1 //! Diagnostics related methods for `Ty`.
3 use std::ops::ControlFlow;
6 visit::TypeVisitable, Const, ConstKind, DefIdTree, ExistentialPredicate, InferConst, InferTy,
7 PolyTraitPredicate, Ty, TyCtxt, TypeSuperVisitable, TypeVisitor,
10 use rustc_data_structures::fx::FxHashMap;
11 use rustc_errors::{Applicability, Diagnostic, DiagnosticArgValue, IntoDiagnosticArg};
13 use rustc_hir::def_id::DefId;
14 use rustc_hir::WherePredicate;
16 use rustc_type_ir::sty::TyKind::*;
18 impl<'tcx> IntoDiagnosticArg for Ty<'tcx> {
19 fn into_diagnostic_arg(self) -> DiagnosticArgValue<'static> {
20 format!("{}", self).into_diagnostic_arg()
25 /// Similar to `Ty::is_primitive`, but also considers inferred numeric values to be primitive.
26 pub fn is_primitive_ty(self) -> bool {
36 | InferTy::FloatVar(_)
37 | InferTy::FreshIntTy(_)
38 | InferTy::FreshFloatTy(_)
43 /// Whether the type is succinctly representable as a type instead of just referred to with a
44 /// description in error messages. This is used in the main error message.
45 pub fn is_simple_ty(self) -> bool {
55 | InferTy::FloatVar(_)
56 | InferTy::FreshIntTy(_)
57 | InferTy::FreshFloatTy(_),
59 Ref(_, x, _) | Array(x, _) | Slice(x) => x.peel_refs().is_simple_ty(),
60 Tuple(tys) if tys.is_empty() => true,
65 /// Whether the type is succinctly representable as a type instead of just referred to with a
66 /// description in error messages. This is used in the primary span label. Beyond what
67 /// `is_simple_ty` includes, it also accepts ADTs with no type arguments and references to
68 /// ADTs with no type arguments.
69 pub fn is_simple_text(self) -> bool {
71 Adt(_, substs) => substs.non_erasable_generics().next().is_none(),
72 Ref(_, ty, _) => ty.is_simple_text(),
73 _ => self.is_simple_ty(),
78 pub trait IsSuggestable<'tcx> {
79 /// Whether this makes sense to suggest in a diagnostic.
81 /// We filter out certain types and constants since they don't provide
82 /// meaningful rendered suggestions when pretty-printed. We leave some
83 /// nonsense, such as region vars, since those render as `'_` and are
84 /// usually okay to reinterpret as elided lifetimes.
86 /// Only if `infer_suggestable` is true, we consider type and const
87 /// inference variables to be suggestable.
88 fn is_suggestable(self, tcx: TyCtxt<'tcx>, infer_suggestable: bool) -> bool;
91 impl<'tcx, T> IsSuggestable<'tcx> for T
93 T: TypeVisitable<'tcx>,
95 fn is_suggestable(self, tcx: TyCtxt<'tcx>, infer_suggestable: bool) -> bool {
96 self.visit_with(&mut IsSuggestableVisitor { tcx, infer_suggestable }).is_continue()
100 pub fn suggest_arbitrary_trait_bound<'tcx>(
102 generics: &hir::Generics<'_>,
103 err: &mut Diagnostic,
104 trait_pred: PolyTraitPredicate<'tcx>,
105 associated_ty: Option<(&'static str, Ty<'tcx>)>,
107 if !trait_pred.is_suggestable(tcx, false) {
111 let param_name = trait_pred.skip_binder().self_ty().to_string();
112 let mut constraint = trait_pred.print_modifiers_and_trait_path().to_string();
114 if let Some((name, term)) = associated_ty {
115 // FIXME: this case overlaps with code in TyCtxt::note_and_explain_type_err.
116 // That should be extracted into a helper function.
117 if constraint.ends_with('>') {
118 constraint = format!("{}, {} = {}>", &constraint[..constraint.len() - 1], name, term);
120 constraint.push_str(&format!("<{} = {}>", name, term));
124 let param = generics.params.iter().find(|p| p.name.ident().as_str() == param_name);
126 // Skip, there is a param named Self
127 if param.is_some() && param_name == "Self" {
131 // Suggest a where clause bound for a non-type parameter.
132 err.span_suggestion_verbose(
133 generics.tail_span_for_predicate_suggestion(),
135 "consider {} `where` clause, but there might be an alternative better way to express \
137 if generics.where_clause_span.is_empty() { "introducing a" } else { "extending the" },
139 format!("{} {}: {}", generics.add_where_or_trailing_comma(), param_name, constraint),
140 Applicability::MaybeIncorrect,
146 enum SuggestChangingConstraintsMessage<'a> {
147 RestrictBoundFurther,
148 RestrictType { ty: &'a str },
149 RestrictTypeFurther { ty: &'a str },
153 fn suggest_removing_unsized_bound(
155 generics: &hir::Generics<'_>,
156 suggestions: &mut Vec<(Span, String, SuggestChangingConstraintsMessage<'_>)>,
157 param: &hir::GenericParam<'_>,
158 def_id: Option<DefId>,
160 // See if there's a `?Sized` bound that can be removed to suggest that.
