rustc_hir_analysis/hir_ty_lowering/
lint.rs1use rustc_ast::TraitObjectSyntax;
2use rustc_errors::codes::*;
3use rustc_errors::{Diag, EmissionGuarantee, ErrorGuaranteed, StashKey, Suggestions};
4use rustc_hir as hir;
5use rustc_hir::def::{DefKind, Namespace, Res};
6use rustc_hir::def_id::DefId;
7use rustc_lint_defs::Applicability;
8use rustc_lint_defs::builtin::BARE_TRAIT_OBJECTS;
9use rustc_span::Span;
10use rustc_span::edit_distance::find_best_match_for_name;
11use rustc_trait_selection::error_reporting::traits::suggestions::NextTypeParamName;
12
13use super::HirTyLowerer;
14
15impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
16 pub(super) fn prohibit_or_lint_bare_trait_object_ty(
21 &self,
22 self_ty: &hir::Ty<'_>,
23 ) -> Option<ErrorGuaranteed> {
24 let tcx = self.tcx();
25
26 let poly_trait_ref = if let hir::TyKind::TraitObject([poly_trait_ref, ..], tagged_ptr) =
27 self_ty.kind
28 && let TraitObjectSyntax::None = tagged_ptr.tag()
29 {
30 poly_trait_ref
31 } else {
32 return None;
33 };
34
35 let in_path = match tcx.parent_hir_node(self_ty.hir_id) {
36 hir::Node::Ty(hir::Ty {
37 kind: hir::TyKind::Path(hir::QPath::TypeRelative(qself, _)),
38 ..
39 })
40 | hir::Node::Expr(hir::Expr {
41 kind: hir::ExprKind::Path(hir::QPath::TypeRelative(qself, _)),
42 ..
43 })
44 | hir::Node::PatExpr(hir::PatExpr {
45 kind: hir::PatExprKind::Path(hir::QPath::TypeRelative(qself, _)),
46 ..
47 }) if qself.hir_id == self_ty.hir_id => true,
48 _ => false,
49 };
50 let needs_bracket = in_path
51 && !tcx
52 .sess
53 .source_map()
54 .span_to_prev_source(self_ty.span)
55 .ok()
56 .is_some_and(|s| s.trim_end().ends_with('<'));
57
58 let is_global = poly_trait_ref.trait_ref.path.is_global();
59
60 let mut sugg = vec![(
61 self_ty.span.shrink_to_lo(),
62 format!(
63 "{}dyn {}",
64 if needs_bracket { "<" } else { "" },
65 if is_global { "(" } else { "" },
66 ),
67 )];
68
69 if is_global || needs_bracket {
70 sugg.push((
71 self_ty.span.shrink_to_hi(),
72 format!(
73 "{}{}",
74 if is_global { ")" } else { "" },
75 if needs_bracket { ">" } else { "" },
76 ),
77 ));
78 }
79
80 if self_ty.span.edition().at_least_rust_2021() {
81 let mut diag = rustc_errors::struct_span_code_err!(
82 self.dcx(),
83 self_ty.span,
84 E0782,
85 "{}",
86 "expected a type, found a trait"
87 );
88 if self_ty.span.can_be_used_for_suggestions()
89 && !self.maybe_suggest_impl_trait(self_ty, &mut diag)
90 && !self.maybe_suggest_dyn_trait(self_ty, sugg, &mut diag)
91 {
92 self.maybe_suggest_add_generic_impl_trait(self_ty, &mut diag);
93 }
94 self.maybe_suggest_blanket_trait_impl(self_ty, &mut diag);
96 self.maybe_suggest_assoc_ty_bound(self_ty, &mut diag);
97 self.maybe_suggest_typoed_method(
98 self_ty,
99 poly_trait_ref.trait_ref.trait_def_id(),
100 &mut diag,
101 );
102 if let Some(mut sugg) =
105 tcx.dcx().steal_non_err(self_ty.span, StashKey::AssociatedTypeSuggestion)
106 && let Suggestions::Enabled(ref mut s1) = diag.suggestions
107 && let Suggestions::Enabled(ref mut s2) = sugg.suggestions
108 {
109 s1.append(s2);
110 sugg.cancel();
111 }
112 Some(diag.emit())
113 } else {
114 tcx.node_span_lint(BARE_TRAIT_OBJECTS, self_ty.hir_id, self_ty.span, |lint| {
115 lint.primary_message("trait objects without an explicit `dyn` are deprecated");
116 if self_ty.span.can_be_used_for_suggestions() {
117 lint.multipart_suggestion_verbose(
118 "if this is a dyn-compatible trait, use `dyn`",
119 sugg,
120 Applicability::MachineApplicable,
121 );
122 }
123 self.maybe_suggest_blanket_trait_impl(self_ty, lint);
124 });
125 None
126 }
127 }
128
129 fn maybe_suggest_add_generic_impl_trait(
132 &self,
133 self_ty: &hir::Ty<'_>,
134 diag: &mut Diag<'_>,
135 ) -> bool {
136 let tcx = self.tcx();
137
138 let parent_hir_id = tcx.parent_hir_id(self_ty.hir_id);
139 let parent_item = tcx.hir_get_parent_item(self_ty.hir_id).def_id;
140
141 let generics = match tcx.hir_node_by_def_id(parent_item) {
142 hir::Node::Item(hir::Item {
143 kind: hir::ItemKind::Struct(_, variant, generics),
144 ..
