rust-clippy/clippy_lints/src/mut_key.rs

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use crate::utils::{match_def_path, paths, span_lint, trait_ref_of_method};
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use rustc_hir as hir;
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use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty::TypeFoldable;
use rustc_middle::ty::{Adt, Array, RawPtr, Ref, Slice, Tuple, Ty, TypeAndMut};
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use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::source_map::Span;
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declare_clippy_lint! {
/// **What it does:** Checks for sets/maps with mutable key types.
///
/// **Why is this bad?** All of `HashMap`, `HashSet`, `BTreeMap` and
/// `BtreeSet` rely on either the hash or the order of keys be unchanging,
/// so having types with interior mutability is a bad idea.
///
/// **Known problems:** It's correct to use a struct, that contains interior mutability
/// as a key, when its `Hash` implementation doesn't access any of the interior mutable types.
/// However, this lint is unable to recognize this, so it causes a false positive in theses cases.
/// The `bytes` crate is a great example of this.
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///
/// **Example:**
/// ```rust
/// use std::cmp::{PartialEq, Eq};
/// use std::collections::HashSet;
/// use std::hash::{Hash, Hasher};
/// use std::sync::atomic::AtomicUsize;
///# #[allow(unused)]
///
/// struct Bad(AtomicUsize);
/// impl PartialEq for Bad {
/// fn eq(&self, rhs: &Self) -> bool {
/// ..
/// ; unimplemented!();
/// }
/// }
///
/// impl Eq for Bad {}
///
/// impl Hash for Bad {
/// fn hash<H: Hasher>(&self, h: &mut H) {
/// ..
/// ; unimplemented!();
/// }
/// }
///
/// fn main() {
/// let _: HashSet<Bad> = HashSet::new();
/// }
/// ```
pub MUTABLE_KEY_TYPE,
correctness,
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"Check for mutable `Map`/`Set` key type"
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}
declare_lint_pass!(MutableKeyType => [ MUTABLE_KEY_TYPE ]);
impl<'tcx> LateLintPass<'tcx> for MutableKeyType {
fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) {
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if let hir::ItemKind::Fn(ref sig, ..) = item.kind {
check_sig(cx, item.hir_id, &sig.decl);
}
}
fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::ImplItem<'tcx>) {
if let hir::ImplItemKind::Fn(ref sig, ..) = item.kind {
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if trait_ref_of_method(cx, item.hir_id).is_none() {
check_sig(cx, item.hir_id, &sig.decl);
}
}
}
fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::TraitItem<'tcx>) {
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if let hir::TraitItemKind::Fn(ref sig, ..) = item.kind {
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check_sig(cx, item.hir_id, &sig.decl);
}
}
fn check_local(&mut self, cx: &LateContext<'_>, local: &hir::Local<'_>) {
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if let hir::PatKind::Wild = local.pat.kind {
return;
}
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check_ty(cx, local.span, cx.typeck_results().pat_ty(&*local.pat));
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}
}
fn check_sig<'tcx>(cx: &LateContext<'tcx>, item_hir_id: hir::HirId, decl: &hir::FnDecl<'_>) {
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let fn_def_id = cx.tcx.hir().local_def_id(item_hir_id);
let fn_sig = cx.tcx.fn_sig(fn_def_id);
for (hir_ty, ty) in decl.inputs.iter().zip(fn_sig.inputs().skip_binder().iter()) {
check_ty(cx, hir_ty.span, ty);
}
check_ty(
cx,
decl.output.span(),
cx.tcx.erase_late_bound_regions(&fn_sig.output()),
);
}
// We want to lint 1. sets or maps with 2. not immutable key types and 3. no unerased
// generics (because the compiler cannot ensure immutability for unknown types).
fn check_ty<'tcx>(cx: &LateContext<'tcx>, span: Span, ty: Ty<'tcx>) {
let ty = ty.peel_refs();
if let Adt(def, substs) = ty.kind() {
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if [&paths::HASHMAP, &paths::BTREEMAP, &paths::HASHSET, &paths::BTREESET]
.iter()
.any(|path| match_def_path(cx, def.did, &**path))
&& is_mutable_type(cx, substs.type_at(0), span)
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{
span_lint(cx, MUTABLE_KEY_TYPE, span, "mutable key type");
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}
}
}
fn is_mutable_type<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, span: Span) -> bool {
match *ty.kind() {
RawPtr(TypeAndMut { ty: inner_ty, mutbl }) | Ref(_, inner_ty, mutbl) => {
mutbl == hir::Mutability::Mut || is_mutable_type(cx, inner_ty, span)
},
Slice(inner_ty) => is_mutable_type(cx, inner_ty, span),
Array(inner_ty, size) => {
size.try_eval_usize(cx.tcx, cx.param_env).map_or(true, |u| u != 0) && is_mutable_type(cx, inner_ty, span)
},
Tuple(..) => ty.tuple_fields().any(|ty| is_mutable_type(cx, ty, span)),
Adt(..) => {
cx.tcx.layout_of(cx.param_env.and(ty)).is_ok()
&& !ty.has_escaping_bound_vars()
&& !ty.is_freeze(cx.tcx.at(span), cx.param_env)
},
_ => false,
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}
}