1 //! Error Reporting Code for the inference engine
3 //! Because of the way inference, and in particular region inference,
4 //! works, it often happens that errors are not detected until far after
5 //! the relevant line of code has been type-checked. Therefore, there is
6 //! an elaborate system to track why a particular constraint in the
7 //! inference graph arose so that we can explain to the user what gave
8 //! rise to a particular error.
10 //! The system is based around a set of "origin" types. An "origin" is the
11 //! reason that a constraint or inference variable arose. There are
12 //! different "origin" enums for different kinds of constraints/variables
13 //! (e.g., `TypeOrigin`, `RegionVariableOrigin`). An origin always has
14 //! a span, but also more information so that we can generate a meaningful
17 //! Having a catalog of all the different reasons an error can arise is
18 //! also useful for other reasons, like cross-referencing FAQs etc, though
19 //! we are not really taking advantage of this yet.
21 //! # Region Inference
23 //! Region inference is particularly tricky because it always succeeds "in
24 //! the moment" and simply registers a constraint. Then, at the end, we
25 //! can compute the full graph and report errors, so we need to be able to
26 //! store and later report what gave rise to the conflicting constraints.
30 //! Determining whether `T1 <: T2` often involves a number of subtypes and
31 //! subconstraints along the way. A "TypeTrace" is an extended version
32 //! of an origin that traces the types and other values that were being
33 //! compared. It is not necessarily comprehensive (in fact, at the time of
34 //! this writing it only tracks the root values being compared) but I'd
35 //! like to extend it to include significant "waypoints". For example, if
36 //! you are comparing `(T1, T2) <: (T3, T4)`, and the problem is that `T2
37 //! <: T4` fails, I'd like the trace to include enough information to say
38 //! "in the 2nd element of the tuple". Similarly, failures when comparing
39 //! arguments or return types in fn types should be able to cite the
40 //! specific position, etc.
44 //! Of course, there is still a LOT of code in typeck that has yet to be
45 //! ported to this system, and which relies on string concatenation at the
46 //! time of error detection.
48 use super::lexical_region_resolve::RegionResolutionError;
49 use super::region_constraints::GenericKind;
50 use super::{InferCtxt, RegionVariableOrigin, SubregionOrigin, TypeTrace, ValuePairs};
53 use crate::infer::error_reporting::nice_region_error::find_anon_type::find_anon_type;
54 use crate::traits::error_reporting::report_object_safety_error;
56 IfExpressionCause, MatchExpressionArmCause, ObligationCause, ObligationCauseCode,
57 StatementAsExpression,
60 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
61 use rustc_errors::{pluralize, struct_span_err, Diagnostic, ErrorGuaranteed};
62 use rustc_errors::{Applicability, DiagnosticBuilder, DiagnosticStyledString, MultiSpan};
64 use rustc_hir::def_id::{DefId, LocalDefId};
65 use rustc_hir::lang_items::LangItem;
67 use rustc_middle::dep_graph::DepContext;
68 use rustc_middle::ty::print::with_no_trimmed_paths;
69 use rustc_middle::ty::{
70 self, error::TypeError, Binder, List, Region, Subst, Ty, TyCtxt, TypeFoldable,
71 TypeSuperVisitable, TypeVisitable,
73 use rustc_span::{sym, symbol::kw, BytePos, DesugaringKind, Pos, Span};
74 use rustc_target::spec::abi;
75 use std::ops::ControlFlow;
76 use std::{cmp, fmt, iter};
81 pub use need_type_info::TypeAnnotationNeeded;
83 pub mod nice_region_error;
85 pub(super) fn note_and_explain_region<'tcx>(
89 region: ty::Region<'tcx>,
91 alt_span: Option<Span>,
93 let (description, span) = match *region {
94 ty::ReEarlyBound(_) | ty::ReFree(_) | ty::ReStatic => {
95 msg_span_from_free_region(tcx, region, alt_span)
98 ty::ReEmpty(ty::UniverseIndex::ROOT) => ("the empty lifetime".to_owned(), alt_span),
100 // uh oh, hope no user ever sees THIS
101 ty::ReEmpty(ui) => (format!("the empty lifetime in universe {:?}", ui), alt_span),
103 ty::RePlaceholder(_) => return,
105 // FIXME(#13998) RePlaceholder should probably print like
106 // ReFree rather than dumping Debug output on the user.
108 // We shouldn't really be having unification failures with ReVar
109 // and ReLateBound though.
110 ty::ReVar(_) | ty::ReLateBound(..) | ty::ReErased => {
111 (format!("lifetime {:?}", region), alt_span)
115 emit_msg_span(err, prefix, description, span, suffix);
118 fn explain_free_region<'tcx>(
120 err: &mut Diagnostic,
122 region: ty::Region<'tcx>,
125 let (description, span) = msg_span_from_free_region(tcx, region, None);
127 label_msg_span(err, prefix, description, span, suffix);
130 fn msg_span_from_free_region<'tcx>(
132 region: ty::Region<'tcx>,
133 alt_span: Option<Span>,
134 ) -> (String, Option<Span>) {
136 ty::ReEarlyBound(_) | ty::ReFree(_) => {
137 let (msg, span) = msg_span_from_early_bound_and_free_regions(tcx, region);
140 ty::ReStatic => ("the static lifetime".to_owned(), alt_span),
141 ty::ReEmpty(ty::UniverseIndex::ROOT) => ("an empty lifetime".to_owned(), alt_span),
142 ty::ReEmpty(ui) => (format!("an empty lifetime in universe {:?}", ui), alt_span),
143 _ => bug!("{:?}", region),
147 fn msg_span_from_early_bound_and_free_regions<'tcx>(
149 region: ty::Region<'tcx>,
150 ) -> (String, Span) {
151 let scope = region.free_region_binding_scope(tcx).expect_local();
153 ty::ReEarlyBound(ref br) => {
154 let mut sp = tcx.def_span(scope);
156 tcx.hir().get_generics(scope).and_then(|generics| generics.get_named(br.name))
160 let text = if br.has_name() {
161 format!("the lifetime `{}` as defined here", br.name)
163 format!("the anonymous lifetime as defined here")
167 ty::ReFree(ref fr) => {
168 if !fr.bound_region.is_named()
169 && let Some((ty, _)) = find_anon_type(tcx, region, &fr.bound_region)
171 ("the anonymous lifetime defined here".to_string(), ty.span)
173 match fr.bound_region {
174 ty::BoundRegionKind::BrNamed(_, name) => {
175 let mut sp = tcx.def_span(scope);
177 tcx.hir().get_generics(scope).and_then(|generics| generics.get_named(name))
181 let text = if name == kw::UnderscoreLifetime {
182 format!("the anonymous lifetime as defined here")
184 format!("the lifetime `{}` as defined here", name)
189 format!("the anonymous lifetime #{} defined here", idx + 1),
193 format!("the lifetime `{}` as defined here", region),
204 err: &mut Diagnostic,
210 let message = format!("{}{}{}", prefix, description, suffix);
212 if let Some(span) = span {
213 err.span_note(span, &message);
220 err: &mut Diagnostic,
226 let message = format!("{}{}{}", prefix, description, suffix);
228 if let Some(span) = span {
229 err.span_label(span, &message);
235 pub fn unexpected_hidden_region_diagnostic<'tcx>(
239 hidden_region: ty::Region<'tcx>,
240 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
241 let mut err = struct_span_err!(
245 "hidden type for `impl Trait` captures lifetime that does not appear in bounds",
248 // Explain the region we are capturing.
249 match *hidden_region {
250 ty::ReEmpty(ty::UniverseIndex::ROOT) => {
251 // All lifetimes shorter than the function body are `empty` in
252 // lexical region resolution. The default explanation of "an empty
253 // lifetime" isn't really accurate here.
254 let message = format!(
255 "hidden type `{}` captures lifetime smaller than the function body",
258 err.span_note(span, &message);
260 ty::ReEarlyBound(_) | ty::ReFree(_) | ty::ReStatic | ty::ReEmpty(_) => {
261 // Assuming regionck succeeded (*), we ought to always be
262 // capturing *some* region from the fn header, and hence it
263 // ought to be free. So under normal circumstances, we will go
264 // down this path which gives a decent human readable
267 // (*) if not, the `tainted_by_errors` field would be set to
268 // `Some(ErrorGuaranteed)` in any case, so we wouldn't be here at all.
272 &format!("hidden type `{}` captures ", hidden_ty),
276 if let Some(reg_info) = tcx.is_suitable_region(hidden_region) {
277 let fn_returns = tcx.return_type_impl_or_dyn_traits(reg_info.def_id);
278 nice_region_error::suggest_new_region_bound(
282 hidden_region.to_string(),
284 format!("captures `{}`", hidden_region),
290 // Ugh. This is a painful case: the hidden region is not one
291 // that we can easily summarize or explain. This can happen
293 // `src/test/ui/multiple-lifetimes/ordinary-bounds-unsuited.rs`:
296 // fn upper_bounds<'a, 'b>(a: Ordinary<'a>, b: Ordinary<'b>) -> impl Trait<'a, 'b> {
297 // if condition() { a } else { b }
301 // Here the captured lifetime is the intersection of `'a` and
302 // `'b`, which we can't quite express.
304 // We can at least report a really cryptic error for now.
305 note_and_explain_region(
308 &format!("hidden type `{}` captures ", hidden_ty),
319 impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
320 pub fn report_region_errors(
322 generic_param_scope: LocalDefId,
323 errors: &[RegionResolutionError<'tcx>],
325 debug!("report_region_errors(): {} errors to start", errors.len());
327 // try to pre-process the errors, which will group some of them
328 // together into a `ProcessedErrors` group:
329 let errors = self.process_errors(errors);
331 debug!("report_region_errors: {} errors after preprocessing", errors.len());
333 for error in errors {
334 debug!("report_region_errors: error = {:?}", error);
336 if !self.try_report_nice_region_error(&error) {
337 match error.clone() {
338 // These errors could indicate all manner of different
339 // problems with many different solutions. Rather
340 // than generate a "one size fits all" error, what we
341 // attempt to do is go through a number of specific
342 // scenarios and try to find the best way to present
343 // the error. If all of these fails, we fall back to a rather
344 // general bit of code that displays the error information
345 RegionResolutionError::ConcreteFailure(origin, sub, sup) => {
346 if sub.is_placeholder() || sup.is_placeholder() {
347 self.report_placeholder_failure(origin, sub, sup).emit();
349 self.report_concrete_failure(origin, sub, sup).emit();
353 RegionResolutionError::GenericBoundFailure(origin, param_ty, sub) => {
354 self.report_generic_bound_failure(
363 RegionResolutionError::SubSupConflict(
372 if sub_r.is_placeholder() {
373 self.report_placeholder_failure(sub_origin, sub_r, sup_r).emit();
374 } else if sup_r.is_placeholder() {
375 self.report_placeholder_failure(sup_origin, sub_r, sup_r).emit();
377 self.report_sub_sup_conflict(
378 var_origin, sub_origin, sub_r, sup_origin, sup_r,
383 RegionResolutionError::UpperBoundUniverseConflict(
390 assert!(sup_r.is_placeholder());
392 // Make a dummy value for the "sub region" --
393 // this is the initial value of the
394 // placeholder. In practice, we expect more
395 // tailored errors that don't really use this
397 let sub_r = self.tcx.mk_region(ty::ReEmpty(var_universe));
399 self.report_placeholder_failure(sup_origin, sub_r, sup_r).emit();
406 // This method goes through all the errors and try to group certain types
407 // of error together, for the purpose of suggesting explicit lifetime
408 // parameters to the user. This is done so that we can have a more
409 // complete view of what lifetimes should be the same.
410 // If the return value is an empty vector, it means that processing
411 // failed (so the return value of this method should not be used).
413 // The method also attempts to weed out messages that seem like
414 // duplicates that will be unhelpful to the end-user. But
415 // obviously it never weeds out ALL errors.
418 errors: &[RegionResolutionError<'tcx>],
419 ) -> Vec<RegionResolutionError<'tcx>> {
420 debug!("process_errors()");
422 // We want to avoid reporting generic-bound failures if we can
423 // avoid it: these have a very high rate of being unhelpful in
424 // practice. This is because they are basically secondary
425 // checks that test the state of the region graph after the
426 // rest of inference is done, and the other kinds of errors
427 // indicate that the region constraint graph is internally
428 // inconsistent, so these test results are likely to be
431 // Therefore, we filter them out of the list unless they are
432 // the only thing in the list.
