lib.rs

#![feature(array_chunks)]
#![feature(box_patterns)]
#![feature(let_chains)]
#![feature(lint_reasons)]
#![feature(never_type)]
#![feature(once_cell)]
#![feature(rustc_private)]
#![recursion_limit = "512"]
#![cfg_attr(feature = "deny-warnings", deny(warnings))]
#![allow(clippy::missing_errors_doc, clippy::missing_panics_doc, clippy::must_use_candidate)]
// warn on the same lints as `clippy_lints`
#![warn(trivial_casts, trivial_numeric_casts)]
// warn on lints, that are included in `rust-lang/rust`s bootstrap
#![warn(rust_2018_idioms, unused_lifetimes)]
// warn on rustc internal lints
#![warn(rustc::internal)]

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

#[macro_use]
pub mod sym_helper;

pub mod ast_utils;
pub mod attrs;
mod check_proc_macro;
pub mod comparisons;
pub mod consts;
pub mod diagnostics;
pub mod eager_or_lazy;
pub mod higher;
mod hir_utils;
pub mod macros;
pub mod mir;
pub mod msrvs;
pub mod numeric_literal;
pub mod paths;
pub mod ptr;
pub mod qualify_min_const_fn;
pub mod source;
pub mod str_utils;
pub mod sugg;
pub mod ty;
pub mod usage;
pub mod visitors;

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

use core::ops::ControlFlow;
use std::collections::hash_map::Entry;
use std::hash::BuildHasherDefault;
use std::sync::OnceLock;
use std::sync::{Mutex, MutexGuard};

use if_chain::if_chain;
use rustc_ast::ast::{self, LitKind};
use rustc_ast::Attribute;
use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::unhash::UnhashMap;
use rustc_hir::def::{DefKind, Res};
use rustc_hir::def_id::{CrateNum, DefId, LocalDefId, LOCAL_CRATE};
use rustc_hir::hir_id::{HirIdMap, HirIdSet};
use rustc_hir::intravisit::{walk_expr, FnKind, Visitor};
use rustc_hir::LangItem::{OptionNone, ResultErr, ResultOk};
use rustc_hir::{
    self as hir, def, Arm, ArrayLen, BindingAnnotation, Block, BlockCheckMode, Body, Closure, Constness, Destination,
    Expr, ExprKind, FnDecl, HirId, Impl, ImplItem, ImplItemKind, ImplItemRef, IsAsync, Item, ItemKind, LangItem, Local,
    MatchSource, Mutability, Node, OwnerId, Param, Pat, PatKind, Path, PathSegment, PrimTy, QPath, Stmt, StmtKind,
    TraitItem, TraitItemKind, TraitItemRef, TraitRef, TyKind, UnOp,
};
use rustc_lexer::{tokenize, TokenKind};
use rustc_lint::{LateContext, Level, Lint, LintContext};
use rustc_middle::hir::place::PlaceBase;
use rustc_middle::ty as rustc_ty;
use rustc_middle::ty::adjustment::{Adjust, Adjustment, AutoBorrow};
use rustc_middle::ty::binding::BindingMode;
use rustc_middle::ty::fast_reject::SimplifiedType::{
    ArraySimplifiedType, BoolSimplifiedType, CharSimplifiedType, FloatSimplifiedType, IntSimplifiedType,
    PtrSimplifiedType, SliceSimplifiedType, StrSimplifiedType, UintSimplifiedType,
};
use rustc_middle::ty::{
    layout::IntegerExt, BorrowKind, ClosureKind, DefIdTree, Ty, TyCtxt, TypeAndMut, TypeVisitableExt, UpvarCapture,
};
use rustc_middle::ty::{FloatTy, IntTy, UintTy};
use rustc_span::hygiene::{ExpnKind, MacroKind};
use rustc_span::source_map::SourceMap;
use rustc_span::sym;
use rustc_span::symbol::{kw, Ident, Symbol};
use rustc_span::Span;
use rustc_target::abi::Integer;

use crate::consts::{constant, Constant};
use crate::ty::{can_partially_move_ty, expr_sig, is_copy, is_recursively_primitive_type, ty_is_fn_once_param};
use crate::visitors::for_each_expr;

use rustc_middle::hir::nested_filter;

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

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

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

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

/// Returns `true` if the given `NodeId` is inside a constant context
///
/// # Example
///
/// ```rust,ignore
/// if in_constant(cx, expr.hir_id) {
///     // Do something
/// }
/// ```
pub fn in_constant(cx: &LateContext<'_>, id: HirId) -> bool {
    let parent_id = cx.tcx.hir().get_parent_item(id).def_id;
    match cx.tcx.hir().get_by_def_id(parent_id) {
        Node::Item(&Item {
            kind: ItemKind::Const(..) | ItemKind::Static(..) | ItemKind::Enum(..),
            ..
        })
        | Node::TraitItem(&TraitItem {
            kind: TraitItemKind::Const(..),
            ..
        })
        | Node::ImplItem(&ImplItem {
            kind: ImplItemKind::Const(..),
            ..
        })
        | Node::AnonConst(_) => true,
        Node::Item(&Item {
            kind: ItemKind::Fn(ref sig, ..),
            ..
        })
        | Node::ImplItem(&ImplItem {
            kind: ImplItemKind::Fn(ref sig, _),
            ..
        }) => sig.header.constness == Constness::Const,
        _ => false,
    }
}

/// Checks if a `Res` refers to a constructor of a `LangItem`
/// For example, use this to check whether a function call or a pattern is `Some(..)`.
pub fn is_res_lang_ctor(cx: &LateContext<'_>, res: Res, lang_item: LangItem) -> bool {
    if let Res::Def(DefKind::Ctor(..), id) = res
        && let Some(lang_id) = cx.tcx.lang_items().get(lang_item)
        && let Some(id) = cx.tcx.opt_parent(id)
    {
        id == lang_id
    } else {
        false
    }
}

pub fn is_res_diagnostic_ctor(cx: &LateContext<'_>, res: Res, diag_item: Symbol) -> bool {
    if let Res::Def(DefKind::Ctor(..), id) = res
        && let Some(id) = cx.tcx.opt_parent(id)
    {
        cx.tcx.is_diagnostic_item(diag_item, id)
    } else {
        false
    }
}

