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};
62 use rustc_errors::{Applicability, DiagnosticBuilder, DiagnosticStyledString};
64 use rustc_hir::def_id::DefId;
65 use rustc_hir::lang_items::LangItem;
66 use rustc_hir::{Item, ItemKind, Node};
67 use rustc_middle::dep_graph::DepContext;
68 use rustc_middle::ty::error::TypeError;
69 use rustc_middle::ty::{
71 subst::{GenericArgKind, Subst, SubstsRef},
72 Region, Ty, TyCtxt, TypeFoldable,
74 use rustc_span::{sym, BytePos, DesugaringKind, MultiSpan, Pos, Span};
75 use rustc_target::spec::abi;
76 use std::ops::ControlFlow;
77 use std::{cmp, fmt, iter};
82 pub use need_type_info::TypeAnnotationNeeded;
84 pub mod nice_region_error;
86 pub(super) fn note_and_explain_region<'tcx>(
88 err: &mut DiagnosticBuilder<'_>,
90 region: ty::Region<'tcx>,
92 alt_span: Option<Span>,
94 let (description, span) = match *region {
95 ty::ReEarlyBound(_) | ty::ReFree(_) | ty::ReStatic => {
96 msg_span_from_free_region(tcx, region, alt_span)
99 ty::ReEmpty(ty::UniverseIndex::ROOT) => ("the empty lifetime".to_owned(), alt_span),
101 // uh oh, hope no user ever sees THIS
102 ty::ReEmpty(ui) => (format!("the empty lifetime in universe {:?}", ui), alt_span),
104 ty::RePlaceholder(_) => return,
106 // FIXME(#13998) RePlaceholder should probably print like
107 // ReFree rather than dumping Debug output on the user.
109 // We shouldn't really be having unification failures with ReVar
110 // and ReLateBound though.
111 ty::ReVar(_) | ty::ReLateBound(..) | ty::ReErased => {
112 (format!("lifetime {:?}", region), alt_span)
116 emit_msg_span(err, prefix, description, span, suffix);
119 fn explain_free_region<'tcx>(
121 err: &mut DiagnosticBuilder<'_>,
123 region: ty::Region<'tcx>,
126 let (description, span) = msg_span_from_free_region(tcx, region, None);
128 label_msg_span(err, prefix, description, span, suffix);
131 fn msg_span_from_free_region<'tcx>(
133 region: ty::Region<'tcx>,
134 alt_span: Option<Span>,
135 ) -> (String, Option<Span>) {
137 ty::ReEarlyBound(_) | ty::ReFree(_) => {
138 let (msg, span) = msg_span_from_early_bound_and_free_regions(tcx, region);
141 ty::ReStatic => ("the static lifetime".to_owned(), alt_span),
142 ty::ReEmpty(ty::UniverseIndex::ROOT) => ("an empty lifetime".to_owned(), alt_span),
143 ty::ReEmpty(ui) => (format!("an empty lifetime in universe {:?}", ui), alt_span),
144 _ => bug!("{:?}", region),
148 fn msg_span_from_early_bound_and_free_regions<'tcx>(
150 region: ty::Region<'tcx>,
151 ) -> (String, Span) {
152 let sm = tcx.sess.source_map();
154 let scope = region.free_region_binding_scope(tcx);
155 let node = tcx.hir().local_def_id_to_hir_id(scope.expect_local());
157 ty::ReEarlyBound(ref br) => {
158 let mut sp = sm.guess_head_span(tcx.hir().span(node));
160 tcx.hir().get_generics(scope).and_then(|generics| generics.get_named(br.name))
164 (format!("the lifetime `{}` as defined here", br.name), sp)
166 ty::ReFree(ty::FreeRegion {
167 bound_region: ty::BoundRegionKind::BrNamed(_, name), ..
169 let mut sp = sm.guess_head_span(tcx.hir().span(node));
171 tcx.hir().get_generics(scope).and_then(|generics| generics.get_named(name))
175 (format!("the lifetime `{}` as defined here", name), sp)
177 ty::ReFree(ref fr) => match fr.bound_region {
179 if let Some((ty, _)) = find_anon_type(tcx, region, &fr.bound_region) {
180 ("the anonymous lifetime defined here".to_string(), ty.span)
183 format!("the anonymous lifetime #{} defined here", idx + 1),
184 tcx.hir().span(node),
189 format!("the lifetime `{}` as defined here", region),
190 sm.guess_head_span(tcx.hir().span(node)),
198 err: &mut DiagnosticBuilder<'_>,
204 let message = format!("{}{}{}", prefix, description, suffix);
206 if let Some(span) = span {
207 err.span_note(span, &message);
214 err: &mut DiagnosticBuilder<'_>,
220 let message = format!("{}{}{}", prefix, description, suffix);
222 if let Some(span) = span {
223 err.span_label(span, &message);
229 pub fn unexpected_hidden_region_diagnostic<'tcx>(
233 hidden_region: ty::Region<'tcx>,
234 ) -> DiagnosticBuilder<'tcx> {
235 let mut err = struct_span_err!(
239 "hidden type for `impl Trait` captures lifetime that does not appear in bounds",
242 // Explain the region we are capturing.
243 match hidden_region {
244 ty::ReEmpty(ty::UniverseIndex::ROOT) => {
245 // All lifetimes shorter than the function body are `empty` in
246 // lexical region resolution. The default explanation of "an empty
247 // lifetime" isn't really accurate here.
248 let message = format!(
249 "hidden type `{}` captures lifetime smaller than the function body",
252 err.span_note(span, &message);
254 ty::ReEarlyBound(_) | ty::ReFree(_) | ty::ReStatic | ty::ReEmpty(_) => {
255 // Assuming regionck succeeded (*), we ought to always be
256 // capturing *some* region from the fn header, and hence it
257 // ought to be free. So under normal circumstances, we will go
258 // down this path which gives a decent human readable
261 // (*) if not, the `tainted_by_errors` field would be set to
262 // `Some(ErrorReported)` in any case, so we wouldn't be here at all.
266 &format!("hidden type `{}` captures ", hidden_ty),
270 if let Some(reg_info) = tcx.is_suitable_region(hidden_region) {
271 let fn_returns = tcx.return_type_impl_or_dyn_traits(reg_info.def_id);
272 nice_region_error::suggest_new_region_bound(
276 hidden_region.to_string(),
278 format!("captures `{}`", hidden_region),
284 // Ugh. This is a painful case: the hidden region is not one
285 // that we can easily summarize or explain. This can happen
287 // `src/test/ui/multiple-lifetimes/ordinary-bounds-unsuited.rs`:
290 // fn upper_bounds<'a, 'b>(a: Ordinary<'a>, b: Ordinary<'b>) -> impl Trait<'a, 'b> {
291 // if condition() { a } else { b }
295 // Here the captured lifetime is the intersection of `'a` and
296 // `'b`, which we can't quite express.
298 // We can at least report a really cryptic error for now.
299 note_and_explain_region(
302 &format!("hidden type `{}` captures ", hidden_ty),
313 /// Structurally compares two types, modulo any inference variables.
315 /// Returns `true` if two types are equal, or if one type is an inference variable compatible
316 /// with the other type. A TyVar inference type is compatible with any type, and an IntVar or
317 /// FloatVar inference type are compatible with themselves or their concrete types (Int and
318 /// Float types, respectively). When comparing two ADTs, these rules apply recursively.
319 pub fn same_type_modulo_infer<'tcx>(a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
320 match (&a.kind(), &b.kind()) {
321 (&ty::Adt(did_a, substs_a), &ty::Adt(did_b, substs_b)) => {
326 substs_a.types().zip(substs_b.types()).all(|(a, b)| same_type_modulo_infer(a, b))
328 (&ty::Int(_), &ty::Infer(ty::InferTy::IntVar(_)))
329 | (&ty::Infer(ty::InferTy::IntVar(_)), &ty::Int(_) | &ty::Infer(ty::InferTy::IntVar(_)))
330 | (&ty::Float(_), &ty::Infer(ty::InferTy::FloatVar(_)))
332 &ty::Infer(ty::InferTy::FloatVar(_)),
333 &ty::Float(_) | &ty::Infer(ty::InferTy::FloatVar(_)),
335 | (&ty::Infer(ty::InferTy::TyVar(_)), _)
336 | (_, &ty::Infer(ty::InferTy::TyVar(_))) => true,
341 impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
342 pub fn report_region_errors(&self, errors: &Vec<RegionResolutionError<'tcx>>) {
343 debug!("report_region_errors(): {} errors to start", errors.len());
345 // try to pre-process the errors, which will group some of them
346 // together into a `ProcessedErrors` group:
347 let errors = self.process_errors(errors);
349 debug!("report_region_errors: {} errors after preprocessing", errors.len());
351 for error in errors {
352 debug!("report_region_errors: error = {:?}", error);
354 if !self.try_report_nice_region_error(&error) {
355 match error.clone() {
356 // These errors could indicate all manner of different
357 // problems with many different solutions. Rather
358 // than generate a "one size fits all" error, what we
359 // attempt to do is go through a number of specific
360 // scenarios and try to find the best way to present
361 // the error. If all of these fails, we fall back to a rather
362 // general bit of code that displays the error information
363 RegionResolutionError::ConcreteFailure(origin, sub, sup) => {
364 if sub.is_placeholder() || sup.is_placeholder() {
365 self.report_placeholder_failure(origin, sub, sup).emit();
367 self.report_concrete_failure(origin, sub, sup).emit();
371 RegionResolutionError::GenericBoundFailure(origin, param_ty, sub) => {
372 self.report_generic_bound_failure(
380 RegionResolutionError::SubSupConflict(
389 if sub_r.is_placeholder() {
390 self.report_placeholder_failure(sub_origin, sub_r, sup_r).emit();
391 } else if sup_r.is_placeholder() {
392 self.report_placeholder_failure(sup_origin, sub_r, sup_r).emit();
394 self.report_sub_sup_conflict(
395 var_origin, sub_origin, sub_r, sup_origin, sup_r,
400 RegionResolutionError::UpperBoundUniverseConflict(
407 assert!(sup_r.is_placeholder());
409 // Make a dummy value for the "sub region" --
410 // this is the initial value of the
411 // placeholder. In practice, we expect more
412 // tailored errors that don't really use this
414 let sub_r = self.tcx.mk_region(ty::ReEmpty(var_universe));
416 self.report_placeholder_failure(sup_origin, sub_r, sup_r).emit();
423 // This method goes through all the errors and try to group certain types
424 // of error together, for the purpose of suggesting explicit lifetime
425 // parameters to the user. This is done so that we can have a more
426 // complete view of what lifetimes should be the same.
