clippy_utils/

hir_utils.rs

use crate::consts::ConstEvalCtxt;
use crate::macros::macro_backtrace;
use crate::source::{SpanRange, SpanRangeExt, walk_span_to_context};
use crate::tokenize_with_text;
use rustc_ast::ast;
use rustc_ast::ast::InlineAsmTemplatePiece;
use rustc_data_structures::fx::{FxHasher, FxIndexMap};
use rustc_hir::MatchSource::TryDesugar;
use rustc_hir::def::{DefKind, Res};
use rustc_hir::def_id::DefId;
use rustc_hir::{
    AssocItemConstraint, BinOpKind, BindingMode, Block, BodyId, ByRef, Closure, ConstArg, ConstArgKind, ConstItemRhs,
    Expr, ExprField, ExprKind, FnDecl, FnRetTy, FnSig, GenericArg, GenericArgs, GenericBound, GenericBounds,
    GenericParam, GenericParamKind, GenericParamSource, Generics, HirId, HirIdMap, InlineAsmOperand, ItemId, ItemKind,
    LetExpr, Lifetime, LifetimeKind, LifetimeParamKind, Node, ParamName, Pat, PatExpr, PatExprKind, PatField, PatKind,
    Path, PathSegment, PreciseCapturingArgKind, PrimTy, QPath, Stmt, StmtKind, StructTailExpr, TraitBoundModifiers, Ty,
    TyKind, TyPat, TyPatKind, UseKind, WherePredicate, WherePredicateKind,
};
use rustc_lexer::{FrontmatterAllowed, TokenKind, tokenize};
use rustc_lint::LateContext;
use rustc_middle::ty::TypeckResults;
use rustc_span::{BytePos, ExpnKind, MacroKind, Symbol, SyntaxContext, sym};
use std::hash::{Hash, Hasher};
use std::ops::Range;
use std::slice;

/// Callback that is called when two expressions are not equal in the sense of `SpanlessEq`, but
/// other conditions would make them equal.
type SpanlessEqCallback<'a> = dyn FnMut(&Expr<'_>, &Expr<'_>) -> bool + 'a;

/// Determines how paths are hashed and compared for equality.
#[derive(Copy, Clone, Debug, Default)]
pub enum PathCheck {
    /// Paths must match exactly and are hashed by their exact HIR tree.
    ///
    /// Thus, `std::iter::Iterator` and `Iterator` are not considered equal even though they refer
    /// to the same item.
    #[default]
    Exact,
    /// Paths are compared and hashed based on their resolution.
    ///
    /// They can appear different in the HIR tree but are still considered equal
    /// and have equal hashes as long as they refer to the same item.
    ///
    /// Note that this is currently only partially implemented specifically for paths that are
    /// resolved before type-checking, i.e. the final segment must have a non-error resolution.
    /// If a path with an error resolution is encountered, it falls back to the default exact
    /// matching behavior.
    Resolution,
}

/// Type used to check whether two ast are the same. This is different from the
/// operator `==` on ast types as this operator would compare true equality with
/// ID and span.
///
/// Note that some expressions kinds are not considered but could be added.
pub struct SpanlessEq<'a, 'tcx> {
    /// Context used to evaluate constant expressions.
    cx: &'a LateContext<'tcx>,
    maybe_typeck_results: Option<(&'tcx TypeckResults<'tcx>, &'tcx TypeckResults<'tcx>)>,
    allow_side_effects: bool,
    expr_fallback: Option<Box<SpanlessEqCallback<'a>>>,
    path_check: PathCheck,
}

impl<'a, 'tcx> SpanlessEq<'a, 'tcx> {
    pub fn new(cx: &'a LateContext<'tcx>) -> Self {
        Self {
            cx,
            maybe_typeck_results: cx.maybe_typeck_results().map(|x| (x, x)),
            allow_side_effects: true,
            expr_fallback: None,
            path_check: PathCheck::default(),
        }
    }

    /// Consider expressions containing potential side effects as not equal.
    #[must_use]
    pub fn deny_side_effects(self) -> Self {
        Self {
            allow_side_effects: false,
            ..self
        }
    }

    /// Check paths by their resolution instead of exact equality. See [`PathCheck`] for more
    /// details.
    #[must_use]
    pub fn paths_by_resolution(self) -> Self {
        Self {
            path_check: PathCheck::Resolution,
            ..self
        }
    }

    #[must_use]
    pub fn expr_fallback(self, expr_fallback: impl FnMut(&Expr<'_>, &Expr<'_>) -> bool + 'a) -> Self {
        Self {
            expr_fallback: Some(Box::new(expr_fallback)),
            ..self
        }
    }

    /// Use this method to wrap comparisons that may involve inter-expression context.
    /// See `self.locals`.
    pub fn inter_expr(&mut self) -> HirEqInterExpr<'_, 'a, 'tcx> {
        HirEqInterExpr {
            inner: self,
            left_ctxt: SyntaxContext::root(),
            right_ctxt: SyntaxContext::root(),
            locals: HirIdMap::default(),
            local_items: FxIndexMap::default(),
        }
    }

    pub fn eq_block(&mut self, left: &Block<'_>, right: &Block<'_>) -> bool {
        self.inter_expr().eq_block(left, right)
    }

    pub fn eq_expr(&mut self, left: &Expr<'_>, right: &Expr<'_>) -> bool {
        self.inter_expr().eq_expr(left, right)
    }

    pub fn eq_path(&mut self, left: &Path<'_>, right: &Path<'_>) -> bool {
        self.inter_expr().eq_path(left, right)
    }

    pub fn eq_path_segment(&mut self, left: &PathSegment<'_>, right: &PathSegment<'_>) -> bool {
        self.inter_expr().eq_path_segment(left, right)
    }

    pub fn eq_path_segments(&mut self, left: &[PathSegment<'_>], right: &[PathSegment<'_>]) -> bool {
        self.inter_expr().eq_path_segments(left, right)
    }

    pub fn eq_modifiers(left: TraitBoundModifiers, right: TraitBoundModifiers) -> bool {
        std::mem::discriminant(&left.constness) == std::mem::discriminant(&right.constness)
            && std::mem::discriminant(&left.polarity) == std::mem::discriminant(&right.polarity)
    }
}

pub struct HirEqInterExpr<'a, 'b, 'tcx> {
    inner: &'a mut SpanlessEq<'b, 'tcx>,
    left_ctxt: SyntaxContext,
    right_ctxt: SyntaxContext,

    // When binding are declared, the binding ID in the left expression is mapped to the one on the
    // right. For example, when comparing `{ let x = 1; x + 2 }` and `{ let y = 1; y + 2 }`,
    // these blocks are considered equal since `x` is mapped to `y`.
    pub locals: HirIdMap<HirId>,
    pub local_items: FxIndexMap<DefId, DefId>,
}

impl HirEqInterExpr<'_, '_, '_> {
    pub fn eq_stmt(&mut self, left: &Stmt<'_>, right: &Stmt<'_>) -> bool {
        match (&left.kind, &right.kind) {
            (StmtKind::Let(l), StmtKind::Let(r)) => {
                // This additional check ensures that the type of the locals are equivalent even if the init
                // expression or type have some inferred parts.
                if let Some((typeck_lhs, typeck_rhs)) = self.inner.maybe_typeck_results {
                    let l_ty = typeck_lhs.pat_ty(l.pat);
                    let r_ty = typeck_rhs.pat_ty(r.pat);
                    if l_ty != r_ty {
                        return false;
                    }
                }

                // eq_pat adds the HirIds to the locals map. We therefore call it last to make sure that
                // these only get added if the init and type is equal.
                both(l.init.as_ref(), r.init.as_ref(), |l, r| self.eq_expr(l, r))
                    && both(l.ty.as_ref(), r.ty.as_ref(), |l, r| self.eq_ty(l, r))
                    && both(l.els.as_ref(), r.els.as_ref(), |l, r| self.eq_block(l, r))
                    && self.eq_pat(l.pat, r.pat)
            },
            (StmtKind::Expr(l), StmtKind::Expr(r)) | (StmtKind::Semi(l), StmtKind::Semi(r)) => self.eq_expr(l, r),
            (StmtKind::Item(l), StmtKind::Item(r)) => self.eq_item(*l, *r),
            _ => false,
        }
    }

