src/tools/clippy/clippy_lints/src/mut_key.rs

   1 use clippy_utils::diagnostics::span_lint;
   2 use clippy_utils::{def_path_def_ids, trait_ref_of_method};
   3 use rustc_data_structures::fx::FxHashSet;
   4 use rustc_hir as hir;
   5 use rustc_lint::{LateContext, LateLintPass};
   6 use rustc_middle::ty::TypeVisitable;
   7 use rustc_middle::ty::{Adt, Array, Ref, Slice, Tuple, Ty};
   8 use rustc_session::{declare_tool_lint, impl_lint_pass};
   9 use rustc_span::source_map::Span;
  10 use rustc_span::symbol::sym;
  11 use std::iter;
  12
  13 declare_clippy_lint! {
  14     /// ### What it does
  15     /// Checks for sets/maps with mutable key types.
  16     ///
  17     /// ### Why is this bad?
  18     /// All of `HashMap`, `HashSet`, `BTreeMap` and
  19     /// `BtreeSet` rely on either the hash or the order of keys be unchanging,
  20     /// so having types with interior mutability is a bad idea.
  21     ///
  22     /// ### Known problems
  23     ///
  24     /// #### False Positives
  25     /// It's correct to use a struct that contains interior mutability as a key, when its
  26     /// implementation of `Hash` or `Ord` doesn't access any of the interior mutable types.
  27     /// However, this lint is unable to recognize this, so it will often cause false positives in
  28     /// theses cases.  The `bytes` crate is a great example of this.
  29     ///
  30     /// #### False Negatives
  31     /// For custom `struct`s/`enum`s, this lint is unable to check for interior mutability behind
  32     /// indirection.  For example, `struct BadKey<'a>(&'a Cell<usize>)` will be seen as immutable
  33     /// and cause a false negative if its implementation of `Hash`/`Ord` accesses the `Cell`.
  34     ///
  35     /// This lint does check a few cases for indirection.  Firstly, using some standard library
  36     /// types (`Option`, `Result`, `Box`, `Rc`, `Arc`, `Vec`, `VecDeque`, `BTreeMap` and
  37     /// `BTreeSet`) directly as keys (e.g. in `HashMap<Box<Cell<usize>>, ()>`) **will** trigger the
  38     /// lint, because the impls of `Hash`/`Ord` for these types directly call `Hash`/`Ord` on their
  39     /// contained type.
  40     ///
  41     /// Secondly, the implementations of `Hash` and `Ord` for raw pointers (`*const T` or `*mut T`)
  42     /// apply only to the **address** of the contained value.  Therefore, interior mutability
  43     /// behind raw pointers (e.g. in `HashSet<*mut Cell<usize>>`) can't impact the value of `Hash`
  44     /// or `Ord`, and therefore will not trigger this link.  For more info, see issue
  45     /// [#6745](https://github.com/rust-lang/rust-clippy/issues/6745).
  46     ///
  47     /// ### Example
  48     /// ```rust
  49     /// use std::cmp::{PartialEq, Eq};
  50     /// use std::collections::HashSet;
  51     /// use std::hash::{Hash, Hasher};
  52     /// use std::sync::atomic::AtomicUsize;
  53     ///# #[allow(unused)]
  54     ///
  55     /// struct Bad(AtomicUsize);
  56     /// impl PartialEq for Bad {
  57     ///     fn eq(&self, rhs: &Self) -> bool {
  58     ///          ..
  59     /// ; unimplemented!();
  60     ///     }
  61     /// }
  62     ///
  63     /// impl Eq for Bad {}
  64     ///
  65     /// impl Hash for Bad {
  66     ///     fn hash<H: Hasher>(&self, h: &mut H) {
  67     ///         ..