/// Checks if a `QPath` resolves to a constructor of a diagnostic item.
pub fn is_diagnostic_ctor(cx: &LateContext<'_>, qpath: &QPath<'_>, diagnostic_item: Symbol) -> bool {
    if let QPath::Resolved(_, path) = qpath {
        if let Res::Def(DefKind::Ctor(..), ctor_id) = path.res {
            return cx.tcx.is_diagnostic_item(diagnostic_item, cx.tcx.parent(ctor_id));
        }
    }
    false
}

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

    cx.tcx.is_diagnostic_item(item, did)
}

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

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

pub fn is_unit_expr(expr: &Expr<'_>) -> bool {
    matches!(
        expr.kind,
        ExprKind::Block(
            Block {
                stmts: [],
                expr: None,
                ..
            },
            _
        ) | ExprKind::Tup([])
    )
}

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

/// Checks if the method call given in `expr` belongs to the given trait.
/// This is a deprecated function, consider using [`is_trait_method`].
pub fn match_trait_method(cx: &LateContext<'_>, expr: &Expr<'_>, path: &[&str]) -> bool {
    let def_id = cx.typeck_results().type_dependent_def_id(expr.hir_id).unwrap();
    let trt_id = cx.tcx.trait_of_item(def_id);
    trt_id.map_or(false, |trt_id| match_def_path(cx, trt_id, path))
}

/// Checks if a method is defined in an impl of a diagnostic item
pub fn is_diag_item_method(cx: &LateContext<'_>, def_id: DefId, diag_item: Symbol) -> bool {
    if let Some(impl_did) = cx.tcx.impl_of_method(def_id) {
        if let Some(adt) = cx.tcx.type_of(impl_did).subst_identity().ty_adt_def() {
            return cx.tcx.is_diagnostic_item(diag_item, adt.did());
        }
    }
    false
}

/// Checks if a method is in a diagnostic item trait
pub fn is_diag_trait_item(cx: &LateContext<'_>, def_id: DefId, diag_item: Symbol) -> bool {
    if let Some(trait_did) = cx.tcx.trait_of_item(def_id) {
        return cx.tcx.is_diagnostic_item(diag_item, trait_did);
    }
    false
}

/// Checks if the method call given in `expr` belongs to the given trait.
pub fn is_trait_method(cx: &LateContext<'_>, expr: &Expr<'_>, diag_item: Symbol) -> bool {
    cx.typeck_results()
        .type_dependent_def_id(expr.hir_id)
        .map_or(false, |did| is_diag_trait_item(cx, did, diag_item))
}

/// Checks if the given expression is a path referring an item on the trait
/// that is marked with the given diagnostic item.
///
/// For checking method call expressions instead of path expressions, use
/// [`is_trait_method`].
///
/// For example, this can be used to find if an expression like `u64::default`
/// refers to an item of the trait `Default`, which is associated with the
/// `diag_item` of `sym::Default`.
pub fn is_trait_item(cx: &LateContext<'_>, expr: &Expr<'_>, diag_item: Symbol) -> bool {
    if let hir::ExprKind::Path(ref qpath) = expr.kind {
        cx.qpath_res(qpath, expr.hir_id)
            .opt_def_id()
            .map_or(false, |def_id| is_diag_trait_item(cx, def_id, diag_item))
    } else {
        false
    }
}

pub fn last_path_segment<'tcx>(path: &QPath<'tcx>) -> &'tcx PathSegment<'tcx> {
    match *path {
        QPath::Resolved(_, path) => path.segments.last().expect("A path must have at least one segment"),
        QPath::TypeRelative(_, seg) => seg,
        QPath::LangItem(..) => panic!("last_path_segment: lang item has no path segments"),
    }
}

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

/// THIS METHOD IS DEPRECATED and will eventually be removed since it does not match against the
/// entire path or resolved `DefId`. Prefer using `match_def_path`. Consider getting a `DefId` from
/// `QPath::Resolved.1.res.opt_def_id()`.
///
/// Matches a `QPath` against a slice of segment string literals.
///
/// There is also `match_path` if you are dealing with a `rustc_hir::Path` instead of a
/// `rustc_hir::QPath`.
///
/// # Examples
/// ```rust,ignore
/// match_qpath(path, &["std", "rt", "begin_unwind"])
/// ```
pub fn match_qpath(path: &QPath<'_>, segments: &[&str]) -> bool {
    match *path {
        QPath::Resolved(_, path) => match_path(path, segments),
        QPath::TypeRelative(ty, segment) => match ty.kind {
            TyKind::Path(ref inner_path) => {
                if let [prefix @ .., end] = segments {
                    if match_qpath(inner_path, prefix) {
                        return segment.ident.name.as_str() == *end;
                    }
                }
                false
            },
            _ => false,
        },
        QPath::LangItem(..) => false,
    }
}

/// If the expression is a path, resolves it to a `DefId` and checks if it matches the given path.
///
/// Please use `is_path_diagnostic_item` if the target is a diagnostic item.
pub fn is_expr_path_def_path(cx: &LateContext<'_>, expr: &Expr<'_>, segments: &[&str]) -> bool {
    path_def_id(cx, expr).map_or(false, |id| match_def_path(cx, id, segments))
}

/// If `maybe_path` is a path node which resolves to an item, resolves it to a `DefId` and checks if
/// it matches the given lang item.
pub fn is_path_lang_item<'tcx>(cx: &LateContext<'_>, maybe_path: &impl MaybePath<'tcx>, lang_item: LangItem) -> bool {
    path_def_id(cx, maybe_path).map_or(false, |id| cx.tcx.lang_items().get(lang_item) == Some(id))
}

/// If `maybe_path` is a path node which resolves to an item, resolves it to a `DefId` and checks if
/// it matches the given diagnostic item.
pub fn is_path_diagnostic_item<'tcx>(
    cx: &LateContext<'_>,
    maybe_path: &impl MaybePath<'tcx>,
    diag_item: Symbol,
) -> bool {
    path_def_id(cx, maybe_path).map_or(false, |id| cx.tcx.is_diagnostic_item(diag_item, id))
}

