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(
154 generics: &hir::Generics<'_>,
155 suggestions: &mut Vec<(Span, String, SuggestChangingConstraintsMessage<'_>)>,
156 param: &hir::GenericParam<'_>,
157 def_id: Option<DefId>,
159 // See if there's a `?Sized` bound that can be removed to suggest that.
160 // First look at the `where` clause because we can have `where T: ?Sized`,
161 // then look at params.
162 for (where_pos, predicate) in generics.predicates.iter().enumerate() {
163 let WherePredicate::BoundPredicate(predicate) = predicate else {
166 if !predicate.is_param_bound(param.def_id.to_def_id()) {
170 for (pos, bound) in predicate.bounds.iter().enumerate() {
171 let hir::GenericBound::Trait(poly, hir::TraitBoundModifier::Maybe) = bound else {
174 if poly.trait_ref.trait_def_id() != def_id {
177 let sp = generics.span_for_bound_removal(where_pos, pos);
181 SuggestChangingConstraintsMessage::RemovingQSized,
187 /// Suggest restricting a type param with a new bound.
188 pub fn suggest_constraining_type_param(
190 generics: &hir::Generics<'_>,
191 err: &mut Diagnostic,
194 def_id: Option<DefId>,
196 suggest_constraining_type_params(
200 [(param_name, constraint, def_id)].into_iter(),
204 /// Suggest restricting a type param with a new bound.
205 pub fn suggest_constraining_type_params<'a>(
207 generics: &hir::Generics<'_>,
208 err: &mut Diagnostic,
209 param_names_and_constraints: impl Iterator<Item = (&'a str, &'a str, Option<DefId>)>,
211 let mut grouped = FxHashMap::default();
212 param_names_and_constraints.for_each(|(param_name, constraint, def_id)| {
213 grouped.entry(param_name).or_insert(Vec::new()).push((constraint, def_id))
216 let mut applicability = Applicability::MachineApplicable;
217 let mut suggestions = Vec::new();
219 for (param_name, mut constraints) in grouped {
220 let param = generics.params.iter().find(|p| p.name.ident().as_str() == param_name);
221 let Some(param) = param else { return false };
224 let mut sized_constraints =
225 constraints.drain_filter(|(_, def_id)| *def_id == tcx.lang_items().sized_trait());
226 if let Some((constraint, def_id)) = sized_constraints.next() {
227 applicability = Applicability::MaybeIncorrect;
231 &format!("this type parameter needs to be `{}`", constraint),
233 suggest_removing_unsized_bound(generics, &mut suggestions, param, def_id);
237 if constraints.is_empty() {
241 let mut constraint = constraints.iter().map(|&(c, _)| c).collect::<Vec<_>>();
244 let constraint = constraint.join(" + ");
245 let mut suggest_restrict = |span, bound_list_non_empty| {
248 if bound_list_non_empty {
249 format!(" + {}", constraint)
251 format!(" {}", constraint)
253 SuggestChangingConstraintsMessage::RestrictBoundFurther,
257 // When the type parameter has been provided bounds
260 // fn foo<T>(t: T) where T: Foo { ... }
263 // help: consider further restricting this bound with `+ Bar`
266 // fn foo<T>(t: T) where T: Foo { ... }
269 // replace with: ` + Bar`
271 // Or, if user has provided some bounds, suggest restricting them:
273 // fn foo<T: Foo>(t: T) { ... }
276 // help: consider further restricting this bound with `+ Bar`
278 // Suggestion for tools in this case is:
280 // fn foo<T: Foo>(t: T) { ... }
283 // replace with: `T: Bar +`
284 if let Some(span) = generics.bounds_span_for_suggestions(param.def_id) {
285 suggest_restrict(span, true);
289 if generics.has_where_clause_predicates {
290 // This part is a bit tricky, because using the `where` clause user can
291 // provide zero, one or many bounds for the same type parameter, so we
292 // have following cases to consider:
294 // When the type parameter has been provided zero bounds
297 // fn foo<X, Y>(x: X, y: Y) where Y: Foo { ... }
298 // - help: consider restricting this type parameter with `where X: Bar`
301 // fn foo<X, Y>(x: X, y: Y) where Y: Foo { ... }
302 // - insert: `, X: Bar`
304 generics.tail_span_for_predicate_suggestion(),
307 .map(|&(constraint, _)| format!(", {}: {}", param_name, constraint))
308 .collect::<String>(),
309 SuggestChangingConstraintsMessage::RestrictTypeFurther { ty: param_name },
314 // Additionally, there may be no `where` clause but the generic parameter has a default:
317 // trait Foo<T=()> {... }
318 // - help: consider further restricting this type parameter with `where T: Zar`
321 // trait Foo<T=()> {... }
322 // - insert: `where T: Zar`
323 if matches!(param.kind, hir::GenericParamKind::Type { default: Some(_), .. }) {
324 // Suggest a bound, but there is no existing `where` clause *and* the type param has a
325 // default (`<T=Foo>`), so we suggest adding `where T: Bar`.
