2 use std::collections::BTreeMap;
4 use rustc_errors::Diagnostic;
6 use rustc_hir::intravisit::{walk_body, walk_expr, walk_inf, walk_ty, Visitor};
7 use rustc_hir::{Body, Expr, ExprKind, GenericArg, Item, ItemKind, QPath, TyKind};
8 use rustc_hir_analysis::hir_ty_to_ty;
9 use rustc_lint::{LateContext, LateLintPass, LintContext};
10 use rustc_middle::hir::nested_filter;
11 use rustc_middle::lint::in_external_macro;
12 use rustc_middle::ty::{Ty, TypeckResults};
13 use rustc_session::{declare_lint_pass, declare_tool_lint};
14 use rustc_span::source_map::Span;
15 use rustc_span::symbol::sym;
17 use if_chain::if_chain;
19 use clippy_utils::diagnostics::{multispan_sugg, span_lint_and_then};
20 use clippy_utils::source::{snippet, snippet_opt};
21 use clippy_utils::ty::is_type_diagnostic_item;
23 declare_clippy_lint! {
25 /// Checks for public `impl` or `fn` missing generalization
26 /// over different hashers and implicitly defaulting to the default hashing
27 /// algorithm (`SipHash`).
29 /// ### Why is this bad?
30 /// `HashMap` or `HashSet` with custom hashers cannot be
33 /// ### Known problems
34 /// Suggestions for replacing constructors can contain
35 /// false-positives. Also applying suggestions can require modification of other
36 /// pieces of code, possibly including external crates.
40 /// # use std::collections::HashMap;
41 /// # use std::hash::{Hash, BuildHasher};
42 /// # trait Serialize {};
43 /// impl<K: Hash + Eq, V> Serialize for HashMap<K, V> { }
45 /// pub fn foo(map: &mut HashMap<i32, i32>) { }
47 /// could be rewritten as
49 /// # use std::collections::HashMap;
50 /// # use std::hash::{Hash, BuildHasher};
51 /// # trait Serialize {};
52 /// impl<K: Hash + Eq, V, S: BuildHasher> Serialize for HashMap<K, V, S> { }
54 /// pub fn foo<S: BuildHasher>(map: &mut HashMap<i32, i32, S>) { }
56 #[clippy::version = "pre 1.29.0"]
59 "missing generalization over different hashers"
62 declare_lint_pass!(ImplicitHasher => [IMPLICIT_HASHER]);
64 impl<'tcx> LateLintPass<'tcx> for ImplicitHasher {
65 #[expect(clippy::cast_possible_truncation, clippy::too_many_lines)]
66 fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
67 use rustc_span::BytePos;
70 cx: &LateContext<'tcx>,
71 diag: &mut Diagnostic,
73 generics_suggestion_span: Span,
74 target: &ImplicitHasherType<'_>,
75 vis: ImplicitHasherConstructorVisitor<'_, '_, '_>,
77 let generics_snip = snippet(cx, generics_span, "");
79 let generics_snip = if generics_snip.is_empty() {
82 &generics_snip[1..generics_snip.len() - 1]
87 "consider adding a type parameter",
90 generics_suggestion_span,
92 "<{generics_snip}{}S: ::std::hash::BuildHasher{}>",
93 if generics_snip.is_empty() { "" } else { ", " },
94 if vis.suggestions.is_empty() {
97 // request users to add `Default` bound so that generic constructors can be used
104 format!("{}<{}, S>", target.type_name(), target.type_arguments(),),
109 if !vis.suggestions.is_empty() {
110 multispan_sugg(diag, "...and use generic constructor", vis.suggestions);
114 if !cx.access_levels.is_exported(item.def_id.def_id) {
119 ItemKind::Impl(impl_) => {
120 let mut vis = ImplicitHasherTypeVisitor::new(cx);
121 vis.visit_ty(impl_.self_ty);
123 for target in &vis.found {
124 if item.span.ctxt() != target.span().ctxt() {
128 let generics_suggestion_span = impl_.generics.span.substitute_dummy({
129 let pos = snippet_opt(cx, item.span.until(target.span()))
130 .and_then(|snip| Some(item.span.lo() + BytePos(snip.find("impl")? as u32 + 4)));
131 if let Some(pos) = pos {
132 Span::new(pos, pos, item.span.ctxt(), item.span.parent())
138 let mut ctr_vis = ImplicitHasherConstructorVisitor::new(cx, target);
139 for item in impl_.items.iter().map(|item| cx.tcx.hir().impl_item(item.id)) {
140 ctr_vis.visit_impl_item(item);
148 "impl for `{}` should be generalized over different hashers",
152 suggestion(cx, diag, impl_.generics.span, generics_suggestion_span, target, ctr_vis);
157 ItemKind::Fn(ref sig, generics, body_id) => {
158 let body = cx.tcx.hir().body(body_id);
160 for ty in sig.decl.inputs {
161 let mut vis = ImplicitHasherTypeVisitor::new(cx);
164 for target in &vis.found {
165 if in_external_macro(cx.sess(), generics.span) {
168 let generics_suggestion_span = generics.span.substitute_dummy({
169 let pos = snippet_opt(
173 body.params[0].pat.span.lo(),
179 let i = snip.find("fn")?;
180 Some(item.span.lo() + BytePos((i + snip[i..].find('(')?) as u32))
182 .expect("failed to create span for type parameters");
183 Span::new(pos, pos, item.span.ctxt(), item.span.parent())
186 let mut ctr_vis = ImplicitHasherConstructorVisitor::new(cx, target);
187 ctr_vis.visit_body(body);
194 "parameter of type `{}` should be generalized over different hashers",
198 suggestion(cx, diag, generics.span, generics_suggestion_span, target, ctr_vis);
209 enum ImplicitHasherType<'tcx> {
210 HashMap(Span, Ty<'tcx>, Cow<'static, str>, Cow<'static, str>),
211 HashSet(Span, Ty<'tcx>, Cow<'static, str>),
214 impl<'tcx> ImplicitHasherType<'tcx> {
215 /// Checks that `ty` is a target type without a `BuildHasher`.