427 // If the return value is an empty vector, it means that processing
428 // failed (so the return value of this method should not be used).
430 // The method also attempts to weed out messages that seem like
431 // duplicates that will be unhelpful to the end-user. But
432 // obviously it never weeds out ALL errors.
435 errors: &[RegionResolutionError<'tcx>],
436 ) -> Vec<RegionResolutionError<'tcx>> {
437 debug!("process_errors()");
439 // We want to avoid reporting generic-bound failures if we can
440 // avoid it: these have a very high rate of being unhelpful in
441 // practice. This is because they are basically secondary
442 // checks that test the state of the region graph after the
443 // rest of inference is done, and the other kinds of errors
444 // indicate that the region constraint graph is internally
445 // inconsistent, so these test results are likely to be
448 // Therefore, we filter them out of the list unless they are
449 // the only thing in the list.
451 let is_bound_failure = |e: &RegionResolutionError<'tcx>| match *e {
452 RegionResolutionError::GenericBoundFailure(..) => true,
453 RegionResolutionError::ConcreteFailure(..)
454 | RegionResolutionError::SubSupConflict(..)
455 | RegionResolutionError::UpperBoundUniverseConflict(..) => false,
458 let mut errors = if errors.iter().all(|e| is_bound_failure(e)) {
461 errors.iter().filter(|&e| !is_bound_failure(e)).cloned().collect()
464 // sort the errors by span, for better error message stability.
465 errors.sort_by_key(|u| match *u {
466 RegionResolutionError::ConcreteFailure(ref sro, _, _) => sro.span(),
467 RegionResolutionError::GenericBoundFailure(ref sro, _, _) => sro.span(),
468 RegionResolutionError::SubSupConflict(_, ref rvo, _, _, _, _, _) => rvo.span(),
469 RegionResolutionError::UpperBoundUniverseConflict(_, ref rvo, _, _, _) => rvo.span(),
474 /// Adds a note if the types come from similarly named crates
475 fn check_and_note_conflicting_crates(
477 err: &mut DiagnosticBuilder<'_>,
478 terr: &TypeError<'tcx>,
480 use hir::def_id::CrateNum;
481 use rustc_hir::definitions::DisambiguatedDefPathData;
482 use ty::print::Printer;
483 use ty::subst::GenericArg;
485 struct AbsolutePathPrinter<'tcx> {
489 struct NonTrivialPath;
491 impl<'tcx> Printer<'tcx> for AbsolutePathPrinter<'tcx> {
492 type Error = NonTrivialPath;
494 type Path = Vec<String>;
497 type DynExistential = !;
500 fn tcx<'a>(&'a self) -> TyCtxt<'tcx> {
504 fn print_region(self, _region: ty::Region<'_>) -> Result<Self::Region, Self::Error> {
508 fn print_type(self, _ty: Ty<'tcx>) -> Result<Self::Type, Self::Error> {
512 fn print_dyn_existential(
514 _predicates: &'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>,
515 ) -> Result<Self::DynExistential, Self::Error> {
519 fn print_const(self, _ct: &'tcx ty::Const<'tcx>) -> Result<Self::Const, Self::Error> {
523 fn path_crate(self, cnum: CrateNum) -> Result<Self::Path, Self::Error> {
524 Ok(vec![self.tcx.crate_name(cnum).to_string()])
529 _trait_ref: Option<ty::TraitRef<'tcx>>,
530 ) -> Result<Self::Path, Self::Error> {
536 _print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
537 _disambiguated_data: &DisambiguatedDefPathData,
539 _trait_ref: Option<ty::TraitRef<'tcx>>,
540 ) -> Result<Self::Path, Self::Error> {
545 print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
546 disambiguated_data: &DisambiguatedDefPathData,
547 ) -> Result<Self::Path, Self::Error> {
548 let mut path = print_prefix(self)?;
549 path.push(disambiguated_data.to_string());
552 fn path_generic_args(
554 print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
555 _args: &[GenericArg<'tcx>],
556 ) -> Result<Self::Path, Self::Error> {
561 let report_path_match = |err: &mut DiagnosticBuilder<'_>, did1: DefId, did2: DefId| {
562 // Only external crates, if either is from a local
563 // module we could have false positives
564 if !(did1.is_local() || did2.is_local()) && did1.krate != did2.krate {
566 |def_id| AbsolutePathPrinter { tcx: self.tcx }.print_def_path(def_id, &[]);
568 // We compare strings because DefPath can be different
569 // for imported and non-imported crates
570 let same_path = || -> Result<_, NonTrivialPath> {
571 Ok(self.tcx.def_path_str(did1) == self.tcx.def_path_str(did2)
572 || abs_path(did1)? == abs_path(did2)?)
574 if same_path().unwrap_or(false) {
575 let crate_name = self.tcx.crate_name(did1.krate);
577 "perhaps two different versions of crate `{}` are being used?",
584 TypeError::Sorts(ref exp_found) => {
585 // if they are both "path types", there's a chance of ambiguity
586 // due to different versions of the same crate
587 if let (&ty::Adt(exp_adt, _), &ty::Adt(found_adt, _)) =
588 (exp_found.expected.kind(), exp_found.found.kind())
590 report_path_match(err, exp_adt.did, found_adt.did);
593 TypeError::Traits(ref exp_found) => {
594 report_path_match(err, exp_found.expected, exp_found.found);
596 _ => (), // FIXME(#22750) handle traits and stuff
600 fn note_error_origin(
602 err: &mut DiagnosticBuilder<'tcx>,
603 cause: &ObligationCause<'tcx>,
604 exp_found: Option<ty::error::ExpectedFound<Ty<'tcx>>>,
605 terr: &TypeError<'tcx>,
607 match *cause.code() {
608 ObligationCauseCode::Pattern { origin_expr: true, span: Some(span), root_ty } => {
609 let ty = self.resolve_vars_if_possible(root_ty);
610 if ty.is_suggestable() {
611 // don't show type `_`
612 err.span_label(span, format!("this expression has type `{}`", ty));
614 if let Some(ty::error::ExpectedFound { found, .. }) = exp_found {
615 if ty.is_box() && ty.boxed_ty() == found {
616 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
619 "consider dereferencing the boxed value",
620 format!("*{}", snippet),
621 Applicability::MachineApplicable,
627 ObligationCauseCode::Pattern { origin_expr: false, span: Some(span), .. } => {
628 err.span_label(span, "expected due to this");
630 ObligationCauseCode::MatchExpressionArm(box MatchExpressionArmCause {
636 opt_suggest_box_span,
641 hir::MatchSource::TryDesugar => {
642 if let Some(ty::error::ExpectedFound { expected, .. }) = exp_found {
643 let scrut_expr = self.tcx.hir().expect_expr(scrut_hir_id);
644 let scrut_ty = if let hir::ExprKind::Call(_, args) = &scrut_expr.kind {
645 let arg_expr = args.first().expect("try desugaring call w/out arg");
646 self.in_progress_typeck_results.and_then(|typeck_results| {
647 typeck_results.borrow().expr_ty_opt(arg_expr)
650 bug!("try desugaring w/out call expr as scrutinee");
654 Some(ty) if expected == ty => {
655 let source_map = self.tcx.sess.source_map();
657 source_map.end_point(cause.span),
658 "try removing this `?`",
660 Applicability::MachineApplicable,
668 // `last_ty` can be `!`, `expected` will have better info when present.
669 let t = self.resolve_vars_if_possible(match exp_found {
670 Some(ty::error::ExpectedFound { expected, .. }) => expected,
673 let source_map = self.tcx.sess.source_map();
674 let mut any_multiline_arm = source_map.is_multiline(arm_span);
675 if prior_arms.len() <= 4 {
676 for sp in prior_arms {
677 any_multiline_arm |= source_map.is_multiline(*sp);
678 err.span_label(*sp, format!("this is found to be of type `{}`", t));
680 } else if let Some(sp) = prior_arms.last() {
681 any_multiline_arm |= source_map.is_multiline(*sp);
684 format!("this and all prior arms are found to be of type `{}`", t),
687 let outer_error_span = if any_multiline_arm {
688 // Cover just `match` and the scrutinee expression, not
689 // the entire match body, to reduce diagram noise.