    pub fn eq_item(&mut self, l: ItemId, r: ItemId) -> bool {
        let left = self.inner.cx.tcx.hir_item(l);
        let right = self.inner.cx.tcx.hir_item(r);
        let eq = match (left.kind, right.kind) {
            (
                ItemKind::Const(l_ident, l_generics, l_ty, ConstItemRhs::Body(l_body)),
                ItemKind::Const(r_ident, r_generics, r_ty, ConstItemRhs::Body(r_body)),
            ) => {
                l_ident.name == r_ident.name
                    && self.eq_generics(l_generics, r_generics)
                    && self.eq_ty(l_ty, r_ty)
                    && self.eq_body(l_body, r_body)
            },
            (ItemKind::Static(l_mut, l_ident, l_ty, l_body), ItemKind::Static(r_mut, r_ident, r_ty, r_body)) => {
                l_mut == r_mut && l_ident.name == r_ident.name && self.eq_ty(l_ty, r_ty) && self.eq_body(l_body, r_body)
            },
            (
                ItemKind::Fn {
                    sig: l_sig,
                    ident: l_ident,
                    generics: l_generics,
                    body: l_body,
                    has_body: l_has_body,
                },
                ItemKind::Fn {
                    sig: r_sig,
                    ident: r_ident,
                    generics: r_generics,
                    body: r_body,
                    has_body: r_has_body,
                },
            ) => {
                l_ident.name == r_ident.name
                    && (l_has_body == r_has_body)
                    && self.eq_fn_sig(&l_sig, &r_sig)
                    && self.eq_generics(l_generics, r_generics)
                    && self.eq_body(l_body, r_body)
            },
            (ItemKind::TyAlias(l_ident, l_generics, l_ty), ItemKind::TyAlias(r_ident, r_generics, r_ty)) => {
                l_ident.name == r_ident.name && self.eq_generics(l_generics, r_generics) && self.eq_ty(l_ty, r_ty)
            },
            (ItemKind::Use(l_path, l_kind), ItemKind::Use(r_path, r_kind)) => {
                self.eq_path_segments(l_path.segments, r_path.segments)
                    && match (l_kind, r_kind) {
                        (UseKind::Single(l_ident), UseKind::Single(r_ident)) => l_ident.name == r_ident.name,
                        (UseKind::Glob, UseKind::Glob) | (UseKind::ListStem, UseKind::ListStem) => true,
                        _ => false,
                    }
            },
            (ItemKind::Mod(l_ident, l_mod), ItemKind::Mod(r_ident, r_mod)) => {
                l_ident.name == r_ident.name && over(l_mod.item_ids, r_mod.item_ids, |l, r| self.eq_item(*l, *r))
            },
            _ => false,
        };
        if eq {
            self.local_items.insert(l.owner_id.to_def_id(), r.owner_id.to_def_id());
        }
        eq
    }

    fn eq_fn_sig(&mut self, left: &FnSig<'_>, right: &FnSig<'_>) -> bool {
        left.header.safety == right.header.safety
            && left.header.constness == right.header.constness
            && left.header.asyncness == right.header.asyncness
            && left.header.abi == right.header.abi
            && self.eq_fn_decl(left.decl, right.decl)
    }

    fn eq_fn_decl(&mut self, left: &FnDecl<'_>, right: &FnDecl<'_>) -> bool {
        over(left.inputs, right.inputs, |l, r| self.eq_ty(l, r))
            && (match (left.output, right.output) {
                (FnRetTy::DefaultReturn(_), FnRetTy::DefaultReturn(_)) => true,
                (FnRetTy::Return(l_ty), FnRetTy::Return(r_ty)) => self.eq_ty(l_ty, r_ty),
                _ => false,
            })
            && left.c_variadic == right.c_variadic
            && left.implicit_self == right.implicit_self
            && left.lifetime_elision_allowed == right.lifetime_elision_allowed
    }

    fn eq_generics(&mut self, left: &Generics<'_>, right: &Generics<'_>) -> bool {
        self.eq_generics_param(left.params, right.params)
            && self.eq_generics_predicate(left.predicates, right.predicates)
    }

    fn eq_generics_predicate(&mut self, left: &[WherePredicate<'_>], right: &[WherePredicate<'_>]) -> bool {
        over(left, right, |l, r| match (l.kind, r.kind) {
            (WherePredicateKind::BoundPredicate(l_bound), WherePredicateKind::BoundPredicate(r_bound)) => {
                l_bound.origin == r_bound.origin
                    && self.eq_ty(l_bound.bounded_ty, r_bound.bounded_ty)
                    && self.eq_generics_param(l_bound.bound_generic_params, r_bound.bound_generic_params)
                    && self.eq_generics_bound(l_bound.bounds, r_bound.bounds)
            },
            (WherePredicateKind::RegionPredicate(l_region), WherePredicateKind::RegionPredicate(r_region)) => {
                Self::eq_lifetime(l_region.lifetime, r_region.lifetime)
                    && self.eq_generics_bound(l_region.bounds, r_region.bounds)
            },
            (WherePredicateKind::EqPredicate(l_eq), WherePredicateKind::EqPredicate(r_eq)) => {
                self.eq_ty(l_eq.lhs_ty, r_eq.lhs_ty)
            },
            _ => false,
        })
    }

    fn eq_generics_bound(&mut self, left: GenericBounds<'_>, right: GenericBounds<'_>) -> bool {
        over(left, right, |l, r| match (l, r) {
            (GenericBound::Trait(l_trait), GenericBound::Trait(r_trait)) => {
                l_trait.modifiers == r_trait.modifiers
                    && self.eq_path(l_trait.trait_ref.path, r_trait.trait_ref.path)
                    && self.eq_generics_param(l_trait.bound_generic_params, r_trait.bound_generic_params)
            },
            (GenericBound::Outlives(l_lifetime), GenericBound::Outlives(r_lifetime)) => {
                Self::eq_lifetime(l_lifetime, r_lifetime)
            },
            (GenericBound::Use(l_capture, _), GenericBound::Use(r_capture, _)) => {
                over(l_capture, r_capture, |l, r| match (l, r) {
                    (PreciseCapturingArgKind::Lifetime(l_lifetime), PreciseCapturingArgKind::Lifetime(r_lifetime)) => {
                        Self::eq_lifetime(l_lifetime, r_lifetime)
                    },
                    (PreciseCapturingArgKind::Param(l_param), PreciseCapturingArgKind::Param(r_param)) => {
                        l_param.ident == r_param.ident && l_param.res == r_param.res
                    },
                    _ => false,
                })
            },
            _ => false,
        })
    }

    fn eq_generics_param(&mut self, left: &[GenericParam<'_>], right: &[GenericParam<'_>]) -> bool {
        over(left, right, |l, r| {
            (match (l.name, r.name) {
                (ParamName::Plain(l_ident), ParamName::Plain(r_ident))
                | (ParamName::Error(l_ident), ParamName::Error(r_ident)) => l_ident.name == r_ident.name,
                (ParamName::Fresh, ParamName::Fresh) => true,
                _ => false,
            }) && l.pure_wrt_drop == r.pure_wrt_drop
                && self.eq_generics_param_kind(&l.kind, &r.kind)
                && (matches!(
                    (l.source, r.source),
                    (GenericParamSource::Generics, GenericParamSource::Generics)
                        | (GenericParamSource::Binder, GenericParamSource::Binder)
                ))
        })
    }

    fn eq_generics_param_kind(&mut self, left: &GenericParamKind<'_>, right: &GenericParamKind<'_>) -> bool {
        match (left, right) {
            (GenericParamKind::Lifetime { kind: l_kind }, GenericParamKind::Lifetime { kind: r_kind }) => {
                match (l_kind, r_kind) {
                    (LifetimeParamKind::Explicit, LifetimeParamKind::Explicit)
                    | (LifetimeParamKind::Error, LifetimeParamKind::Error) => true,
                    (LifetimeParamKind::Elided(l_lifetime_kind), LifetimeParamKind::Elided(r_lifetime_kind)) => {
                        l_lifetime_kind == r_lifetime_kind
                    },
                    _ => false,
                }
            },
            (
                GenericParamKind::Type {
                    default: l_default,
                    synthetic: l_synthetic,
                },
                GenericParamKind::Type {
                    default: r_default,
                    synthetic: r_synthetic,
                },
            ) => both(*l_default, *r_default, |l, r| self.eq_ty(l, r)) && l_synthetic == r_synthetic,
            (
                GenericParamKind::Const {
                    ty: l_ty,
                    default: l_default,
                },
                GenericParamKind::Const {
                    ty: r_ty,
                    default: r_default,
                },
            ) => self.eq_ty(l_ty, r_ty) && both(*l_default, *r_default, |l, r| self.eq_const_arg(l, r)),
            _ => false,
        }
    }

    /// Checks whether two blocks are the same.
    fn eq_block(&mut self, left: &Block<'_>, right: &Block<'_>) -> bool {
        use TokenKind::{Semi, Whitespace};
        if left.stmts.len() != right.stmts.len() {
            return false;
        }
        let lspan = left.span.data();
        let rspan = right.span.data();
        if lspan.ctxt != SyntaxContext::root() && rspan.ctxt != SyntaxContext::root() {
            // Don't try to check in between statements inside macros.
            return over(left.stmts, right.stmts, |left, right| self.eq_stmt(left, right))
                && both(left.expr.as_ref(), right.expr.as_ref(), |left, right| {
                    self.eq_expr(left, right)
                });
        }
        if lspan.ctxt != rspan.ctxt {
            return false;
        }

        let mut lstart = lspan.lo;
        let mut rstart = rspan.lo;

        for (left, right) in left.stmts.iter().zip(right.stmts) {
            if !self.eq_stmt(left, right) {
                return false;
            }

