1 use clippy_utils::diagnostics::span_lint;
2 use clippy_utils::{def_path_res, trait_ref_of_method};
3 use rustc_data_structures::fx::FxHashSet;
5 use rustc_hir::def::Namespace;
6 use rustc_lint::{LateContext, LateLintPass};
7 use rustc_middle::ty::TypeVisitable;
8 use rustc_middle::ty::{Adt, Array, Ref, Slice, Tuple, Ty};
9 use rustc_session::{declare_tool_lint, impl_lint_pass};
10 use rustc_span::source_map::Span;
11 use rustc_span::symbol::sym;
14 declare_clippy_lint! {
16 /// Checks for sets/maps with mutable key types.
18 /// ### Why is this bad?
19 /// All of `HashMap`, `HashSet`, `BTreeMap` and
20 /// `BtreeSet` rely on either the hash or the order of keys be unchanging,
21 /// so having types with interior mutability is a bad idea.
23 /// ### Known problems
25 /// #### False Positives
26 /// It's correct to use a struct that contains interior mutability as a key, when its
27 /// implementation of `Hash` or `Ord` doesn't access any of the interior mutable types.
28 /// However, this lint is unable to recognize this, so it will often cause false positives in
29 /// theses cases. The `bytes` crate is a great example of this.
31 /// #### False Negatives
32 /// For custom `struct`s/`enum`s, this lint is unable to check for interior mutability behind
33 /// indirection. For example, `struct BadKey<'a>(&'a Cell<usize>)` will be seen as immutable
34 /// and cause a false negative if its implementation of `Hash`/`Ord` accesses the `Cell`.
36 /// This lint does check a few cases for indirection. Firstly, using some standard library
37 /// types (`Option`, `Result`, `Box`, `Rc`, `Arc`, `Vec`, `VecDeque`, `BTreeMap` and
38 /// `BTreeSet`) directly as keys (e.g. in `HashMap<Box<Cell<usize>>, ()>`) **will** trigger the
39 /// lint, because the impls of `Hash`/`Ord` for these types directly call `Hash`/`Ord` on their
42 /// Secondly, the implementations of `Hash` and `Ord` for raw pointers (`*const T` or `*mut T`)
43 /// apply only to the **address** of the contained value. Therefore, interior mutability
44 /// behind raw pointers (e.g. in `HashSet<*mut Cell<usize>>`) can't impact the value of `Hash`
45 /// or `Ord`, and therefore will not trigger this link. For more info, see issue
46 /// [#6745](https://github.com/rust-lang/rust-clippy/issues/6745).
50 /// use std::cmp::{PartialEq, Eq};
51 /// use std::collections::HashSet;
52 /// use std::hash::{Hash, Hasher};
53 /// use std::sync::atomic::AtomicUsize;
56 /// struct Bad(AtomicUsize);
57 /// impl PartialEq for Bad {
58 /// fn eq(&self, rhs: &Self) -> bool {
60 /// ; unimplemented!();
64 /// impl Eq for Bad {}
66 /// impl Hash for Bad {
67 /// fn hash<H: Hasher>(&self, h: &mut H) {
69 /// ; unimplemented!();
74 /// let _: HashSet<Bad> = HashSet::new();
77 #[clippy::version = "1.42.0"]
80 "Check for mutable `Map`/`Set` key type"
84 pub struct MutableKeyType {
85 ignore_interior_mutability: Vec<String>,
86 ignore_mut_def_ids: FxHashSet<hir::def_id::DefId>,
89 impl_lint_pass!(MutableKeyType => [ MUTABLE_KEY_TYPE ]);
91 impl<'tcx> LateLintPass<'tcx> for MutableKeyType {
92 fn check_crate(&mut self, cx: &LateContext<'tcx>) {
93 self.ignore_mut_def_ids.clear();
94 let mut path = Vec::new();
95 for ty in &self.ignore_interior_mutability {
96 path.extend(ty.split("::"));
97 if let Some(id) = def_path_res(cx, &path[..], Some(Namespace::TypeNS)).opt_def_id() {
98 self.ignore_mut_def_ids.insert(id);
104 fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) {