161 // First look at the `where` clause because we can have `where T: ?Sized`,
162 // then look at params.
163 let param_def_id = tcx.hir().local_def_id(param.hir_id);
164 for (where_pos, predicate) in generics.predicates.iter().enumerate() {
165 let WherePredicate::BoundPredicate(predicate) = predicate else {
168 if !predicate.is_param_bound(param_def_id.to_def_id()) {
172 for (pos, bound) in predicate.bounds.iter().enumerate() {
173 let hir::GenericBound::Trait(poly, hir::TraitBoundModifier::Maybe) = bound else {
176 if poly.trait_ref.trait_def_id() != def_id {
179 let sp = generics.span_for_bound_removal(where_pos, pos);
183 SuggestChangingConstraintsMessage::RemovingQSized,
189 /// Suggest restricting a type param with a new bound.
190 pub fn suggest_constraining_type_param(
192 generics: &hir::Generics<'_>,
193 err: &mut Diagnostic,
196 def_id: Option<DefId>,
198 suggest_constraining_type_params(
202 [(param_name, constraint, def_id)].into_iter(),
206 /// Suggest restricting a type param with a new bound.
207 pub fn suggest_constraining_type_params<'a>(
209 generics: &hir::Generics<'_>,
210 err: &mut Diagnostic,
211 param_names_and_constraints: impl Iterator<Item = (&'a str, &'a str, Option<DefId>)>,
213 let mut grouped = FxHashMap::default();
214 param_names_and_constraints.for_each(|(param_name, constraint, def_id)| {
215 grouped.entry(param_name).or_insert(Vec::new()).push((constraint, def_id))
218 let mut applicability = Applicability::MachineApplicable;
219 let mut suggestions = Vec::new();
221 for (param_name, mut constraints) in grouped {
222 let param = generics.params.iter().find(|p| p.name.ident().as_str() == param_name);
223 let Some(param) = param else { return false };
226 let mut sized_constraints =
227 constraints.drain_filter(|(_, def_id)| *def_id == tcx.lang_items().sized_trait());
228 if let Some((constraint, def_id)) = sized_constraints.next() {
229 applicability = Applicability::MaybeIncorrect;
233 &format!("this type parameter needs to be `{}`", constraint),
235 suggest_removing_unsized_bound(tcx, generics, &mut suggestions, param, def_id);
239 if constraints.is_empty() {
243 let mut constraint = constraints.iter().map(|&(c, _)| c).collect::<Vec<_>>();
246 let constraint = constraint.join(" + ");
247 let mut suggest_restrict = |span, bound_list_non_empty| {
250 if bound_list_non_empty {
251 format!(" + {}", constraint)
253 format!(" {}", constraint)
255 SuggestChangingConstraintsMessage::RestrictBoundFurther,
259 // When the type parameter has been provided bounds
262 // fn foo<T>(t: T) where T: Foo { ... }
265 // help: consider further restricting this bound with `+ Bar`
268 // fn foo<T>(t: T) where T: Foo { ... }
271 // replace with: ` + Bar`
273 // Or, if user has provided some bounds, suggest restricting them:
275 // fn foo<T: Foo>(t: T) { ... }
278 // help: consider further restricting this bound with `+ Bar`
280 // Suggestion for tools in this case is:
282 // fn foo<T: Foo>(t: T) { ... }
285 // replace with: `T: Bar +`
286 let param_def_id = tcx.hir().local_def_id(param.hir_id);
287 if let Some(span) = generics.bounds_span_for_suggestions(param_def_id) {
288 suggest_restrict(span, true);
292 if generics.has_where_clause_predicates {
293 // This part is a bit tricky, because using the `where` clause user can
294 // provide zero, one or many bounds for the same type parameter, so we
295 // have following cases to consider:
297 // When the type parameter has been provided zero bounds
300 // fn foo<X, Y>(x: X, y: Y) where Y: Foo { ... }
301 // - help: consider restricting this type parameter with `where X: Bar`
304 // fn foo<X, Y>(x: X, y: Y) where Y: Foo { ... }
305 // - insert: `, X: Bar`
307 generics.tail_span_for_predicate_suggestion(),
310 .map(|&(constraint, _)| format!(", {}: {}", param_name, constraint))
311 .collect::<String>(),
312 SuggestChangingConstraintsMessage::RestrictTypeFurther { ty: param_name },
317 // Additionally, there may be no `where` clause but the generic parameter has a default:
320 // trait Foo<T=()> {... }
321 // - help: consider further restricting this type parameter with `where T: Zar`
324 // trait Foo<T=()> {... }
325 // - insert: `where T: Zar`
326 if matches!(param.kind, hir::GenericParamKind::Type { default: Some(_), .. }) {
327 // Suggest a bound, but there is no existing `where` clause *and* the type param has a
328 // default (`<T=Foo>`), so we suggest adding `where T: Bar`.