145 }) => {
146 if !variant.fields().iter().any(|field| field.hir_id == parent_hir_id) {
147 return false;
148 }
149 generics
150 }
151 hir::Node::Item(hir::Item { kind: hir::ItemKind::Enum(_, def, generics), .. }) => {
152 if !def
153 .variants
154 .iter()
155 .flat_map(|variant| variant.data.fields().iter())
156 .any(|field| field.hir_id == parent_hir_id)
157 {
158 return false;
159 }
160 generics
161 }
162 _ => return false,
163 };
164
165 let Ok(rendered_ty) = tcx.sess.source_map().span_to_snippet(self_ty.span) else {
166 return false;
167 };
168
169 let param = "TUV"
170 .chars()
171 .map(|c| c.to_string())
172 .chain((0..).map(|i| format!("P{i}")))
173 .find(|s| !generics.params.iter().any(|param| param.name.ident().as_str() == s))
174 .expect("we definitely can find at least one param name to generate");
175 let mut sugg = vec![(self_ty.span, param.to_string())];
176 if let Some(insertion_span) = generics.span_for_param_suggestion() {
177 sugg.push((insertion_span, format!(", {param}: {}", rendered_ty)));
178 } else {
179 sugg.push((generics.where_clause_span, format!("<{param}: {}>", rendered_ty)));
180 }
181 diag.multipart_suggestion_verbose(
182 "you might be missing a type parameter",
183 sugg,
184 Applicability::MachineApplicable,
185 );
186 true
187 }
188 fn maybe_suggest_blanket_trait_impl<G: EmissionGuarantee>(
190 &self,
191 self_ty: &hir::Ty<'_>,
192 diag: &mut Diag<'_, G>,
193 ) {
194 let tcx = self.tcx();
195 let parent_id = tcx.hir_get_parent_item(self_ty.hir_id).def_id;
196 if let hir::Node::Item(hir::Item {
197 kind: hir::ItemKind::Impl(hir::Impl { self_ty: impl_self_ty, of_trait, generics, .. }),
198 ..
199 }) = tcx.hir_node_by_def_id(parent_id)
200 && self_ty.hir_id == impl_self_ty.hir_id
201 {
202 let Some(of_trait_ref) = of_trait else {
203 diag.span_suggestion_verbose(
204 impl_self_ty.span.shrink_to_hi(),
205 "you might have intended to implement this trait for a given type",
206 format!(" for /* Type */"),
207 Applicability::HasPlaceholders,
208 );
209 return;
210 };
211 if !of_trait_ref.trait_def_id().is_some_and(|def_id| def_id.is_local()) {
212 return;
213 }
214 let of_trait_span = of_trait_ref.path.span;
215 let Ok(of_trait_name) = tcx.sess.source_map().span_to_snippet(of_trait_span) else {
217 return;
218 };
219
220 let Ok(impl_trait_name) = self.tcx().sess.source_map().span_to_snippet(self_ty.span)
221 else {
222 return;
223 };
224 let sugg = self.add_generic_param_suggestion(generics, self_ty.span, &impl_trait_name);
225 diag.multipart_suggestion(
226 format!(
227 "alternatively use a blanket implementation to implement `{of_trait_name}` for \
228 all types that also implement `{impl_trait_name}`"
229 ),
230 sugg,
231 Applicability::MaybeIncorrect,
232 );
233 }
234 }
235
236 fn maybe_suggest_dyn_trait(
244 &self,
245 self_ty: &hir::Ty<'_>,
246 sugg: Vec<(Span, String)>,
247 diag: &mut Diag<'_>,
248 ) -> bool {
249 let tcx = self.tcx();
250
251 match tcx.parent_hir_node(self_ty.hir_id) {
254 hir::Node::Ty(_)
260 | hir::Node::Expr(_)
261 | hir::Node::PatExpr(_)
262 | hir::Node::PathSegment(_)
263 | hir::Node::AssocItemConstraint(_)
264 | hir::Node::TraitRef(_)
265 | hir::Node::Item(_)
266 | hir::Node::WherePredicate(_) => {}
267
268 hir::Node::Field(field) => {
269 if let hir::Node::Item(hir::Item {
271 kind: hir::ItemKind::Struct(_, variant, _), ..