  68     /// ; unimplemented!();
  69     ///     }
  70     /// }
  71     ///
  72     /// fn main() {
  73     ///     let _: HashSet<Bad> = HashSet::new();
  74     /// }
  75     /// ```
  76     #[clippy::version = "1.42.0"]
  77     pub MUTABLE_KEY_TYPE,
  78     suspicious,
  79     "Check for mutable `Map`/`Set` key type"
  80 }
  81
  82 #[derive(Clone)]
  83 pub struct MutableKeyType {
  84     ignore_interior_mutability: Vec<String>,
  85     ignore_mut_def_ids: FxHashSet<hir::def_id::DefId>,
  86 }
  87
  88 impl_lint_pass!(MutableKeyType => [ MUTABLE_KEY_TYPE ]);
  89
  90 impl<'tcx> LateLintPass<'tcx> for MutableKeyType {
  91     fn check_crate(&mut self, cx: &LateContext<'tcx>) {
  92         self.ignore_mut_def_ids.clear();
  93         let mut path = Vec::new();
  94         for ty in &self.ignore_interior_mutability {
  95             path.extend(ty.split("::"));
  96             for id in def_path_def_ids(cx, &path[..]) {
  97                 self.ignore_mut_def_ids.insert(id);
  98             }
  99             path.clear();
 100         }
 101     }
 102
 103     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) {
 104         if let hir::ItemKind::Fn(ref sig, ..) = item.kind {
 105             self.check_sig(cx, item.hir_id(), sig.decl);
 106         }
 107     }
 108
 109     fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::ImplItem<'tcx>) {
 110         if let hir::ImplItemKind::Fn(ref sig, ..) = item.kind {
 111             if trait_ref_of_method(cx, item.owner_id.def_id).is_none() {
 112                 self.check_sig(cx, item.hir_id(), sig.decl);
 113             }
 114         }
 115     }
 116
 117     fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::TraitItem<'tcx>) {
 118         if let hir::TraitItemKind::Fn(ref sig, ..) = item.kind {
 119             self.check_sig(cx, item.hir_id(), sig.decl);
 120         }
 121     }
 122
 123     fn check_local(&mut self, cx: &LateContext<'_>, local: &hir::Local<'_>) {
 124         if let hir::PatKind::Wild = local.pat.kind {
 125             return;
 126         }
 127         self.check_ty_(cx, local.span, cx.typeck_results().pat_ty(local.pat));
 128     }
 129 }
 130
 131 impl MutableKeyType {
 132     pub fn new(ignore_interior_mutability: Vec<String>) -> Self {
 133         Self {
 134             ignore_interior_mutability,
 135             ignore_mut_def_ids: FxHashSet::default(),
 136         }
 137     }
 138
 139     fn check_sig(&self, cx: &LateContext<'_>, item_hir_id: hir::HirId, decl: &hir::FnDecl<'_>) {
 140         let fn_def_id = cx.tcx.hir().local_def_id(item_hir_id);
 141         let fn_sig = cx.tcx.fn_sig(fn_def_id);
 142         for (hir_ty, ty) in iter::zip(decl.inputs, fn_sig.inputs().skip_binder()) {
 143             self.check_ty_(cx, hir_ty.span, *ty);
 144         }
 145         self.check_ty_(cx, decl.output.span(), cx.tcx.erase_late_bound_regions(fn_sig.output()));
 146     }
 147
 148     // We want to lint 1. sets or maps with 2. not immutable key types and 3. no unerased
 149     // generics (because the compiler cannot ensure immutability for unknown types).
 150     fn check_ty_<'tcx>(&self, cx: &LateContext<'tcx>, span: Span, ty: Ty<'tcx>) {
 151         let ty = ty.peel_refs();
 152         if let Adt(def, substs) = ty.kind() {
 153             let is_keyed_type = [sym::HashMap, sym::BTreeMap, sym::HashSet, sym::BTreeSet]
 154                 .iter()
 155                 .any(|diag_item| cx.tcx.is_diagnostic_item(*diag_item, def.did()));
 156             if is_keyed_type && self.is_interior_mutable_type(cx, substs.type_at(0)) {
 157                 span_lint(cx, MUTABLE_KEY_TYPE, span, "mutable key type");
 158             }
 159         }
 160     }
 161
 162     /// Determines if a type contains interior mutability which would affect its implementation of
 163     /// [`Hash`] or [`Ord`].
 164     fn is_interior_mutable_type<'tcx>(&self, cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
 165         match *ty.kind() {
 166             Ref(_, inner_ty, mutbl) => mutbl == hir::Mutability::Mut || self.is_interior_mutable_type(cx, inner_ty),
 167             Slice(inner_ty) => self.is_interior_mutable_type(cx, inner_ty),
 168             Array(inner_ty, size) => {
 169                 size.try_eval_usize(cx.tcx, cx.param_env).map_or(true, |u| u != 0)
 170                     && self.is_interior_mutable_type(cx, inner_ty)
 171             },
 172             Tuple(fields) => fields.iter().any(|ty| self.is_interior_mutable_type(cx, ty)),
 173             Adt(def, substs) => {
 174                 // Special case for collections in `std` who's impl of `Hash` or `Ord` delegates to
 175                 // that of their type parameters.  Note: we don't include `HashSet` and `HashMap`
 176                 // because they have no impl for `Hash` or `Ord`.
 177                 let def_id = def.did();
 178                 let is_std_collection = [
 179                     sym::Option,
 180                     sym::Result,
 181                     sym::LinkedList,
 182                     sym::Vec,
 183                     sym::VecDeque,
 184                     sym::BTreeMap,
 185                     sym::BTreeSet,
 186                     sym::Rc,
 187                     sym::Arc,
 188                 ]
 189                 .iter()
 190                 .any(|diag_item| cx.tcx.is_diagnostic_item(*diag_item, def_id));
 191                 let is_box = Some(def_id) == cx.tcx.lang_items().owned_box();
 192                 if is_std_collection || is_box || self.ignore_mut_def_ids.contains(&def_id) {
 193                     // The type is mutable if any of its type parameters are
 194                     substs.types().any(|ty| self.is_interior_mutable_type(cx, ty))
 195                 } else {
 196                     !ty.has_escaping_bound_vars()
 197                         && cx.tcx.layout_of(cx.param_env.and(ty)).is_ok()
 198                         && !ty.is_freeze(cx.tcx, cx.param_env)
 199                 }
 200             },
 201             _ => false,
 202         }
 203     }
 204 }