434 let is_bound_failure = |e: &RegionResolutionError<'tcx>| match *e {
435 RegionResolutionError::GenericBoundFailure(..) => true,
436 RegionResolutionError::ConcreteFailure(..)
437 | RegionResolutionError::SubSupConflict(..)
438 | RegionResolutionError::UpperBoundUniverseConflict(..) => false,
441 let mut errors = if errors.iter().all(|e| is_bound_failure(e)) {
444 errors.iter().filter(|&e| !is_bound_failure(e)).cloned().collect()
447 // sort the errors by span, for better error message stability.
448 errors.sort_by_key(|u| match *u {
449 RegionResolutionError::ConcreteFailure(ref sro, _, _) => sro.span(),
450 RegionResolutionError::GenericBoundFailure(ref sro, _, _) => sro.span(),
451 RegionResolutionError::SubSupConflict(_, ref rvo, _, _, _, _, _) => rvo.span(),
452 RegionResolutionError::UpperBoundUniverseConflict(_, ref rvo, _, _, _) => rvo.span(),
457 /// Adds a note if the types come from similarly named crates
458 fn check_and_note_conflicting_crates(&self, err: &mut Diagnostic, terr: &TypeError<'tcx>) {
459 use hir::def_id::CrateNum;
460 use rustc_hir::definitions::DisambiguatedDefPathData;
461 use ty::print::Printer;
462 use ty::subst::GenericArg;
464 struct AbsolutePathPrinter<'tcx> {
468 struct NonTrivialPath;
470 impl<'tcx> Printer<'tcx> for AbsolutePathPrinter<'tcx> {
471 type Error = NonTrivialPath;
473 type Path = Vec<String>;
476 type DynExistential = !;
479 fn tcx<'a>(&'a self) -> TyCtxt<'tcx> {
483 fn print_region(self, _region: ty::Region<'_>) -> Result<Self::Region, Self::Error> {
487 fn print_type(self, _ty: Ty<'tcx>) -> Result<Self::Type, Self::Error> {
491 fn print_dyn_existential(
493 _predicates: &'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>,
494 ) -> Result<Self::DynExistential, Self::Error> {
498 fn print_const(self, _ct: ty::Const<'tcx>) -> Result<Self::Const, Self::Error> {
502 fn path_crate(self, cnum: CrateNum) -> Result<Self::Path, Self::Error> {
503 Ok(vec![self.tcx.crate_name(cnum).to_string()])
508 _trait_ref: Option<ty::TraitRef<'tcx>>,
509 ) -> Result<Self::Path, Self::Error> {
515 _print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
516 _disambiguated_data: &DisambiguatedDefPathData,
518 _trait_ref: Option<ty::TraitRef<'tcx>>,
519 ) -> Result<Self::Path, Self::Error> {
524 print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
525 disambiguated_data: &DisambiguatedDefPathData,
526 ) -> Result<Self::Path, Self::Error> {
527 let mut path = print_prefix(self)?;
528 path.push(disambiguated_data.to_string());
531 fn path_generic_args(
533 print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
534 _args: &[GenericArg<'tcx>],
535 ) -> Result<Self::Path, Self::Error> {
540 let report_path_match = |err: &mut Diagnostic, did1: DefId, did2: DefId| {
541 // Only external crates, if either is from a local
542 // module we could have false positives
543 if !(did1.is_local() || did2.is_local()) && did1.krate != did2.krate {
545 |def_id| AbsolutePathPrinter { tcx: self.tcx }.print_def_path(def_id, &[]);
547 // We compare strings because DefPath can be different
548 // for imported and non-imported crates
549 let same_path = || -> Result<_, NonTrivialPath> {
550 Ok(self.tcx.def_path_str(did1) == self.tcx.def_path_str(did2)
551 || abs_path(did1)? == abs_path(did2)?)
553 if same_path().unwrap_or(false) {
554 let crate_name = self.tcx.crate_name(did1.krate);
556 "perhaps two different versions of crate `{}` are being used?",
563 TypeError::Sorts(ref exp_found) => {
564 // if they are both "path types", there's a chance of ambiguity
565 // due to different versions of the same crate
566 if let (&ty::Adt(exp_adt, _), &ty::Adt(found_adt, _)) =
567 (exp_found.expected.kind(), exp_found.found.kind())
569 report_path_match(err, exp_adt.did(), found_adt.did());
572 TypeError::Traits(ref exp_found) => {
573 report_path_match(err, exp_found.expected, exp_found.found);
575 _ => (), // FIXME(#22750) handle traits and stuff
579 fn note_error_origin(
581 err: &mut Diagnostic,
582 cause: &ObligationCause<'tcx>,
583 exp_found: Option<ty::error::ExpectedFound<Ty<'tcx>>>,
584 terr: &TypeError<'tcx>,
586 match *cause.code() {
587 ObligationCauseCode::Pattern { origin_expr: true, span: Some(span), root_ty } => {
588 let ty = self.resolve_vars_if_possible(root_ty);
589 if !matches!(ty.kind(), ty::Infer(ty::InferTy::TyVar(_) | ty::InferTy::FreshTy(_)))
591 // don't show type `_`
592 if span.desugaring_kind() == Some(DesugaringKind::ForLoop)
593 && let ty::Adt(def, substs) = ty.kind()
594 && Some(def.did()) == self.tcx.get_diagnostic_item(sym::Option)
596 err.span_label(span, format!("this is an iterator with items of type `{}`", substs.type_at(0)));
598 err.span_label(span, format!("this expression has type `{}`", ty));
601 if let Some(ty::error::ExpectedFound { found, .. }) = exp_found
602 && ty.is_box() && ty.boxed_ty() == found
603 && let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span)
607 "consider dereferencing the boxed value",
608 format!("*{}", snippet),
609 Applicability::MachineApplicable,
613 ObligationCauseCode::Pattern { origin_expr: false, span: Some(span), .. } => {
614 err.span_label(span, "expected due to this");
616 ObligationCauseCode::MatchExpressionArm(box MatchExpressionArmCause {
626 opt_suggest_box_span,
630 hir::MatchSource::TryDesugar => {
631 if let Some(ty::error::ExpectedFound { expected, .. }) = exp_found {
632 let scrut_expr = self.tcx.hir().expect_expr(scrut_hir_id);
633 let scrut_ty = if let hir::ExprKind::Call(_, args) = &scrut_expr.kind {
634 let arg_expr = args.first().expect("try desugaring call w/out arg");
635 self.in_progress_typeck_results.and_then(|typeck_results| {
636 typeck_results.borrow().expr_ty_opt(arg_expr)
639 bug!("try desugaring w/out call expr as scrutinee");
643 Some(ty) if expected == ty => {
644 let source_map = self.tcx.sess.source_map();
646 source_map.end_point(cause.span),
647 "try removing this `?`",
649 Applicability::MachineApplicable,
657 // `prior_arm_ty` can be `!`, `expected` will have better info when present.
658 let t = self.resolve_vars_if_possible(match exp_found {
659 Some(ty::error::ExpectedFound { expected, .. }) => expected,
662 let source_map = self.tcx.sess.source_map();
663 let mut any_multiline_arm = source_map.is_multiline(arm_span);
664 if prior_arms.len() <= 4 {
665 for sp in prior_arms {
666 any_multiline_arm |= source_map.is_multiline(*sp);
667 err.span_label(*sp, format!("this is found to be of type `{}`", t));
669 } else if let Some(sp) = prior_arms.last() {
670 any_multiline_arm |= source_map.is_multiline(*sp);
673 format!("this and all prior arms are found to be of type `{}`", t),
676 let outer_error_span = if any_multiline_arm {
677 // Cover just `match` and the scrutinee expression, not
678 // the entire match body, to reduce diagram noise.
679 cause.span.shrink_to_lo().to(scrut_span)
683 let msg = "`match` arms have incompatible types";
684 err.span_label(outer_error_span, msg);
685 self.suggest_remove_semi_or_return_binding(
694 if let Some(ret_sp) = opt_suggest_box_span {
695 // Get return type span and point to it.
696 self.suggest_boxing_for_return_impl_trait(
699 prior_arms.iter().chain(std::iter::once(&arm_span)).map(|s| *s),
704 ObligationCauseCode::IfExpression(box IfExpressionCause {
710 opt_suggest_box_span,
712 let then_span = self.find_block_span_from_hir_id(then_id);
713 let else_span = self.find_block_span_from_hir_id(then_id);
714 err.span_label(then_span, "expected because of this");
715 if let Some(sp) = outer_span {
716 err.span_label(sp, "`if` and `else` have incompatible types");
718 self.suggest_remove_semi_or_return_binding(
727 if let Some(ret_sp) = opt_suggest_box_span {
728 self.suggest_boxing_for_return_impl_trait(
731 [then_span, else_span].into_iter(),
735 ObligationCauseCode::LetElse => {
736 err.help("try adding a diverging expression, such as `return` or `panic!(..)`");
737 err.help("...or use `match` instead of `let...else`");
740 if let ObligationCauseCode::BindingObligation(_, binding_span) =
741 cause.code().peel_derives()
743 if matches!(terr, TypeError::RegionsPlaceholderMismatch) {
744 err.span_note(*binding_span, "the lifetime requirement is introduced here");
751 fn suggest_remove_semi_or_return_binding(
753 err: &mut Diagnostic,
754 first_id: Option<hir::HirId>,
757 second_id: Option<hir::HirId>,
761 let remove_semicolon =
762 [(first_id, second_ty), (second_id, first_ty)].into_iter().find_map(|(id, ty)| {
763 let hir::Node::Block(blk) = self.tcx.hir().get(id?) else { return None };
764 self.could_remove_semicolon(blk, ty)
766 match remove_semicolon {
767 Some((sp, StatementAsExpression::NeedsBoxing)) => {
768 err.multipart_suggestion(
769 "consider removing this semicolon and boxing the expressions",
771 (first_span.shrink_to_lo(), "Box::new(".to_string()),
772 (first_span.shrink_to_hi(), ")".to_string()),
773 (second_span.shrink_to_lo(), "Box::new(".to_string()),
774 (second_span.shrink_to_hi(), ")".to_string()),
777 Applicability::MachineApplicable,
780 Some((sp, StatementAsExpression::CorrectType)) => {
781 err.span_suggestion_short(
783 "consider removing this semicolon",
785 Applicability::MachineApplicable,
789 for (id, ty) in [(first_id, second_ty), (second_id, first_ty)] {
791 && let hir::Node::Block(blk) = self.tcx.hir().get(id)
792 && self.consider_returning_binding(blk, ty, err)
801 fn suggest_boxing_for_return_impl_trait(
803 err: &mut Diagnostic,
805 arm_spans: impl Iterator<Item = Span>,
807 err.multipart_suggestion(
808 "you could change the return type to be a boxed trait object",
810 (return_sp.with_hi(return_sp.lo() + BytePos(4)), "Box<dyn".to_string()),
811 (return_sp.shrink_to_hi(), ">".to_string()),
813 Applicability::MaybeIncorrect,
817 [(sp.shrink_to_lo(), "Box::new(".to_string()), (sp.shrink_to_hi(), ")".to_string())]
820 .collect::<Vec<_>>();
821 err.multipart_suggestion(
822 "if you change the return type to expect trait objects, box the returned expressions",
824 Applicability::MaybeIncorrect,
828 /// Given that `other_ty` is the same as a type argument for `name` in `sub`, populate `value`
829 /// highlighting `name` and every type argument that isn't at `pos` (which is `other_ty`), and
830 /// populate `other_value` with `other_ty`.
834 /// ^^^^--------^ this is highlighted
836 /// | this type argument is exactly the same as the other type, not highlighted
837 /// this is highlighted
839 /// -------- this type is the same as a type argument in the other type, not highlighted
843 value: &mut DiagnosticStyledString,
844 other_value: &mut DiagnosticStyledString,
846 sub: ty::subst::SubstsRef<'tcx>,
850 // `value` and `other_value` hold two incomplete type representation for display.