272 }) = tcx.parent_hir_node(field.hir_id)
273 && variant
274 .fields()
275 .last()
276 .is_some_and(|tail_field| tail_field.hir_id == field.hir_id)
277 {
278 } else {
280 return false;
281 }
282 }
283 _ => return false,
284 }
285
286 diag.multipart_suggestion_verbose(
288 "you can add the `dyn` keyword if you want a trait object",
289 sugg,
290 Applicability::MachineApplicable,
291 );
292 true
293 }
294
295 fn add_generic_param_suggestion(
296 &self,
297 generics: &hir::Generics<'_>,
298 self_ty_span: Span,
299 impl_trait_name: &str,
300 ) -> Vec<(Span, String)> {
301 let param_name = generics.params.next_type_param_name(None);
303
304 let add_generic_sugg = if let Some(span) = generics.span_for_param_suggestion() {
305 (span, format!(", {param_name}: {impl_trait_name}"))
306 } else {
307 (generics.span, format!("<{param_name}: {impl_trait_name}>"))
308 };
309 vec![(self_ty_span, param_name), add_generic_sugg]
310 }
311
312 fn maybe_suggest_impl_trait(&self, self_ty: &hir::Ty<'_>, diag: &mut Diag<'_>) -> bool {
314 let tcx = self.tcx();
315 let parent_id = tcx.hir_get_parent_item(self_ty.hir_id).def_id;
316 let (sig, generics) = match tcx.hir_node_by_def_id(parent_id) {
323 hir::Node::Item(hir::Item {
324 kind: hir::ItemKind::Fn { sig, generics, .. }, ..
325 }) => (sig, generics),
326 hir::Node::TraitItem(hir::TraitItem {
327 kind: hir::TraitItemKind::Fn(sig, _),
328 generics,
329 ..
330 }) => (sig, generics),
331 hir::Node::ImplItem(hir::ImplItem {
332 kind: hir::ImplItemKind::Fn(sig, _),
333 generics,
334 ..
335 }) => (sig, generics),
336 _ => return false,
337 };
338 let Ok(trait_name) = tcx.sess.source_map().span_to_snippet(self_ty.span) else {
339 return false;
340 };
341 let impl_sugg = vec![(self_ty.span.shrink_to_lo(), "impl ".to_string())];
342 let is_dyn_compatible = match self_ty.kind {
344 hir::TyKind::TraitObject(objects, ..) => {
345 objects.iter().all(|o| match o.trait_ref.path.res {
346 Res::Def(DefKind::Trait, id) => tcx.is_dyn_compatible(id),
347 _ => false,
348 })
349 }
350 _ => false,
351 };
352
353 let borrowed = matches!(
354 tcx.parent_hir_node(self_ty.hir_id),
355 hir::Node::Ty(hir::Ty { kind: hir::TyKind::Ref(..), .. })
356 );
357
358 if let hir::FnRetTy::Return(ty) = sig.decl.output
360 && ty.peel_refs().hir_id == self_ty.hir_id
361 {
362 let pre = if !is_dyn_compatible {
363 format!("`{trait_name}` is dyn-incompatible, ")
364 } else {
365 String::new()
366 };
367 let msg = format!(
368 "{pre}use `impl {trait_name}` to return an opaque type, as long as you return a \
369 single underlying type",
370 );
371
372 diag.multipart_suggestion_verbose(msg, impl_sugg, Applicability::MachineApplicable);
373
374 if is_dyn_compatible {
376 let suggestion = if borrowed {
380 vec![(ty.span, format!("Box<dyn {trait_name}>"))]
381 } else {
382 vec![
383 (ty.span.shrink_to_lo(), "Box<dyn ".to_string()),
384 (ty.span.shrink_to_hi(), ">".to_string()),
385 ]
386 };
387
388 diag.multipart_suggestion_verbose(
389 "alternatively, you can return an owned trait object",
390 suggestion,
391 Applicability::MachineApplicable,
392 );
393 }
394 return true;
395 }
396
397 for ty in sig.decl.inputs {
399 if ty.peel_refs().hir_id != self_ty.hir_id {
400 continue;
401 }
402 let sugg = self.add_generic_param_suggestion(generics, self_ty.span, &trait_name);