690 cause.span.shrink_to_lo().to(scrut_span)
694 let msg = "`match` arms have incompatible types";
695 err.span_label(outer_error_span, msg);
696 if let Some((sp, boxed)) = semi_span {
697 if let (StatementAsExpression::NeedsBoxing, [.., prior_arm]) =
698 (boxed, &prior_arms[..])
700 err.multipart_suggestion(
701 "consider removing this semicolon and boxing the expressions",
703 (prior_arm.shrink_to_lo(), "Box::new(".to_string()),
704 (prior_arm.shrink_to_hi(), ")".to_string()),
705 (arm_span.shrink_to_lo(), "Box::new(".to_string()),
706 (arm_span.shrink_to_hi(), ")".to_string()),
709 Applicability::HasPlaceholders,
711 } else if matches!(boxed, StatementAsExpression::NeedsBoxing) {
712 err.span_suggestion_short(
714 "consider removing this semicolon and boxing the expressions",
716 Applicability::MachineApplicable,
719 err.span_suggestion_short(
721 "consider removing this semicolon",
723 Applicability::MachineApplicable,
727 if let Some(ret_sp) = opt_suggest_box_span {
728 // Get return type span and point to it.
729 self.suggest_boxing_for_return_impl_trait(
732 prior_arms.iter().chain(std::iter::once(&arm_span)).map(|s| *s),
737 ObligationCauseCode::IfExpression(box IfExpressionCause {
742 opt_suggest_box_span,
744 err.span_label(then, "expected because of this");
745 if let Some(sp) = outer {
746 err.span_label(sp, "`if` and `else` have incompatible types");
748 if let Some((sp, boxed)) = semicolon {
749 if matches!(boxed, StatementAsExpression::NeedsBoxing) {
750 err.multipart_suggestion(
751 "consider removing this semicolon and boxing the expression",
753 (then.shrink_to_lo(), "Box::new(".to_string()),
754 (then.shrink_to_hi(), ")".to_string()),
755 (else_sp.shrink_to_lo(), "Box::new(".to_string()),
756 (else_sp.shrink_to_hi(), ")".to_string()),
759 Applicability::MachineApplicable,
762 err.span_suggestion_short(
764 "consider removing this semicolon",
766 Applicability::MachineApplicable,
770 if let Some(ret_sp) = opt_suggest_box_span {
771 self.suggest_boxing_for_return_impl_trait(
774 vec![then, else_sp].into_iter(),
778 ObligationCauseCode::LetElse => {
779 err.help("try adding a diverging expression, such as `return` or `panic!(..)`");
780 err.help("...or use `match` instead of `let...else`");
783 if let ObligationCauseCode::BindingObligation(_, binding_span) =
784 cause.code().peel_derives()
786 if matches!(terr, TypeError::RegionsPlaceholderMismatch) {
787 err.span_note(*binding_span, "the lifetime requirement is introduced here");
794 fn suggest_boxing_for_return_impl_trait(
796 err: &mut DiagnosticBuilder<'tcx>,
798 arm_spans: impl Iterator<Item = Span>,
800 err.multipart_suggestion(
801 "you could change the return type to be a boxed trait object",
803 (return_sp.with_hi(return_sp.lo() + BytePos(4)), "Box<dyn".to_string()),
804 (return_sp.shrink_to_hi(), ">".to_string()),
806 Applicability::MaybeIncorrect,
811 (sp.shrink_to_lo(), "Box::new(".to_string()),
812 (sp.shrink_to_hi(), ")".to_string()),
816 .collect::<Vec<_>>();
817 err.multipart_suggestion(
818 "if you change the return type to expect trait objects, box the returned expressions",
820 Applicability::MaybeIncorrect,
824 /// Given that `other_ty` is the same as a type argument for `name` in `sub`, populate `value`
825 /// highlighting `name` and every type argument that isn't at `pos` (which is `other_ty`), and
826 /// populate `other_value` with `other_ty`.
830 /// ^^^^--------^ this is highlighted
832 /// | this type argument is exactly the same as the other type, not highlighted
833 /// this is highlighted
835 /// -------- this type is the same as a type argument in the other type, not highlighted
839 value: &mut DiagnosticStyledString,
840 other_value: &mut DiagnosticStyledString,
842 sub: ty::subst::SubstsRef<'tcx>,
846 // `value` and `other_value` hold two incomplete type representation for display.
847 // `name` is the path of both types being compared. `sub`
848 value.push_highlighted(name);
851 value.push_highlighted("<");
854 // Output the lifetimes for the first type
858 let s = lifetime.to_string();
859 if s.is_empty() { "'_".to_string() } else { s }
863 if !lifetimes.is_empty() {
864 if sub.regions().count() < len {
865 value.push_normal(lifetimes + ", ");
867 value.push_normal(lifetimes);
871 // Highlight all the type arguments that aren't at `pos` and compare the type argument at
872 // `pos` and `other_ty`.
873 for (i, type_arg) in sub.types().enumerate() {
875 let values = self.cmp(type_arg, other_ty);
876 value.0.extend((values.0).0);
877 other_value.0.extend((values.1).0);
879 value.push_highlighted(type_arg.to_string());
882 if len > 0 && i != len - 1 {
883 value.push_normal(", ");
887 value.push_highlighted(">");
891 /// If `other_ty` is the same as a type argument present in `sub`, highlight `path` in `t1_out`,
892 /// as that is the difference to the other type.
894 /// For the following code:
897 /// let x: Foo<Bar<Qux>> = foo::<Bar<Qux>>();
900 /// The type error output will behave in the following way:
904 /// ^^^^--------^ this is highlighted
906 /// | this type argument is exactly the same as the other type, not highlighted
907 /// this is highlighted
909 /// -------- this type is the same as a type argument in the other type, not highlighted
913 mut t1_out: &mut DiagnosticStyledString,
914 mut t2_out: &mut DiagnosticStyledString,
916 sub: ty::subst::SubstsRef<'tcx>,
920 for (i, ta) in sub.types().enumerate() {
922 self.highlight_outer(&mut t1_out, &mut t2_out, path, sub, i, &other_ty);
925 if let ty::Adt(def, _) = ta.kind() {
926 let path_ = self.tcx.def_path_str(def.did);
927 if path_ == other_path {
928 self.highlight_outer(&mut t1_out, &mut t2_out, path, sub, i, &other_ty);
936 /// Adds a `,` to the type representation only if it is appropriate.
939 value: &mut DiagnosticStyledString,
940 other_value: &mut DiagnosticStyledString,
944 if len > 0 && pos != len - 1 {
945 value.push_normal(", ");
946 other_value.push_normal(", ");
950 /// For generic types with parameters with defaults, remove the parameters corresponding to
951 /// the defaults. This repeats a lot of the logic found in `ty::print::pretty`.
952 fn strip_generic_default_params(
955 substs: ty::subst::SubstsRef<'tcx>,
956 ) -> SubstsRef<'tcx> {
957 let generics = self.tcx.generics_of(def_id);
958 let mut num_supplied_defaults = 0;
960 let default_params = generics.params.iter().rev().filter_map(|param| match param.kind {
961 ty::GenericParamDefKind::Type { has_default: true, .. } => Some(param.def_id),
962 ty::GenericParamDefKind::Const { has_default: true } => Some(param.def_id),
965 for (def_id, actual) in iter::zip(default_params, substs.iter().rev()) {
966 match actual.unpack() {
967 GenericArgKind::Const(c) => {
968 if self.tcx.const_param_default(def_id).subst(self.tcx, substs) != c {
972 GenericArgKind::Type(ty) => {
973 if self.tcx.type_of(def_id).subst(self.tcx, substs) != ty {
979 num_supplied_defaults += 1;
981 let len = generics.params.len();
982 let mut generics = generics.clone();
983 generics.params.truncate(len - num_supplied_defaults);
984 substs.truncate_to(self.tcx, &generics)
987 /// Given two `fn` signatures highlight only sub-parts that are different.