851 // `name` is the path of both types being compared. `sub`
852 value.push_highlighted(name);
855 value.push_highlighted("<");
858 // Output the lifetimes for the first type
862 let s = lifetime.to_string();
863 if s.is_empty() { "'_".to_string() } else { s }
867 if !lifetimes.is_empty() {
868 if sub.regions().count() < len {
869 value.push_normal(lifetimes + ", ");
871 value.push_normal(lifetimes);
875 // Highlight all the type arguments that aren't at `pos` and compare the type argument at
876 // `pos` and `other_ty`.
877 for (i, type_arg) in sub.types().enumerate() {
879 let values = self.cmp(type_arg, other_ty);
880 value.0.extend((values.0).0);
881 other_value.0.extend((values.1).0);
883 value.push_highlighted(type_arg.to_string());
886 if len > 0 && i != len - 1 {
887 value.push_normal(", ");
891 value.push_highlighted(">");
895 /// If `other_ty` is the same as a type argument present in `sub`, highlight `path` in `t1_out`,
896 /// as that is the difference to the other type.
898 /// For the following code:
900 /// ```ignore (illustrative)
901 /// let x: Foo<Bar<Qux>> = foo::<Bar<Qux>>();
904 /// The type error output will behave in the following way:
908 /// ^^^^--------^ this is highlighted
910 /// | this type argument is exactly the same as the other type, not highlighted
911 /// this is highlighted
913 /// -------- this type is the same as a type argument in the other type, not highlighted
917 mut t1_out: &mut DiagnosticStyledString,
918 mut t2_out: &mut DiagnosticStyledString,
920 sub: &'tcx [ty::GenericArg<'tcx>],
924 // FIXME/HACK: Go back to `SubstsRef` to use its inherent methods,
925 // ideally that shouldn't be necessary.
926 let sub = self.tcx.intern_substs(sub);
927 for (i, ta) in sub.types().enumerate() {
929 self.highlight_outer(&mut t1_out, &mut t2_out, path, sub, i, other_ty);
932 if let ty::Adt(def, _) = ta.kind() {
933 let path_ = self.tcx.def_path_str(def.did());
934 if path_ == other_path {
935 self.highlight_outer(&mut t1_out, &mut t2_out, path, sub, i, other_ty);
943 /// Adds a `,` to the type representation only if it is appropriate.
946 value: &mut DiagnosticStyledString,
947 other_value: &mut DiagnosticStyledString,
951 if len > 0 && pos != len - 1 {
952 value.push_normal(", ");
953 other_value.push_normal(", ");
957 /// Given two `fn` signatures highlight only sub-parts that are different.
960 sig1: &ty::PolyFnSig<'tcx>,
961 sig2: &ty::PolyFnSig<'tcx>,
962 ) -> (DiagnosticStyledString, DiagnosticStyledString) {
963 let get_lifetimes = |sig| {
964 use rustc_hir::def::Namespace;
965 let (_, sig, reg) = ty::print::FmtPrinter::new(self.tcx, Namespace::TypeNS)
966 .name_all_regions(sig)
968 let lts: Vec<String> = reg.into_iter().map(|(_, kind)| kind.to_string()).collect();
969 (if lts.is_empty() { String::new() } else { format!("for<{}> ", lts.join(", ")) }, sig)
972 let (lt1, sig1) = get_lifetimes(sig1);
973 let (lt2, sig2) = get_lifetimes(sig2);
975 // unsafe extern "C" for<'a> fn(&'a T) -> &'a T
977 DiagnosticStyledString::normal("".to_string()),
978 DiagnosticStyledString::normal("".to_string()),
981 // unsafe extern "C" for<'a> fn(&'a T) -> &'a T
983 values.0.push(sig1.unsafety.prefix_str(), sig1.unsafety != sig2.unsafety);
984 values.1.push(sig2.unsafety.prefix_str(), sig1.unsafety != sig2.unsafety);
986 // unsafe extern "C" for<'a> fn(&'a T) -> &'a T
988 if sig1.abi != abi::Abi::Rust {
989 values.0.push(format!("extern {} ", sig1.abi), sig1.abi != sig2.abi);
991 if sig2.abi != abi::Abi::Rust {
992 values.1.push(format!("extern {} ", sig2.abi), sig1.abi != sig2.abi);
995 // unsafe extern "C" for<'a> fn(&'a T) -> &'a T
997 let lifetime_diff = lt1 != lt2;
998 values.0.push(lt1, lifetime_diff);
999 values.1.push(lt2, lifetime_diff);
1001 // unsafe extern "C" for<'a> fn(&'a T) -> &'a T
1003 values.0.push_normal("fn(");
1004 values.1.push_normal("fn(");
1006 // unsafe extern "C" for<'a> fn(&'a T) -> &'a T
1008 let len1 = sig1.inputs().len();
1009 let len2 = sig2.inputs().len();
1011 for (i, (l, r)) in iter::zip(sig1.inputs(), sig2.inputs()).enumerate() {
1012 let (x1, x2) = self.cmp(*l, *r);
1013 (values.0).0.extend(x1.0);
1014 (values.1).0.extend(x2.0);
1015 self.push_comma(&mut values.0, &mut values.1, len1, i);
1018 for (i, l) in sig1.inputs().iter().enumerate() {
1019 values.0.push_highlighted(l.to_string());
1021 values.0.push_highlighted(", ");
1024 for (i, r) in sig2.inputs().iter().enumerate() {
1025 values.1.push_highlighted(r.to_string());
1027 values.1.push_highlighted(", ");
1032 if sig1.c_variadic {
1034 values.0.push_normal(", ");
1036 values.0.push("...", !sig2.c_variadic);
1038 if sig2.c_variadic {
1040 values.1.push_normal(", ");
1042 values.1.push("...", !sig1.c_variadic);
1045 // unsafe extern "C" for<'a> fn(&'a T) -> &'a T
1047 values.0.push_normal(")");
1048 values.1.push_normal(")");
1050 // unsafe extern "C" for<'a> fn(&'a T) -> &'a T
1052 let output1 = sig1.output();
1053 let output2 = sig2.output();
1054 let (x1, x2) = self.cmp(output1, output2);
1055 if !output1.is_unit() {
1056 values.0.push_normal(" -> ");
1057 (values.0).0.extend(x1.0);
1059 if !output2.is_unit() {
1060 values.1.push_normal(" -> ");
1061 (values.1).0.extend(x2.0);
1066 /// Compares two given types, eliding parts that are the same between them and highlighting
1067 /// relevant differences, and return two representation of those types for highlighted printing.
1072 ) -> (DiagnosticStyledString, DiagnosticStyledString) {
1073 debug!("cmp(t1={}, t1.kind={:?}, t2={}, t2.kind={:?})", t1, t1.kind(), t2, t2.kind());
1076 fn equals<'tcx>(a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
1077 match (a.kind(), b.kind()) {
1078 (a, b) if *a == *b => true,
1079 (&ty::Int(_), &ty::Infer(ty::InferTy::IntVar(_)))
1081 &ty::Infer(ty::InferTy::IntVar(_)),
1082 &ty::Int(_) | &ty::Infer(ty::InferTy::IntVar(_)),
1084 | (&ty::Float(_), &ty::Infer(ty::InferTy::FloatVar(_)))
1086 &ty::Infer(ty::InferTy::FloatVar(_)),
1087 &ty::Float(_) | &ty::Infer(ty::InferTy::FloatVar(_)),
1093 fn push_ty_ref<'tcx>(
1094 region: ty::Region<'tcx>,
1096 mutbl: hir::Mutability,
1097 s: &mut DiagnosticStyledString,
1099 let mut r = region.to_string();
1105 s.push_highlighted(format!("&{}{}", r, mutbl.prefix_str()));
1106 s.push_normal(ty.to_string());
1109 // process starts here
1110 match (t1.kind(), t2.kind()) {
1111 (&ty::Adt(def1, sub1), &ty::Adt(def2, sub2)) => {
1112 let did1 = def1.did();
1113 let did2 = def2.did();
1114 let sub_no_defaults_1 =
1115 self.tcx.generics_of(did1).own_substs_no_defaults(self.tcx, sub1);
1116 let sub_no_defaults_2 =
1117 self.tcx.generics_of(did2).own_substs_no_defaults(self.tcx, sub2);
1118 let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new());
1119 let path1 = self.tcx.def_path_str(did1);
1120 let path2 = self.tcx.def_path_str(did2);
1122 // Easy case. Replace same types with `_` to shorten the output and highlight
1123 // the differing ones.
1124 // let x: Foo<Bar, Qux> = y::<Foo<Quz, Qux>>();
1127 // --- ^ type argument elided
1129 // highlighted in output
1130 values.0.push_normal(path1);
1131 values.1.push_normal(path2);
1133 // Avoid printing out default generic parameters that are common to both
1135 let len1 = sub_no_defaults_1.len();
1136 let len2 = sub_no_defaults_2.len();
1137 let common_len = cmp::min(len1, len2);
1138 let remainder1: Vec<_> = sub1.types().skip(common_len).collect();
1139 let remainder2: Vec<_> = sub2.types().skip(common_len).collect();
1140 let common_default_params =
1141 iter::zip(remainder1.iter().rev(), remainder2.iter().rev())
1142 .filter(|(a, b)| a == b)
1144 let len = sub1.len() - common_default_params;
1145 let consts_offset = len - sub1.consts().count();
1147 // Only draw `<...>` if there are lifetime/type arguments.
1149 values.0.push_normal("<");
1150 values.1.push_normal("<");
1153 fn lifetime_display(lifetime: Region<'_>) -> String {
1154 let s = lifetime.to_string();
1155 if s.is_empty() { "'_".to_string() } else { s }
1157 // At one point we'd like to elide all lifetimes here, they are irrelevant for
1158 // all diagnostics that use this output
1162 // ^^ ^^ --- type arguments are not elided
1164 // | elided as they were the same
1165 // not elided, they were different, but irrelevant
1167 // For bound lifetimes, keep the names of the lifetimes,
1168 // even if they are the same so that it's clear what's happening
1169 // if we have something like
1171 // for<'r, 's> fn(Inv<'r>, Inv<'s>)
1172 // for<'r> fn(Inv<'r>, Inv<'r>)
1173 let lifetimes = sub1.regions().zip(sub2.regions());
1174 for (i, lifetimes) in lifetimes.enumerate() {
1175 let l1 = lifetime_display(lifetimes.0);
1176 let l2 = lifetime_display(lifetimes.1);
1177 if lifetimes.0 != lifetimes.1 {
1178 values.0.push_highlighted(l1);
1179 values.1.push_highlighted(l2);
1180 } else if lifetimes.0.is_late_bound() {
1181 values.0.push_normal(l1);
1182 values.1.push_normal(l2);
1184 values.0.push_normal("'_");
1185 values.1.push_normal("'_");
1187 self.push_comma(&mut values.0, &mut values.1, len, i);
1190 // We're comparing two types with the same path, so we compare the type
1191 // arguments for both. If they are the same, do not highlight and elide from the
1195 // ^ elided type as this type argument was the same in both sides
1196 let type_arguments = sub1.types().zip(sub2.types());
1197 let regions_len = sub1.regions().count();
1198 let num_display_types = consts_offset - regions_len;
1199 for (i, (ta1, ta2)) in type_arguments.take(num_display_types).enumerate() {
1200 let i = i + regions_len;
1202 values.0.push_normal("_");
1203 values.1.push_normal("_");
1205 let (x1, x2) = self.cmp(ta1, ta2);
1206 (values.0).0.extend(x1.0);
1207 (values.1).0.extend(x2.0);
1209 self.push_comma(&mut values.0, &mut values.1, len, i);
1212 // Do the same for const arguments, if they are equal, do not highlight and
1213 // elide them from the output.
1214 let const_arguments = sub1.consts().zip(sub2.consts());
1215 for (i, (ca1, ca2)) in const_arguments.enumerate() {
1216 let i = i + consts_offset;
1218 values.0.push_normal("_");
1219 values.1.push_normal("_");
1221 values.0.push_highlighted(ca1.to_string());
1222 values.1.push_highlighted(ca2.to_string());
1224 self.push_comma(&mut values.0, &mut values.1, len, i);
1227 // Close the type argument bracket.
1228 // Only draw `<...>` if there are lifetime/type arguments.