            // Try to detect any `cfg`ed statements or empty macro expansions.
            let Some(lstmt_span) = walk_span_to_context(left.span, lspan.ctxt) else {
                return false;
            };
            let Some(rstmt_span) = walk_span_to_context(right.span, rspan.ctxt) else {
                return false;
            };
            let lstmt_span = lstmt_span.data();
            let rstmt_span = rstmt_span.data();

            if lstmt_span.lo < lstart && rstmt_span.lo < rstart {
                // Can happen when macros expand to multiple statements, or rearrange statements.
                // Nothing in between the statements to check in this case.
                continue;
            }
            if lstmt_span.lo < lstart || rstmt_span.lo < rstart {
                // Only one of the blocks had a weird macro.
                return false;
            }
            if !eq_span_tokens(self.inner.cx, lstart..lstmt_span.lo, rstart..rstmt_span.lo, |t| {
                !matches!(t, Whitespace | Semi)
            }) {
                return false;
            }

            lstart = lstmt_span.hi;
            rstart = rstmt_span.hi;
        }

        let (lend, rend) = match (left.expr, right.expr) {
            (Some(left), Some(right)) => {
                if !self.eq_expr(left, right) {
                    return false;
                }
                let Some(lexpr_span) = walk_span_to_context(left.span, lspan.ctxt) else {
                    return false;
                };
                let Some(rexpr_span) = walk_span_to_context(right.span, rspan.ctxt) else {
                    return false;
                };
                (lexpr_span.lo(), rexpr_span.lo())
            },
            (None, None) => (lspan.hi, rspan.hi),
            (Some(_), None) | (None, Some(_)) => return false,
        };

        if lend < lstart && rend < rstart {
            // Can happen when macros rearrange the input.
            // Nothing in between the statements to check in this case.
            return true;
        } else if lend < lstart || rend < rstart {
            // Only one of the blocks had a weird macro
            return false;
        }
        eq_span_tokens(self.inner.cx, lstart..lend, rstart..rend, |t| {
            !matches!(t, Whitespace | Semi)
        })
    }

    fn should_ignore(&self, expr: &Expr<'_>) -> bool {
        macro_backtrace(expr.span).last().is_some_and(|macro_call| {
            matches!(
                self.inner.cx.tcx.get_diagnostic_name(macro_call.def_id),
                Some(sym::todo_macro | sym::unimplemented_macro)
            )
        })
    }

    pub fn eq_body(&mut self, left: BodyId, right: BodyId) -> bool {
        // swap out TypeckResults when hashing a body
        let old_maybe_typeck_results = self.inner.maybe_typeck_results.replace((
            self.inner.cx.tcx.typeck_body(left),
            self.inner.cx.tcx.typeck_body(right),
        ));
        let res = self.eq_expr(
            self.inner.cx.tcx.hir_body(left).value,
            self.inner.cx.tcx.hir_body(right).value,
        );
        self.inner.maybe_typeck_results = old_maybe_typeck_results;
        res
    }

    #[expect(clippy::too_many_lines)]
    pub fn eq_expr(&mut self, left: &Expr<'_>, right: &Expr<'_>) -> bool {
        if !self.check_ctxt(left.span.ctxt(), right.span.ctxt()) {
            return false;
        }

        if let Some((typeck_lhs, typeck_rhs)) = self.inner.maybe_typeck_results
            && typeck_lhs.expr_ty(left) == typeck_rhs.expr_ty(right)
            && let (Some(l), Some(r)) = (
                ConstEvalCtxt::with_env(self.inner.cx.tcx, self.inner.cx.typing_env(), typeck_lhs)
                    .eval_local(left, self.left_ctxt),
                ConstEvalCtxt::with_env(self.inner.cx.tcx, self.inner.cx.typing_env(), typeck_rhs)
                    .eval_local(right, self.right_ctxt),
            )
            && l == r
        {
            return true;
        }

        let is_eq = match (
            reduce_exprkind(self.inner.cx, &left.kind),
            reduce_exprkind(self.inner.cx, &right.kind),
        ) {
            (ExprKind::AddrOf(lb, l_mut, le), ExprKind::AddrOf(rb, r_mut, re)) => {
                lb == rb && l_mut == r_mut && self.eq_expr(le, re)
            },
            (ExprKind::Array(l), ExprKind::Array(r)) => self.eq_exprs(l, r),
            (ExprKind::Assign(ll, lr, _), ExprKind::Assign(rl, rr, _)) => {
                self.inner.allow_side_effects && self.eq_expr(ll, rl) && self.eq_expr(lr, rr)
            },
            (ExprKind::AssignOp(lo, ll, lr), ExprKind::AssignOp(ro, rl, rr)) => {
                self.inner.allow_side_effects && lo.node == ro.node && self.eq_expr(ll, rl) && self.eq_expr(lr, rr)
            },
            (ExprKind::Block(l, _), ExprKind::Block(r, _)) => self.eq_block(l, r),
            (ExprKind::Binary(l_op, ll, lr), ExprKind::Binary(r_op, rl, rr)) => {
                l_op.node == r_op.node && self.eq_expr(ll, rl) && self.eq_expr(lr, rr)
                    || swap_binop(self.inner.cx, l_op.node, ll, lr).is_some_and(|(l_op, ll, lr)| {
                        l_op == r_op.node && self.eq_expr(ll, rl) && self.eq_expr(lr, rr)
                    })
            },
            (ExprKind::Break(li, le), ExprKind::Break(ri, re)) => {
                both(li.label.as_ref(), ri.label.as_ref(), |l, r| l.ident.name == r.ident.name)
                    && both(le.as_ref(), re.as_ref(), |l, r| self.eq_expr(l, r))
            },
            (ExprKind::Call(l_fun, l_args), ExprKind::Call(r_fun, r_args)) => {
                self.inner.allow_side_effects && self.eq_expr(l_fun, r_fun) && self.eq_exprs(l_args, r_args)
            },
            (ExprKind::Cast(lx, lt), ExprKind::Cast(rx, rt)) => {
                self.eq_expr(lx, rx) && self.eq_ty(lt, rt)
            },
            (ExprKind::Closure(_l), ExprKind::Closure(_r)) => false,
            (ExprKind::ConstBlock(lb), ExprKind::ConstBlock(rb)) => self.eq_body(lb.body, rb.body),
            (ExprKind::Continue(li), ExprKind::Continue(ri)) => {
                both(li.label.as_ref(), ri.label.as_ref(), |l, r| l.ident.name == r.ident.name)
            },
            (ExprKind::DropTemps(le), ExprKind::DropTemps(re)) => self.eq_expr(le, re),
            (ExprKind::Field(l_f_exp, l_f_ident), ExprKind::Field(r_f_exp, r_f_ident)) => {
                l_f_ident.name == r_f_ident.name && self.eq_expr(l_f_exp, r_f_exp)
            },
            (ExprKind::Index(la, li, _), ExprKind::Index(ra, ri, _)) => self.eq_expr(la, ra) && self.eq_expr(li, ri),
            (ExprKind::If(lc, lt, le), ExprKind::If(rc, rt, re)) => {
                self.eq_expr(lc, rc) && self.eq_expr(lt, rt)
                    && both(le.as_ref(), re.as_ref(), |l, r| self.eq_expr(l, r))
            },
            (ExprKind::Let(l), ExprKind::Let(r)) => {
                self.eq_pat(l.pat, r.pat)
                    && both(l.ty.as_ref(), r.ty.as_ref(), |l, r| self.eq_ty(l, r))
                    && self.eq_expr(l.init, r.init)
            },
            (ExprKind::Lit(l), ExprKind::Lit(r)) => l.node == r.node,
            (ExprKind::Loop(lb, ll, lls, _), ExprKind::Loop(rb, rl, rls, _)) => {
                lls == rls && self.eq_block(lb, rb)
                    && both(ll.as_ref(), rl.as_ref(), |l, r| l.ident.name == r.ident.name)
            },
            (ExprKind::Match(le, la, ls), ExprKind::Match(re, ra, rs)) => {
                (ls == rs || (matches!((ls, rs), (TryDesugar(_), TryDesugar(_)))))
                    && self.eq_expr(le, re)
                    && over(la, ra, |l, r| {
                        self.eq_pat(l.pat, r.pat)
                            && both(l.guard.as_ref(), r.guard.as_ref(), |l, r| self.eq_expr(l, r))
                            && self.eq_expr(l.body, r.body)
                    })
            },
            (
                ExprKind::MethodCall(l_path, l_receiver, l_args, _),
                ExprKind::MethodCall(r_path, r_receiver, r_args, _),
            ) => {
                self.inner.allow_side_effects
                    && self.eq_path_segment(l_path, r_path)
                    && self.eq_expr(l_receiver, r_receiver)
                    && self.eq_exprs(l_args, r_args)
            },
            (ExprKind::UnsafeBinderCast(lkind, le, None), ExprKind::UnsafeBinderCast(rkind, re, None)) =>
                lkind == rkind && self.eq_expr(le, re),
            (ExprKind::UnsafeBinderCast(lkind, le, Some(lt)), ExprKind::UnsafeBinderCast(rkind, re, Some(rt))) =>
                lkind == rkind && self.eq_expr(le, re) && self.eq_ty(lt, rt),
            (ExprKind::OffsetOf(l_container, l_fields), ExprKind::OffsetOf(r_container, r_fields)) => {
                self.eq_ty(l_container, r_container) && over(l_fields, r_fields, |l, r| l.name == r.name)
            },
            (ExprKind::Path(l), ExprKind::Path(r)) => self.eq_qpath(l, r),
            (ExprKind::Repeat(le, ll), ExprKind::Repeat(re, rl)) => {
                self.eq_expr(le, re) && self.eq_const_arg(ll, rl)
            },
            (ExprKind::Ret(l), ExprKind::Ret(r)) => both(l.as_ref(), r.as_ref(), |l, r| self.eq_expr(l, r)),
            (ExprKind::Struct(l_path, lf, lo), ExprKind::Struct(r_path, rf, ro)) => {
                self.eq_qpath(l_path, r_path)
                    && match (lo, ro) {
                        (StructTailExpr::Base(l),StructTailExpr::Base(r)) => self.eq_expr(l, r),
                        (StructTailExpr::None, StructTailExpr::None) |
                        (StructTailExpr::DefaultFields(_), StructTailExpr::DefaultFields(_)) => true,
                        _ => false,
                    }
                    && over(lf, rf, |l, r| self.eq_expr_field(l, r))
            },
            (ExprKind::Tup(l_tup), ExprKind::Tup(r_tup)) => self.eq_exprs(l_tup, r_tup),
            (ExprKind::Use(l_expr, _), ExprKind::Use(r_expr, _)) => self.eq_expr(l_expr, r_expr),
            (ExprKind::Type(le, lt), ExprKind::Type(re, rt)) => self.eq_expr(le, re) && self.eq_ty(lt, rt),
            (ExprKind::Unary(l_op, le), ExprKind::Unary(r_op, re)) => l_op == r_op && self.eq_expr(le, re),
            (ExprKind::Yield(le, _), ExprKind::Yield(re, _)) => return self.eq_expr(le, re),
            (
                // Else branches for branches above, grouped as per `match_same_arms`.
                | ExprKind::AddrOf(..)
                | ExprKind::Array(..)
                | ExprKind::Assign(..)
                | ExprKind::AssignOp(..)
                | ExprKind::Binary(..)
                | ExprKind::Become(..)
                | ExprKind::Block(..)
                | ExprKind::Break(..)
                | ExprKind::Call(..)
                | ExprKind::Cast(..)
                | ExprKind::ConstBlock(..)
                | ExprKind::Continue(..)
                | ExprKind::DropTemps(..)
                | ExprKind::Field(..)
                | ExprKind::Index(..)
                | ExprKind::If(..)
                | ExprKind::Let(..)
                | ExprKind::Lit(..)
                | ExprKind::Loop(..)
                | ExprKind::Match(..)
                | ExprKind::MethodCall(..)
                | ExprKind::OffsetOf(..)
                | ExprKind::Path(..)
                | ExprKind::Repeat(..)
                | ExprKind::Ret(..)
                | ExprKind::Struct(..)
                | ExprKind::Tup(..)
                | ExprKind::Use(..)
                | ExprKind::Type(..)
                | ExprKind::Unary(..)
                | ExprKind::Yield(..)
                | ExprKind::UnsafeBinderCast(..)