990 sig1: &ty::PolyFnSig<'tcx>,
991 sig2: &ty::PolyFnSig<'tcx>,
992 ) -> (DiagnosticStyledString, DiagnosticStyledString) {
993 let get_lifetimes = |sig| {
994 use rustc_hir::def::Namespace;
995 let mut s = String::new();
996 let (_, sig, reg) = ty::print::FmtPrinter::new(self.tcx, &mut s, Namespace::TypeNS)
997 .name_all_regions(sig)
999 let lts: Vec<String> = reg.into_iter().map(|(_, kind)| kind.to_string()).collect();
1000 (if lts.is_empty() { String::new() } else { format!("for<{}> ", lts.join(", ")) }, sig)
1003 let (lt1, sig1) = get_lifetimes(sig1);
1004 let (lt2, sig2) = get_lifetimes(sig2);
1006 // unsafe extern "C" for<'a> fn(&'a T) -> &'a T
1008 DiagnosticStyledString::normal("".to_string()),
1009 DiagnosticStyledString::normal("".to_string()),
1012 // unsafe extern "C" for<'a> fn(&'a T) -> &'a T
1014 values.0.push(sig1.unsafety.prefix_str(), sig1.unsafety != sig2.unsafety);
1015 values.1.push(sig2.unsafety.prefix_str(), sig1.unsafety != sig2.unsafety);
1017 // unsafe extern "C" for<'a> fn(&'a T) -> &'a T
1019 if sig1.abi != abi::Abi::Rust {
1020 values.0.push(format!("extern {} ", sig1.abi), sig1.abi != sig2.abi);
1022 if sig2.abi != abi::Abi::Rust {
1023 values.1.push(format!("extern {} ", sig2.abi), sig1.abi != sig2.abi);
1026 // unsafe extern "C" for<'a> fn(&'a T) -> &'a T
1028 let lifetime_diff = lt1 != lt2;
1029 values.0.push(lt1, lifetime_diff);
1030 values.1.push(lt2, lifetime_diff);
1032 // unsafe extern "C" for<'a> fn(&'a T) -> &'a T
1034 values.0.push_normal("fn(");
1035 values.1.push_normal("fn(");
1037 // unsafe extern "C" for<'a> fn(&'a T) -> &'a T
1039 let len1 = sig1.inputs().len();
1040 let len2 = sig2.inputs().len();
1042 for (i, (l, r)) in iter::zip(sig1.inputs(), sig2.inputs()).enumerate() {
1043 let (x1, x2) = self.cmp(l, r);
1044 (values.0).0.extend(x1.0);
1045 (values.1).0.extend(x2.0);
1046 self.push_comma(&mut values.0, &mut values.1, len1, i);
1049 for (i, l) in sig1.inputs().iter().enumerate() {
1050 values.0.push_highlighted(l.to_string());
1052 values.0.push_highlighted(", ");
1055 for (i, r) in sig2.inputs().iter().enumerate() {
1056 values.1.push_highlighted(r.to_string());
1058 values.1.push_highlighted(", ");
1063 if sig1.c_variadic {
1065 values.0.push_normal(", ");
1067 values.0.push("...", !sig2.c_variadic);
1069 if sig2.c_variadic {
1071 values.1.push_normal(", ");
1073 values.1.push("...", !sig1.c_variadic);
1076 // unsafe extern "C" for<'a> fn(&'a T) -> &'a T
1078 values.0.push_normal(")");
1079 values.1.push_normal(")");
1081 // unsafe extern "C" for<'a> fn(&'a T) -> &'a T
1083 let output1 = sig1.output();
1084 let output2 = sig2.output();
1085 let (x1, x2) = self.cmp(output1, output2);
1086 if !output1.is_unit() {
1087 values.0.push_normal(" -> ");
1088 (values.0).0.extend(x1.0);
1090 if !output2.is_unit() {
1091 values.1.push_normal(" -> ");
1092 (values.1).0.extend(x2.0);
1097 /// Compares two given types, eliding parts that are the same between them and highlighting
1098 /// relevant differences, and return two representation of those types for highlighted printing.
1099 fn cmp(&self, t1: Ty<'tcx>, t2: Ty<'tcx>) -> (DiagnosticStyledString, DiagnosticStyledString) {
1100 debug!("cmp(t1={}, t1.kind={:?}, t2={}, t2.kind={:?})", t1, t1.kind(), t2, t2.kind());
1103 fn equals<'tcx>(a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
1104 match (a.kind(), b.kind()) {
1105 (a, b) if *a == *b => true,
1106 (&ty::Int(_), &ty::Infer(ty::InferTy::IntVar(_)))
1108 &ty::Infer(ty::InferTy::IntVar(_)),
1109 &ty::Int(_) | &ty::Infer(ty::InferTy::IntVar(_)),
1111 | (&ty::Float(_), &ty::Infer(ty::InferTy::FloatVar(_)))
1113 &ty::Infer(ty::InferTy::FloatVar(_)),
1114 &ty::Float(_) | &ty::Infer(ty::InferTy::FloatVar(_)),
1120 fn push_ty_ref<'tcx>(
1121 region: &ty::Region<'tcx>,
1123 mutbl: hir::Mutability,
1124 s: &mut DiagnosticStyledString,
1126 let mut r = region.to_string();
1132 s.push_highlighted(format!("&{}{}", r, mutbl.prefix_str()));
1133 s.push_normal(ty.to_string());
1136 // process starts here
1137 match (t1.kind(), t2.kind()) {
1138 (&ty::Adt(def1, sub1), &ty::Adt(def2, sub2)) => {
1139 let sub_no_defaults_1 = self.strip_generic_default_params(def1.did, sub1);
1140 let sub_no_defaults_2 = self.strip_generic_default_params(def2.did, sub2);
1141 let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new());
1142 let path1 = self.tcx.def_path_str(def1.did);
1143 let path2 = self.tcx.def_path_str(def2.did);
1144 if def1.did == def2.did {
1145 // Easy case. Replace same types with `_` to shorten the output and highlight
1146 // the differing ones.
1147 // let x: Foo<Bar, Qux> = y::<Foo<Quz, Qux>>();
1150 // --- ^ type argument elided
1152 // highlighted in output
1153 values.0.push_normal(path1);
1154 values.1.push_normal(path2);
1156 // Avoid printing out default generic parameters that are common to both
1158 let len1 = sub_no_defaults_1.len();
1159 let len2 = sub_no_defaults_2.len();
1160 let common_len = cmp::min(len1, len2);
1161 let remainder1: Vec<_> = sub1.types().skip(common_len).collect();
1162 let remainder2: Vec<_> = sub2.types().skip(common_len).collect();
1163 let common_default_params =
1164 iter::zip(remainder1.iter().rev(), remainder2.iter().rev())
1165 .filter(|(a, b)| a == b)
1167 let len = sub1.len() - common_default_params;
1168 let consts_offset = len - sub1.consts().count();
1170 // Only draw `<...>` if there're lifetime/type arguments.
1172 values.0.push_normal("<");
1173 values.1.push_normal("<");
1176 fn lifetime_display(lifetime: Region<'_>) -> String {
1177 let s = lifetime.to_string();
1178 if s.is_empty() { "'_".to_string() } else { s }
1180 // At one point we'd like to elide all lifetimes here, they are irrelevant for
1181 // all diagnostics that use this output
1185 // ^^ ^^ --- type arguments are not elided
1187 // | elided as they were the same
1188 // not elided, they were different, but irrelevant
1190 // For bound lifetimes, keep the names of the lifetimes,
1191 // even if they are the same so that it's clear what's happening
1192 // if we have something like
1194 // for<'r, 's> fn(Inv<'r>, Inv<'s>)
1195 // for<'r> fn(Inv<'r>, Inv<'r>)
1196 let lifetimes = sub1.regions().zip(sub2.regions());
1197 for (i, lifetimes) in lifetimes.enumerate() {
1198 let l1 = lifetime_display(lifetimes.0);
1199 let l2 = lifetime_display(lifetimes.1);
1200 if lifetimes.0 != lifetimes.1 {
1201 values.0.push_highlighted(l1);
1202 values.1.push_highlighted(l2);
1203 } else if lifetimes.0.is_late_bound() {
1204 values.0.push_normal(l1);
1205 values.1.push_normal(l2);
1207 values.0.push_normal("'_");
1208 values.1.push_normal("'_");
1210 self.push_comma(&mut values.0, &mut values.1, len, i);
1213 // We're comparing two types with the same path, so we compare the type
1214 // arguments for both. If they are the same, do not highlight and elide from the
1218 // ^ elided type as this type argument was the same in both sides
1219 let type_arguments = sub1.types().zip(sub2.types());
1220 let regions_len = sub1.regions().count();
1221 let num_display_types = consts_offset - regions_len;
1222 for (i, (ta1, ta2)) in type_arguments.take(num_display_types).enumerate() {
1223 let i = i + regions_len;
1225 values.0.push_normal("_");
1226 values.1.push_normal("_");
1228 let (x1, x2) = self.cmp(ta1, ta2);
1229 (values.0).0.extend(x1.0);
1230 (values.1).0.extend(x2.0);
1232 self.push_comma(&mut values.0, &mut values.1, len, i);
1235 // Do the same for const arguments, if they are equal, do not highlight and
1236 // elide them from the output.
1237 let const_arguments = sub1.consts().zip(sub2.consts());
1238 for (i, (ca1, ca2)) in const_arguments.enumerate() {
1239 let i = i + consts_offset;
1241 values.0.push_normal("_");
1242 values.1.push_normal("_");
1244 values.0.push_highlighted(ca1.to_string());
1245 values.1.push_highlighted(ca2.to_string());
1247 self.push_comma(&mut values.0, &mut values.1, len, i);
1250 // Close the type argument bracket.
1251 // Only draw `<...>` if there're lifetime/type arguments.
1253 values.0.push_normal(">");
1254 values.1.push_normal(">");
1259 // let x: Foo<Bar<Qux> = foo::<Bar<Qux>>();
1261 // ------- this type argument is exactly the same as the other type
1277 // let x: Bar<Qux> = y:<Foo<Bar<Qux>>>();
1280 // ------- this type argument is exactly the same as the other type
1295 // We can't find anything in common, highlight relevant part of type path.