1230 values.0.push_normal(">");
1231 values.1.push_normal(">");
1236 // let x: Foo<Bar<Qux> = foo::<Bar<Qux>>();
1238 // ------- this type argument is exactly the same as the other type
1254 // let x: Bar<Qux> = y:<Foo<Bar<Qux>>>();
1257 // ------- this type argument is exactly the same as the other type
1272 // We can't find anything in common, highlight relevant part of type path.
1273 // let x: foo::bar::Baz<Qux> = y:<foo::bar::Bar<Zar>>();
1274 // foo::bar::Baz<Qux>
1275 // foo::bar::Bar<Zar>
1276 // -------- this part of the path is different
1278 let t1_str = t1.to_string();
1279 let t2_str = t2.to_string();
1280 let min_len = t1_str.len().min(t2_str.len());
1282 const SEPARATOR: &str = "::";
1283 let separator_len = SEPARATOR.len();
1284 let split_idx: usize =
1285 iter::zip(t1_str.split(SEPARATOR), t2_str.split(SEPARATOR))
1286 .take_while(|(mod1_str, mod2_str)| mod1_str == mod2_str)
1287 .map(|(mod_str, _)| mod_str.len() + separator_len)
1291 "cmp: separator_len={}, split_idx={}, min_len={}",
1292 separator_len, split_idx, min_len
1295 if split_idx >= min_len {
1296 // paths are identical, highlight everything
1298 DiagnosticStyledString::highlighted(t1_str),
1299 DiagnosticStyledString::highlighted(t2_str),
1302 let (common, uniq1) = t1_str.split_at(split_idx);
1303 let (_, uniq2) = t2_str.split_at(split_idx);
1304 debug!("cmp: common={}, uniq1={}, uniq2={}", common, uniq1, uniq2);
1306 values.0.push_normal(common);
1307 values.0.push_highlighted(uniq1);
1308 values.1.push_normal(common);
1309 values.1.push_highlighted(uniq2);
1316 // When finding T != &T, highlight only the borrow
1317 (&ty::Ref(r1, ref_ty1, mutbl1), _) if equals(ref_ty1, t2) => {
1318 let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new());
1319 push_ty_ref(r1, ref_ty1, mutbl1, &mut values.0);
1320 values.1.push_normal(t2.to_string());
1323 (_, &ty::Ref(r2, ref_ty2, mutbl2)) if equals(t1, ref_ty2) => {
1324 let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new());
1325 values.0.push_normal(t1.to_string());
1326 push_ty_ref(r2, ref_ty2, mutbl2, &mut values.1);
1330 // When encountering &T != &mut T, highlight only the borrow
1331 (&ty::Ref(r1, ref_ty1, mutbl1), &ty::Ref(r2, ref_ty2, mutbl2))
1332 if equals(ref_ty1, ref_ty2) =>
1334 let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new());
1335 push_ty_ref(r1, ref_ty1, mutbl1, &mut values.0);
1336 push_ty_ref(r2, ref_ty2, mutbl2, &mut values.1);
1340 // When encountering tuples of the same size, highlight only the differing types
1341 (&ty::Tuple(substs1), &ty::Tuple(substs2)) if substs1.len() == substs2.len() => {
1343 (DiagnosticStyledString::normal("("), DiagnosticStyledString::normal("("));
1344 let len = substs1.len();
1345 for (i, (left, right)) in substs1.iter().zip(substs2).enumerate() {
1346 let (x1, x2) = self.cmp(left, right);
1347 (values.0).0.extend(x1.0);
1348 (values.1).0.extend(x2.0);
1349 self.push_comma(&mut values.0, &mut values.1, len, i);
1352 // Keep the output for single element tuples as `(ty,)`.
1353 values.0.push_normal(",");
1354 values.1.push_normal(",");
1356 values.0.push_normal(")");
1357 values.1.push_normal(")");
1361 (ty::FnDef(did1, substs1), ty::FnDef(did2, substs2)) => {
1362 let sig1 = self.tcx.bound_fn_sig(*did1).subst(self.tcx, substs1);
1363 let sig2 = self.tcx.bound_fn_sig(*did2).subst(self.tcx, substs2);
1364 let mut values = self.cmp_fn_sig(&sig1, &sig2);
1365 let path1 = format!(" {{{}}}", self.tcx.def_path_str_with_substs(*did1, substs1));
1366 let path2 = format!(" {{{}}}", self.tcx.def_path_str_with_substs(*did2, substs2));
1367 let same_path = path1 == path2;
1368 values.0.push(path1, !same_path);
1369 values.1.push(path2, !same_path);
1373 (ty::FnDef(did1, substs1), ty::FnPtr(sig2)) => {
1374 let sig1 = self.tcx.bound_fn_sig(*did1).subst(self.tcx, substs1);
1375 let mut values = self.cmp_fn_sig(&sig1, sig2);
1376 values.0.push_highlighted(format!(
1378 self.tcx.def_path_str_with_substs(*did1, substs1)
1383 (ty::FnPtr(sig1), ty::FnDef(did2, substs2)) => {
1384 let sig2 = self.tcx.bound_fn_sig(*did2).subst(self.tcx, substs2);
1385 let mut values = self.cmp_fn_sig(sig1, &sig2);
1386 values.1.push_normal(format!(
1388 self.tcx.def_path_str_with_substs(*did2, substs2)
1393 (ty::FnPtr(sig1), ty::FnPtr(sig2)) => self.cmp_fn_sig(sig1, sig2),
1397 // The two types are the same, elide and don't highlight.
1398 (DiagnosticStyledString::normal("_"), DiagnosticStyledString::normal("_"))
1400 // We couldn't find anything in common, highlight everything.
1402 DiagnosticStyledString::highlighted(t1.to_string()),
1403 DiagnosticStyledString::highlighted(t2.to_string()),
1410 /// Extend a type error with extra labels pointing at "non-trivial" types, like closures and
1411 /// the return type of `async fn`s.
1413 /// `secondary_span` gives the caller the opportunity to expand `diag` with a `span_label`.
1415 /// `swap_secondary_and_primary` is used to make projection errors in particular nicer by using
1416 /// the message in `secondary_span` as the primary label, and apply the message that would
1417 /// otherwise be used for the primary label on the `secondary_span` `Span`. This applies on
1418 /// E0271, like `src/test/ui/issues/issue-39970.stderr`.
1419 #[tracing::instrument(
1421 skip(self, diag, secondary_span, swap_secondary_and_primary, force_label)
1423 pub fn note_type_err(
1425 diag: &mut Diagnostic,
1426 cause: &ObligationCause<'tcx>,
1427 secondary_span: Option<(Span, String)>,
1428 mut values: Option<ValuePairs<'tcx>>,
1429 terr: &TypeError<'tcx>,
1430 swap_secondary_and_primary: bool,
1433 let span = cause.span();
1435 // For some types of errors, expected-found does not make
1436 // sense, so just ignore the values we were given.
1437 if let TypeError::CyclicTy(_) = terr {
1440 struct OpaqueTypesVisitor<'tcx> {
1441 types: FxHashMap<TyCategory, FxHashSet<Span>>,
1442 expected: FxHashMap<TyCategory, FxHashSet<Span>>,
1443 found: FxHashMap<TyCategory, FxHashSet<Span>>,
1448 impl<'tcx> OpaqueTypesVisitor<'tcx> {
1449 fn visit_expected_found(
1455 let mut types_visitor = OpaqueTypesVisitor {
1456 types: Default::default(),
1457 expected: Default::default(),
1458 found: Default::default(),
1462 // The visitor puts all the relevant encountered types in `self.types`, but in
1463 // here we want to visit two separate types with no relation to each other, so we
1464 // move the results from `types` to `expected` or `found` as appropriate.
1465 expected.visit_with(&mut types_visitor);
1466 std::mem::swap(&mut types_visitor.expected, &mut types_visitor.types);
1467 found.visit_with(&mut types_visitor);
1468 std::mem::swap(&mut types_visitor.found, &mut types_visitor.types);
1472 fn report(&self, err: &mut Diagnostic) {
1473 self.add_labels_for_types(err, "expected", &self.expected);
1474 self.add_labels_for_types(err, "found", &self.found);
1477 fn add_labels_for_types(
1479 err: &mut Diagnostic,
1481 types: &FxHashMap<TyCategory, FxHashSet<Span>>,
1483 for (key, values) in types.iter() {
1484 let count = values.len();
1485 let kind = key.descr();
1486 let mut returned_async_output_error = false;
1488 if sp.is_desugaring(DesugaringKind::Async) && !returned_async_output_error {
1489 if [sp] != err.span.primary_spans() {
1490 let mut span: MultiSpan = sp.into();
1491 span.push_span_label(
1494 "checked the `Output` of this `async fn`, {}{} {}{}",
1495 if count > 1 { "one of the " } else { "" },
1503 "while checking the return type of the `async fn`",
1509 "checked the `Output` of this `async fn`, {}{} {}{}",
1510 if count > 1 { "one of the " } else { "" },
1516 err.note("while checking the return type of the `async fn`");
1518 returned_async_output_error = true;
1524 if count == 1 { "the " } else { "one of the " },
1536 impl<'tcx> ty::visit::TypeVisitor<'tcx> for OpaqueTypesVisitor<'tcx> {
1537 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1538 if let Some((kind, def_id)) = TyCategory::from_ty(self.tcx, t) {
1539 let span = self.tcx.def_span(def_id);
1540 // Avoid cluttering the output when the "found" and error span overlap:
1542 // error[E0308]: mismatched types
1543 // --> $DIR/issue-20862.rs:2:5
1548 // | the found closure
1549 // | expected `()`, found closure
1551 // = note: expected unit type `()`
1552 // found closure `[closure@$DIR/issue-20862.rs:2:5: 2:14 x:_]`
1553 if !self.ignore_span.overlaps(span) {
1554 self.types.entry(kind).or_default().insert(span);
1557 t.super_visit_with(self)
1561 debug!("note_type_err(diag={:?})", diag);
1563 Variable(ty::error::ExpectedFound<Ty<'a>>),
1564 Fixed(&'static str),
1566 let (expected_found, exp_found, is_simple_error, values) = match values {
1567 None => (None, Mismatch::Fixed("type"), false, None),
1569 let values = self.resolve_vars_if_possible(values);
1570 let (is_simple_error, exp_found) = match values {
1571 ValuePairs::Terms(infer::ExpectedFound {
1572 expected: ty::Term::Ty(expected),
1573 found: ty::Term::Ty(found),
1575 let is_simple_err = expected.is_simple_text() && found.is_simple_text();
1576 OpaqueTypesVisitor::visit_expected_found(self.tcx, expected, found, span)
1581 Mismatch::Variable(infer::ExpectedFound { expected, found }),
1584 ValuePairs::TraitRefs(_) | ValuePairs::PolyTraitRefs(_) => {
1585 (false, Mismatch::Fixed("trait"))
1587 _ => (false, Mismatch::Fixed("type")),
1589 let vals = match self.values_str(values) {
1590 Some((expected, found)) => Some((expected, found)),
1592 // Derived error. Cancel the emitter.
1593 // NOTE(eddyb) this was `.cancel()`, but `diag`
1594 // is borrowed, so we can't fully defuse it.