327 generics.tail_span_for_predicate_suggestion(),
328 format!(" where {}: {}", param_name, constraint),
329 SuggestChangingConstraintsMessage::RestrictTypeFurther { ty: param_name },
334 // If user has provided a colon, don't suggest adding another:
336 // fn foo<T:>(t: T) { ... }
337 // - insert: consider restricting this type parameter with `T: Foo`
338 if let Some(colon_span) = param.colon_span {
340 colon_span.shrink_to_hi(),
341 format!(" {}", constraint),
342 SuggestChangingConstraintsMessage::RestrictType { ty: param_name },
347 // If user hasn't provided any bounds, suggest adding a new one:
349 // fn foo<T>(t: T) { ... }
350 // - help: consider restricting this type parameter with `T: Foo`
352 param.span.shrink_to_hi(),
353 format!(": {}", constraint),
354 SuggestChangingConstraintsMessage::RestrictType { ty: param_name },
358 if suggestions.len() == 1 {
359 let (span, suggestion, msg) = suggestions.pop().unwrap();
362 let msg = match msg {
363 SuggestChangingConstraintsMessage::RestrictBoundFurther => {
364 "consider further restricting this bound"
366 SuggestChangingConstraintsMessage::RestrictType { ty } => {
367 s = format!("consider restricting type parameter `{}`", ty);
370 SuggestChangingConstraintsMessage::RestrictTypeFurther { ty } => {
371 s = format!("consider further restricting type parameter `{}`", ty);
374 SuggestChangingConstraintsMessage::RemovingQSized => {
375 "consider removing the `?Sized` bound to make the type parameter `Sized`"
379 err.span_suggestion_verbose(span, msg, suggestion, applicability);
380 } else if suggestions.len() > 1 {
381 err.multipart_suggestion_verbose(
382 "consider restricting type parameters",
383 suggestions.into_iter().map(|(span, suggestion, _)| (span, suggestion)).collect(),
391 /// Collect al types that have an implicit `'static` obligation that we could suggest `'_` for.
392 pub struct TraitObjectVisitor<'tcx>(pub Vec<&'tcx hir::Ty<'tcx>>, pub crate::hir::map::Map<'tcx>);
394 impl<'v> hir::intravisit::Visitor<'v> for TraitObjectVisitor<'v> {
395 fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
397 hir::TyKind::TraitObject(
401 hir::LifetimeName::ImplicitObjectLifetimeDefault | hir::LifetimeName::Static,
408 hir::TyKind::OpaqueDef(item_id, _, _) => {
410 let item = self.1.item(item_id);
411 hir::intravisit::walk_item(self, item);
415 hir::intravisit::walk_ty(self, ty);
419 /// Collect al types that have an implicit `'static` obligation that we could suggest `'_` for.
420 pub struct StaticLifetimeVisitor<'tcx>(pub Vec<Span>, pub crate::hir::map::Map<'tcx>);
422 impl<'v> hir::intravisit::Visitor<'v> for StaticLifetimeVisitor<'v> {
423 fn visit_lifetime(&mut self, lt: &'v hir::Lifetime) {
424 if let hir::LifetimeName::ImplicitObjectLifetimeDefault | hir::LifetimeName::Static =
427 self.0.push(lt.span);
432 pub struct IsSuggestableVisitor<'tcx> {
434 infer_suggestable: bool,
437 impl<'tcx> TypeVisitor<'tcx> for IsSuggestableVisitor<'tcx> {
440 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
442 Infer(InferTy::TyVar(_)) if self.infer_suggestable => {}
448 | GeneratorWitness(..)
452 return ControlFlow::Break(());
456 let parent = self.tcx.parent(*did);
457 if let hir::def::DefKind::TyAlias | hir::def::DefKind::AssocTy = self.tcx.def_kind(parent)
458 && let Opaque(parent_did, _) = self.tcx.type_of(parent).kind()
463 return ControlFlow::Break(());
467 Dynamic(dty, _, _) => {
469 match pred.skip_binder() {
470 ExistentialPredicate::Trait(_) | ExistentialPredicate::Projection(_) => {
473 _ => return ControlFlow::Break(()),
479 // FIXME: It would be nice to make this not use string manipulation,
480 // but it's pretty hard to do this, since `ty::ParamTy` is missing
481 // sufficient info to determine if it is synthetic, and we don't
482 // always have a convenient way of getting `ty::Generics` at the call
483 // sites we invoke `IsSuggestable::is_suggestable`.
484 if param.name.as_str().starts_with("impl ") {
485 return ControlFlow::Break(());
492 t.super_visit_with(self)
495 fn visit_const(&mut self, c: Const<'tcx>) -> ControlFlow<Self::BreakTy> {
497 ConstKind::Infer(InferConst::Var(_)) if self.infer_suggestable => {}
500 | ConstKind::Bound(..)
501 | ConstKind::Placeholder(..)
502 | ConstKind::Error(..) => {
503 return ControlFlow::Break(());
508 c.super_visit_with(self)
512 #[derive(Diagnostic)]
513 #[diag(borrowck_const_not_used_in_type_alias)]
514 pub(super) struct ConstNotUsedTraitAlias {