/// THIS METHOD IS DEPRECATED and will eventually be removed since it does not match against the
/// entire path or resolved `DefId`. Prefer using `match_def_path`. Consider getting a `DefId` from
/// `QPath::Resolved.1.res.opt_def_id()`.
///
/// Matches a `Path` against a slice of segment string literals.
///
/// There is also `match_qpath` if you are dealing with a `rustc_hir::QPath` instead of a
/// `rustc_hir::Path`.
///
/// # Examples
///
/// ```rust,ignore
/// if match_path(&trait_ref.path, &paths::HASH) {
///     // This is the `std::hash::Hash` trait.
/// }
///
/// if match_path(ty_path, &["rustc", "lint", "Lint"]) {
///     // This is a `rustc_middle::lint::Lint`.
/// }
/// ```
pub fn match_path(path: &Path<'_>, segments: &[&str]) -> bool {
    path.segments
        .iter()
        .rev()
        .zip(segments.iter().rev())
        .all(|(a, b)| a.ident.name.as_str() == *b)
}

/// If the expression is a path to a local, returns the canonical `HirId` of the local.
pub fn path_to_local(expr: &Expr<'_>) -> Option<HirId> {
    if let ExprKind::Path(QPath::Resolved(None, path)) = expr.kind {
        if let Res::Local(id) = path.res {
            return Some(id);
        }
    }
    None
}

/// Returns true if the expression is a path to a local with the specified `HirId`.
/// Use this function to see if an expression matches a function argument or a match binding.
pub fn path_to_local_id(expr: &Expr<'_>, id: HirId) -> bool {
    path_to_local(expr) == Some(id)
}

pub trait MaybePath<'hir> {
    fn hir_id(&self) -> HirId;
    fn qpath_opt(&self) -> Option<&QPath<'hir>>;
}

macro_rules! maybe_path {
    ($ty:ident, $kind:ident) => {
        impl<'hir> MaybePath<'hir> for hir::$ty<'hir> {
            fn hir_id(&self) -> HirId {
                self.hir_id
            }
            fn qpath_opt(&self) -> Option<&QPath<'hir>> {
                match &self.kind {
                    hir::$kind::Path(qpath) => Some(qpath),
                    _ => None,
                }
            }
        }
    };
}
maybe_path!(Expr, ExprKind);
maybe_path!(Pat, PatKind);
maybe_path!(Ty, TyKind);

/// If `maybe_path` is a path node, resolves it, otherwise returns `Res::Err`
pub fn path_res<'tcx>(cx: &LateContext<'_>, maybe_path: &impl MaybePath<'tcx>) -> Res {
    match maybe_path.qpath_opt() {
        None => Res::Err,
        Some(qpath) => cx.qpath_res(qpath, maybe_path.hir_id()),
    }
}

/// If `maybe_path` is a path node which resolves to an item, retrieves the item ID
pub fn path_def_id<'tcx>(cx: &LateContext<'_>, maybe_path: &impl MaybePath<'tcx>) -> Option<DefId> {
    path_res(cx, maybe_path).opt_def_id()
}

fn find_primitive_impls<'tcx>(tcx: TyCtxt<'tcx>, name: &str) -> impl Iterator<Item = DefId> + 'tcx {
    let ty = match name {
        "bool" => BoolSimplifiedType,
        "char" => CharSimplifiedType,
        "str" => StrSimplifiedType,
        "array" => ArraySimplifiedType,
        "slice" => SliceSimplifiedType,
        // FIXME: rustdoc documents these two using just `pointer`.
        //
        // Maybe this is something we should do here too.
        "const_ptr" => PtrSimplifiedType(Mutability::Not),
        "mut_ptr" => PtrSimplifiedType(Mutability::Mut),
        "isize" => IntSimplifiedType(IntTy::Isize),
        "i8" => IntSimplifiedType(IntTy::I8),
        "i16" => IntSimplifiedType(IntTy::I16),
        "i32" => IntSimplifiedType(IntTy::I32),
        "i64" => IntSimplifiedType(IntTy::I64),
        "i128" => IntSimplifiedType(IntTy::I128),
        "usize" => UintSimplifiedType(UintTy::Usize),
        "u8" => UintSimplifiedType(UintTy::U8),
        "u16" => UintSimplifiedType(UintTy::U16),
        "u32" => UintSimplifiedType(UintTy::U32),
        "u64" => UintSimplifiedType(UintTy::U64),
        "u128" => UintSimplifiedType(UintTy::U128),
        "f32" => FloatSimplifiedType(FloatTy::F32),
        "f64" => FloatSimplifiedType(FloatTy::F64),
        _ => return [].iter().copied(),
    };

    tcx.incoherent_impls(ty).iter().copied()
}

fn non_local_item_children_by_name(tcx: TyCtxt<'_>, def_id: DefId, name: Symbol) -> Vec<Res> {
    match tcx.def_kind(def_id) {
        DefKind::Mod | DefKind::Enum | DefKind::Trait => tcx
            .module_children(def_id)
            .iter()
            .filter(|item| item.ident.name == name)
            .map(|child| child.res.expect_non_local())
            .collect(),
        DefKind::Impl { .. } => tcx
            .associated_item_def_ids(def_id)
            .iter()
            .copied()
            .filter(|assoc_def_id| tcx.item_name(*assoc_def_id) == name)
            .map(|assoc_def_id| Res::Def(tcx.def_kind(assoc_def_id), assoc_def_id))
            .collect(),
        _ => Vec::new(),
    }
}

fn local_item_children_by_name(tcx: TyCtxt<'_>, local_id: LocalDefId, name: Symbol) -> Vec<Res> {
    let hir = tcx.hir();

    let root_mod;
    let item_kind = match hir.find_by_def_id(local_id) {
        Some(Node::Crate(r#mod)) => {
            root_mod = ItemKind::Mod(r#mod);
            &root_mod
        },
        Some(Node::Item(item)) => &item.kind,
        _ => return Vec::new(),
    };