1595 diag.downgrade_to_delayed_bug();
1599 (vals, exp_found, is_simple_error, Some(values))
1604 // Ignore msg for object safe coercion
1605 // since E0038 message will be printed
1606 TypeError::ObjectUnsafeCoercion(_) => {}
1608 let mut label_or_note = |span: Span, msg: &str| {
1609 if force_label || &[span] == diag.span.primary_spans() {
1610 diag.span_label(span, msg);
1612 diag.span_note(span, msg);
1615 if let Some((sp, msg)) = secondary_span {
1616 if swap_secondary_and_primary {
1617 let terr = if let Some(infer::ValuePairs::Terms(infer::ExpectedFound {
1622 format!("expected this to be `{}`", expected)
1626 label_or_note(sp, &terr);
1627 label_or_note(span, &msg);
1629 label_or_note(span, &terr.to_string());
1630 label_or_note(sp, &msg);
1633 label_or_note(span, &terr.to_string());
1637 if let Some((expected, found)) = expected_found {
1638 let (expected_label, found_label, exp_found) = match exp_found {
1639 Mismatch::Variable(ef) => (
1640 ef.expected.prefix_string(self.tcx),
1641 ef.found.prefix_string(self.tcx),
1644 Mismatch::Fixed(s) => (s.into(), s.into(), None),
1646 match (&terr, expected == found) {
1647 (TypeError::Sorts(values), extra) => {
1648 let sort_string = |ty: Ty<'tcx>| match (extra, ty.kind()) {
1649 (true, ty::Opaque(def_id, _)) => {
1650 let sm = self.tcx.sess.source_map();
1651 let pos = sm.lookup_char_pos(self.tcx.def_span(*def_id).lo());
1653 " (opaque type at <{}:{}:{}>)",
1654 sm.filename_for_diagnostics(&pos.file.name),
1656 pos.col.to_usize() + 1,
1659 (true, _) => format!(" ({})", ty.sort_string(self.tcx)),
1660 (false, _) => "".to_string(),
1662 if !(values.expected.is_simple_text() && values.found.is_simple_text())
1663 || (exp_found.map_or(false, |ef| {
1664 // This happens when the type error is a subset of the expectation,
1665 // like when you have two references but one is `usize` and the other
1666 // is `f32`. In those cases we still want to show the `note`. If the
1667 // value from `ef` is `Infer(_)`, then we ignore it.
1668 if !ef.expected.is_ty_infer() {
1669 ef.expected != values.expected
1670 } else if !ef.found.is_ty_infer() {
1671 ef.found != values.found
1677 diag.note_expected_found_extra(
1682 &sort_string(values.expected),
1683 &sort_string(values.found),
1687 (TypeError::ObjectUnsafeCoercion(_), _) => {
1688 diag.note_unsuccessful_coercion(found, expected);
1692 "note_type_err: exp_found={:?}, expected={:?} found={:?}",
1693 exp_found, expected, found
1695 if !is_simple_error || terr.must_include_note() {
1696 diag.note_expected_found(&expected_label, expected, &found_label, found);
1701 let exp_found = match exp_found {
1702 Mismatch::Variable(exp_found) => Some(exp_found),
1703 Mismatch::Fixed(_) => None,
1705 let exp_found = match terr {
1706 // `terr` has more accurate type information than `exp_found` in match expressions.
1707 ty::error::TypeError::Sorts(terr)
1708 if exp_found.map_or(false, |ef| terr.found == ef.found) =>
1714 debug!("exp_found {:?} terr {:?} cause.code {:?}", exp_found, terr, cause.code());
1715 if let Some(exp_found) = exp_found {
1716 let should_suggest_fixes =
1717 if let ObligationCauseCode::Pattern { root_ty, .. } = cause.code() {
1718 // Skip if the root_ty of the pattern is not the same as the expected_ty.
1719 // If these types aren't equal then we've probably peeled off a layer of arrays.
1720 self.same_type_modulo_infer(*root_ty, exp_found.expected)
1725 if should_suggest_fixes {
1726 self.suggest_tuple_pattern(cause, &exp_found, diag);
1727 self.suggest_as_ref_where_appropriate(span, &exp_found, diag);
1728 self.suggest_accessing_field_where_appropriate(cause, &exp_found, diag);
1729 self.suggest_await_on_expect_found(cause, span, &exp_found, diag);
1733 // In some (most?) cases cause.body_id points to actual body, but in some cases
1734 // it's an actual definition. According to the comments (e.g. in
1735 // librustc_typeck/check/compare_method.rs:compare_predicate_entailment) the latter
1736 // is relied upon by some other code. This might (or might not) need cleanup.
1737 let body_owner_def_id =
1738 self.tcx.hir().opt_local_def_id(cause.body_id).unwrap_or_else(|| {
1739 self.tcx.hir().body_owner_def_id(hir::BodyId { hir_id: cause.body_id })
1741 self.check_and_note_conflicting_crates(diag, terr);
1742 self.tcx.note_and_explain_type_err(diag, terr, cause, span, body_owner_def_id.to_def_id());
1744 if let Some(ValuePairs::PolyTraitRefs(exp_found)) = values
1745 && let ty::Closure(def_id, _) = exp_found.expected.skip_binder().self_ty().kind()
1746 && let Some(def_id) = def_id.as_local()
1748 let span = self.tcx.def_span(def_id);
1749 diag.span_note(span, "this closure does not fulfill the lifetime requirements");
1752 // It reads better to have the error origin as the final
1754 self.note_error_origin(diag, cause, exp_found, terr);
1759 fn suggest_tuple_pattern(
1761 cause: &ObligationCause<'tcx>,
1762 exp_found: &ty::error::ExpectedFound<Ty<'tcx>>,
1763 diag: &mut Diagnostic,
1765 // Heavily inspired by `FnCtxt::suggest_compatible_variants`, with
1766 // some modifications due to that being in typeck and this being in infer.
1767 if let ObligationCauseCode::Pattern { .. } = cause.code() {
1768 if let ty::Adt(expected_adt, substs) = exp_found.expected.kind() {
1769 let compatible_variants: Vec<_> = expected_adt
1773 variant.fields.len() == 1 && variant.ctor_kind == hir::def::CtorKind::Fn
1775 .filter_map(|variant| {
1776 let sole_field = &variant.fields[0];
1777 let sole_field_ty = sole_field.ty(self.tcx, substs);
1778 if self.same_type_modulo_infer(sole_field_ty, exp_found.found) {
1780 with_no_trimmed_paths!(self.tcx.def_path_str(variant.def_id));
1781 // FIXME #56861: DRYer prelude filtering
1782 if let Some(path) = variant_path.strip_prefix("std::prelude::") {
1783 if let Some((_, path)) = path.split_once("::") {
1784 return Some(path.to_string());
1793 match &compatible_variants[..] {
1796 diag.multipart_suggestion_verbose(
1797 &format!("try wrapping the pattern in `{}`", variant),
1799 (cause.span.shrink_to_lo(), format!("{}(", variant)),
1800 (cause.span.shrink_to_hi(), ")".to_string()),
1802 Applicability::MaybeIncorrect,
1806 // More than one matching variant.
1807 diag.multipart_suggestions(
1809 "try wrapping the pattern in a variant of `{}`",
1810 self.tcx.def_path_str(expected_adt.did())
1812 compatible_variants.into_iter().map(|variant| {
1814 (cause.span.shrink_to_lo(), format!("{}(", variant)),
1815 (cause.span.shrink_to_hi(), ")".to_string()),
1818 Applicability::MaybeIncorrect,
1826 pub fn get_impl_future_output_ty(&self, ty: Ty<'tcx>) -> Option<Binder<'tcx, Ty<'tcx>>> {
1827 if let ty::Opaque(def_id, substs) = ty.kind() {
1828 let future_trait = self.tcx.require_lang_item(LangItem::Future, None);
1830 let item_def_id = self.tcx.associated_item_def_ids(future_trait)[0];
1832 let bounds = self.tcx.bound_explicit_item_bounds(*def_id);
1834 for predicate in bounds.transpose_iter().map(|e| e.map_bound(|(p, _)| *p)) {
1835 let predicate = predicate.subst(self.tcx, substs);
1836 let output = predicate
1838 .map_bound(|kind| match kind {
1839 ty::PredicateKind::Projection(projection_predicate)
1840 if projection_predicate.projection_ty.item_def_id == item_def_id =>
1842 projection_predicate.term.ty()
1847 if output.is_some() {
1848 // We don't account for multiple `Future::Output = Ty` constraints.
1856 /// A possible error is to forget to add `.await` when using futures:
1858 /// ```compile_fail,E0308
1859 /// async fn make_u32() -> u32 {
1863 /// fn take_u32(x: u32) {}
1865 /// async fn foo() {
1866 /// let x = make_u32();
1871 /// This routine checks if the found type `T` implements `Future<Output=U>` where `U` is the
1872 /// expected type. If this is the case, and we are inside of an async body, it suggests adding
1873 /// `.await` to the tail of the expression.
1874 fn suggest_await_on_expect_found(
1876 cause: &ObligationCause<'tcx>,
1878 exp_found: &ty::error::ExpectedFound<Ty<'tcx>>,
1879 diag: &mut Diagnostic,
1882 "suggest_await_on_expect_found: exp_span={:?}, expected_ty={:?}, found_ty={:?}",
1883 exp_span, exp_found.expected, exp_found.found,
1886 if let ObligationCauseCode::CompareImplMethodObligation { .. } = cause.code() {
1891 self.get_impl_future_output_ty(exp_found.expected).map(Binder::skip_binder),
1892 self.get_impl_future_output_ty(exp_found.found).map(Binder::skip_binder),
1894 (Some(exp), Some(found)) if self.same_type_modulo_infer(exp, found) => match cause
1897 ObligationCauseCode::IfExpression(box IfExpressionCause { then_id, .. }) => {
1898 let then_span = self.find_block_span_from_hir_id(*then_id);
1899 diag.multipart_suggestion(
1900 "consider `await`ing on both `Future`s",
1902 (then_span.shrink_to_hi(), ".await".to_string()),
1903 (exp_span.shrink_to_hi(), ".await".to_string()),
1905 Applicability::MaybeIncorrect,
1908 ObligationCauseCode::MatchExpressionArm(box MatchExpressionArmCause {
1912 if let [.., arm_span] = &prior_arms[..] {
1913 diag.multipart_suggestion(
1914 "consider `await`ing on both `Future`s",
1916 (arm_span.shrink_to_hi(), ".await".to_string()),
1917 (exp_span.shrink_to_hi(), ".await".to_string()),
1919 Applicability::MaybeIncorrect,
1922 diag.help("consider `await`ing on both `Future`s");
1926 diag.help("consider `await`ing on both `Future`s");
1929 (_, Some(ty)) if self.same_type_modulo_infer(exp_found.expected, ty) => {
1930 diag.span_suggestion_verbose(
1931 exp_span.shrink_to_hi(),
1932 "consider `await`ing on the `Future`",
1934 Applicability::MaybeIncorrect,
1937 (Some(ty), _) if self.same_type_modulo_infer(ty, exp_found.found) => match cause.code()
1939 ObligationCauseCode::Pattern { span: Some(then_span), .. } => {
1940 diag.span_suggestion_verbose(
1941 then_span.shrink_to_hi(),
1942 "consider `await`ing on the `Future`",
1944 Applicability::MaybeIncorrect,
1947 ObligationCauseCode::IfExpression(box IfExpressionCause { then_id, .. }) => {
1948 let then_span = self.find_block_span_from_hir_id(*then_id);
1949 diag.span_suggestion_verbose(
1950 then_span.shrink_to_hi(),
1951 "consider `await`ing on the `Future`",
1953 Applicability::MaybeIncorrect,
1956 ObligationCauseCode::MatchExpressionArm(box MatchExpressionArmCause {
1960 diag.multipart_suggestion_verbose(
1961 "consider `await`ing on the `Future`",
1964 .map(|arm| (arm.shrink_to_hi(), ".await".to_string()))
1966 Applicability::MaybeIncorrect,
1975 fn suggest_accessing_field_where_appropriate(
1977 cause: &ObligationCause<'tcx>,
1978 exp_found: &ty::error::ExpectedFound<Ty<'tcx>>,
1979 diag: &mut Diagnostic,
1982 "suggest_accessing_field_where_appropriate(cause={:?}, exp_found={:?})",
1985 if let ty::Adt(expected_def, expected_substs) = exp_found.expected.kind() {
1986 if expected_def.is_enum() {
1990 if let Some((name, ty)) = expected_def
1994 .filter(|field| field.vis.is_accessible_from(field.did, self.tcx))
1995 .map(|field| (field.name, field.ty(self.tcx, expected_substs)))
1996 .find(|(_, ty)| self.same_type_modulo_infer(*ty, exp_found.found))
1998 if let ObligationCauseCode::Pattern { span: Some(span), .. } = *cause.code() {
1999 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
2000 let suggestion = if expected_def.is_struct() {
2001 format!("{}.{}", snippet, name)
2002 } else if expected_def.is_union() {