                // --- Special cases that do not have a positive branch.

                // `Err` represents an invalid expression, so let's never assume that
                // an invalid expressions is equal to anything.
                | ExprKind::Err(..)

                // For the time being, we always consider that two closures are unequal.
                // This behavior may change in the future.
                | ExprKind::Closure(..)
                // For the time being, we always consider that two instances of InlineAsm are different.
                // This behavior may change in the future.
                | ExprKind::InlineAsm(_)
                , _
            ) => false,
        };
        (is_eq && (!self.should_ignore(left) || !self.should_ignore(right)))
            || self.inner.expr_fallback.as_mut().is_some_and(|f| f(left, right))
    }

    fn eq_exprs(&mut self, left: &[Expr<'_>], right: &[Expr<'_>]) -> bool {
        over(left, right, |l, r| self.eq_expr(l, r))
    }

    fn eq_expr_field(&mut self, left: &ExprField<'_>, right: &ExprField<'_>) -> bool {
        left.ident.name == right.ident.name && self.eq_expr(left.expr, right.expr)
    }

    fn eq_generic_arg(&mut self, left: &GenericArg<'_>, right: &GenericArg<'_>) -> bool {
        match (left, right) {
            (GenericArg::Const(l), GenericArg::Const(r)) => self.eq_const_arg(l.as_unambig_ct(), r.as_unambig_ct()),
            (GenericArg::Lifetime(l_lt), GenericArg::Lifetime(r_lt)) => Self::eq_lifetime(l_lt, r_lt),
            (GenericArg::Type(l_ty), GenericArg::Type(r_ty)) => self.eq_ty(l_ty.as_unambig_ty(), r_ty.as_unambig_ty()),
            (GenericArg::Infer(l_inf), GenericArg::Infer(r_inf)) => self.eq_ty(&l_inf.to_ty(), &r_inf.to_ty()),
            _ => false,
        }
    }

    fn eq_const_arg(&mut self, left: &ConstArg<'_>, right: &ConstArg<'_>) -> bool {
        if !self.check_ctxt(left.span.ctxt(), right.span.ctxt()) {
            return false;
        }

        match (&left.kind, &right.kind) {
            (ConstArgKind::Tup(l_t), ConstArgKind::Tup(r_t)) => {
                l_t.len() == r_t.len() && l_t.iter().zip(*r_t).all(|(l_c, r_c)| self.eq_const_arg(l_c, r_c))
            },
            (ConstArgKind::Path(l_p), ConstArgKind::Path(r_p)) => self.eq_qpath(l_p, r_p),
            (ConstArgKind::Anon(l_an), ConstArgKind::Anon(r_an)) => self.eq_body(l_an.body, r_an.body),
            (ConstArgKind::Infer(..), ConstArgKind::Infer(..)) => true,
            (ConstArgKind::Struct(path_a, inits_a), ConstArgKind::Struct(path_b, inits_b)) => {
                self.eq_qpath(path_a, path_b)
                    && inits_a
                        .iter()
                        .zip(*inits_b)
                        .all(|(init_a, init_b)| self.eq_const_arg(init_a.expr, init_b.expr))
            },
            (ConstArgKind::TupleCall(path_a, args_a), ConstArgKind::TupleCall(path_b, args_b)) => {
                self.eq_qpath(path_a, path_b)
                    && args_a
                        .iter()
                        .zip(*args_b)
                        .all(|(arg_a, arg_b)| self.eq_const_arg(arg_a, arg_b))
            },
            (ConstArgKind::Literal(kind_l), ConstArgKind::Literal(kind_r)) => kind_l == kind_r,
            (ConstArgKind::Array(l_arr), ConstArgKind::Array(r_arr)) => {
                l_arr.elems.len() == r_arr.elems.len()
                    && l_arr
                        .elems
                        .iter()
                        .zip(r_arr.elems.iter())
                        .all(|(l_elem, r_elem)| self.eq_const_arg(l_elem, r_elem))
            },
            // Use explicit match for now since ConstArg is undergoing flux.
            (
                ConstArgKind::Path(..)
                | ConstArgKind::Tup(..)
                | ConstArgKind::Anon(..)
                | ConstArgKind::TupleCall(..)
                | ConstArgKind::Infer(..)
                | ConstArgKind::Struct(..)
                | ConstArgKind::Literal(..)
                | ConstArgKind::Array(..)
                | ConstArgKind::Error(..),
                _,
            ) => false,
        }
    }

    fn eq_lifetime(left: &Lifetime, right: &Lifetime) -> bool {
        left.kind == right.kind
    }

    fn eq_pat_field(&mut self, left: &PatField<'_>, right: &PatField<'_>) -> bool {
        let (PatField { ident: li, pat: lp, .. }, PatField { ident: ri, pat: rp, .. }) = (&left, &right);
        li.name == ri.name && self.eq_pat(lp, rp)
    }

    fn eq_pat_expr(&mut self, left: &PatExpr<'_>, right: &PatExpr<'_>) -> bool {
        match (&left.kind, &right.kind) {
            (
                PatExprKind::Lit {
                    lit: left,
                    negated: left_neg,
                },
                PatExprKind::Lit {
                    lit: right,
                    negated: right_neg,
                },
            ) => left_neg == right_neg && left.node == right.node,
            (PatExprKind::Path(left), PatExprKind::Path(right)) => self.eq_qpath(left, right),
            (PatExprKind::Lit { .. } | PatExprKind::Path(..), _) => false,
        }
    }