    let res = |ident: Ident, owner_id: OwnerId| {
        if ident.name == name {
            let def_id = owner_id.to_def_id();
            Some(Res::Def(tcx.def_kind(def_id), def_id))
        } else {
            None
        }
    };

    match item_kind {
        ItemKind::Mod(r#mod) => r#mod
            .item_ids
            .iter()
            .filter_map(|&item_id| res(hir.item(item_id).ident, item_id.owner_id))
            .collect(),
        ItemKind::Impl(r#impl) => r#impl
            .items
            .iter()
            .filter_map(|&ImplItemRef { ident, id, .. }| res(ident, id.owner_id))
            .collect(),
        ItemKind::Trait(.., trait_item_refs) => trait_item_refs
            .iter()
            .filter_map(|&TraitItemRef { ident, id, .. }| res(ident, id.owner_id))
            .collect(),
        _ => Vec::new(),
    }
}

fn item_children_by_name(tcx: TyCtxt<'_>, def_id: DefId, name: Symbol) -> Vec<Res> {
    if let Some(local_id) = def_id.as_local() {
        local_item_children_by_name(tcx, local_id, name)
    } else {
        non_local_item_children_by_name(tcx, def_id, name)
    }
}

/// Resolves a def path like `std::vec::Vec`.
///
/// Can return multiple resolutions when there are multiple versions of the same crate, e.g.
/// `memchr::memchr` could return the functions from both memchr 1.0 and memchr 2.0.
///
/// Also returns multiple results when there are mulitple paths under the same name e.g. `std::vec`
/// would have both a [`DefKind::Mod`] and [`DefKind::Macro`].
///
/// This function is expensive and should be used sparingly.
pub fn def_path_res(cx: &LateContext<'_>, path: &[&str]) -> Vec<Res> {
    fn find_crates(tcx: TyCtxt<'_>, name: Symbol) -> impl Iterator<Item = DefId> + '_ {
        tcx.crates(())
            .iter()
            .copied()
            .filter(move |&num| tcx.crate_name(num) == name)
            .map(CrateNum::as_def_id)
    }

    let tcx = cx.tcx;

    let (base, mut path) = match *path {
        [primitive] => {
            return vec![PrimTy::from_name(Symbol::intern(primitive)).map_or(Res::Err, Res::PrimTy)];
        },
        [base, ref path @ ..] => (base, path),
        _ => return Vec::new(),
    };

    let base_sym = Symbol::intern(base);

    let local_crate = if tcx.crate_name(LOCAL_CRATE) == base_sym {
        Some(LOCAL_CRATE.as_def_id())
    } else {
        None
    };

    let starts = find_primitive_impls(tcx, base)
        .chain(find_crates(tcx, base_sym))
        .chain(local_crate)
        .map(|id| Res::Def(tcx.def_kind(id), id));

    let mut resolutions: Vec<Res> = starts.collect();

    while let [segment, rest @ ..] = path {
        path = rest;
        let segment = Symbol::intern(segment);

        resolutions = resolutions
            .into_iter()
            .filter_map(|res| res.opt_def_id())
            .flat_map(|def_id| {
                // When the current def_id is e.g. `struct S`, check the impl items in
                // `impl S { ... }`
                let inherent_impl_children = tcx
                    .inherent_impls(def_id)
                    .iter()
                    .flat_map(|&impl_def_id| item_children_by_name(tcx, impl_def_id, segment));

                let direct_children = item_children_by_name(tcx, def_id, segment);

                inherent_impl_children.chain(direct_children)
            })
            .collect();
    }

    resolutions
}

/// Resolves a def path like `std::vec::Vec` to its [`DefId`]s, see [`def_path_res`].
pub fn def_path_def_ids(cx: &LateContext<'_>, path: &[&str]) -> impl Iterator<Item = DefId> {
    def_path_res(cx, path).into_iter().filter_map(|res| res.opt_def_id())
}

/// Convenience function to get the `DefId` of a trait by path.
/// It could be a trait or trait alias.
///
/// This function is expensive and should be used sparingly.
pub fn get_trait_def_id(cx: &LateContext<'_>, path: &[&str]) -> Option<DefId> {
    def_path_res(cx, path).into_iter().find_map(|res| match res {
        Res::Def(DefKind::Trait | DefKind::TraitAlias, trait_id) => Some(trait_id),
        _ => None,
    })
}

/// Gets the `hir::TraitRef` of the trait the given method is implemented for.
///
/// Use this if you want to find the `TraitRef` of the `Add` trait in this example:
///
/// ```rust
/// struct Point(isize, isize);
///
/// impl std::ops::Add for Point {
///     type Output = Self;
///
///     fn add(self, other: Self) -> Self {
///         Point(0, 0)
///     }
/// }
/// ```
pub fn trait_ref_of_method<'tcx>(cx: &LateContext<'tcx>, def_id: LocalDefId) -> Option<&'tcx TraitRef<'tcx>> {
    // Get the implemented trait for the current function
    let hir_id = cx.tcx.hir().local_def_id_to_hir_id(def_id);
    let parent_impl = cx.tcx.hir().get_parent_item(hir_id);
    if_chain! {
        if parent_impl != hir::CRATE_OWNER_ID;
        if let hir::Node::Item(item) = cx.tcx.hir().get_by_def_id(parent_impl.def_id);
        if let hir::ItemKind::Impl(impl_) = &item.kind;
        then {
            return impl_.of_trait.as_ref();
        }
    }
    None
}

/// This method will return tuple of projection stack and root of the expression,
/// used in `can_mut_borrow_both`.
///
/// For example, if `e` represents the `v[0].a.b[x]`
/// this method will return a tuple, composed of a `Vec`
/// containing the `Expr`s for `v[0], v[0].a, v[0].a.b, v[0].a.b[x]`
/// and an `Expr` for root of them, `v`
fn projection_stack<'a, 'hir>(mut e: &'a Expr<'hir>) -> (Vec<&'a Expr<'hir>>, &'a Expr<'hir>) {
    let mut result = vec![];
    let root = loop {
        match e.kind {
            ExprKind::Index(ep, _) | ExprKind::Field(ep, _) => {
                result.push(e);
                e = ep;
            },
            _ => break e,
        };
    };
    result.reverse();
    (result, root)
}