2003 format!("unsafe {{ {}.{} }}", snippet, name)
2007 diag.span_suggestion(
2010 "you might have meant to use field `{}` whose type is `{}`",
2014 Applicability::MaybeIncorrect,
2022 /// When encountering a case where `.as_ref()` on a `Result` or `Option` would be appropriate,
2024 fn suggest_as_ref_where_appropriate(
2027 exp_found: &ty::error::ExpectedFound<Ty<'tcx>>,
2028 diag: &mut Diagnostic,
2030 if let (ty::Adt(exp_def, exp_substs), ty::Ref(_, found_ty, _)) =
2031 (exp_found.expected.kind(), exp_found.found.kind())
2033 if let ty::Adt(found_def, found_substs) = *found_ty.kind() {
2034 let path_str = format!("{:?}", exp_def);
2035 if exp_def == &found_def {
2036 let opt_msg = "you can convert from `&Option<T>` to `Option<&T>` using \
2038 let result_msg = "you can convert from `&Result<T, E>` to \
2039 `Result<&T, &E>` using `.as_ref()`";
2040 let have_as_ref = &[
2041 ("std::option::Option", opt_msg),
2042 ("core::option::Option", opt_msg),
2043 ("std::result::Result", result_msg),
2044 ("core::result::Result", result_msg),
2046 if let Some(msg) = have_as_ref
2048 .find_map(|(path, msg)| (&path_str == path).then_some(msg))
2050 let mut show_suggestion = true;
2051 for (exp_ty, found_ty) in
2052 iter::zip(exp_substs.types(), found_substs.types())
2054 match *exp_ty.kind() {
2055 ty::Ref(_, exp_ty, _) => {
2056 match (exp_ty.kind(), found_ty.kind()) {
2060 | (ty::Infer(_), _) => {}
2061 _ if self.same_type_modulo_infer(exp_ty, found_ty) => {}
2062 _ => show_suggestion = false,
2065 ty::Param(_) | ty::Infer(_) => {}
2066 _ => show_suggestion = false,
2069 if let (Ok(snippet), true) =
2070 (self.tcx.sess.source_map().span_to_snippet(span), show_suggestion)
2072 diag.span_suggestion(
2075 format!("{}.as_ref()", snippet),
2076 Applicability::MachineApplicable,
2085 pub fn report_and_explain_type_error(
2087 trace: TypeTrace<'tcx>,
2088 terr: &TypeError<'tcx>,
2089 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
2090 use crate::traits::ObligationCauseCode::MatchExpressionArm;
2092 debug!("report_and_explain_type_error(trace={:?}, terr={:?})", trace, terr);
2094 let span = trace.cause.span();
2095 let failure_code = trace.cause.as_failure_code(terr);
2096 let mut diag = match failure_code {
2097 FailureCode::Error0038(did) => {
2098 let violations = self.tcx.object_safety_violations(did);
2099 report_object_safety_error(self.tcx, span, did, violations)
2101 FailureCode::Error0317(failure_str) => {
2102 struct_span_err!(self.tcx.sess, span, E0317, "{}", failure_str)
2104 FailureCode::Error0580(failure_str) => {
2105 struct_span_err!(self.tcx.sess, span, E0580, "{}", failure_str)
2107 FailureCode::Error0308(failure_str) => {
2108 let mut err = struct_span_err!(self.tcx.sess, span, E0308, "{}", failure_str);
2109 if let Some((expected, found)) = trace.values.ty() {
2110 match (expected.kind(), found.kind()) {
2111 (ty::Tuple(_), ty::Tuple(_)) => {}
2112 // If a tuple of length one was expected and the found expression has
2113 // parentheses around it, perhaps the user meant to write `(expr,)` to
2114 // build a tuple (issue #86100)
2115 (ty::Tuple(fields), _) => {
2116 self.emit_tuple_wrap_err(&mut err, span, found, fields)
2118 // If a character was expected and the found expression is a string literal
2119 // containing a single character, perhaps the user meant to write `'c'` to
2120 // specify a character literal (issue #92479)
2121 (ty::Char, ty::Ref(_, r, _)) if r.is_str() => {
2122 if let Ok(code) = self.tcx.sess().source_map().span_to_snippet(span)
2123 && let Some(code) = code.strip_prefix('"').and_then(|s| s.strip_suffix('"'))
2124 && code.chars().count() == 1
2126 err.span_suggestion(
2128 "if you meant to write a `char` literal, use single quotes",
2129 format!("'{}'", code),
2130 Applicability::MachineApplicable,
2134 // If a string was expected and the found expression is a character literal,
2135 // perhaps the user meant to write `"s"` to specify a string literal.
2136 (ty::Ref(_, r, _), ty::Char) if r.is_str() => {
2137 if let Ok(code) = self.tcx.sess().source_map().span_to_snippet(span) {
2139 code.strip_prefix('\'').and_then(|s| s.strip_suffix('\''))
2141 err.span_suggestion(
2143 "if you meant to write a `str` literal, use double quotes",
2144 format!("\"{}\"", code),
2145 Applicability::MachineApplicable,
2153 let code = trace.cause.code();
2154 if let &MatchExpressionArm(box MatchExpressionArmCause { source, .. }) = code
2155 && let hir::MatchSource::TryDesugar = source
2156 && let Some((expected_ty, found_ty)) = self.values_str(trace.values)
2159 "`?` operator cannot convert from `{}` to `{}`",
2161 expected_ty.content(),
2166 FailureCode::Error0644(failure_str) => {
2167 struct_span_err!(self.tcx.sess, span, E0644, "{}", failure_str)
2170 self.note_type_err(&mut diag, &trace.cause, None, Some(trace.values), terr, false, false);
2174 fn emit_tuple_wrap_err(
2176 err: &mut Diagnostic,
2179 expected_fields: &List<Ty<'tcx>>,
2181 let [expected_tup_elem] = expected_fields[..] else { return };
2183 if !self.same_type_modulo_infer(expected_tup_elem, found) {
2187 let Ok(code) = self.tcx.sess().source_map().span_to_snippet(span)
2190 let msg = "use a trailing comma to create a tuple with one element";
2191 if code.starts_with('(') && code.ends_with(')') {
2192 let before_close = span.hi() - BytePos::from_u32(1);
2193 err.span_suggestion(
2194 span.with_hi(before_close).shrink_to_hi(),
2197 Applicability::MachineApplicable,
2200 err.multipart_suggestion(
2202 vec![(span.shrink_to_lo(), "(".into()), (span.shrink_to_hi(), ",)".into())],
2203 Applicability::MachineApplicable,
2210 values: ValuePairs<'tcx>,
2211 ) -> Option<(DiagnosticStyledString, DiagnosticStyledString)> {
2213 infer::Regions(exp_found) => self.expected_found_str(exp_found),
2214 infer::Terms(exp_found) => self.expected_found_str_term(exp_found),
2215 infer::TraitRefs(exp_found) => {
2216 let pretty_exp_found = ty::error::ExpectedFound {
2217 expected: exp_found.expected.print_only_trait_path(),
2218 found: exp_found.found.print_only_trait_path(),
2220 match self.expected_found_str(pretty_exp_found) {
2221 Some((expected, found)) if expected == found => {
2222 self.expected_found_str(exp_found)
2227 infer::PolyTraitRefs(exp_found) => {
2228 let pretty_exp_found = ty::error::ExpectedFound {
2229 expected: exp_found.expected.print_only_trait_path(),
2230 found: exp_found.found.print_only_trait_path(),
2232 match self.expected_found_str(pretty_exp_found) {
2233 Some((expected, found)) if expected == found => {
2234 self.expected_found_str(exp_found)
2242 fn expected_found_str_term(
2244 exp_found: ty::error::ExpectedFound<ty::Term<'tcx>>,
2245 ) -> Option<(DiagnosticStyledString, DiagnosticStyledString)> {
2246 let exp_found = self.resolve_vars_if_possible(exp_found);
2247 if exp_found.references_error() {
2251 Some(match (exp_found.expected, exp_found.found) {
2252 (ty::Term::Ty(expected), ty::Term::Ty(found)) => self.cmp(expected, found),
2253 (expected, found) => (
2254 DiagnosticStyledString::highlighted(expected.to_string()),
2255 DiagnosticStyledString::highlighted(found.to_string()),
2260 /// Returns a string of the form "expected `{}`, found `{}`".
2261 fn expected_found_str<T: fmt::Display + TypeFoldable<'tcx>>(
2263 exp_found: ty::error::ExpectedFound<T>,
2264 ) -> Option<(DiagnosticStyledString, DiagnosticStyledString)> {
2265 let exp_found = self.resolve_vars_if_possible(exp_found);
2266 if exp_found.references_error() {
2271 DiagnosticStyledString::highlighted(exp_found.expected.to_string()),
2272 DiagnosticStyledString::highlighted(exp_found.found.to_string()),
2276 pub fn report_generic_bound_failure(
2278 generic_param_scope: LocalDefId,
2280 origin: Option<SubregionOrigin<'tcx>>,
2281 bound_kind: GenericKind<'tcx>,
2284 self.construct_generic_bound_failure(generic_param_scope, span, origin, bound_kind, sub)
2288 pub fn construct_generic_bound_failure(
2290 generic_param_scope: LocalDefId,
2292 origin: Option<SubregionOrigin<'tcx>>,
2293 bound_kind: GenericKind<'tcx>,
2295 ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
2296 // Attempt to obtain the span of the parameter so we can
2297 // suggest adding an explicit lifetime bound to it.
2298 let generics = self.tcx.generics_of(generic_param_scope);
2299 // type_param_span is (span, has_bounds)
2300 let type_param_span = match bound_kind {
2301 GenericKind::Param(ref param) => {
2302 // Account for the case where `param` corresponds to `Self`,
2303 // which doesn't have the expected type argument.
2304 if !(generics.has_self && param.index == 0) {
2305 let type_param = generics.type_param(param, self.tcx);
2306 type_param.def_id.as_local().map(|def_id| {
2307 // Get the `hir::Param` to verify whether it already has any bounds.
2308 // We do this to avoid suggesting code that ends up as `T: 'a'b`,
2309 // instead we suggest `T: 'a + 'b` in that case.
2310 let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
2311 let ast_generics = self.tcx.hir().get_generics(hir_id.owner);
2313 ast_generics.and_then(|g| g.bounds_span_for_suggestions(def_id));
2314 // `sp` only covers `T`, change it so that it covers
2315 // `T:` when appropriate
2316 if let Some(span) = bounds {
2319 let sp = self.tcx.def_span(def_id);
2320 (sp.shrink_to_hi(), false)
2331 let mut possible = (b'a'..=b'z').map(|c| format!("'{}", c as char));
2333 iter::successors(Some(generics), |g| g.parent.map(|p| self.tcx.generics_of(p)))
2334 .flat_map(|g| &g.params)
2335 .filter(|p| matches!(p.kind, ty::GenericParamDefKind::Lifetime))
2336 .map(|p| p.name.as_str())
2337 .collect::<Vec<_>>();
2339 .find(|candidate| !lts_names.contains(&&candidate[..]))
2340 .unwrap_or("'lt".to_string())
2343 let add_lt_sugg = generics
2346 .and_then(|param| param.def_id.as_local())
2347 .map(|def_id| (self.tcx.def_span(def_id).shrink_to_lo(), format!("{}, ", new_lt)));
2349 let labeled_user_string = match bound_kind {
2350 GenericKind::Param(ref p) => format!("the parameter type `{}`", p),
2351 GenericKind::Projection(ref p) => format!("the associated type `{}`", p),
2354 if let Some(SubregionOrigin::CompareImplMethodObligation {
2360 return self.report_extra_impl_obligation(
2364 &format!("`{}: {}`", bound_kind, sub),
2368 fn binding_suggestion<'tcx, S: fmt::Display>(
2369 err: &mut Diagnostic,
2370 type_param_span: Option<(Span, bool)>,
2371 bound_kind: GenericKind<'tcx>,
2374 let msg = "consider adding an explicit lifetime bound";
2375 if let Some((sp, has_lifetimes)) = type_param_span {
2377 if has_lifetimes { format!(" + {}", sub) } else { format!(": {}", sub) };
2378 err.span_suggestion_verbose(
2380 &format!("{}...", msg),
2382 Applicability::MaybeIncorrect, // Issue #41966
2385 let consider = format!("{} `{}: {}`...", msg, bound_kind, sub,);
2386 err.help(&consider);
2390 let new_binding_suggestion =
2391 |err: &mut Diagnostic, type_param_span: Option<(Span, bool)>| {
2392 let msg = "consider introducing an explicit lifetime bound";
2393 if let Some((sp, has_lifetimes)) = type_param_span {
2394 let suggestion = if has_lifetimes {
2395 format!(" + {}", new_lt)
2397 format!(": {}", new_lt)
2400 vec![(sp, suggestion), (span.shrink_to_hi(), format!(" + {}", new_lt))];
2401 if let Some(lt) = add_lt_sugg {
2403 sugg.rotate_right(1);
2405 // `MaybeIncorrect` due to issue #41966.