105 if let hir::ItemKind::Fn(ref sig, ..) = item.kind {
106 self.check_sig(cx, item.hir_id(), sig.decl);
110 fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::ImplItem<'tcx>) {
111 if let hir::ImplItemKind::Fn(ref sig, ..) = item.kind {
112 if trait_ref_of_method(cx, item.def_id.def_id).is_none() {
113 self.check_sig(cx, item.hir_id(), sig.decl);
118 fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::TraitItem<'tcx>) {
119 if let hir::TraitItemKind::Fn(ref sig, ..) = item.kind {
120 self.check_sig(cx, item.hir_id(), sig.decl);
124 fn check_local(&mut self, cx: &LateContext<'_>, local: &hir::Local<'_>) {
125 if let hir::PatKind::Wild = local.pat.kind {
128 self.check_ty_(cx, local.span, cx.typeck_results().pat_ty(local.pat));
132 impl MutableKeyType {
133 pub fn new(ignore_interior_mutability: Vec<String>) -> Self {
135 ignore_interior_mutability,
136 ignore_mut_def_ids: FxHashSet::default(),
140 fn check_sig(&self, cx: &LateContext<'_>, item_hir_id: hir::HirId, decl: &hir::FnDecl<'_>) {
141 let fn_def_id = cx.tcx.hir().local_def_id(item_hir_id);
142 let fn_sig = cx.tcx.fn_sig(fn_def_id);
143 for (hir_ty, ty) in iter::zip(decl.inputs, fn_sig.inputs().skip_binder()) {
144 self.check_ty_(cx, hir_ty.span, *ty);
146 self.check_ty_(cx, decl.output.span(), cx.tcx.erase_late_bound_regions(fn_sig.output()));
149 // We want to lint 1. sets or maps with 2. not immutable key types and 3. no unerased
150 // generics (because the compiler cannot ensure immutability for unknown types).
151 fn check_ty_<'tcx>(&self, cx: &LateContext<'tcx>, span: Span, ty: Ty<'tcx>) {
152 let ty = ty.peel_refs();
153 if let Adt(def, substs) = ty.kind() {
154 let is_keyed_type = [sym::HashMap, sym::BTreeMap, sym::HashSet, sym::BTreeSet]
156 .any(|diag_item| cx.tcx.is_diagnostic_item(*diag_item, def.did()));
157 if is_keyed_type && self.is_interior_mutable_type(cx, substs.type_at(0), span) {
158 span_lint(cx, MUTABLE_KEY_TYPE, span, "mutable key type");
163 /// Determines if a type contains interior mutability which would affect its implementation of
164 /// [`Hash`] or [`Ord`].
165 fn is_interior_mutable_type<'tcx>(&self, cx: &LateContext<'tcx>, ty: Ty<'tcx>, span: Span) -> bool {
167 Ref(_, inner_ty, mutbl) => {
168 mutbl == hir::Mutability::Mut || self.is_interior_mutable_type(cx, inner_ty, span)
170 Slice(inner_ty) => self.is_interior_mutable_type(cx, inner_ty, span),
171 Array(inner_ty, size) => {
172 size.try_eval_usize(cx.tcx, cx.param_env).map_or(true, |u| u != 0)
173 && self.is_interior_mutable_type(cx, inner_ty, span)
175 Tuple(fields) => fields.iter().any(|ty| self.is_interior_mutable_type(cx, ty, span)),
176 Adt(def, substs) => {
177 // Special case for collections in `std` who's impl of `Hash` or `Ord` delegates to
178 // that of their type parameters. Note: we don't include `HashSet` and `HashMap`
179 // because they have no impl for `Hash` or `Ord`.
180 let def_id = def.did();
181 let is_std_collection = [
193 .any(|diag_item| cx.tcx.is_diagnostic_item(*diag_item, def_id));
194 let is_box = Some(def_id) == cx.tcx.lang_items().owned_box();
195 if is_std_collection || is_box || self.ignore_mut_def_ids.contains(&def_id) {
196 // The type is mutable if any of its type parameters are
197 substs.types().any(|ty| self.is_interior_mutable_type(cx, ty, span))
199 !ty.has_escaping_bound_vars()
200 && cx.tcx.layout_of(cx.param_env.and(ty)).is_ok()
201 && !ty.is_freeze(cx.tcx.at(span), cx.param_env)