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

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

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

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

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

    if let QPath::TypeRelative(_, method) = path {
        if method.ident.name == sym::new {
            if let Some(impl_did) = cx.tcx.impl_of_method(def_id) {
                if let Some(adt) = cx.tcx.type_of(impl_did).subst_identity().ty_adt_def() {
                    return std_types_symbols.iter().any(|&symbol| {
                        cx.tcx.is_diagnostic_item(symbol, adt.did()) || Some(adt.did()) == cx.tcx.lang_items().string()
                    });
                }
            }
        }
    }
    false
}

/// Return true if the expr is equal to `Default::default` when evaluated.
pub fn is_default_equivalent_call(cx: &LateContext<'_>, repl_func: &Expr<'_>) -> bool {
    if_chain! {
        if let hir::ExprKind::Path(ref repl_func_qpath) = repl_func.kind;
        if let Some(repl_def_id) = cx.qpath_res(repl_func_qpath, repl_func.hir_id).opt_def_id();
        if is_diag_trait_item(cx, repl_def_id, sym::Default)
            || is_default_equivalent_ctor(cx, repl_def_id, repl_func_qpath);
        then { true } else { false }
    }
}

/// Returns true if the expr is equal to `Default::default()` of it's type when evaluated.
/// It doesn't cover all cases, for example indirect function calls (some of std
/// functions are supported) but it is the best we have.
pub fn is_default_equivalent(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
    match &e.kind {
        ExprKind::Lit(lit) => match lit.node {
            LitKind::Bool(false) | LitKind::Int(0, _) => true,
            LitKind::Str(s, _) => s.is_empty(),
            _ => false,
        },
        ExprKind::Tup(items) | ExprKind::Array(items) => items.iter().all(|x| is_default_equivalent(cx, x)),
        ExprKind::Repeat(x, ArrayLen::Body(len)) => if_chain! {
            if let ExprKind::Lit(ref const_lit) = cx.tcx.hir().body(len.body).value.kind;
            if let LitKind::Int(v, _) = const_lit.node;
            if v <= 32 && is_default_equivalent(cx, x);
            then {
                true
            }
            else {
                false
            }
        },
        ExprKind::Call(repl_func, []) => is_default_equivalent_call(cx, repl_func),
        ExprKind::Call(from_func, [ref arg]) => is_default_equivalent_from(cx, from_func, arg),
        ExprKind::Path(qpath) => is_res_lang_ctor(cx, cx.qpath_res(qpath, e.hir_id), OptionNone),
        ExprKind::AddrOf(rustc_hir::BorrowKind::Ref, _, expr) => matches!(expr.kind, ExprKind::Array([])),
        _ => false,
    }
}

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

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

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

/// Given an expression referencing a local, determines how it would be captured in a closure.
/// Note as this will walk up to parent expressions until the capture can be determined it should
/// only be used while making a closure somewhere a value is consumed. e.g. a block, match arm, or
/// function argument (other than a receiver).
pub fn capture_local_usage(cx: &LateContext<'_>, e: &Expr<'_>) -> CaptureKind {
    fn pat_capture_kind(cx: &LateContext<'_>, pat: &Pat<'_>) -> CaptureKind {
        let mut capture = CaptureKind::Ref(Mutability::Not);
        pat.each_binding_or_first(&mut |_, id, span, _| match cx
            .typeck_results()
            .extract_binding_mode(cx.sess(), id, span)
            .unwrap()
        {
            BindingMode::BindByValue(_) if !is_copy(cx, cx.typeck_results().node_type(id)) => {
                capture = CaptureKind::Value;
            },
            BindingMode::BindByReference(Mutability::Mut) if capture != CaptureKind::Value => {
                capture = CaptureKind::Ref(Mutability::Mut);
            },
            _ => (),
        });
        capture
    }

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

    let mut child_id = e.hir_id;
    let mut capture = CaptureKind::Value;
    let mut capture_expr_ty = e;

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

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

        child_id = parent_id;
    }

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

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

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

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

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

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

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

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

    (method_names, arg_lists, spans)
}

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

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

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

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

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

impl<'a, 'tcx> Visitor<'tcx> for ContainsName<'a, 'tcx> {
    type NestedFilter = nested_filter::OnlyBodies;

    fn visit_name(&mut self, name: Symbol) {
        if self.name == name {
            self.result = true;
        }
    }

    fn nested_visit_map(&mut self) -> Self::Map {
        self.cx.tcx.hir()
    }
}

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

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

/// Gets the parent node, if any.
pub fn get_parent_node(tcx: TyCtxt<'_>, id: HirId) -> Option<Node<'_>> {
    tcx.hir().find_parent(id)
}

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

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

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

/// Gets the loop or closure enclosing the given expression, if any.
pub fn get_enclosing_loop_or_multi_call_closure<'tcx>(
    cx: &LateContext<'tcx>,
    expr: &Expr<'_>,
) -> Option<&'tcx Expr<'tcx>> {
    for (_, node) in cx.tcx.hir().parent_iter(expr.hir_id) {
        match node {
            Node::Expr(e) => match e.kind {
                ExprKind::Closure { .. } => {
                    if let rustc_ty::Closure(_, subs) = cx.typeck_results().expr_ty(e).kind()
                        && subs.as_closure().kind() == ClosureKind::FnOnce
                    {
                        continue;
                    }
                    let is_once = walk_to_expr_usage(cx, e, |node, id| {
                        let Node::Expr(e) = node else {
                            return None;
                        };
                        match e.kind {
                            ExprKind::Call(f, _) if f.hir_id == id => Some(()),
                            ExprKind::Call(f, args) => {
                                let i = args.iter().position(|arg| arg.hir_id == id)?;
                                let sig = expr_sig(cx, f)?;
                                let predicates = sig
                                    .predicates_id()
                                    .map_or(cx.param_env, |id| cx.tcx.param_env(id))
                                    .caller_bounds();
                                sig.input(i).and_then(|ty| {
                                    ty_is_fn_once_param(cx.tcx, ty.skip_binder(), predicates).then_some(())
                                })
                            },
                            ExprKind::MethodCall(_, receiver, args, _) => {
                                let i = std::iter::once(receiver)
                                    .chain(args.iter())
                                    .position(|arg| arg.hir_id == id)?;
                                let id = cx.typeck_results().type_dependent_def_id(e.hir_id)?;
                                let ty = cx.tcx.fn_sig(id).subst_identity().skip_binder().inputs()[i];
                                ty_is_fn_once_param(cx.tcx, ty, cx.tcx.param_env(id).caller_bounds()).then_some(())
                            },
                            _ => None,
                        }
                    })
                    .is_some();
                    if !is_once {
                        return Some(e);
                    }
                },
                ExprKind::Loop(..) => return Some(e),
                _ => (),
            },
            Node::Stmt(_) | Node::Block(_) | Node::Local(_) | Node::Arm(_) => (),
            _ => break,
        }
    }
    None
}