216 fn new(cx: &LateContext<'tcx>, hir_ty: &hir::Ty<'_>) -> Option<Self> {
217 if let TyKind::Path(QPath::Resolved(None, path)) = hir_ty.kind {
218 let params: Vec<_> = path
226 .filter_map(|arg| match arg {
227 GenericArg::Type(ty) => Some(ty),
231 let params_len = params.len();
233 let ty = hir_ty_to_ty(cx.tcx, hir_ty);
235 if is_type_diagnostic_item(cx, ty, sym::HashMap) && params_len == 2 {
236 Some(ImplicitHasherType::HashMap(
239 snippet(cx, params[0].span, "K"),
240 snippet(cx, params[1].span, "V"),
242 } else if is_type_diagnostic_item(cx, ty, sym::HashSet) && params_len == 1 {
243 Some(ImplicitHasherType::HashSet(
246 snippet(cx, params[0].span, "T"),
256 fn type_name(&self) -> &'static str {
258 ImplicitHasherType::HashMap(..) => "HashMap",
259 ImplicitHasherType::HashSet(..) => "HashSet",
263 fn type_arguments(&self) -> String {
265 ImplicitHasherType::HashMap(.., ref k, ref v) => format!("{k}, {v}"),
266 ImplicitHasherType::HashSet(.., ref t) => format!("{t}"),
270 fn ty(&self) -> Ty<'tcx> {
272 ImplicitHasherType::HashMap(_, ty, ..) | ImplicitHasherType::HashSet(_, ty, ..) => ty,
276 fn span(&self) -> Span {
278 ImplicitHasherType::HashMap(span, ..) | ImplicitHasherType::HashSet(span, ..) => span,
283 struct ImplicitHasherTypeVisitor<'a, 'tcx> {
284 cx: &'a LateContext<'tcx>,
285 found: Vec<ImplicitHasherType<'tcx>>,
288 impl<'a, 'tcx> ImplicitHasherTypeVisitor<'a, 'tcx> {
289 fn new(cx: &'a LateContext<'tcx>) -> Self {
290 Self { cx, found: vec![] }
294 impl<'a, 'tcx> Visitor<'tcx> for ImplicitHasherTypeVisitor<'a, 'tcx> {
295 fn visit_ty(&mut self, t: &'tcx hir::Ty<'_>) {
296 if let Some(target) = ImplicitHasherType::new(self.cx, t) {
297 self.found.push(target);
303 fn visit_infer(&mut self, inf: &'tcx hir::InferArg) {
304 if let Some(target) = ImplicitHasherType::new(self.cx, &inf.to_ty()) {
305 self.found.push(target);
312 /// Looks for default-hasher-dependent constructors like `HashMap::new`.
313 struct ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
314 cx: &'a LateContext<'tcx>,
315 maybe_typeck_results: Option<&'tcx TypeckResults<'tcx>>,
316 target: &'b ImplicitHasherType<'tcx>,
317 suggestions: BTreeMap<Span, String>,
320 impl<'a, 'b, 'tcx> ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
321 fn new(cx: &'a LateContext<'tcx>, target: &'b ImplicitHasherType<'tcx>) -> Self {
324 maybe_typeck_results: cx.maybe_typeck_results(),
326 suggestions: BTreeMap::new(),
331 impl<'a, 'b, 'tcx> Visitor<'tcx> for ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
332 type NestedFilter = nested_filter::OnlyBodies;
334 fn visit_body(&mut self, body: &'tcx Body<'_>) {
335 let old_maybe_typeck_results = self.maybe_typeck_results.replace(self.cx.tcx.typeck_body(body.id()));
336 walk_body(self, body);
337 self.maybe_typeck_results = old_maybe_typeck_results;
340 fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
342 if let ExprKind::Call(fun, args) = e.kind;
343 if let ExprKind::Path(QPath::TypeRelative(ty, method)) = fun.kind;
344 if let TyKind::Path(QPath::Resolved(None, ty_path)) = ty.kind;
345 if let Some(ty_did) = ty_path.res.opt_def_id();
347 if self.target.ty() != self.maybe_typeck_results.unwrap().expr_ty(e) {
351 if self.cx.tcx.is_diagnostic_item(sym::HashMap, ty_did) {
352 if method.ident.name == sym::new {
354 .insert(e.span, "HashMap::default()".to_string());
355 } else if method.ident.name == sym!(with_capacity) {
356 self.suggestions.insert(
359 "HashMap::with_capacity_and_hasher({}, Default::default())",
360 snippet(self.cx, args[0].span, "capacity"),
364 } else if self.cx.tcx.is_diagnostic_item(sym::HashSet, ty_did) {
365 if method.ident.name == sym::new {
367 .insert(e.span, "HashSet::default()".to_string());
368 } else if method.ident.name == sym!(with_capacity) {
369 self.suggestions.insert(
372 "HashSet::with_capacity_and_hasher({}, Default::default())",
373 snippet(self.cx, args[0].span, "capacity"),
384 fn nested_visit_map(&mut self) -> Self::Map {