403 diag.multipart_suggestion_verbose(
404 format!("use a new generic type parameter, constrained by `{trait_name}`"),
405 sugg,
406 Applicability::MachineApplicable,
407 );
408 diag.multipart_suggestion_verbose(
409 "you can also use an opaque type, but users won't be able to specify the type \
410 parameter when calling the `fn`, having to rely exclusively on type inference",
411 impl_sugg,
412 Applicability::MachineApplicable,
413 );
414 if !is_dyn_compatible {
415 diag.note(format!(
416 "`{trait_name}` is dyn-incompatible, otherwise a trait object could be used"
417 ));
418 } else {
419 let (dyn_str, paren_dyn_str) =
421 if borrowed { ("dyn ", "(dyn ") } else { ("&dyn ", "&(dyn ") };
422
423 let sugg = if let hir::TyKind::TraitObject([_, _, ..], _) = self_ty.kind {
424 vec![
426 (self_ty.span.shrink_to_lo(), paren_dyn_str.to_string()),
427 (self_ty.span.shrink_to_hi(), ")".to_string()),
428 ]
429 } else {
430 vec![(self_ty.span.shrink_to_lo(), dyn_str.to_string())]
431 };
432 diag.multipart_suggestion_verbose(
433 format!(
434 "alternatively, use a trait object to accept any type that implements \
435 `{trait_name}`, accessing its methods at runtime using dynamic dispatch",
436 ),
437 sugg,
438 Applicability::MachineApplicable,
439 );
440 }
441 return true;
442 }
443 false
444 }
445
446 fn maybe_suggest_assoc_ty_bound(&self, self_ty: &hir::Ty<'_>, diag: &mut Diag<'_>) {
447 let mut parents = self.tcx().hir_parent_iter(self_ty.hir_id);
448
449 if let Some((_, hir::Node::AssocItemConstraint(constraint))) = parents.next()
450 && let Some(obj_ty) = constraint.ty()
451 {
452 if let Some((_, hir::Node::TraitRef(..))) = parents.next()
453 && let Some((_, hir::Node::Ty(ty))) = parents.next()
454 && let hir::TyKind::TraitObject(..) = ty.kind
455 {
456 return;
458 }
459
460 let lo = if constraint.gen_args.span_ext.is_dummy() {
461 constraint.ident.span
462 } else {
463 constraint.gen_args.span_ext
464 };
465 let hi = obj_ty.span;
466
467 if !lo.eq_ctxt(hi) {
468 return;
469 }
470
471 diag.span_suggestion_verbose(
472 lo.between(hi),
473 "you might have meant to write a bound here",
474 ": ",
475 Applicability::MaybeIncorrect,
476 );
477 }
478 }
479
480 fn maybe_suggest_typoed_method(
481 &self,
482 self_ty: &hir::Ty<'_>,
483 trait_def_id: Option<DefId>,
484 diag: &mut Diag<'_>,
485 ) {
486 let tcx = self.tcx();
487 let Some(trait_def_id) = trait_def_id else {
488 return;
489 };
490 let hir::Node::Expr(hir::Expr {
491 kind: hir::ExprKind::Path(hir::QPath::TypeRelative(path_ty, segment)),
492 ..
493 }) = tcx.parent_hir_node(self_ty.hir_id)
494 else {
495 return;
496 };
497 if path_ty.hir_id != self_ty.hir_id {
498 return;
499 }
500 let names: Vec<_> = tcx
501 .associated_items(trait_def_id)
502 .in_definition_order()
503 .filter(|assoc| assoc.kind.namespace() == Namespace::ValueNS)
504 .map(|cand| cand.name)
505 .collect();
506 if let Some(typo) = find_best_match_for_name(&names, segment.ident.name, None) {
507 diag.span_suggestion_verbose(
508 segment.ident.span,
509 format!(
510 "you may have misspelled this associated item, causing `{}` \
511 to be interpreted as a type rather than a trait",
512 tcx.item_name(trait_def_id),
513 ),
514 typo,
515 Applicability::MaybeIncorrect,
516 );
517 }
518 }
519}