2406 err.multipart_suggestion(msg, sugg, Applicability::MaybeIncorrect);
2411 enum SubOrigin<'hir> {
2412 GAT(&'hir hir::Generics<'hir>),
2413 Impl(&'hir hir::Generics<'hir>),
2414 Trait(&'hir hir::Generics<'hir>),
2415 Fn(&'hir hir::Generics<'hir>),
2418 let sub_origin = 'origin: {
2420 ty::ReEarlyBound(ty::EarlyBoundRegion { def_id, .. }) => {
2421 let node = self.tcx.hir().get_if_local(def_id).unwrap();
2423 Node::GenericParam(param) => {
2424 for h in self.tcx.hir().parent_iter(param.hir_id) {
2425 break 'origin match h.1 {
2426 Node::ImplItem(hir::ImplItem {
2427 kind: hir::ImplItemKind::TyAlias(..),
2430 }) => SubOrigin::GAT(generics),
2431 Node::ImplItem(hir::ImplItem {
2432 kind: hir::ImplItemKind::Fn(..),
2435 }) => SubOrigin::Fn(generics),
2436 Node::TraitItem(hir::TraitItem {
2437 kind: hir::TraitItemKind::Type(..),
2440 }) => SubOrigin::GAT(generics),
2441 Node::TraitItem(hir::TraitItem {
2442 kind: hir::TraitItemKind::Fn(..),
2445 }) => SubOrigin::Fn(generics),
2446 Node::Item(hir::Item {
2447 kind: hir::ItemKind::Trait(_, _, generics, _, _),
2449 }) => SubOrigin::Trait(generics),
2450 Node::Item(hir::Item {
2451 kind: hir::ItemKind::Impl(hir::Impl { generics, .. }),
2453 }) => SubOrigin::Impl(generics),
2454 Node::Item(hir::Item {
2455 kind: hir::ItemKind::Fn(_, generics, _),
2457 }) => SubOrigin::Fn(generics),
2469 debug!(?sub_origin);
2471 let mut err = match (*sub, sub_origin) {
2472 // In the case of GATs, we have to be careful. If we a type parameter `T` on an impl,
2473 // but a lifetime `'a` on an associated type, then we might need to suggest adding
2474 // `where T: 'a`. Importantly, this is on the GAT span, not on the `T` declaration.
2475 (ty::ReEarlyBound(ty::EarlyBoundRegion { name: _, .. }), SubOrigin::GAT(generics)) => {
2476 // Does the required lifetime have a nice name we can print?
2477 let mut err = struct_span_err!(
2481 "{} may not live long enough",
2484 let pred = format!("{}: {}", bound_kind, sub);
2485 let suggestion = format!("{} {}", generics.add_where_or_trailing_comma(), pred,);
2486 err.span_suggestion(
2487 generics.tail_span_for_predicate_suggestion(),
2488 "consider adding a where clause",
2490 Applicability::MaybeIncorrect,
2495 ty::ReEarlyBound(ty::EarlyBoundRegion { name, .. })
2496 | ty::ReFree(ty::FreeRegion { bound_region: ty::BrNamed(_, name), .. }),
2498 ) if name != kw::UnderscoreLifetime => {
2499 // Does the required lifetime have a nice name we can print?
2500 let mut err = struct_span_err!(
2504 "{} may not live long enough",
2507 // Explicitly use the name instead of `sub`'s `Display` impl. The `Display` impl
2508 // for the bound is not suitable for suggestions when `-Zverbose` is set because it
2509 // uses `Debug` output, so we handle it specially here so that suggestions are
2511 binding_suggestion(&mut err, type_param_span, bound_kind, name);
2515 (ty::ReStatic, _) => {
2516 // Does the required lifetime have a nice name we can print?
2517 let mut err = struct_span_err!(
2521 "{} may not live long enough",
2524 binding_suggestion(&mut err, type_param_span, bound_kind, "'static");
2529 // If not, be less specific.
2530 let mut err = struct_span_err!(
2534 "{} may not live long enough",
2537 note_and_explain_region(
2540 &format!("{} must be valid for ", labeled_user_string),
2545 if let Some(infer::RelateParamBound(_, t, _)) = origin {
2546 let return_impl_trait =
2547 self.tcx.return_type_impl_trait(generic_param_scope).is_some();
2548 let t = self.resolve_vars_if_possible(t);
2551 // fn get_later<G, T>(g: G, dest: &mut T) -> impl FnOnce() + '_
2553 // fn get_later<'a, G: 'a, T>(g: G, dest: &mut T) -> impl FnOnce() + '_ + 'a
2554 ty::Closure(_, _substs) | ty::Opaque(_, _substs) if return_impl_trait => {
2555 new_binding_suggestion(&mut err, type_param_span);
2558 binding_suggestion(&mut err, type_param_span, bound_kind, new_lt);
2566 if let Some(origin) = origin {
2567 self.note_region_origin(&mut err, &origin);
2572 fn report_sub_sup_conflict(
2574 var_origin: RegionVariableOrigin,
2575 sub_origin: SubregionOrigin<'tcx>,
2576 sub_region: Region<'tcx>,
2577 sup_origin: SubregionOrigin<'tcx>,
2578 sup_region: Region<'tcx>,
2580 let mut err = self.report_inference_failure(var_origin);
2582 note_and_explain_region(
2585 "first, the lifetime cannot outlive ",
2591 debug!("report_sub_sup_conflict: var_origin={:?}", var_origin);
2592 debug!("report_sub_sup_conflict: sub_region={:?}", sub_region);
2593 debug!("report_sub_sup_conflict: sub_origin={:?}", sub_origin);
2594 debug!("report_sub_sup_conflict: sup_region={:?}", sup_region);
2595 debug!("report_sub_sup_conflict: sup_origin={:?}", sup_origin);
2597 if let (&infer::Subtype(ref sup_trace), &infer::Subtype(ref sub_trace)) =
2598 (&sup_origin, &sub_origin)
2600 debug!("report_sub_sup_conflict: sup_trace={:?}", sup_trace);
2601 debug!("report_sub_sup_conflict: sub_trace={:?}", sub_trace);
2602 debug!("report_sub_sup_conflict: sup_trace.values={:?}", sup_trace.values);
2603 debug!("report_sub_sup_conflict: sub_trace.values={:?}", sub_trace.values);
2605 if let (Some((sup_expected, sup_found)), Some((sub_expected, sub_found))) =
2606 (self.values_str(sup_trace.values), self.values_str(sub_trace.values))
2608 if sub_expected == sup_expected && sub_found == sup_found {
2609 note_and_explain_region(
2612 "...but the lifetime must also be valid for ",
2618 sup_trace.cause.span,
2619 &format!("...so that the {}", sup_trace.cause.as_requirement_str()),
2622 err.note_expected_found(&"", sup_expected, &"", sup_found);
2629 self.note_region_origin(&mut err, &sup_origin);
2631 note_and_explain_region(
2634 "but, the lifetime must be valid for ",
2640 self.note_region_origin(&mut err, &sub_origin);
2644 /// Determine whether an error associated with the given span and definition
2645 /// should be treated as being caused by the implicit `From` conversion
2646 /// within `?` desugaring.
2647 pub fn is_try_conversion(&self, span: Span, trait_def_id: DefId) -> bool {
2648 span.is_desugaring(DesugaringKind::QuestionMark)
2649 && self.tcx.is_diagnostic_item(sym::From, trait_def_id)
2652 /// Structurally compares two types, modulo any inference variables.
2654 /// Returns `true` if two types are equal, or if one type is an inference variable compatible
2655 /// with the other type. A TyVar inference type is compatible with any type, and an IntVar or
2656 /// FloatVar inference type are compatible with themselves or their concrete types (Int and
2657 /// Float types, respectively). When comparing two ADTs, these rules apply recursively.
2658 pub fn same_type_modulo_infer(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
2659 let (a, b) = self.resolve_vars_if_possible((a, b));
2660 match (a.kind(), b.kind()) {
2661 (&ty::Adt(def_a, substs_a), &ty::Adt(def_b, substs_b)) => {
2668 .zip(substs_b.types())
2669 .all(|(a, b)| self.same_type_modulo_infer(a, b))
2671 (&ty::FnDef(did_a, substs_a), &ty::FnDef(did_b, substs_b)) => {
2678 .zip(substs_b.types())
2679 .all(|(a, b)| self.same_type_modulo_infer(a, b))
2681 (&ty::Int(_) | &ty::Uint(_), &ty::Infer(ty::InferTy::IntVar(_)))
2683 &ty::Infer(ty::InferTy::IntVar(_)),
2684 &ty::Int(_) | &ty::Uint(_) | &ty::Infer(ty::InferTy::IntVar(_)),
2686 | (&ty::Float(_), &ty::Infer(ty::InferTy::FloatVar(_)))
2688 &ty::Infer(ty::InferTy::FloatVar(_)),
2689 &ty::Float(_) | &ty::Infer(ty::InferTy::FloatVar(_)),
2691 | (&ty::Infer(ty::InferTy::TyVar(_)), _)
2692 | (_, &ty::Infer(ty::InferTy::TyVar(_))) => true,
2693 (&ty::Ref(_, ty_a, mut_a), &ty::Ref(_, ty_b, mut_b)) => {
2694 mut_a == mut_b && self.same_type_modulo_infer(ty_a, ty_b)
2696 (&ty::RawPtr(a), &ty::RawPtr(b)) => {
2697 a.mutbl == b.mutbl && self.same_type_modulo_infer(a.ty, b.ty)
2699 (&ty::Slice(a), &ty::Slice(b)) => self.same_type_modulo_infer(a, b),
2700 (&ty::Array(a_ty, a_ct), &ty::Array(b_ty, b_ct)) => {
2701 self.same_type_modulo_infer(a_ty, b_ty) && a_ct == b_ct
2703 (&ty::Tuple(a), &ty::Tuple(b)) => {
2704 if a.len() != b.len() {
2707 std::iter::zip(a.iter(), b.iter()).all(|(a, b)| self.same_type_modulo_infer(a, b))
2709 (&ty::FnPtr(a), &ty::FnPtr(b)) => {
2710 let a = a.skip_binder().inputs_and_output;
2711 let b = b.skip_binder().inputs_and_output;
2712 if a.len() != b.len() {
2715 std::iter::zip(a.iter(), b.iter()).all(|(a, b)| self.same_type_modulo_infer(a, b))
2717 // FIXME(compiler-errors): This needs to be generalized more
2723 impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
2724 fn report_inference_failure(
2726 var_origin: RegionVariableOrigin,
2727 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
2728 let br_string = |br: ty::BoundRegionKind| {
2729 let mut s = match br {
2730 ty::BrNamed(_, name) => name.to_string(),
2738 let var_description = match var_origin {
2739 infer::MiscVariable(_) => String::new(),
2740 infer::PatternRegion(_) => " for pattern".to_string(),
2741 infer::AddrOfRegion(_) => " for borrow expression".to_string(),
2742 infer::Autoref(_) => " for autoref".to_string(),
2743 infer::Coercion(_) => " for automatic coercion".to_string(),
2744 infer::LateBoundRegion(_, br, infer::FnCall) => {
2745 format!(" for lifetime parameter {}in function call", br_string(br))
2747 infer::LateBoundRegion(_, br, infer::HigherRankedType) => {
2748 format!(" for lifetime parameter {}in generic type", br_string(br))
2750 infer::LateBoundRegion(_, br, infer::AssocTypeProjection(def_id)) => format!(
2751 " for lifetime parameter {}in trait containing associated type `{}`",
2753 self.tcx.associated_item(def_id).name
2755 infer::EarlyBoundRegion(_, name) => format!(" for lifetime parameter `{}`", name),
2756 infer::UpvarRegion(ref upvar_id, _) => {
2757 let var_name = self.tcx.hir().name(upvar_id.var_path.hir_id);
2758 format!(" for capture of `{}` by closure", var_name)
2760 infer::Nll(..) => bug!("NLL variable found in lexical phase"),
2767 "cannot infer an appropriate lifetime{} due to conflicting requirements",
2773 pub enum FailureCode {
2775 Error0317(&'static str),
2776 Error0580(&'static str),
2777 Error0308(&'static str),
2778 Error0644(&'static str),
2781 pub trait ObligationCauseExt<'tcx> {
2782 fn as_failure_code(&self, terr: &TypeError<'tcx>) -> FailureCode;
2783 fn as_requirement_str(&self) -> &'static str;
2786 impl<'tcx> ObligationCauseExt<'tcx> for ObligationCause<'tcx> {
2787 fn as_failure_code(&self, terr: &TypeError<'tcx>) -> FailureCode {
2788 use self::FailureCode::*;
2789 use crate::traits::ObligationCauseCode::*;
2791 CompareImplMethodObligation { .. } => Error0308("method not compatible with trait"),
2792 CompareImplTypeObligation { .. } => Error0308("type not compatible with trait"),
2793 MatchExpressionArm(box MatchExpressionArmCause { source, .. }) => {
2794 Error0308(match source {
2795 hir::MatchSource::TryDesugar => "`?` operator has incompatible types",
2796 _ => "`match` arms have incompatible types",
2799 IfExpression { .. } => Error0308("`if` and `else` have incompatible types"),
2800 IfExpressionWithNoElse => Error0317("`if` may be missing an `else` clause"),
2801 LetElse => Error0308("`else` clause of `let...else` does not diverge"),
2802 MainFunctionType => Error0580("`main` function has wrong type"),
2803 StartFunctionType => Error0308("`#[start]` function has wrong type"),
2804 IntrinsicType => Error0308("intrinsic has wrong type"),
2805 MethodReceiver => Error0308("mismatched `self` parameter type"),
2807 // In the case where we have no more specific thing to
2808 // say, also take a look at the error code, maybe we can
2811 TypeError::CyclicTy(ty) if ty.is_closure() || ty.is_generator() => {
2812 Error0644("closure/generator type that references itself")
2814 TypeError::IntrinsicCast => {
2815 Error0308("cannot coerce intrinsics to function pointers")
2817 TypeError::ObjectUnsafeCoercion(did) => Error0038(*did),
2818 _ => Error0308("mismatched types"),
2823 fn as_requirement_str(&self) -> &'static str {
2824 use crate::traits::ObligationCauseCode::*;
2826 CompareImplMethodObligation { .. } => "method type is compatible with trait",
2827 CompareImplTypeObligation { .. } => "associated type is compatible with trait",
2828 ExprAssignable => "expression is assignable",
2829 IfExpression { .. } => "`if` and `else` have incompatible types",
2830 IfExpressionWithNoElse => "`if` missing an `else` returns `()`",
2831 MainFunctionType => "`main` function has the correct type",
2832 StartFunctionType => "`#[start]` function has the correct type",
2833 IntrinsicType => "intrinsic has the correct type",
2834 MethodReceiver => "method receiver has the correct type",
2835 _ => "types are compatible",
2840 /// This is a bare signal of what kind of type we're dealing with. `ty::TyKind` tracks
2841 /// extra information about each type, but we only care about the category.