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

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

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

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

/// Checks whether the given expression is a constant integer of the given value.
/// unlike `is_integer_literal`, this version does const folding
pub fn is_integer_const(cx: &LateContext<'_>, e: &Expr<'_>, value: u128) -> bool {
    if is_integer_literal(e, value) {
        return true;
    }
    let enclosing_body = cx.tcx.hir().enclosing_body_owner(e.hir_id);
    if let Some((Constant::Int(v), _)) = constant(cx, cx.tcx.typeck(enclosing_body), e) {
        return value == v;
    }
    false
}

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

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

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

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

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

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

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

    None
}

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

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

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

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

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

    match pat.kind {
        PatKind::Wild => false,
        PatKind::Binding(_, _, _, pat) => pat.map_or(false, |pat| is_refutable(cx, pat)),
        PatKind::Box(pat) | PatKind::Ref(pat, _) => is_refutable(cx, pat),
        PatKind::Lit(..) | PatKind::Range(..) => true,
        PatKind::Path(ref qpath) => is_enum_variant(cx, qpath, pat.hir_id),
        PatKind::Or(pats) => {
            // TODO: should be the honest check, that pats is exhaustive set
            are_refutable(cx, pats)
        },
        PatKind::Tuple(pats, _) => are_refutable(cx, pats),
        PatKind::Struct(ref qpath, fields, _) => {
            is_enum_variant(cx, qpath, pat.hir_id) || are_refutable(cx, fields.iter().map(|field| field.pat))
        },
        PatKind::TupleStruct(ref qpath, pats, _) => is_enum_variant(cx, qpath, pat.hir_id) || are_refutable(cx, pats),
        PatKind::Slice(head, middle, tail) => {
            match &cx.typeck_results().node_type(pat.hir_id).kind() {
                rustc_ty::Slice(..) => {
                    // [..] is the only irrefutable slice pattern.
                    !head.is_empty() || middle.is_none() || !tail.is_empty()
                },
                rustc_ty::Array(..) => are_refutable(cx, head.iter().chain(middle).chain(tail.iter())),
                _ => {
                    // unreachable!()
                    true
                },
            }
        },
    }
}

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

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

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

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

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

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

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

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

    None
}

/// Returns `true` if the lint is allowed in the current context. This is useful for
/// skipping long running code when it's unnecessary
///
/// This function should check the lint level for the same node, that the lint will
/// be emitted at. If the information is buffered to be emitted at a later point, please
/// make sure to use `span_lint_hir` functions to emit the lint. This ensures that
/// expectations at the checked nodes will be fulfilled.
pub fn is_lint_allowed(cx: &LateContext<'_>, lint: &'static Lint, id: HirId) -> bool {
    cx.tcx.lint_level_at_node(lint, id).0 == Level::Allow
}

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

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

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

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

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

pub fn has_attr(attrs: &[ast::Attribute], symbol: Symbol) -> bool {
    attrs.iter().any(|attr| attr.has_name(symbol))
}

pub fn has_repr_attr(cx: &LateContext<'_>, hir_id: HirId) -> bool {
    has_attr(cx.tcx.hir().attrs(hir_id), sym::repr)
}

pub fn any_parent_has_attr(tcx: TyCtxt<'_>, node: HirId, symbol: Symbol) -> bool {
    let map = &tcx.hir();
    let mut prev_enclosing_node = None;
    let mut enclosing_node = node;
    while Some(enclosing_node) != prev_enclosing_node {
        if has_attr(map.attrs(enclosing_node), symbol) {
            return true;
        }
        prev_enclosing_node = Some(enclosing_node);
        enclosing_node = map.get_parent_item(enclosing_node).into();
    }

    false
}

pub fn any_parent_is_automatically_derived(tcx: TyCtxt<'_>, node: HirId) -> bool {
    any_parent_has_attr(tcx, node, sym::automatically_derived)
}

/// Matches a function call with the given path and returns the arguments.
///
/// Usage:
///
/// ```rust,ignore
/// if let Some(args) = match_function_call(cx, cmp_max_call, &paths::CMP_MAX);
/// ```
/// This function is deprecated. Use [`match_function_call_with_def_id`].
pub fn match_function_call<'tcx>(
    cx: &LateContext<'tcx>,
    expr: &'tcx Expr<'_>,
    path: &[&str],
) -> Option<&'tcx [Expr<'tcx>]> {
    if_chain! {
        if let ExprKind::Call(fun, args) = expr.kind;
        if let ExprKind::Path(ref qpath) = fun.kind;
        if let Some(fun_def_id) = cx.qpath_res(qpath, fun.hir_id).opt_def_id();
        if match_def_path(cx, fun_def_id, path);
        then {
            return Some(args);
        }
    };
    None
}

pub fn match_function_call_with_def_id<'tcx>(
    cx: &LateContext<'tcx>,
    expr: &'tcx Expr<'_>,
    fun_def_id: DefId,
) -> Option<&'tcx [Expr<'tcx>]> {
    if_chain! {
        if let ExprKind::Call(fun, args) = expr.kind;
        if let ExprKind::Path(ref qpath) = fun.kind;
        if cx.qpath_res(qpath, fun.hir_id).opt_def_id() == Some(fun_def_id);
        then {
            return Some(args);
        }
    };
    None
}