1296 // let x: foo::bar::Baz<Qux> = y:<foo::bar::Bar<Zar>>();
1297 // foo::bar::Baz<Qux>
1298 // foo::bar::Bar<Zar>
1299 // -------- this part of the path is different
1301 let t1_str = t1.to_string();
1302 let t2_str = t2.to_string();
1303 let min_len = t1_str.len().min(t2_str.len());
1305 const SEPARATOR: &str = "::";
1306 let separator_len = SEPARATOR.len();
1307 let split_idx: usize =
1308 iter::zip(t1_str.split(SEPARATOR), t2_str.split(SEPARATOR))
1309 .take_while(|(mod1_str, mod2_str)| mod1_str == mod2_str)
1310 .map(|(mod_str, _)| mod_str.len() + separator_len)
1314 "cmp: separator_len={}, split_idx={}, min_len={}",
1315 separator_len, split_idx, min_len
1318 if split_idx >= min_len {
1319 // paths are identical, highlight everything
1321 DiagnosticStyledString::highlighted(t1_str),
1322 DiagnosticStyledString::highlighted(t2_str),
1325 let (common, uniq1) = t1_str.split_at(split_idx);
1326 let (_, uniq2) = t2_str.split_at(split_idx);
1327 debug!("cmp: common={}, uniq1={}, uniq2={}", common, uniq1, uniq2);
1329 values.0.push_normal(common);
1330 values.0.push_highlighted(uniq1);
1331 values.1.push_normal(common);
1332 values.1.push_highlighted(uniq2);
1339 // When finding T != &T, highlight only the borrow
1340 (&ty::Ref(r1, ref_ty1, mutbl1), _) if equals(&ref_ty1, &t2) => {
1341 let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new());
1342 push_ty_ref(&r1, ref_ty1, mutbl1, &mut values.0);
1343 values.1.push_normal(t2.to_string());
1346 (_, &ty::Ref(r2, ref_ty2, mutbl2)) if equals(&t1, &ref_ty2) => {
1347 let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new());
1348 values.0.push_normal(t1.to_string());
1349 push_ty_ref(&r2, ref_ty2, mutbl2, &mut values.1);
1353 // When encountering &T != &mut T, highlight only the borrow
1354 (&ty::Ref(r1, ref_ty1, mutbl1), &ty::Ref(r2, ref_ty2, mutbl2))
1355 if equals(&ref_ty1, &ref_ty2) =>
1357 let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new());
1358 push_ty_ref(&r1, ref_ty1, mutbl1, &mut values.0);
1359 push_ty_ref(&r2, ref_ty2, mutbl2, &mut values.1);
1363 // When encountering tuples of the same size, highlight only the differing types
1364 (&ty::Tuple(substs1), &ty::Tuple(substs2)) if substs1.len() == substs2.len() => {
1366 (DiagnosticStyledString::normal("("), DiagnosticStyledString::normal("("));
1367 let len = substs1.len();
1368 for (i, (left, right)) in substs1.types().zip(substs2.types()).enumerate() {
1369 let (x1, x2) = self.cmp(left, right);
1370 (values.0).0.extend(x1.0);
1371 (values.1).0.extend(x2.0);
1372 self.push_comma(&mut values.0, &mut values.1, len, i);
1375 // Keep the output for single element tuples as `(ty,)`.
1376 values.0.push_normal(",");
1377 values.1.push_normal(",");
1379 values.0.push_normal(")");
1380 values.1.push_normal(")");
1384 (ty::FnDef(did1, substs1), ty::FnDef(did2, substs2)) => {
1385 let sig1 = self.tcx.fn_sig(*did1).subst(self.tcx, substs1);
1386 let sig2 = self.tcx.fn_sig(*did2).subst(self.tcx, substs2);
1387 let mut values = self.cmp_fn_sig(&sig1, &sig2);
1388 let path1 = format!(" {{{}}}", self.tcx.def_path_str_with_substs(*did1, substs1));
1389 let path2 = format!(" {{{}}}", self.tcx.def_path_str_with_substs(*did2, substs2));
1390 let same_path = path1 == path2;
1391 values.0.push(path1, !same_path);
1392 values.1.push(path2, !same_path);
1396 (ty::FnDef(did1, substs1), ty::FnPtr(sig2)) => {
1397 let sig1 = self.tcx.fn_sig(*did1).subst(self.tcx, substs1);
1398 let mut values = self.cmp_fn_sig(&sig1, sig2);
1399 values.0.push_highlighted(format!(
1401 self.tcx.def_path_str_with_substs(*did1, substs1)
1406 (ty::FnPtr(sig1), ty::FnDef(did2, substs2)) => {
1407 let sig2 = self.tcx.fn_sig(*did2).subst(self.tcx, substs2);
1408 let mut values = self.cmp_fn_sig(sig1, &sig2);
1409 values.1.push_normal(format!(
1411 self.tcx.def_path_str_with_substs(*did2, substs2)
1416 (ty::FnPtr(sig1), ty::FnPtr(sig2)) => self.cmp_fn_sig(sig1, sig2),
1420 // The two types are the same, elide and don't highlight.
1421 (DiagnosticStyledString::normal("_"), DiagnosticStyledString::normal("_"))
1423 // We couldn't find anything in common, highlight everything.
1425 DiagnosticStyledString::highlighted(t1.to_string()),
1426 DiagnosticStyledString::highlighted(t2.to_string()),
1433 /// Extend a type error with extra labels pointing at "non-trivial" types, like closures and
1434 /// the return type of `async fn`s.
1436 /// `secondary_span` gives the caller the opportunity to expand `diag` with a `span_label`.
1438 /// `swap_secondary_and_primary` is used to make projection errors in particular nicer by using
1439 /// the message in `secondary_span` as the primary label, and apply the message that would
1440 /// otherwise be used for the primary label on the `secondary_span` `Span`. This applies on
1441 /// E0271, like `src/test/ui/issues/issue-39970.stderr`.
1442 pub fn note_type_err(
1444 diag: &mut DiagnosticBuilder<'tcx>,
1445 cause: &ObligationCause<'tcx>,
1446 secondary_span: Option<(Span, String)>,
1447 mut values: Option<ValuePairs<'tcx>>,
1448 terr: &TypeError<'tcx>,
1449 swap_secondary_and_primary: bool,
1451 let span = cause.span(self.tcx);
1452 debug!("note_type_err cause={:?} values={:?}, terr={:?}", cause, values, terr);
1454 // For some types of errors, expected-found does not make
1455 // sense, so just ignore the values we were given.
1456 if let TypeError::CyclicTy(_) = terr {
1459 struct OpaqueTypesVisitor<'tcx> {
1460 types: FxHashMap<TyCategory, FxHashSet<Span>>,
1461 expected: FxHashMap<TyCategory, FxHashSet<Span>>,
1462 found: FxHashMap<TyCategory, FxHashSet<Span>>,
1467 impl<'tcx> OpaqueTypesVisitor<'tcx> {
1468 fn visit_expected_found(
1474 let mut types_visitor = OpaqueTypesVisitor {
1475 types: Default::default(),
1476 expected: Default::default(),
1477 found: Default::default(),
1481 // The visitor puts all the relevant encountered types in `self.types`, but in
1482 // here we want to visit two separate types with no relation to each other, so we
1483 // move the results from `types` to `expected` or `found` as appropriate.
1484 expected.visit_with(&mut types_visitor);
1485 std::mem::swap(&mut types_visitor.expected, &mut types_visitor.types);
1486 found.visit_with(&mut types_visitor);
1487 std::mem::swap(&mut types_visitor.found, &mut types_visitor.types);
1491 fn report(&self, err: &mut DiagnosticBuilder<'_>) {
1492 self.add_labels_for_types(err, "expected", &self.expected);
1493 self.add_labels_for_types(err, "found", &self.found);
1496 fn add_labels_for_types(
1498 err: &mut DiagnosticBuilder<'_>,
1500 types: &FxHashMap<TyCategory, FxHashSet<Span>>,
1502 for (key, values) in types.iter() {
1503 let count = values.len();
1504 let kind = key.descr();
1505 let mut returned_async_output_error = false;
1507 if sp.is_desugaring(DesugaringKind::Async) && !returned_async_output_error {
1508 if [sp] != err.span.primary_spans() {
1509 let mut span: MultiSpan = sp.into();
1510 span.push_span_label(
1513 "checked the `Output` of this `async fn`, {}{} {}{}",
1514 if count > 1 { "one of the " } else { "" },
1522 "while checking the return type of the `async fn`",
1528 "checked the `Output` of this `async fn`, {}{} {}{}",
1529 if count > 1 { "one of the " } else { "" },
1535 err.note("while checking the return type of the `async fn`");
1537 returned_async_output_error = true;
1543 if count == 1 { "the " } else { "one of the " },
1555 impl<'tcx> ty::fold::TypeVisitor<'tcx> for OpaqueTypesVisitor<'tcx> {
1556 fn tcx_for_anon_const_substs(&self) -> Option<TyCtxt<'tcx>> {
1560 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1561 if let Some((kind, def_id)) = TyCategory::from_ty(self.tcx, t) {
1562 let span = self.tcx.def_span(def_id);
1563 // Avoid cluttering the output when the "found" and error span overlap:
1565 // error[E0308]: mismatched types
1566 // --> $DIR/issue-20862.rs:2:5
1571 // | the found closure
1572 // | expected `()`, found closure
1574 // = note: expected unit type `()`
1575 // found closure `[closure@$DIR/issue-20862.rs:2:5: 2:14 x:_]`
1576 if !self.ignore_span.overlaps(span) {
1577 self.types.entry(kind).or_default().insert(span);
1580 t.super_visit_with(self)
1584 debug!("note_type_err(diag={:?})", diag);
1586 Variable(ty::error::ExpectedFound<Ty<'a>>),
1587 Fixed(&'static str),
1589 let (expected_found, exp_found, is_simple_error) = match values {
1590 None => (None, Mismatch::Fixed("type"), false),
1592 let (is_simple_error, exp_found) = match values {
1593 ValuePairs::Types(exp_found) => {
1595 exp_found.expected.is_simple_text() && exp_found.found.is_simple_text();
1596 OpaqueTypesVisitor::visit_expected_found(
1604 (is_simple_err, Mismatch::Variable(exp_found))
1606 ValuePairs::TraitRefs(_) => (false, Mismatch::Fixed("trait")),
1607 _ => (false, Mismatch::Fixed("type")),
1609 let vals = match self.values_str(values) {
1610 Some((expected, found)) => Some((expected, found)),
1612 // Derived error. Cancel the emitter.
