, depth)
            },
            ty::Tuple(fields) => fields
                .iter()
                .find_map(|ty| self.interior_mut_ty_chain_inner(cx, ty, depth)),
            ty::Adt(def, _) if def.is_unsafe_cell() => Some(ty::List::empty()),
            ty::Adt(def, args) => {
                let is_std_collection = matches!(
                    cx.tcx.get_diagnostic_name(def.did()),
                    Some(
                        sym::LinkedList
                            | sym::Vec
                            | sym::VecDeque
                            | sym::BTreeMap
                            | sym::BTreeSet
                            | sym::HashMap
                            | sym::HashSet
                            | sym::Arc
                            | sym::Rc
                    )
                );

                if is_std_collection || def.is_box() {
                    // Include the types from std collections that are behind pointers internally
                    args.types()
                        .find_map(|ty| self.interior_mut_ty_chain_inner(cx, ty, depth))
                } else if self.ignored_def_ids.contains(&def.did()) || def.is_phantom_data() {
                    None
                } else {
                    def.all_fields()
                        .find_map(|f| self.interior_mut_ty_chain_inner(cx, f.ty(cx.tcx, args).skip_norm_wip(), depth))
                }
            },
            ty::Alias(AliasTy {
                kind: ty::Projection { .. },
                ..
            }) => match cx
                .tcx
                .try_normalize_erasing_regions(cx.typing_env(), Unnormalized::new_wip(ty))
            {
                Ok(normalized_ty) if ty != normalized_ty => self.interior_mut_ty_chain_inner(cx, normalized_ty, depth),
                _ => None,
            },
            _ => None,
        };

        chain.map(|chain| {
            let list = cx.tcx.mk_type_list_from_iter(chain.iter().chain([ty]));
            self.tys.insert(ty, Some(list));
            list
        })
    }

    /// Check if given type has interior mutability such as [`std::cell::Cell`] or
    /// [`std::cell::RefCell`] etc.
    pub fn is_interior_mut_ty(&mut self, cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
        self.interior_mut_ty_chain(cx, ty).is_some()
    }
}

pub fn make_normalized_projection_with_regions<'tcx>(
    tcx: TyCtxt<'tcx>,
    typing_env: ty::TypingEnv<'tcx>,
    container_id: DefId,
    assoc_ty: Symbol,
    args: impl IntoIterator<Item = impl Into<GenericArg<'tcx>>>,
) -> Option<Ty<'tcx>> {
    fn helper<'tcx>(tcx: TyCtxt<'tcx>, typing_env: ty::TypingEnv<'tcx>, ty: AliasTy<'tcx>) -> Option<Ty<'tcx>> {
        #[cfg(debug_assertions)]
        if let Some((i, arg)) = ty
            .args
            .iter()
            .enumerate()
            .find(|(_, arg)| arg.has_escaping_bound_vars())
        {
            debug_assert!(
                false,
                "args contain late-bound region at index `{i}` which can't be normalized.\n\
                    use `TyCtxt::instantiate_bound_regions_with_erased`\n\
                    note: arg is `{arg:#?}`",
            );
            return None;
        }
        let cause = ObligationCause::dummy();
        let (infcx, param_env) = tcx.infer_ctxt().build_with_typing_env(typing_env);
        match infcx
            .at(&cause, param_env)
            .query_normalize(Ty::new_projection_from_args(tcx, ty.kind.def_id(), ty.args))
        {
            Ok(ty) => Some(ty.value),
            Err(e) => {
                debug_assert!(false, "failed to normalize type `{ty}`: {e:#?}");
                None
            },
        }
    }
    helper(tcx, typing_env, make_projection(tcx, container_id, assoc_ty, args)?)
}

pub fn normalize_with_regions<'tcx>(tcx: TyCtxt<'tcx>, typing_env: ty::TypingEnv<'tcx>, ty: Ty<'tcx>) -> Ty<'tcx> {
    let cause = ObligationCause::dummy();
    let (infcx, param_env) = tcx.infer_ctxt().build_with_typing_env(typing_env);
    infcx
        .at(&cause, param_env)
        .query_normalize(ty)
        .map_or(ty, |ty| ty.value)
}

/// Checks if the type is `core::mem::ManuallyDrop<_>`
pub fn is_manually_drop(ty: Ty<'_>) -> bool {
    ty.ty_adt_def().is_some_and(AdtDef::is_manually_drop)
}

/// Returns the deref chain of a type, starting with the type itself.
pub fn deref_chain<'cx, 'tcx>(cx: &'cx LateContext<'tcx>, ty: Ty<'tcx>) -> impl Iterator<Item = Ty<'tcx>> + 'cx {
    iter::successors(Some(ty), |&ty| {
        if let Some(deref_did) = cx.tcx.lang_items().deref_trait()
            && implements_trait(cx, ty, deref_did, &[])
        {
            make_normalized_projection(cx.tcx, cx.typing_env(), deref_did, sym::Target, [ty])
        } else {
            None
        }
    })
}

/// Checks if a Ty<'_> has some inherent method Symbol.
///
/// This does not look for impls in the type's `Deref::Target` type.
/// If you need this, you should wrap this call in `clippy_utils::ty::deref_chain().any(...)`.
pub fn get_adt_inherent_method<'a>(cx: &'a LateContext<'_>, ty: Ty<'_>, method_name: Symbol) -> Option<&'a AssocItem> {
    let ty_did = ty.ty_adt_def().map(AdtDef::did)?;
    cx.tcx.inherent_impls(ty_did).iter().find_map(|&did| {
        cx.tcx
            .associated_items(did)
            .filter_by_name_unhygienic(method_name)
            .next()
            .filter(|item| item.tag() == AssocTag::Fn)
    })
}