/// Checks if the given `DefId` matches any of the paths. Returns the index of matching path, if
/// any.
///
/// Please use `tcx.get_diagnostic_name` if the targets are all diagnostic items.
pub fn match_any_def_paths(cx: &LateContext<'_>, did: DefId, paths: &[&[&str]]) -> Option<usize> {
    let search_path = cx.get_def_path(did);
    paths
        .iter()
        .position(|p| p.iter().map(|x| Symbol::intern(x)).eq(search_path.iter().copied()))
}

/// Checks if the given `DefId` matches the path.
pub fn match_def_path(cx: &LateContext<'_>, did: DefId, syms: &[&str]) -> bool {
    // We should probably move to Symbols in Clippy as well rather than interning every time.
    let path = cx.get_def_path(did);
    syms.iter().map(|x| Symbol::intern(x)).eq(path.iter().copied())
}

/// Checks if the given `DefId` matches the `libc` item.
pub fn match_libc_symbol(cx: &LateContext<'_>, did: DefId, name: &str) -> bool {
    let path = cx.get_def_path(did);
    // libc is meant to be used as a flat list of names, but they're all actually defined in different
    // modules based on the target platform. Ignore everything but crate name and the item name.
    path.first().map_or(false, |s| s.as_str() == "libc") && path.last().map_or(false, |s| s.as_str() == name)
}

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

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

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

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

    (conds, blocks)
}

/// Checks if the given function kind is an async function.
pub fn is_async_fn(kind: FnKind<'_>) -> bool {
    match kind {
        FnKind::ItemFn(_, _, header) => header.asyncness == IsAsync::Async,
        FnKind::Method(_, sig) => sig.header.asyncness == IsAsync::Async,
        FnKind::Closure => false,
    }
}

/// Peels away all the compiler generated code surrounding the body of an async function,
pub fn get_async_fn_body<'tcx>(tcx: TyCtxt<'tcx>, body: &Body<'_>) -> Option<&'tcx Expr<'tcx>> {
    if let ExprKind::Closure(&Closure { body, .. }) = body.value.kind {
        if let ExprKind::Block(
            Block {
                stmts: [],
                expr:
                    Some(Expr {
                        kind: ExprKind::DropTemps(expr),
                        ..
                    }),
                ..
            },
            _,
        ) = tcx.hir().body(body).value.kind
        {
            return Some(expr);
        }
    };
    None
}

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

    did.map_or(false, |did| cx.tcx.has_attr(did, sym::must_use))
}

/// Checks if an expression represents the identity function
/// Only examines closures and `std::convert::identity`
pub fn is_expr_identity_function(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
    /// Checks if a function's body represents the identity function. Looks for bodies of the form:
    /// * `|x| x`
    /// * `|x| return x`
    /// * `|x| { return x }`
    /// * `|x| { return x; }`
    fn is_body_identity_function(cx: &LateContext<'_>, func: &Body<'_>) -> bool {
        let id = if_chain! {
            if let [param] = func.params;
            if let PatKind::Binding(_, id, _, _) = param.pat.kind;
            then {
                id
            } else {
                return false;
            }
        };

        let mut expr = func.value;
        loop {
            match expr.kind {
                #[rustfmt::skip]
                ExprKind::Block(&Block { stmts: [], expr: Some(e), .. }, _, )
                | ExprKind::Ret(Some(e)) => expr = e,
                #[rustfmt::skip]
                ExprKind::Block(&Block { stmts: [stmt], expr: None, .. }, _) => {
                    if_chain! {
                        if let StmtKind::Semi(e) | StmtKind::Expr(e) = stmt.kind;
                        if let ExprKind::Ret(Some(ret_val)) = e.kind;
                        then {
                            expr = ret_val;
                        } else {
                            return false;
                        }
                    }
                },
                _ => return path_to_local_id(expr, id) && cx.typeck_results().expr_adjustments(expr).is_empty(),
            }
        }
    }

    match expr.kind {
        ExprKind::Closure(&Closure { body, .. }) => is_body_identity_function(cx, cx.tcx.hir().body(body)),
        _ => path_def_id(cx, expr).map_or(false, |id| match_def_path(cx, id, &paths::CONVERT_IDENTITY)),
    }
}

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

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

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

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

pub fn is_no_std_crate(cx: &LateContext<'_>) -> bool {
    cx.tcx.hir().attrs(hir::CRATE_HIR_ID).iter().any(|attr| {
        if let ast::AttrKind::Normal(ref normal) = attr.kind {
            normal.item.path == sym::no_std
        } else {
            false
        }
    })
}

pub fn is_no_core_crate(cx: &LateContext<'_>) -> bool {
    cx.tcx.hir().attrs(hir::CRATE_HIR_ID).iter().any(|attr| {
        if let ast::AttrKind::Normal(ref normal) = attr.kind {
            normal.item.path == sym::no_core
        } else {
            false
        }
    })
}

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

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

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

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

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

/// returns list of all pairs (a, b) from `exprs` such that `eq(a, b)`
/// `hash` must be comformed with `eq`
pub fn search_same<T, Hash, Eq>(exprs: &[T], hash: Hash, eq: Eq) -> Vec<(&T, &T)>
where
    Hash: Fn(&T) -> u64,
    Eq: Fn(&T, &T) -> bool,
{
    match exprs {
        [a, b] if eq(a, b) => return vec![(a, b)],
        _ if exprs.len() <= 2 => return vec![],
        _ => {},
    }

    let mut match_expr_list: Vec<(&T, &T)> = Vec::new();

    let mut map: UnhashMap<u64, Vec<&_>> =
        UnhashMap::with_capacity_and_hasher(exprs.len(), BuildHasherDefault::default());

    for expr in exprs {
        match map.entry(hash(expr)) {
            Entry::Occupied(mut o) => {
                for o in o.get() {
                    if eq(o, expr) {
                        match_expr_list.push((o, expr));
                    }
                }
                o.get_mut().push(expr);
            },
            Entry::Vacant(v) => {
                v.insert(vec![expr]);
            },
        }
    }