330 generics.tail_span_for_predicate_suggestion(),
331 format!(" where {}: {}", param_name, constraint),
332 SuggestChangingConstraintsMessage::RestrictTypeFurther { ty: param_name },
337 // If user has provided a colon, don't suggest adding another:
339 // fn foo<T:>(t: T) { ... }
340 // - insert: consider restricting this type parameter with `T: Foo`
341 if let Some(colon_span) = param.colon_span {
343 colon_span.shrink_to_hi(),
344 format!(" {}", constraint),
345 SuggestChangingConstraintsMessage::RestrictType { ty: param_name },
350 // If user hasn't provided any bounds, suggest adding a new one:
352 // fn foo<T>(t: T) { ... }
353 // - help: consider restricting this type parameter with `T: Foo`
355 param.span.shrink_to_hi(),
356 format!(": {}", constraint),
357 SuggestChangingConstraintsMessage::RestrictType { ty: param_name },
361 if suggestions.len() == 1 {
362 let (span, suggestion, msg) = suggestions.pop().unwrap();
365 let msg = match msg {
366 SuggestChangingConstraintsMessage::RestrictBoundFurther => {
367 "consider further restricting this bound"
369 SuggestChangingConstraintsMessage::RestrictType { ty } => {
370 s = format!("consider restricting type parameter `{}`", ty);
373 SuggestChangingConstraintsMessage::RestrictTypeFurther { ty } => {
374 s = format!("consider further restricting type parameter `{}`", ty);
377 SuggestChangingConstraintsMessage::RemovingQSized => {
378 "consider removing the `?Sized` bound to make the type parameter `Sized`"
382 err.span_suggestion_verbose(span, msg, suggestion, applicability);
383 } else if suggestions.len() > 1 {
384 err.multipart_suggestion_verbose(
385 "consider restricting type parameters",
386 suggestions.into_iter().map(|(span, suggestion, _)| (span, suggestion)).collect(),
394 /// Collect al types that have an implicit `'static` obligation that we could suggest `'_` for.
395 pub struct TraitObjectVisitor<'tcx>(pub Vec<&'tcx hir::Ty<'tcx>>, pub crate::hir::map::Map<'tcx>);
397 impl<'v> hir::intravisit::Visitor<'v> for TraitObjectVisitor<'v> {
398 fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
400 hir::TyKind::TraitObject(
404 hir::LifetimeName::ImplicitObjectLifetimeDefault | hir::LifetimeName::Static,
411 hir::TyKind::OpaqueDef(item_id, _, _) => {
413 let item = self.1.item(item_id);
414 hir::intravisit::walk_item(self, item);
418 hir::intravisit::walk_ty(self, ty);
422 /// Collect al types that have an implicit `'static` obligation that we could suggest `'_` for.
423 pub struct StaticLifetimeVisitor<'tcx>(pub Vec<Span>, pub crate::hir::map::Map<'tcx>);
425 impl<'v> hir::intravisit::Visitor<'v> for StaticLifetimeVisitor<'v> {
426 fn visit_lifetime(&mut self, lt: &'v hir::Lifetime) {
427 if let hir::LifetimeName::ImplicitObjectLifetimeDefault | hir::LifetimeName::Static =
430 self.0.push(lt.span);
435 pub struct IsSuggestableVisitor<'tcx> {
437 infer_suggestable: bool,
440 impl<'tcx> TypeVisitor<'tcx> for IsSuggestableVisitor<'tcx> {
443 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
445 Infer(InferTy::TyVar(_)) if self.infer_suggestable => {}
451 | GeneratorWitness(..)
455 return ControlFlow::Break(());
459 let parent = self.tcx.parent(*did);
460 if let hir::def::DefKind::TyAlias | hir::def::DefKind::AssocTy = self.tcx.def_kind(parent)
461 && let Opaque(parent_did, _) = self.tcx.type_of(parent).kind()
466 return ControlFlow::Break(());
470 Dynamic(dty, _, _) => {
472 match pred.skip_binder() {
473 ExistentialPredicate::Trait(_) | ExistentialPredicate::Projection(_) => {
476 _ => return ControlFlow::Break(()),
482 // FIXME: It would be nice to make this not use string manipulation,
483 // but it's pretty hard to do this, since `ty::ParamTy` is missing
484 // sufficient info to determine if it is synthetic, and we don't
485 // always have a convenient way of getting `ty::Generics` at the call
486 // sites we invoke `IsSuggestable::is_suggestable`.
487 if param.name.as_str().starts_with("impl ") {
488 return ControlFlow::Break(());
495 t.super_visit_with(self)
498 fn visit_const(&mut self, c: Const<'tcx>) -> ControlFlow<Self::BreakTy> {
500 ConstKind::Infer(InferConst::Var(_)) if self.infer_suggestable => {}
503 | ConstKind::Bound(..)
504 | ConstKind::Placeholder(..)
505 | ConstKind::Error(..) => {
506 return ControlFlow::Break(());
511 c.super_visit_with(self)