1617 (vals, exp_found, is_simple_error)
1621 // Ignore msg for object safe coercion
1622 // since E0038 message will be printed
1624 TypeError::ObjectUnsafeCoercion(_) => {}
1626 let mut label_or_note = |span: Span, msg: &str| {
1627 if &[span] == diag.span.primary_spans() {
1628 diag.span_label(span, msg);
1630 diag.span_note(span, msg);
1633 if let Some((sp, msg)) = secondary_span {
1634 if swap_secondary_and_primary {
1635 let terr = if let Some(infer::ValuePairs::Types(infer::ExpectedFound {
1640 format!("expected this to be `{}`", expected)
1644 label_or_note(sp, &terr);
1645 label_or_note(span, &msg);
1647 label_or_note(span, &terr.to_string());
1648 label_or_note(sp, &msg);
1651 label_or_note(span, &terr.to_string());
1655 if let Some((expected, found)) = expected_found {
1656 let (expected_label, found_label, exp_found) = match exp_found {
1657 Mismatch::Variable(ef) => (
1658 ef.expected.prefix_string(self.tcx),
1659 ef.found.prefix_string(self.tcx),
1662 Mismatch::Fixed(s) => (s.into(), s.into(), None),
1664 match (&terr, expected == found) {
1665 (TypeError::Sorts(values), extra) => {
1666 let sort_string = |ty: Ty<'tcx>| match (extra, ty.kind()) {
1667 (true, ty::Opaque(def_id, _)) => {
1668 let sm = self.tcx.sess.source_map();
1669 let pos = sm.lookup_char_pos(self.tcx.def_span(*def_id).lo());
1671 " (opaque type at <{}:{}:{}>)",
1672 sm.filename_for_diagnostics(&pos.file.name),
1674 pos.col.to_usize() + 1,
1677 (true, _) => format!(" ({})", ty.sort_string(self.tcx)),
1678 (false, _) => "".to_string(),
1680 if !(values.expected.is_simple_text() && values.found.is_simple_text())
1681 || (exp_found.map_or(false, |ef| {
1682 // This happens when the type error is a subset of the expectation,
1683 // like when you have two references but one is `usize` and the other
1684 // is `f32`. In those cases we still want to show the `note`. If the
1685 // value from `ef` is `Infer(_)`, then we ignore it.
1686 if !ef.expected.is_ty_infer() {
1687 ef.expected != values.expected
1688 } else if !ef.found.is_ty_infer() {
1689 ef.found != values.found
1695 diag.note_expected_found_extra(
1700 &sort_string(values.expected),
1701 &sort_string(values.found),
1705 (TypeError::ObjectUnsafeCoercion(_), _) => {
1706 diag.note_unsuccessful_coercion(found, expected);
1710 "note_type_err: exp_found={:?}, expected={:?} found={:?}",
1711 exp_found, expected, found
1713 if !is_simple_error || terr.must_include_note() {
1714 diag.note_expected_found(&expected_label, expected, &found_label, found);
1719 let exp_found = match exp_found {
1720 Mismatch::Variable(exp_found) => Some(exp_found),
1721 Mismatch::Fixed(_) => None,
1723 let exp_found = match terr {
1724 // `terr` has more accurate type information than `exp_found` in match expressions.
1725 ty::error::TypeError::Sorts(terr)
1726 if exp_found.map_or(false, |ef| terr.found == ef.found) =>
1732 debug!("exp_found {:?} terr {:?} cause.code {:?}", exp_found, terr, cause.code());
1733 if let Some(exp_found) = exp_found {
1734 let should_suggest_fixes = if let ObligationCauseCode::Pattern { root_ty, .. } =
1737 // Skip if the root_ty of the pattern is not the same as the expected_ty.
1738 // If these types aren't equal then we've probably peeled off a layer of arrays.
1739 same_type_modulo_infer(self.resolve_vars_if_possible(*root_ty), exp_found.expected)
1744 if should_suggest_fixes {
1745 self.suggest_as_ref_where_appropriate(span, &exp_found, diag);
1746 self.suggest_accessing_field_where_appropriate(cause, &exp_found, diag);
1747 self.suggest_await_on_expect_found(cause, span, &exp_found, diag);
1751 // In some (most?) cases cause.body_id points to actual body, but in some cases
1752 // it's an actual definition. According to the comments (e.g. in
1753 // librustc_typeck/check/compare_method.rs:compare_predicate_entailment) the latter
1754 // is relied upon by some other code. This might (or might not) need cleanup.
1755 let body_owner_def_id =
1756 self.tcx.hir().opt_local_def_id(cause.body_id).unwrap_or_else(|| {
1757 self.tcx.hir().body_owner_def_id(hir::BodyId { hir_id: cause.body_id })
1759 self.check_and_note_conflicting_crates(diag, terr);
1760 self.tcx.note_and_explain_type_err(diag, terr, cause, span, body_owner_def_id.to_def_id());
1762 if let Some(ValuePairs::PolyTraitRefs(exp_found)) = values {
1763 if let ty::Closure(def_id, _) = exp_found.expected.skip_binder().self_ty().kind() {
1764 if let Some(def_id) = def_id.as_local() {
1765 let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
1766 let span = self.tcx.hir().span(hir_id);
1767 diag.span_note(span, "this closure does not fulfill the lifetime requirements");
1772 // It reads better to have the error origin as the final
1774 self.note_error_origin(diag, cause, exp_found, terr);
1777 pub fn get_impl_future_output_ty(&self, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
1778 if let ty::Opaque(def_id, substs) = ty.kind() {
1779 let future_trait = self.tcx.require_lang_item(LangItem::Future, None);
1781 let item_def_id = self.tcx.associated_item_def_ids(future_trait)[0];
1783 let bounds = self.tcx.explicit_item_bounds(*def_id);
1785 for (predicate, _) in bounds {
1786 let predicate = predicate.subst(self.tcx, substs);
1787 if let ty::PredicateKind::Projection(projection_predicate) =
1788 predicate.kind().skip_binder()
1790 if projection_predicate.projection_ty.item_def_id == item_def_id {
1791 // We don't account for multiple `Future::Output = Ty` contraints.
1792 return Some(projection_predicate.ty);
1800 /// A possible error is to forget to add `.await` when using futures:
1803 /// async fn make_u32() -> u32 {
1807 /// fn take_u32(x: u32) {}
1809 /// async fn foo() {
1810 /// let x = make_u32();
1815 /// This routine checks if the found type `T` implements `Future<Output=U>` where `U` is the
1816 /// expected type. If this is the case, and we are inside of an async body, it suggests adding
1817 /// `.await` to the tail of the expression.