2842 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
2843 pub enum TyCategory {
2846 Generator(hir::GeneratorKind),
2851 fn descr(&self) -> &'static str {
2853 Self::Closure => "closure",
2854 Self::Opaque => "opaque type",
2855 Self::Generator(gk) => gk.descr(),
2856 Self::Foreign => "foreign type",
2860 pub fn from_ty(tcx: TyCtxt<'_>, ty: Ty<'_>) -> Option<(Self, DefId)> {
2862 ty::Closure(def_id, _) => Some((Self::Closure, def_id)),
2863 ty::Opaque(def_id, _) => Some((Self::Opaque, def_id)),
2864 ty::Generator(def_id, ..) => {
2865 Some((Self::Generator(tcx.generator_kind(def_id).unwrap()), def_id))
2867 ty::Foreign(def_id) => Some((Self::Foreign, def_id)),
2873 impl<'tcx> InferCtxt<'_, 'tcx> {
2874 /// Given a [`hir::Block`], get the span of its last expression or
2875 /// statement, peeling off any inner blocks.
2876 pub fn find_block_span(&self, block: &'tcx hir::Block<'tcx>) -> Span {
2877 let block = block.innermost_block();
2878 if let Some(expr) = &block.expr {
2880 } else if let Some(stmt) = block.stmts.last() {
2881 // possibly incorrect trailing `;` in the else arm
2884 // empty block; point at its entirety
2889 /// Given a [`hir::HirId`] for a block, get the span of its last expression
2890 /// or statement, peeling off any inner blocks.
2891 pub fn find_block_span_from_hir_id(&self, hir_id: hir::HirId) -> Span {
2892 match self.tcx.hir().get(hir_id) {
2893 hir::Node::Block(blk) => self.find_block_span(blk),
2894 // The parser was in a weird state if either of these happen, but
2895 // it's better not to panic.
2896 hir::Node::Expr(e) => e.span,
2897 _ => rustc_span::DUMMY_SP,
2901 /// Be helpful when the user wrote `{... expr; }` and taking the `;` off
2902 /// is enough to fix the error.
2903 pub fn could_remove_semicolon(
2905 blk: &'tcx hir::Block<'tcx>,
2906 expected_ty: Ty<'tcx>,
2907 ) -> Option<(Span, StatementAsExpression)> {
2908 let blk = blk.innermost_block();
2909 // Do not suggest if we have a tail expr.
2910 if blk.expr.is_some() {
2913 let last_stmt = blk.stmts.last()?;
2914 let hir::StmtKind::Semi(ref last_expr) = last_stmt.kind else {
2917 let last_expr_ty = self.in_progress_typeck_results?.borrow().expr_ty_opt(*last_expr)?;
2918 let needs_box = match (last_expr_ty.kind(), expected_ty.kind()) {
2919 _ if last_expr_ty.references_error() => return None,
2920 _ if self.same_type_modulo_infer(last_expr_ty, expected_ty) => {
2921 StatementAsExpression::CorrectType
2923 (ty::Opaque(last_def_id, _), ty::Opaque(exp_def_id, _))
2924 if last_def_id == exp_def_id =>
2926 StatementAsExpression::CorrectType
2928 (ty::Opaque(last_def_id, last_bounds), ty::Opaque(exp_def_id, exp_bounds)) => {
2930 "both opaque, likely future {:?} {:?} {:?} {:?}",
2931 last_def_id, last_bounds, exp_def_id, exp_bounds
2934 let last_local_id = last_def_id.as_local()?;
2935 let exp_local_id = exp_def_id.as_local()?;
2938 &self.tcx.hir().expect_item(last_local_id).kind,
2939 &self.tcx.hir().expect_item(exp_local_id).kind,
2942 hir::ItemKind::OpaqueTy(hir::OpaqueTy { bounds: last_bounds, .. }),
2943 hir::ItemKind::OpaqueTy(hir::OpaqueTy { bounds: exp_bounds, .. }),
2944 ) if iter::zip(*last_bounds, *exp_bounds).all(|(left, right)| {
2945 match (left, right) {
2947 hir::GenericBound::Trait(tl, ml),
2948 hir::GenericBound::Trait(tr, mr),
2949 ) if tl.trait_ref.trait_def_id() == tr.trait_ref.trait_def_id()
2955 hir::GenericBound::LangItemTrait(langl, _, _, argsl),
2956 hir::GenericBound::LangItemTrait(langr, _, _, argsr),
2957 ) if langl == langr => {
2958 // FIXME: consider the bounds!
2959 debug!("{:?} {:?}", argsl, argsr);
2966 StatementAsExpression::NeedsBoxing
2968 _ => StatementAsExpression::CorrectType,
2973 let span = if last_stmt.span.from_expansion() {
2974 let mac_call = rustc_span::source_map::original_sp(last_stmt.span, blk.span);
2975 self.tcx.sess.source_map().mac_call_stmt_semi_span(mac_call)?
2977 last_stmt.span.with_lo(last_stmt.span.hi() - BytePos(1))
2979 Some((span, needs_box))
2982 /// Suggest returning a local binding with a compatible type if the block
2983 /// has no return expression.
2984 pub fn consider_returning_binding(
2986 blk: &'tcx hir::Block<'tcx>,
2987 expected_ty: Ty<'tcx>,
2988 err: &mut Diagnostic,
2990 let blk = blk.innermost_block();
2991 // Do not suggest if we have a tail expr.
2992 if blk.expr.is_some() {
2995 let mut shadowed = FxHashSet::default();
2996 let mut candidate_idents = vec![];
2997 let mut find_compatible_candidates = |pat: &hir::Pat<'_>| {
2998 if let hir::PatKind::Binding(_, hir_id, ident, _) = &pat.kind
2999 && let Some(pat_ty) = self
3000 .in_progress_typeck_results
3001 .and_then(|typeck_results| typeck_results.borrow().node_type_opt(*hir_id))
3003 let pat_ty = self.resolve_vars_if_possible(pat_ty);
3004 if self.same_type_modulo_infer(pat_ty, expected_ty)
3005 && !(pat_ty, expected_ty).references_error()
3006 && shadowed.insert(ident.name)
3008 candidate_idents.push((*ident, pat_ty));
3014 let hir = self.tcx.hir();
3015 for stmt in blk.stmts.iter().rev() {
3016 let hir::StmtKind::Local(local) = &stmt.kind else { continue; };
3017 local.pat.walk(&mut find_compatible_candidates);
3019 match hir.find(hir.get_parent_node(blk.hir_id)) {
3020 Some(hir::Node::Expr(hir::Expr { hir_id, .. })) => {
3021 match hir.find(hir.get_parent_node(*hir_id)) {
3022 Some(hir::Node::Arm(hir::Arm { pat, .. })) => {
3023 pat.walk(&mut find_compatible_candidates);
3026 hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, _, body), .. })
3027 | hir::Node::ImplItem(hir::ImplItem {
3028 kind: hir::ImplItemKind::Fn(_, body),
3031 | hir::Node::TraitItem(hir::TraitItem {
3032 kind: hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(body)),
3035 | hir::Node::Expr(hir::Expr {
3036 kind: hir::ExprKind::Closure(hir::Closure { body, .. }),
3040 for param in hir.body(*body).params {
3041 param.pat.walk(&mut find_compatible_candidates);
3044 Some(hir::Node::Expr(hir::Expr {
3047 hir::Expr { kind: hir::ExprKind::Let(let_), .. },
3052 })) if then_block.hir_id == *hir_id => {
3053 let_.pat.walk(&mut find_compatible_candidates);
3061 match &candidate_idents[..] {
3063 let sm = self.tcx.sess.source_map();
3064 if let Some(stmt) = blk.stmts.last() {
3065 let stmt_span = sm.stmt_span(stmt.span, blk.span);
3066 let sugg = if sm.is_multiline(blk.span)
3067 && let Some(spacing) = sm.indentation_before(stmt_span)
3069 format!("\n{spacing}{ident}")
3073 err.span_suggestion_verbose(
3074 stmt_span.shrink_to_hi(),
3075 format!("consider returning the local binding `{ident}`"),
3077 Applicability::MaybeIncorrect,
3080 let sugg = if sm.is_multiline(blk.span)
3081 && let Some(spacing) = sm.indentation_before(blk.span.shrink_to_lo())
3083 format!("\n{spacing} {ident}\n{spacing}")
3085 format!(" {ident} ")
3087 let left_span = sm.span_through_char(blk.span, '{').shrink_to_hi();
3088 err.span_suggestion_verbose(
3089 sm.span_extend_while(left_span, |c| c.is_whitespace()).unwrap_or(left_span),
3090 format!("consider returning the local binding `{ident}`"),
3092 Applicability::MaybeIncorrect,
3097 values if (1..3).contains(&values.len()) => {
3098 let spans = values.iter().map(|(ident, _)| ident.span).collect::<Vec<_>>();
3099 err.span_note(spans, "consider returning one of these bindings");