    /// Checks whether two patterns are the same.
    fn eq_pat(&mut self, left: &Pat<'_>, right: &Pat<'_>) -> bool {
        match (&left.kind, &right.kind) {
            (PatKind::Box(l), PatKind::Box(r)) => self.eq_pat(l, r),
            (PatKind::Struct(lp, la, ..), PatKind::Struct(rp, ra, ..)) => {
                self.eq_qpath(lp, rp) && over(la, ra, |l, r| self.eq_pat_field(l, r))
            },
            (PatKind::TupleStruct(lp, la, ls), PatKind::TupleStruct(rp, ra, rs)) => {
                self.eq_qpath(lp, rp) && over(la, ra, |l, r| self.eq_pat(l, r)) && ls == rs
            },
            (PatKind::Binding(lb, li, _, lp), PatKind::Binding(rb, ri, _, rp)) => {
                let eq = lb == rb && both(lp.as_ref(), rp.as_ref(), |l, r| self.eq_pat(l, r));
                if eq {
                    self.locals.insert(*li, *ri);
                }
                eq
            },
            (PatKind::Expr(l), PatKind::Expr(r)) => self.eq_pat_expr(l, r),
            (PatKind::Tuple(l, ls), PatKind::Tuple(r, rs)) => ls == rs && over(l, r, |l, r| self.eq_pat(l, r)),
            (PatKind::Range(ls, le, li), PatKind::Range(rs, re, ri)) => {
                both(ls.as_ref(), rs.as_ref(), |a, b| self.eq_pat_expr(a, b))
                    && both(le.as_ref(), re.as_ref(), |a, b| self.eq_pat_expr(a, b))
                    && (li == ri)
            },
            (PatKind::Ref(le, lp, lm), PatKind::Ref(re, rp, rm)) => lp == rp && lm == rm && self.eq_pat(le, re),
            (PatKind::Slice(ls, li, le), PatKind::Slice(rs, ri, re)) => {
                over(ls, rs, |l, r| self.eq_pat(l, r))
                    && over(le, re, |l, r| self.eq_pat(l, r))
                    && both(li.as_ref(), ri.as_ref(), |l, r| self.eq_pat(l, r))
            },
            (PatKind::Wild, PatKind::Wild) => true,
            _ => false,
        }
    }

    fn eq_qpath(&mut self, left: &QPath<'_>, right: &QPath<'_>) -> bool {
        match (left, right) {
            (QPath::Resolved(lty, lpath), QPath::Resolved(rty, rpath)) => {
                both(lty.as_ref(), rty.as_ref(), |l, r| self.eq_ty(l, r)) && self.eq_path(lpath, rpath)
            },
            (QPath::TypeRelative(lty, lseg), QPath::TypeRelative(rty, rseg)) => {
                self.eq_ty(lty, rty) && self.eq_path_segment(lseg, rseg)
            },
            _ => false,
        }
    }

    pub fn eq_path(&mut self, left: &Path<'_>, right: &Path<'_>) -> bool {
        match (left.res, right.res) {
            (Res::Local(l), Res::Local(r)) => l == r || self.locals.get(&l) == Some(&r),
            (Res::Local(_), _) | (_, Res::Local(_)) => false,
            (Res::Def(l_kind, l), Res::Def(r_kind, r))
                if l_kind == r_kind
                    && let DefKind::Const
                    | DefKind::Static { .. }
                    | DefKind::Fn
                    | DefKind::TyAlias
                    | DefKind::Use
                    | DefKind::Mod = l_kind =>
            {
                (l == r || self.local_items.get(&l) == Some(&r)) && self.eq_path_segments(left.segments, right.segments)
            },
            _ => self.eq_path_segments(left.segments, right.segments),
        }
    }

    fn eq_path_parameters(&mut self, left: &GenericArgs<'_>, right: &GenericArgs<'_>) -> bool {
        if left.parenthesized == right.parenthesized {
            over(left.args, right.args, |l, r| self.eq_generic_arg(l, r)) // FIXME(flip1995): may not work
                && over(left.constraints, right.constraints, |l, r| self.eq_assoc_eq_constraint(l, r))
        } else {
            false
        }
    }

    pub fn eq_path_segments<'tcx>(
        &mut self,
        mut left: &'tcx [PathSegment<'tcx>],
        mut right: &'tcx [PathSegment<'tcx>],
    ) -> bool {
        if let PathCheck::Resolution = self.inner.path_check
            && let Some(left_seg) = generic_path_segments(left)
            && let Some(right_seg) = generic_path_segments(right)
        {
            // If we compare by resolution, then only check the last segments that could possibly have generic
            // arguments
            left = left_seg;
            right = right_seg;
        }

        over(left, right, |l, r| self.eq_path_segment(l, r))
    }

    pub fn eq_path_segment(&mut self, left: &PathSegment<'_>, right: &PathSegment<'_>) -> bool {
        if !self.eq_path_parameters(left.args(), right.args()) {
            return false;
        }

        if let PathCheck::Resolution = self.inner.path_check
            && left.res != Res::Err
            && right.res != Res::Err
        {
            left.res == right.res
        } else {
            // The == of idents doesn't work with different contexts,
            // we have to be explicit about hygiene
            left.ident.name == right.ident.name
        }
    }

    pub fn eq_ty(&mut self, left: &Ty<'_>, right: &Ty<'_>) -> bool {
        match (&left.kind, &right.kind) {
            (TyKind::Slice(l_vec), TyKind::Slice(r_vec)) => self.eq_ty(l_vec, r_vec),
            (TyKind::Array(lt, ll), TyKind::Array(rt, rl)) => self.eq_ty(lt, rt) && self.eq_const_arg(ll, rl),
            (TyKind::Ptr(l_mut), TyKind::Ptr(r_mut)) => l_mut.mutbl == r_mut.mutbl && self.eq_ty(l_mut.ty, r_mut.ty),
            (TyKind::Ref(_, l_rmut), TyKind::Ref(_, r_rmut)) => {
                l_rmut.mutbl == r_rmut.mutbl && self.eq_ty(l_rmut.ty, r_rmut.ty)
            },
            (TyKind::Path(l), TyKind::Path(r)) => self.eq_qpath(l, r),
            (TyKind::Tup(l), TyKind::Tup(r)) => over(l, r, |l, r| self.eq_ty(l, r)),
            (TyKind::Infer(()), TyKind::Infer(())) => true,
            _ => false,
        }
    }

    /// Checks whether two constraints designate the same equality constraint (same name, and same
    /// type or const).
    fn eq_assoc_eq_constraint(&mut self, left: &AssocItemConstraint<'_>, right: &AssocItemConstraint<'_>) -> bool {
        // TODO: this could be extended to check for identical associated item bound constraints
        left.ident.name == right.ident.name
            && (both_some_and(left.ty(), right.ty(), |l, r| self.eq_ty(l, r))
                || both_some_and(left.ct(), right.ct(), |l, r| self.eq_const_arg(l, r)))
    }

    fn check_ctxt(&mut self, left: SyntaxContext, right: SyntaxContext) -> bool {
        if self.left_ctxt == left && self.right_ctxt == right {
            return true;
        } else if self.left_ctxt == left || self.right_ctxt == right {
            // Only one context has changed. This can only happen if the two nodes are written differently.
            return false;
        } else if left != SyntaxContext::root() {
            let mut left_data = left.outer_expn_data();
            let mut right_data = right.outer_expn_data();
            loop {
                use TokenKind::{BlockComment, LineComment, Whitespace};
                if left_data.macro_def_id != right_data.macro_def_id
                    || (matches!(
                        left_data.kind,
                        ExpnKind::Macro(MacroKind::Bang, name)
                        if name == sym::cfg || name == sym::option_env
                    ) && !eq_span_tokens(self.inner.cx, left_data.call_site, right_data.call_site, |t| {
                        !matches!(t, Whitespace | LineComment { .. } | BlockComment { .. })
                    }))
                {
                    // Either a different chain of macro calls, or different arguments to the `cfg` macro.
                    return false;
                }
                let left_ctxt = left_data.call_site.ctxt();
                let right_ctxt = right_data.call_site.ctxt();
                if left_ctxt == SyntaxContext::root() && right_ctxt == SyntaxContext::root() {
                    break;
                }
                if left_ctxt == SyntaxContext::root() || right_ctxt == SyntaxContext::root() {
                    // Different lengths for the expansion stack. This can only happen if nodes are written differently,
                    // or shouldn't be compared to start with.
                    return false;
                }
                left_data = left_ctxt.outer_expn_data();
                right_data = right_ctxt.outer_expn_data();
            }
        }
        self.left_ctxt = left;
        self.right_ctxt = right;
        true
    }
}

/// Some simple reductions like `{ return }` => `return`
fn reduce_exprkind<'hir>(cx: &LateContext<'_>, kind: &'hir ExprKind<'hir>) -> &'hir ExprKind<'hir> {
    if let ExprKind::Block(block, _) = kind {
        match (block.stmts, block.expr) {
            // From an `if let` expression without an `else` block. The arm for the implicit wild pattern is an empty
            // block with an empty span.
            ([], None) if block.span.is_empty() => &ExprKind::Tup(&[]),
            // `{}` => `()`
            ([], None)
                if block.span.check_source_text(cx, |src| {
                    tokenize(src, FrontmatterAllowed::No)
                        .map(|t| t.kind)
                        .filter(|t| {
                            !matches!(
                                t,
                                TokenKind::LineComment { .. } | TokenKind::BlockComment { .. } | TokenKind::Whitespace
                            )
                        })
                        .eq([TokenKind::OpenBrace, TokenKind::CloseBrace].iter().copied())
                }) =>
            {
                &ExprKind::Tup(&[])
            },
            ([], Some(expr)) => match expr.kind {
                // `{ return .. }` => `return ..`
                ExprKind::Ret(..) => &expr.kind,
                _ => kind,
            },
            ([stmt], None) => match stmt.kind {
                StmtKind::Expr(expr) | StmtKind::Semi(expr) => match expr.kind {
                    // `{ return ..; }` => `return ..`
                    ExprKind::Ret(..) => &expr.kind,
                    _ => kind,
                },
                _ => kind,
            },
            _ => kind,
        }
    } else {
        kind
    }
}

fn swap_binop<'a>(
    cx: &LateContext<'_>,
    binop: BinOpKind,
    lhs: &'a Expr<'a>,
    rhs: &'a Expr<'a>,
) -> Option<(BinOpKind, &'a Expr<'a>, &'a Expr<'a>)> {
    match binop {
        // `==` and `!=`, are commutative
        BinOpKind::Eq | BinOpKind::Ne => Some((binop, rhs, lhs)),
        // Comparisons can be reversed
        BinOpKind::Lt => Some((BinOpKind::Gt, rhs, lhs)),
        BinOpKind::Le => Some((BinOpKind::Ge, rhs, lhs)),
        BinOpKind::Ge => Some((BinOpKind::Le, rhs, lhs)),
        BinOpKind::Gt => Some((BinOpKind::Lt, rhs, lhs)),
        // Non-commutative operators
        BinOpKind::Shl | BinOpKind::Shr | BinOpKind::Rem | BinOpKind::Sub | BinOpKind::Div => None,
        // We know that those operators are commutative for primitive types,
        // and we don't assume anything for other types
        BinOpKind::Mul
        | BinOpKind::Add
        | BinOpKind::And
        | BinOpKind::Or
        | BinOpKind::BitAnd
        | BinOpKind::BitXor
        | BinOpKind::BitOr => cx
            .typeck_results()
            .expr_ty_adjusted(lhs)
            .peel_refs()
            .is_primitive()
            .then_some((binop, rhs, lhs)),
    }
}