1818 fn suggest_await_on_expect_found(
1820 cause: &ObligationCause<'tcx>,
1822 exp_found: &ty::error::ExpectedFound<Ty<'tcx>>,
1823 diag: &mut DiagnosticBuilder<'tcx>,
1826 "suggest_await_on_expect_found: exp_span={:?}, expected_ty={:?}, found_ty={:?}",
1827 exp_span, exp_found.expected, exp_found.found,
1830 if let ObligationCauseCode::CompareImplMethodObligation { .. } = cause.code() {
1835 self.get_impl_future_output_ty(exp_found.expected),
1836 self.get_impl_future_output_ty(exp_found.found),
1838 (Some(exp), Some(found)) if same_type_modulo_infer(exp, found) => match cause.code() {
1839 ObligationCauseCode::IfExpression(box IfExpressionCause { then, .. }) => {
1840 diag.multipart_suggestion(
1841 "consider `await`ing on both `Future`s",
1843 (then.shrink_to_hi(), ".await".to_string()),
1844 (exp_span.shrink_to_hi(), ".await".to_string()),
1846 Applicability::MaybeIncorrect,
1849 ObligationCauseCode::MatchExpressionArm(box MatchExpressionArmCause {
1853 if let [.., arm_span] = &prior_arms[..] {
1854 diag.multipart_suggestion(
1855 "consider `await`ing on both `Future`s",
1857 (arm_span.shrink_to_hi(), ".await".to_string()),
1858 (exp_span.shrink_to_hi(), ".await".to_string()),
1860 Applicability::MaybeIncorrect,
1863 diag.help("consider `await`ing on both `Future`s");
1867 diag.help("consider `await`ing on both `Future`s");
1870 (_, Some(ty)) if same_type_modulo_infer(exp_found.expected, ty) => {
1871 diag.span_suggestion_verbose(
1872 exp_span.shrink_to_hi(),
1873 "consider `await`ing on the `Future`",
1874 ".await".to_string(),
1875 Applicability::MaybeIncorrect,
1878 (Some(ty), _) if same_type_modulo_infer(ty, exp_found.found) => match cause.code() {
1879 ObligationCauseCode::Pattern { span: Some(span), .. }
1880 | ObligationCauseCode::IfExpression(box IfExpressionCause { then: span, .. }) => {
1881 diag.span_suggestion_verbose(
1882 span.shrink_to_hi(),
1883 "consider `await`ing on the `Future`",
1884 ".await".to_string(),
1885 Applicability::MaybeIncorrect,
1888 ObligationCauseCode::MatchExpressionArm(box MatchExpressionArmCause {
1892 diag.multipart_suggestion_verbose(
1893 "consider `await`ing on the `Future`",
1896 .map(|arm| (arm.shrink_to_hi(), ".await".to_string()))
1898 Applicability::MaybeIncorrect,
1907 fn suggest_accessing_field_where_appropriate(
1909 cause: &ObligationCause<'tcx>,
1910 exp_found: &ty::error::ExpectedFound<Ty<'tcx>>,
1911 diag: &mut DiagnosticBuilder<'tcx>,
1914 "suggest_accessing_field_where_appropriate(cause={:?}, exp_found={:?})",
1917 if let ty::Adt(expected_def, expected_substs) = exp_found.expected.kind() {
1918 if expected_def.is_enum() {
1922 if let Some((name, ty)) = expected_def
1926 .filter(|field| field.vis.is_accessible_from(field.did, self.tcx))
1927 .map(|field| (field.ident.name, field.ty(self.tcx, expected_substs)))
1928 .find(|(_, ty)| same_type_modulo_infer(ty, exp_found.found))
1930 if let ObligationCauseCode::Pattern { span: Some(span), .. } = *cause.code() {
1931 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
1932 let suggestion = if expected_def.is_struct() {
1933 format!("{}.{}", snippet, name)
1934 } else if expected_def.is_union() {
1935 format!("unsafe {{ {}.{} }}", snippet, name)
1939 diag.span_suggestion(
1942 "you might have meant to use field `{}` whose type is `{}`",
1946 Applicability::MaybeIncorrect,
1954 /// When encountering a case where `.as_ref()` on a `Result` or `Option` would be appropriate,
1956 fn suggest_as_ref_where_appropriate(
1959 exp_found: &ty::error::ExpectedFound<Ty<'tcx>>,
1960 diag: &mut DiagnosticBuilder<'tcx>,
1962 if let (ty::Adt(exp_def, exp_substs), ty::Ref(_, found_ty, _)) =
1963 (exp_found.expected.kind(), exp_found.found.kind())
1965 if let ty::Adt(found_def, found_substs) = *found_ty.kind() {
1966 let path_str = format!("{:?}", exp_def);
1967 if exp_def == &found_def {
1968 let opt_msg = "you can convert from `&Option<T>` to `Option<&T>` using \
1970 let result_msg = "you can convert from `&Result<T, E>` to \
1971 `Result<&T, &E>` using `.as_ref()`";
1972 let have_as_ref = &[
1973 ("std::option::Option", opt_msg),
1974 ("core::option::Option", opt_msg),
1975 ("std::result::Result", result_msg),
1976 ("core::result::Result", result_msg),
1978 if let Some(msg) = have_as_ref
1980 .find_map(|(path, msg)| (&path_str == path).then_some(msg))
1982 let mut show_suggestion = true;
1983 for (exp_ty, found_ty) in
1984 iter::zip(exp_substs.types(), found_substs.types())
1986 match *exp_ty.kind() {
1987 ty::Ref(_, exp_ty, _) => {
1988 match (exp_ty.kind(), found_ty.kind()) {
1992 | (ty::Infer(_), _) => {}
1993 _ if same_type_modulo_infer(exp_ty, found_ty) => {}
1994 _ => show_suggestion = false,
1997 ty::Param(_) | ty::Infer(_) => {}
1998 _ => show_suggestion = false,
2001 if let (Ok(snippet), true) =
2002 (self.tcx.sess.source_map().span_to_snippet(span), show_suggestion)
2004 diag.span_suggestion(
2007 format!("{}.as_ref()", snippet),
2008 Applicability::MachineApplicable,
2017 pub fn report_and_explain_type_error(
2019 trace: TypeTrace<'tcx>,
2020 terr: &TypeError<'tcx>,
2021 ) -> DiagnosticBuilder<'tcx> {
2022 use crate::traits::ObligationCauseCode::MatchExpressionArm;
2024 debug!("report_and_explain_type_error(trace={:?}, terr={:?})", trace, terr);
2026 let span = trace.cause.span(self.tcx);
2027 let failure_code = trace.cause.as_failure_code(terr);
2028 let mut diag = match failure_code {
2029 FailureCode::Error0038(did) => {
2030 let violations = self.tcx.object_safety_violations(did);
2031 report_object_safety_error(self.tcx, span, did, violations)
2033 FailureCode::Error0317(failure_str) => {
2034 struct_span_err!(self.tcx.sess, span, E0317, "{}", failure_str)
2036 FailureCode::Error0580(failure_str) => {
2037 struct_span_err!(self.tcx.sess, span, E0580, "{}", failure_str)
2039 FailureCode::Error0308(failure_str) => {
2040 let mut err = struct_span_err!(self.tcx.sess, span, E0308, "{}", failure_str);
2041 if let ValuePairs::Types(ty::error::ExpectedFound { expected, found }) =
2044 match (expected.kind(), found.kind()) {
2045 (ty::Tuple(_), ty::Tuple(_)) => {}
2046 // If a tuple of length one was expected and the found expression has
2047 // parentheses around it, perhaps the user meant to write `(expr,)` to
2048 // build a tuple (issue #86100)
2049 (ty::Tuple(_), _) if expected.tuple_fields().count() == 1 => {
2050 if let Ok(code) = self.tcx.sess().source_map().span_to_snippet(span) {
2052 code.strip_prefix('(').and_then(|s| s.strip_suffix(')'))
2054 err.span_suggestion(
2056 "use a trailing comma to create a tuple with one element",
2057 format!("({},)", code),
2058 Applicability::MaybeIncorrect,
2063 // If a character was expected and the found expression is a string literal
2064 // containing a single character, perhaps the user meant to write `'c'` to
2065 // specify a character literal (issue #92479)
2066 (ty::Char, ty::Ref(_, r, _)) if r.is_str() => {
2067 if let Ok(code) = self.tcx.sess().source_map().span_to_snippet(span) {
2069 code.strip_prefix('"').and_then(|s| s.strip_suffix('"'))
2071 if code.chars().nth(1).is_none() {
2072 err.span_suggestion(
2074 "if you meant to write a `char` literal, use single quotes",
2075 format!("'{}'", code),
2076 Applicability::MachineApplicable,
2082 // If a string was expected and the found expression is a character literal,
2083 // perhaps the user meant to write `"s"` to specify a string literal.
2084 (ty::Ref(_, r, _), ty::Char) if r.is_str() => {
2085 if let Ok(code) = self.tcx.sess().source_map().span_to_snippet(span) {
2087 code.strip_prefix('\'').and_then(|s| s.strip_suffix('\''))
2089 err.span_suggestion(
2091 "if you meant to write a `str` literal, use double quotes",
2092 format!("\"{}\"", code),
2093 Applicability::MachineApplicable,
2101 if let MatchExpressionArm(box MatchExpressionArmCause { source, .. }) =
2104 if let hir::MatchSource::TryDesugar = source {
2105 if let Some((expected_ty, found_ty)) = self.values_str(trace.values) {
2107 "`?` operator cannot convert from `{}` to `{}`",
2109 expected_ty.content(),
2116 FailureCode::Error0644(failure_str) => {
2117 struct_span_err!(self.tcx.sess, span, E0644, "{}", failure_str)
2120 self.note_type_err(&mut diag, &trace.cause, None, Some(trace.values), terr, false);
2126 values: ValuePairs<'tcx>,
2127 ) -> Option<(DiagnosticStyledString, DiagnosticStyledString)> {
2129 infer::Types(exp_found) => self.expected_found_str_ty(exp_found),
2130 infer::Regions(exp_found) => self.expected_found_str(exp_found),
2131 infer::Consts(exp_found) => self.expected_found_str(exp_found),
2132 infer::TraitRefs(exp_found) => {
2133 let pretty_exp_found = ty::error::ExpectedFound {
2134 expected: exp_found.expected.print_only_trait_path(),
2135 found: exp_found.found.print_only_trait_path(),
2137 match self.expected_found_str(pretty_exp_found) {
2138 Some((expected, found)) if expected == found => {
2139 self.expected_found_str(exp_found)
2144 infer::PolyTraitRefs(exp_found) => {
2145 let pretty_exp_found = ty::error::ExpectedFound {
2146 expected: exp_found.expected.print_only_trait_path(),
2147 found: exp_found.found.print_only_trait_path(),
2149 match self.expected_found_str(pretty_exp_found) {
2150 Some((expected, found)) if expected == found => {
2151 self.expected_found_str(exp_found)
2159 fn expected_found_str_ty(
2161 exp_found: ty::error::ExpectedFound<Ty<'tcx>>,
2162 ) -> Option<(DiagnosticStyledString, DiagnosticStyledString)> {
2163 let exp_found = self.resolve_vars_if_possible(exp_found);
2164 if exp_found.references_error() {
2168 Some(self.cmp(exp_found.expected, exp_found.found))
2171 /// Returns a string of the form "expected `{}`, found `{}`".