/// Gets the type of a field by name.
pub fn get_field_by_name<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, name: Symbol) -> Option<Ty<'tcx>> {
    match *ty.kind() {
        ty::Adt(def, args) if def.is_union() || def.is_struct() => def
            .non_enum_variant()
            .fields
            .iter()
            .find(|f| f.name == name)
            .map(|f| f.ty(tcx, args).skip_norm_wip()),
        ty::Tuple(args) => name.as_str().parse::<usize>().ok().and_then(|i| args.get(i).copied()),
        _ => None,
    }
}

pub fn get_field_def_id_by_name(ty: Ty<'_>, name: Symbol) -> Option<DefId> {
    let ty::Adt(adt_def, ..) = ty.kind() else { return None };
    adt_def
        .all_fields()
        .find_map(|field| if field.name == name { Some(field.did) } else { None })
}

/// Check if `ty` is an `Option` and return its argument type if it is.
pub fn option_arg_ty<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
    match *ty.kind() {
        ty::Adt(adt, args)
            if let [arg] = &**args
                && let Some(arg) = arg.as_type()
                && adt.is_diag_item(cx, sym::Option) =>
        {
            Some(arg)
        },
        _ => None,
    }
}

/// Check if a Ty<'_> of `Iterator` contains any mutable access to non-owning types by checking if
/// it contains fields of mutable references or pointers, or references/pointers to non-`Freeze`
/// types, or `PhantomData` types containing any of the previous. This can be used to check whether
/// skipping iterating over an iterator will change its behavior.
pub fn has_non_owning_mutable_access<'tcx>(cx: &LateContext<'tcx>, iter_ty: Ty<'tcx>) -> bool {
    fn normalize_ty<'tcx>(cx: &LateContext<'tcx>, ty: Unnormalized<'tcx, Ty<'tcx>>) -> Ty<'tcx> {
        cx.tcx
            .try_normalize_erasing_regions(cx.typing_env(), ty)
            .unwrap_or(ty.skip_norm_wip())
    }

    /// Check if `ty` contains mutable references or equivalent, which includes:
    /// - A mutable reference/pointer.
    /// - A reference/pointer to a non-`Freeze` type.
    /// - A `PhantomData` type containing any of the previous.
    fn has_non_owning_mutable_access_inner<'tcx>(
        cx: &LateContext<'tcx>,
        phantoms: &mut FxHashSet<Ty<'tcx>>,
        ty: Ty<'tcx>,
    ) -> bool {
        match ty.kind() {
            ty::Adt(adt_def, args) if adt_def.is_phantom_data() => {
                phantoms.insert(ty)
                    && args
                        .types()
                        .any(|arg_ty| has_non_owning_mutable_access_inner(cx, phantoms, arg_ty))
            },
            ty::Adt(adt_def, args) => adt_def.all_fields().any(|field| {
                has_non_owning_mutable_access_inner(cx, phantoms, normalize_ty(cx, field.ty(cx.tcx, args)))
            }),
            ty::Array(elem_ty, _) | ty::Slice(elem_ty) => has_non_owning_mutable_access_inner(cx, phantoms, *elem_ty),
            ty::RawPtr(pointee_ty, mutability) | ty::Ref(_, pointee_ty, mutability) => {
                mutability.is_mut() || !pointee_ty.is_freeze(cx.tcx, cx.typing_env())
            },
            ty::Closure(_, closure_args) => {
                matches!(closure_args.types().next_back(),
                         Some(captures) if has_non_owning_mutable_access_inner(cx, phantoms, captures))
            },
            ty::Tuple(tuple_args) => tuple_args
                .iter()
                .any(|arg_ty| has_non_owning_mutable_access_inner(cx, phantoms, arg_ty)),
            _ => false,
        }
    }

    let mut phantoms = FxHashSet::default();
    has_non_owning_mutable_access_inner(cx, &mut phantoms, iter_ty)
}

/// Check if `ty` is slice-like, i.e., `&[T]`, `[T; N]`, or `Vec<T>`.
pub fn is_slice_like<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
    ty.is_slice() || ty.is_array() || ty.is_diag_item(cx, sym::Vec)
}

pub fn get_field_idx_by_name(ty: Ty<'_>, name: Symbol) -> Option<usize> {
    match *ty.kind() {
        ty::Adt(def, _) if def.is_union() || def.is_struct() => {
            def.non_enum_variant().fields.iter().position(|f| f.name == name)
        },
        ty::Tuple(_) => name.as_str().parse::<usize>().ok(),
        _ => None,
    }
}

/// Checks if the adjustments contain a mutable dereference of a `ManuallyDrop<_>`.
pub fn adjust_derefs_manually_drop<'tcx>(adjustments: &'tcx [Adjustment<'tcx>], mut ty: Ty<'tcx>) -> bool {
    adjustments.iter().any(|a| {
        let ty = mem::replace(&mut ty, a.target);
        matches!(a.kind, Adjust::Deref(DerefAdjustKind::Overloaded(op)) if op.mutbl == Mutability::Mut)
            && is_manually_drop(ty)
    })
}