/// Checks if the two `Option`s are both `None` or some equal values as per
/// `eq_fn`.
pub fn both<X>(l: Option<&X>, r: Option<&X>, mut eq_fn: impl FnMut(&X, &X) -> bool) -> bool {
    l.as_ref()
        .map_or_else(|| r.is_none(), |x| r.as_ref().is_some_and(|y| eq_fn(x, y)))
}

/// Checks if the two `Option`s are both `Some` and pass the predicate function.
pub fn both_some_and<X, Y>(l: Option<X>, r: Option<Y>, mut pred: impl FnMut(X, Y) -> bool) -> bool {
    l.is_some_and(|l| r.is_some_and(|r| pred(l, r)))
}

/// Checks if two slices are equal as per `eq_fn`.
pub fn over<X, Y>(left: &[X], right: &[Y], mut eq_fn: impl FnMut(&X, &Y) -> bool) -> bool {
    left.len() == right.len() && left.iter().zip(right).all(|(x, y)| eq_fn(x, y))
}

/// Counts how many elements of the slices are equal as per `eq_fn`.
pub fn count_eq<X: Sized>(
    left: &mut dyn Iterator<Item = X>,
    right: &mut dyn Iterator<Item = X>,
    mut eq_fn: impl FnMut(&X, &X) -> bool,
) -> usize {
    left.zip(right).take_while(|(l, r)| eq_fn(l, r)).count()
}

/// Checks if two expressions evaluate to the same value, and don't contain any side effects.
pub fn eq_expr_value(cx: &LateContext<'_>, left: &Expr<'_>, right: &Expr<'_>) -> bool {
    SpanlessEq::new(cx).deny_side_effects().eq_expr(left, right)
}

/// Returns the segments of a path that might have generic parameters.
/// Usually just the last segment for free items, except for when the path resolves to an associated
/// item, in which case it is the last two
fn generic_path_segments<'tcx>(segments: &'tcx [PathSegment<'tcx>]) -> Option<&'tcx [PathSegment<'tcx>]> {
    match segments.last()?.res {
        Res::Def(DefKind::AssocConst | DefKind::AssocFn | DefKind::AssocTy, _) => {
            // <Ty as module::Trait<T>>::assoc::<U>
            //        ^^^^^^^^^^^^^^^^   ^^^^^^^^^^ segments: [module, Trait<T>, assoc<U>]
            Some(&segments[segments.len().checked_sub(2)?..])
        },
        Res::Err => None,
        _ => Some(slice::from_ref(segments.last()?)),
    }
}

/// Type used to hash an ast element. This is different from the `Hash` trait
/// on ast types as this
/// trait would consider IDs and spans.
///
/// All expressions kind are hashed, but some might have a weaker hash.
pub struct SpanlessHash<'a, 'tcx> {
    /// Context used to evaluate constant expressions.
    cx: &'a LateContext<'tcx>,
    maybe_typeck_results: Option<&'tcx TypeckResults<'tcx>>,
    s: FxHasher,
    path_check: PathCheck,
}

impl<'a, 'tcx> SpanlessHash<'a, 'tcx> {
    pub fn new(cx: &'a LateContext<'tcx>) -> Self {
        Self {
            cx,
            maybe_typeck_results: cx.maybe_typeck_results(),
            s: FxHasher::default(),
            path_check: PathCheck::default(),
        }
    }

    /// Check paths by their resolution instead of exact equality. See [`PathCheck`] for more
    /// details.
    #[must_use]
    pub fn paths_by_resolution(self) -> Self {
        Self {
            path_check: PathCheck::Resolution,
            ..self
        }
    }

    pub fn finish(self) -> u64 {
        self.s.finish()
    }

    pub fn hash_block(&mut self, b: &Block<'_>) {
        for s in b.stmts {
            self.hash_stmt(s);
        }

        if let Some(e) = b.expr {
            self.hash_expr(e);
        }

        std::mem::discriminant(&b.rules).hash(&mut self.s);
    }

    #[expect(clippy::too_many_lines)]
    pub fn hash_expr(&mut self, e: &Expr<'_>) {
        let simple_const = self.maybe_typeck_results.and_then(|typeck_results| {
            ConstEvalCtxt::with_env(self.cx.tcx, self.cx.typing_env(), typeck_results).eval_local(e, e.span.ctxt())
        });

        // const hashing may result in the same hash as some unrelated node, so add a sort of
        // discriminant depending on which path we're choosing next
        simple_const.hash(&mut self.s);
        if simple_const.is_some() {
            return;
        }

        std::mem::discriminant(&e.kind).hash(&mut self.s);

        match &e.kind {
            ExprKind::AddrOf(kind, m, e) => {
                std::mem::discriminant(kind).hash(&mut self.s);
                m.hash(&mut self.s);
                self.hash_expr(e);
            },
            ExprKind::Continue(i) => {
                if let Some(i) = i.label {
                    self.hash_name(i.ident.name);
                }
            },
            ExprKind::Array(v) => {
                self.hash_exprs(v);
            },
            ExprKind::Assign(l, r, _) => {
                self.hash_expr(l);
                self.hash_expr(r);
            },
            ExprKind::AssignOp(o, l, r) => {
                std::mem::discriminant(&o.node).hash(&mut self.s);
                self.hash_expr(l);
                self.hash_expr(r);
            },
            ExprKind::Become(f) => {
                self.hash_expr(f);
            },
            ExprKind::Block(b, _) => {
                self.hash_block(b);
            },
            ExprKind::Binary(op, l, r) => {
                std::mem::discriminant(&op.node).hash(&mut self.s);
                self.hash_expr(l);
                self.hash_expr(r);
            },
            ExprKind::Break(i, j) => {
                if let Some(i) = i.label {
                    self.hash_name(i.ident.name);
                }
                if let Some(j) = j {
                    self.hash_expr(j);
                }
            },
            ExprKind::Call(fun, args) => {
                self.hash_expr(fun);
                self.hash_exprs(args);
            },
            ExprKind::Cast(e, ty) | ExprKind::Type(e, ty) => {
                self.hash_expr(e);
                self.hash_ty(ty);
            },
            ExprKind::Closure(Closure {
                capture_clause, body, ..
            }) => {
                std::mem::discriminant(capture_clause).hash(&mut self.s);
                // closures inherit TypeckResults
                self.hash_expr(self.cx.tcx.hir_body(*body).value);
            },
            ExprKind::ConstBlock(l_id) => {
                self.hash_body(l_id.body);
            },
            ExprKind::DropTemps(e) | ExprKind::Yield(e, _) => {
                self.hash_expr(e);
            },
            ExprKind::Field(e, f) => {
                self.hash_expr(e);
                self.hash_name(f.name);
            },
            ExprKind::Index(a, i, _) => {
                self.hash_expr(a);
                self.hash_expr(i);
            },
            ExprKind::InlineAsm(asm) => {
                for piece in asm.template {
                    match piece {
                        InlineAsmTemplatePiece::String(s) => s.hash(&mut self.s),
                        InlineAsmTemplatePiece::Placeholder {
                            operand_idx,
                            modifier,
                            span: _,
                        } => {
                            operand_idx.hash(&mut self.s);
                            modifier.hash(&mut self.s);
                        },
                    }
                }
                asm.options.hash(&mut self.s);
                for (op, _op_sp) in asm.operands {
                    match op {
                        InlineAsmOperand::In { reg, expr } => {
                            reg.hash(&mut self.s);
                            self.hash_expr(expr);
                        },
                        InlineAsmOperand::Out { reg, late, expr } => {
                            reg.hash(&mut self.s);
                            late.hash(&mut self.s);
                            if let Some(expr) = expr {
                                self.hash_expr(expr);
                            }
                        },
                        InlineAsmOperand::InOut { reg, late, expr } => {
                            reg.hash(&mut self.s);
                            late.hash(&mut self.s);
                            self.hash_expr(expr);
                        },
                        InlineAsmOperand::SplitInOut {
                            reg,
                            late,
                            in_expr,
                            out_expr,
                        } => {
                            reg.hash(&mut self.s);
                            late.hash(&mut self.s);
                            self.hash_expr(in_expr);
                            if let Some(out_expr) = out_expr {
                                self.hash_expr(out_expr);
                            }
                        },
                        InlineAsmOperand::SymFn { expr } => {
                            self.hash_expr(expr);
                        },
                        InlineAsmOperand::Const { anon_const } => {
                            self.hash_body(anon_const.body);
                        },
                        InlineAsmOperand::SymStatic { path, def_id: _ } => self.hash_qpath(path),
                        InlineAsmOperand::Label { block } => self.hash_block(block),
                    }
                }
            },
            ExprKind::Let(LetExpr { pat, init, ty, .. }) => {
                self.hash_expr(init);
                if let Some(ty) = ty {
                    self.hash_ty(ty);
                }
                self.hash_pat(pat);
            },
            ExprKind::Lit(l) => {
                l.node.hash(&mut self.s);
            },
            ExprKind::Loop(b, i, ..) => {
                self.hash_block(b);
                if let Some(i) = i {
                    self.hash_name(i.ident.name);
                }
            },
            ExprKind::If(cond, then, else_opt) => {
                self.hash_expr(cond);
                self.hash_expr(then);
                if let Some(e) = else_opt {
                    self.hash_expr(e);
                }
            },
            ExprKind::Match(scrutinee, arms, _) => {
                self.hash_expr(scrutinee);