    match_expr_list
}

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

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

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

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

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

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

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

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

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

fn with_test_item_names(tcx: TyCtxt<'_>, module: LocalDefId, f: impl Fn(&[Symbol]) -> bool) -> bool {
    let cache = TEST_ITEM_NAMES_CACHE.get_or_init(|| Mutex::new(FxHashMap::default()));
    let mut map: MutexGuard<'_, FxHashMap<LocalDefId, Vec<Symbol>>> = cache.lock().unwrap();
    let value = map.entry(module);
    match value {
        Entry::Occupied(entry) => f(entry.get()),
        Entry::Vacant(entry) => {
            let mut names = Vec::new();
            for id in tcx.hir().module_items(module) {
                if matches!(tcx.def_kind(id.owner_id), DefKind::Const)
                    && let item = tcx.hir().item(id)
                    && let ItemKind::Const(ty, _body) = item.kind {
                    if let TyKind::Path(QPath::Resolved(_, path)) = ty.kind {
                        // We could also check for the type name `test::TestDescAndFn`
                        if let Res::Def(DefKind::Struct, _) = path.res {
                            let has_test_marker = tcx
                                .hir()
                                .attrs(item.hir_id())
                                .iter()
                                .any(|a| a.has_name(sym::rustc_test_marker));
                            if has_test_marker {
                                names.push(item.ident.name);
                            }
                        }
                    }
                }
            }
            names.sort_unstable();
            f(entry.insert(names))
        },
    }
}

/// Checks if the function containing the given `HirId` is a `#[test]` function
///
/// Note: Add `// compile-flags: --test` to UI tests with a `#[test]` function
pub fn is_in_test_function(tcx: TyCtxt<'_>, id: hir::HirId) -> bool {
    with_test_item_names(tcx, tcx.parent_module(id), |names| {
        tcx.hir()
            .parent_iter(id)
            // Since you can nest functions we need to collect all until we leave
            // function scope
            .any(|(_id, node)| {
                if let Node::Item(item) = node {
                    if let ItemKind::Fn(_, _, _) = item.kind {
                        // Note that we have sorted the item names in the visitor,
                        // so the binary_search gets the same as `contains`, but faster.
                        return names.binary_search(&item.ident.name).is_ok();
                    }
                }
                false
            })
    })
}

/// Checks if the item containing the given `HirId` has `#[cfg(test)]` attribute applied
///
/// Note: Add `// compile-flags: --test` to UI tests with a `#[cfg(test)]` function
pub fn is_in_cfg_test(tcx: TyCtxt<'_>, id: hir::HirId) -> bool {
    fn is_cfg_test(attr: &Attribute) -> bool {
        if attr.has_name(sym::cfg)
            && let Some(items) = attr.meta_item_list()
            && let [item] = &*items
            && item.has_name(sym::test)
        {
            true
        } else {
            false
        }
    }
    tcx.hir()
        .parent_iter(id)
        .flat_map(|(parent_id, _)| tcx.hir().attrs(parent_id))
        .any(is_cfg_test)
}

/// Checks whether item either has `test` attribute applied, or
/// is a module with `test` in its name.
///
/// Note: Add `// compile-flags: --test` to UI tests with a `#[test]` function
pub fn is_test_module_or_function(tcx: TyCtxt<'_>, item: &Item<'_>) -> bool {
    is_in_test_function(tcx, item.hir_id())
        || matches!(item.kind, ItemKind::Mod(..))
            && item.ident.name.as_str().split('_').any(|a| a == "test" || a == "tests")
}

/// Walks the HIR tree from the given expression, up to the node where the value produced by the
/// expression is consumed. Calls the function for every node encountered this way until it returns
/// `Some`.
///
/// This allows walking through `if`, `match`, `break`, block expressions to find where the value
/// produced by the expression is consumed.
pub fn walk_to_expr_usage<'tcx, T>(
    cx: &LateContext<'tcx>,
    e: &Expr<'tcx>,
    mut f: impl FnMut(Node<'tcx>, HirId) -> Option<T>,
) -> Option<T> {
    let map = cx.tcx.hir();
    let mut iter = map.parent_iter(e.hir_id);
    let mut child_id = e.hir_id;

    while let Some((parent_id, parent)) = iter.next() {
        if let Some(x) = f(parent, child_id) {
            return Some(x);
        }
        let parent = match parent {
            Node::Expr(e) => e,
            Node::Block(Block { expr: Some(body), .. }) | Node::Arm(Arm { body, .. }) if body.hir_id == child_id => {
                child_id = parent_id;
                continue;
            },
            Node::Arm(a) if a.body.hir_id == child_id => {
                child_id = parent_id;
                continue;
            },
            _ => return None,
        };
        match parent.kind {
            ExprKind::If(child, ..) | ExprKind::Match(child, ..) if child.hir_id != child_id => child_id = parent_id,
            ExprKind::Break(Destination { target_id: Ok(id), .. }, _) => {
                child_id = id;
                iter = map.parent_iter(id);
            },
            ExprKind::Block(..) => child_id = parent_id,
            _ => return None,
        }
    }
    None
}

/// Checks whether a given span has any comment token
/// This checks for all types of comment: line "//", block "/**", doc "///" "//!"
pub fn span_contains_comment(sm: &SourceMap, span: Span) -> bool {
    let Ok(snippet) = sm.span_to_snippet(span) else { return false };
    return tokenize(&snippet).any(|token| {
        matches!(
            token.kind,
            TokenKind::BlockComment { .. } | TokenKind::LineComment { .. }
        )
    });
}

/// Return all the comments a given span contains
/// Comments are returned wrapped with their relevant delimiters
pub fn span_extract_comment(sm: &SourceMap, span: Span) -> String {
    let snippet = sm.span_to_snippet(span).unwrap_or_default();
    let mut comments_buf: Vec<String> = Vec::new();
    let mut index: usize = 0;

    for token in tokenize(&snippet) {
        let token_range = index..(index + token.len as usize);
        index += token.len as usize;
        match token.kind {
            TokenKind::BlockComment { .. } | TokenKind::LineComment { .. } => {
                if let Some(comment) = snippet.get(token_range) {
                    comments_buf.push(comment.to_string());
                }
            },
            _ => (),
        }
    }

    comments_buf.join("\n")
}

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

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

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

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

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