                for arm in *arms {
                    self.hash_pat(arm.pat);
                    if let Some(e) = arm.guard {
                        self.hash_expr(e);
                    }
                    self.hash_expr(arm.body);
                }
            },
            ExprKind::MethodCall(path, receiver, args, _fn_span) => {
                self.hash_name(path.ident.name);
                self.hash_expr(receiver);
                self.hash_exprs(args);
            },
            ExprKind::OffsetOf(container, fields) => {
                self.hash_ty(container);
                for field in *fields {
                    self.hash_name(field.name);
                }
            },
            ExprKind::Path(qpath) => {
                self.hash_qpath(qpath);
            },
            ExprKind::Repeat(e, len) => {
                self.hash_expr(e);
                self.hash_const_arg(len);
            },
            ExprKind::Ret(e) => {
                if let Some(e) = e {
                    self.hash_expr(e);
                }
            },
            ExprKind::Struct(path, fields, expr) => {
                self.hash_qpath(path);

                for f in *fields {
                    self.hash_name(f.ident.name);
                    self.hash_expr(f.expr);
                }

                if let StructTailExpr::Base(e) = expr {
                    self.hash_expr(e);
                }
            },
            ExprKind::Tup(tup) => {
                self.hash_exprs(tup);
            },
            ExprKind::Use(expr, _) => {
                self.hash_expr(expr);
            },
            ExprKind::Unary(l_op, le) => {
                std::mem::discriminant(l_op).hash(&mut self.s);
                self.hash_expr(le);
            },
            ExprKind::UnsafeBinderCast(kind, expr, ty) => {
                std::mem::discriminant(kind).hash(&mut self.s);
                self.hash_expr(expr);
                if let Some(ty) = ty {
                    self.hash_ty(ty);
                }
            },
            ExprKind::Err(_) => {},
        }
    }

    pub fn hash_exprs(&mut self, e: &[Expr<'_>]) {
        for e in e {
            self.hash_expr(e);
        }
    }

    pub fn hash_name(&mut self, n: Symbol) {
        n.hash(&mut self.s);
    }

    pub fn hash_qpath(&mut self, p: &QPath<'_>) {
        match p {
            QPath::Resolved(_, path) => {
                self.hash_path(path);
            },
            QPath::TypeRelative(_, path) => {
                self.hash_name(path.ident.name);
            },
        }
        // self.maybe_typeck_results.unwrap().qpath_res(p, id).hash(&mut self.s);
    }

    pub fn hash_pat_expr(&mut self, lit: &PatExpr<'_>) {
        std::mem::discriminant(&lit.kind).hash(&mut self.s);
        match &lit.kind {
            PatExprKind::Lit { lit, negated } => {
                lit.node.hash(&mut self.s);
                negated.hash(&mut self.s);
            },
            PatExprKind::Path(qpath) => self.hash_qpath(qpath),
        }
    }

    pub fn hash_ty_pat(&mut self, pat: &TyPat<'_>) {
        std::mem::discriminant(&pat.kind).hash(&mut self.s);
        match pat.kind {
            TyPatKind::Range(s, e) => {
                self.hash_const_arg(s);
                self.hash_const_arg(e);
            },
            TyPatKind::Or(variants) => {
                for variant in variants {
                    self.hash_ty_pat(variant);
                }
            },
            TyPatKind::NotNull | TyPatKind::Err(_) => {},
        }
    }

    pub fn hash_pat(&mut self, pat: &Pat<'_>) {
        std::mem::discriminant(&pat.kind).hash(&mut self.s);
        match &pat.kind {
            PatKind::Missing => unreachable!(),
            PatKind::Binding(BindingMode(by_ref, mutability), _, _, pat) => {
                std::mem::discriminant(by_ref).hash(&mut self.s);
                if let ByRef::Yes(pi, mu) = by_ref {
                    std::mem::discriminant(pi).hash(&mut self.s);
                    std::mem::discriminant(mu).hash(&mut self.s);
                }
                std::mem::discriminant(mutability).hash(&mut self.s);
                if let Some(pat) = pat {
                    self.hash_pat(pat);
                }
            },
            PatKind::Box(pat) | PatKind::Deref(pat) => self.hash_pat(pat),
            PatKind::Expr(expr) => self.hash_pat_expr(expr),
            PatKind::Or(pats) => {
                for pat in *pats {
                    self.hash_pat(pat);
                }
            },
            PatKind::Range(s, e, i) => {
                if let Some(s) = s {
                    self.hash_pat_expr(s);
                }
                if let Some(e) = e {
                    self.hash_pat_expr(e);
                }
                std::mem::discriminant(i).hash(&mut self.s);
            },
            PatKind::Ref(pat, pi, mu) => {
                self.hash_pat(pat);
                std::mem::discriminant(pi).hash(&mut self.s);
                std::mem::discriminant(mu).hash(&mut self.s);
            },
            PatKind::Guard(pat, guard) => {
                self.hash_pat(pat);
                self.hash_expr(guard);
            },
            PatKind::Slice(l, m, r) => {
                for pat in *l {
                    self.hash_pat(pat);
                }
                if let Some(pat) = m {
                    self.hash_pat(pat);
                }
                for pat in *r {
                    self.hash_pat(pat);
                }
            },
            PatKind::Struct(qpath, fields, e) => {
                self.hash_qpath(qpath);
                for f in *fields {
                    self.hash_name(f.ident.name);
                    self.hash_pat(f.pat);
                }
                e.hash(&mut self.s);
            },
            PatKind::Tuple(pats, e) => {
                for pat in *pats {
                    self.hash_pat(pat);
                }
                e.hash(&mut self.s);
            },
            PatKind::TupleStruct(qpath, pats, e) => {
                self.hash_qpath(qpath);
                for pat in *pats {
                    self.hash_pat(pat);
                }
                e.hash(&mut self.s);
            },
            PatKind::Never | PatKind::Wild | PatKind::Err(_) => {},
        }
    }

    pub fn hash_path(&mut self, path: &Path<'_>) {
        match path.res {
            // constant hash since equality is dependant on inter-expression context
            // e.g. The expressions `if let Some(x) = foo() {}` and `if let Some(y) = foo() {}` are considered equal
            // even though the binding names are different and they have different `HirId`s.
            Res::Local(_) => 1_usize.hash(&mut self.s),
            _ => {
                if let PathCheck::Resolution = self.path_check
                    && let [.., last] = path.segments
                    && let Some(segments) = generic_path_segments(path.segments)
                {
                    for seg in segments {
                        self.hash_generic_args(seg.args().args);
                    }
                    last.res.hash(&mut self.s);
                } else {
                    for seg in path.segments {
                        self.hash_name(seg.ident.name);
                        self.hash_generic_args(seg.args().args);
                    }
                }
            },
        }
    }

    pub fn hash_modifiers(&mut self, modifiers: TraitBoundModifiers) {
        let TraitBoundModifiers { constness, polarity } = modifiers;
        std::mem::discriminant(&polarity).hash(&mut self.s);
        std::mem::discriminant(&constness).hash(&mut self.s);
    }

    pub fn hash_stmt(&mut self, b: &Stmt<'_>) {
        std::mem::discriminant(&b.kind).hash(&mut self.s);

        match &b.kind {
            StmtKind::Let(local) => {
                self.hash_pat(local.pat);
                if let Some(init) = local.init {
                    self.hash_expr(init);
                }
                if let Some(els) = local.els {
                    self.hash_block(els);
                }
            },
            StmtKind::Item(..) => {},
            StmtKind::Expr(expr) | StmtKind::Semi(expr) => {
                self.hash_expr(expr);
            },
        }
    }

    pub fn hash_lifetime(&mut self, lifetime: &Lifetime) {
        lifetime.ident.name.hash(&mut self.s);
        std::mem::discriminant(&lifetime.kind).hash(&mut self.s);
        if let LifetimeKind::Param(param_id) = lifetime.kind {
            param_id.hash(&mut self.s);
        }
    }

    pub fn hash_ty(&mut self, ty: &Ty<'_>) {
        std::mem::discriminant(&ty.kind).hash(&mut self.s);
        self.hash_tykind(&ty.kind);
    }

    pub fn hash_tykind(&mut self, ty: &TyKind<'_>) {
        match ty {
            TyKind::Slice(ty) => {
                self.hash_ty(ty);
            },
            TyKind::Array(ty, len) => {
                self.hash_ty(ty);
                self.hash_const_arg(len);
            },
            TyKind::Pat(ty, pat) => {
                self.hash_ty(ty);
                self.hash_ty_pat(pat);
            },
            TyKind::Ptr(mut_ty) => {
                self.hash_ty(mut_ty.ty);
                mut_ty.mutbl.hash(&mut self.s);
            },
            TyKind::Ref(lifetime, mut_ty) => {
                self.hash_lifetime(lifetime);
                self.hash_ty(mut_ty.ty);
                mut_ty.mutbl.hash(&mut self.s);
            },
            TyKind::FnPtr(fn_ptr) => {
                fn_ptr.safety.hash(&mut self.s);
                fn_ptr.abi.hash(&mut self.s);
                for arg in fn_ptr.decl.inputs {
                    self.hash_ty(arg);
                }
                std::mem::discriminant(&fn_ptr.decl.output).hash(&mut self.s);
                match fn_ptr.decl.output {
                    FnRetTy::DefaultReturn(_) => {},
                    FnRetTy::Return(ty) => {
                        self.hash_ty(ty);
                    },
                }
                fn_ptr.decl.c_variadic.hash(&mut self.s);
            },
            TyKind::Tup(ty_list) => {
                for ty in *ty_list {
                    self.hash_ty(ty);
                }
            },
            TyKind::Path(qpath) => self.hash_qpath(qpath),
            TyKind::TraitObject(_, lifetime) => {
                self.hash_lifetime(lifetime);
            },
            TyKind::UnsafeBinder(binder) => {
                self.hash_ty(binder.inner_ty);
            },
            TyKind::Err(_)
            | TyKind::Infer(())
            | TyKind::Never
            | TyKind::InferDelegation(..)
            | TyKind::OpaqueDef(_)
            | TyKind::TraitAscription(_) => {},
        }
    }

    pub fn hash_body(&mut self, body_id: BodyId) {
        // swap out TypeckResults when hashing a body
        let old_maybe_typeck_results = self.maybe_typeck_results.replace(self.cx.tcx.typeck_body(body_id));
        self.hash_expr(self.cx.tcx.hir_body(body_id).value);
        self.maybe_typeck_results = old_maybe_typeck_results;
    }

    fn hash_const_arg(&mut self, const_arg: &ConstArg<'_>) {
        match &const_arg.kind {
            ConstArgKind::Tup(tup) => {
                for arg in *tup {
                    self.hash_const_arg(arg);
                }
            },
            ConstArgKind::Path(path) => self.hash_qpath(path),
            ConstArgKind::Anon(anon) => self.hash_body(anon.body),
            ConstArgKind::Struct(path, inits) => {
                self.hash_qpath(path);
                for init in *inits {
                    self.hash_const_arg(init.expr);
                }
            },
            ConstArgKind::TupleCall(path, args) => {
                self.hash_qpath(path);
                for arg in *args {
                    self.hash_const_arg(arg);
                }
            },
            ConstArgKind::Array(array_expr) => {
                for elem in array_expr.elems {
                    self.hash_const_arg(elem);
                }
            },
            ConstArgKind::Infer(..) | ConstArgKind::Error(..) => {},
            ConstArgKind::Literal(lit) => lit.hash(&mut self.s),
        }
    }

    fn hash_generic_args(&mut self, arg_list: &[GenericArg<'_>]) {
        for arg in arg_list {
            match arg {
                GenericArg::Lifetime(l) => self.hash_lifetime(l),
                GenericArg::Type(ty) => self.hash_ty(ty.as_unambig_ty()),
                GenericArg::Const(ca) => self.hash_const_arg(ca.as_unambig_ct()),
                GenericArg::Infer(inf) => self.hash_ty(&inf.to_ty()),
            }
        }
    }
}

pub fn hash_stmt(cx: &LateContext<'_>, s: &Stmt<'_>) -> u64 {
    let mut h = SpanlessHash::new(cx);
    h.hash_stmt(s);
    h.finish()
}

pub fn is_bool(ty: &Ty<'_>) -> bool {
    if let TyKind::Path(QPath::Resolved(_, path)) = ty.kind {
        matches!(path.res, Res::PrimTy(PrimTy::Bool))
    } else {
        false
    }
}

pub fn hash_expr(cx: &LateContext<'_>, e: &Expr<'_>) -> u64 {
    let mut h = SpanlessHash::new(cx);
    h.hash_expr(e);
    h.finish()
}

fn eq_span_tokens(
    cx: &LateContext<'_>,
    left: impl SpanRange,
    right: impl SpanRange,
    pred: impl Fn(TokenKind) -> bool,
) -> bool {
    fn f(cx: &LateContext<'_>, left: Range<BytePos>, right: Range<BytePos>, pred: impl Fn(TokenKind) -> bool) -> bool {
        if let Some(lsrc) = left.get_source_range(cx)
            && let Some(lsrc) = lsrc.as_str()
            && let Some(rsrc) = right.get_source_range(cx)
            && let Some(rsrc) = rsrc.as_str()
        {
            let pred = |&(token, ..): &(TokenKind, _, _)| pred(token);
            let map = |(_, source, _)| source;

            let ltok = tokenize_with_text(lsrc).filter(pred).map(map);
            let rtok = tokenize_with_text(rsrc).filter(pred).map(map);
            ltok.eq(rtok)
        } else {
            // Unable to access the source. Conservatively assume the blocks aren't equal.
            false
        }
    }
    f(cx, left.into_range(), right.into_range(), pred)
}

/// Returns true if the expression contains ambiguous literals (unsuffixed float or int literals)
/// that could be interpreted as either f32/f64 or i32/i64 depending on context.
pub fn has_ambiguous_literal_in_expr(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
    match expr.kind {
        ExprKind::Path(ref qpath) => {
            if let Res::Local(hir_id) = cx.qpath_res(qpath, expr.hir_id)
                && let Node::LetStmt(local) = cx.tcx.parent_hir_node(hir_id)
                && local.ty.is_none()
                && let Some(init) = local.init
            {
                return has_ambiguous_literal_in_expr(cx, init);
            }
            false
        },
        ExprKind::Lit(lit) => matches!(
            lit.node,
            ast::LitKind::Float(_, ast::LitFloatType::Unsuffixed) | ast::LitKind::Int(_, ast::LitIntType::Unsuffixed)
        ),

        ExprKind::Array(exprs) | ExprKind::Tup(exprs) => exprs.iter().any(|e| has_ambiguous_literal_in_expr(cx, e)),

        ExprKind::Assign(lhs, rhs, _) | ExprKind::AssignOp(_, lhs, rhs) | ExprKind::Binary(_, lhs, rhs) => {
            has_ambiguous_literal_in_expr(cx, lhs) || has_ambiguous_literal_in_expr(cx, rhs)
        },

        ExprKind::Unary(_, e)
        | ExprKind::Cast(e, _)
        | ExprKind::Type(e, _)
        | ExprKind::DropTemps(e)
        | ExprKind::AddrOf(_, _, e)
        | ExprKind::Field(e, _)
        | ExprKind::Index(e, _, _)
        | ExprKind::Yield(e, _) => has_ambiguous_literal_in_expr(cx, e),

        ExprKind::MethodCall(_, receiver, args, _) | ExprKind::Call(receiver, args) => {
            has_ambiguous_literal_in_expr(cx, receiver) || args.iter().any(|e| has_ambiguous_literal_in_expr(cx, e))
        },

        ExprKind::Closure(Closure { body, .. }) => {
            let body = cx.tcx.hir_body(*body);
            let closure_expr = crate::peel_blocks(body.value);
            has_ambiguous_literal_in_expr(cx, closure_expr)
        },

        ExprKind::Block(blk, _) => blk.expr.as_ref().is_some_and(|e| has_ambiguous_literal_in_expr(cx, e)),

        ExprKind::If(cond, then_expr, else_expr) => {
            has_ambiguous_literal_in_expr(cx, cond)
                || has_ambiguous_literal_in_expr(cx, then_expr)
                || else_expr.as_ref().is_some_and(|e| has_ambiguous_literal_in_expr(cx, e))
        },

        ExprKind::Match(scrutinee, arms, _) => {
            has_ambiguous_literal_in_expr(cx, scrutinee)
                || arms.iter().any(|arm| has_ambiguous_literal_in_expr(cx, arm.body))
        },

        ExprKind::Loop(body, ..) => body.expr.is_some_and(|e| has_ambiguous_literal_in_expr(cx, e)),

        ExprKind::Ret(opt_expr) | ExprKind::Break(_, opt_expr) => {
            opt_expr.as_ref().is_some_and(|e| has_ambiguous_literal_in_expr(cx, e))
        },

        _ => false,
    }
}