2172 fn expected_found_str<T: fmt::Display + TypeFoldable<'tcx>>(
2174 exp_found: ty::error::ExpectedFound<T>,
2175 ) -> Option<(DiagnosticStyledString, DiagnosticStyledString)> {
2176 let exp_found = self.resolve_vars_if_possible(exp_found);
2177 if exp_found.references_error() {
2182 DiagnosticStyledString::highlighted(exp_found.expected.to_string()),
2183 DiagnosticStyledString::highlighted(exp_found.found.to_string()),
2187 pub fn report_generic_bound_failure(
2190 origin: Option<SubregionOrigin<'tcx>>,
2191 bound_kind: GenericKind<'tcx>,
2194 self.construct_generic_bound_failure(span, origin, bound_kind, sub).emit();
2197 pub fn construct_generic_bound_failure(
2200 origin: Option<SubregionOrigin<'tcx>>,
2201 bound_kind: GenericKind<'tcx>,
2203 ) -> DiagnosticBuilder<'a> {
2204 let hir = &self.tcx.hir();
2205 // Attempt to obtain the span of the parameter so we can
2206 // suggest adding an explicit lifetime bound to it.
2208 .in_progress_typeck_results
2209 .map(|typeck_results| typeck_results.borrow().hir_owner)
2211 let hir_id = hir.local_def_id_to_hir_id(owner);
2212 let parent_id = hir.get_parent_item(hir_id);
2214 // Parent item could be a `mod`, so we check the HIR before calling:
2215 if let Some(Node::Item(Item {
2216 kind: ItemKind::Trait(..) | ItemKind::Impl { .. },
2218 })) = hir.find(parent_id)
2220 Some(self.tcx.generics_of(hir.local_def_id(parent_id).to_def_id()))
2224 self.tcx.generics_of(owner.to_def_id()),
2229 let span = match generics {
2230 // This is to get around the trait identity obligation, that has a `DUMMY_SP` as signal
2231 // for other diagnostics, so we need to recover it here.
2232 Some((_, _, node)) if span.is_dummy() => node,
2236 let type_param_span = match (generics, bound_kind) {
2237 (Some((_, ref generics, _)), GenericKind::Param(ref param)) => {
2238 // Account for the case where `param` corresponds to `Self`,
2239 // which doesn't have the expected type argument.
2240 if !(generics.has_self && param.index == 0) {
2241 let type_param = generics.type_param(param, self.tcx);
2242 type_param.def_id.as_local().map(|def_id| {
2243 // Get the `hir::Param` to verify whether it already has any bounds.
2244 // We do this to avoid suggesting code that ends up as `T: 'a'b`,
2245 // instead we suggest `T: 'a + 'b` in that case.
2246 let id = hir.local_def_id_to_hir_id(def_id);
2247 let mut has_bounds = false;
2248 if let Node::GenericParam(param) = hir.get(id) {
2249 has_bounds = !param.bounds.is_empty();
2251 let sp = hir.span(id);
2252 // `sp` only covers `T`, change it so that it covers
2253 // `T:` when appropriate
2254 let is_impl_trait = bound_kind.to_string().starts_with("impl ");
2255 let sp = if has_bounds && !is_impl_trait {
2260 .next_point(self.tcx.sess.source_map().next_point(sp)))
2264 (sp, has_bounds, is_impl_trait)
2272 let new_lt = generics
2274 .and_then(|(parent_g, g, _)| {
2275 let mut possible = (b'a'..=b'z').map(|c| format!("'{}", c as char));
2276 let mut lts_names = g
2279 .filter(|p| matches!(p.kind, ty::GenericParamDefKind::Lifetime))
2280 .map(|p| p.name.as_str())
2281 .collect::<Vec<_>>();
2282 if let Some(g) = parent_g {
2286 .filter(|p| matches!(p.kind, ty::GenericParamDefKind::Lifetime))
2287 .map(|p| p.name.as_str()),
2290 possible.find(|candidate| !lts_names.contains(&&candidate[..]))
2292 .unwrap_or("'lt".to_string());
2293 let add_lt_sugg = generics
2295 .and_then(|(_, g, _)| g.params.first())
2296 .and_then(|param| param.def_id.as_local())
2299 hir.span(hir.local_def_id_to_hir_id(def_id)).shrink_to_lo(),
2300 format!("{}, ", new_lt),
2304 let labeled_user_string = match bound_kind {
2305 GenericKind::Param(ref p) => format!("the parameter type `{}`", p),
2306 GenericKind::Projection(ref p) => format!("the associated type `{}`", p),
2309 if let Some(SubregionOrigin::CompareImplMethodObligation {
2315 return self.report_extra_impl_obligation(
2319 &format!("`{}: {}`", bound_kind, sub),
2323 fn binding_suggestion<'tcx, S: fmt::Display>(
2324 err: &mut DiagnosticBuilder<'tcx>,
2325 type_param_span: Option<(Span, bool, bool)>,
2326 bound_kind: GenericKind<'tcx>,
2329 let msg = "consider adding an explicit lifetime bound";
2330 if let Some((sp, has_lifetimes, is_impl_trait)) = type_param_span {
2331 let suggestion = if is_impl_trait {
2332 format!("{} + {}", bound_kind, sub)
2334 let tail = if has_lifetimes { " + " } else { "" };
2335 format!("{}: {}{}", bound_kind, sub, tail)
2337 err.span_suggestion(
2339 &format!("{}...", msg),
2341 Applicability::MaybeIncorrect, // Issue #41966
2344 let consider = format!(
2347 if type_param_span.map_or(false, |(_, _, is_impl_trait)| is_impl_trait) {
2348 format!(" `{}` to `{}`", sub, bound_kind)
2350 format!("`{}: {}`", bound_kind, sub)
2353 err.help(&consider);
2357 let new_binding_suggestion =
2358 |err: &mut DiagnosticBuilder<'tcx>,
2359 type_param_span: Option<(Span, bool, bool)>,
2360 bound_kind: GenericKind<'tcx>| {
2361 let msg = "consider introducing an explicit lifetime bound";
2362 if let Some((sp, has_lifetimes, is_impl_trait)) = type_param_span {
2363 let suggestion = if is_impl_trait {
2364 (sp.shrink_to_hi(), format!(" + {}", new_lt))
2366 let tail = if has_lifetimes { " +" } else { "" };
2367 (sp, format!("{}: {}{}", bound_kind, new_lt, tail))
2370 vec![suggestion, (span.shrink_to_hi(), format!(" + {}", new_lt))];
2371 if let Some(lt) = add_lt_sugg {
2373 sugg.rotate_right(1);
2375 // `MaybeIncorrect` due to issue #41966.
2376 err.multipart_suggestion(msg, sugg, Applicability::MaybeIncorrect);
2381 enum SubOrigin<'hir> {
2382 GAT(&'hir hir::Generics<'hir>),
2383 Impl(&'hir hir::Generics<'hir>),
2384 Trait(&'hir hir::Generics<'hir>),
2385 Fn(&'hir hir::Generics<'hir>),
2388 let sub_origin = 'origin: {
2390 ty::ReEarlyBound(ty::EarlyBoundRegion { def_id, .. }) => {
2391 let node = self.tcx.hir().get_if_local(def_id).unwrap();
2393 Node::GenericParam(param) => {
2394 for h in self.tcx.hir().parent_iter(param.hir_id) {
2395 break 'origin match h.1 {
2396 Node::ImplItem(hir::ImplItem {
2397 kind: hir::ImplItemKind::TyAlias(..),
2400 }) => SubOrigin::GAT(generics),
2401 Node::ImplItem(hir::ImplItem {
2402 kind: hir::ImplItemKind::Fn(..),
2405 }) => SubOrigin::Fn(generics),
2406 Node::TraitItem(hir::TraitItem {
2407 kind: hir::TraitItemKind::Type(..),
2410 }) => SubOrigin::GAT(generics),
2411 Node::TraitItem(hir::TraitItem {
2412 kind: hir::TraitItemKind::Fn(..),
2415 }) => SubOrigin::Fn(generics),
2416 Node::Item(hir::Item {
2417 kind: hir::ItemKind::Trait(_, _, generics, _, _),
2419 }) => SubOrigin::Trait(generics),
2420 Node::Item(hir::Item {
2421 kind: hir::ItemKind::Impl(hir::Impl { generics, .. }),
2423 }) => SubOrigin::Impl(generics),
2424 Node::Item(hir::Item {
2425 kind: hir::ItemKind::Fn(_, generics, _),
2427 }) => SubOrigin::Fn(generics),
2439 debug!(?sub_origin);
2441 let mut err = match (*sub, sub_origin) {
2442 // In the case of GATs, we have to be careful. If we a type parameter `T` on an impl,
2443 // but a lifetime `'a` on an associated type, then we might need to suggest adding
2444 // `where T: 'a`. Importantly, this is on the GAT span, not on the `T` declaration.
2445 (ty::ReEarlyBound(ty::EarlyBoundRegion { name: _, .. }), SubOrigin::GAT(generics)) => {
2446 // Does the required lifetime have a nice name we can print?
2447 let mut err = struct_span_err!(
2451 "{} may not live long enough",
2454 let pred = format!("{}: {}", bound_kind, sub);
2455 let suggestion = format!(
2457 if !generics.where_clause.predicates.is_empty() { "," } else { " where" },
2460 err.span_suggestion(
2461 generics.where_clause.tail_span_for_suggestion(),
2462 "consider adding a where clause",
2464 Applicability::MaybeIncorrect,
2469 ty::ReEarlyBound(ty::EarlyBoundRegion { name, .. })
2470 | ty::ReFree(ty::FreeRegion { bound_region: ty::BrNamed(_, name), .. }),
2473 // Does the required lifetime have a nice name we can print?
2474 let mut err = struct_span_err!(
2478 "{} may not live long enough",
2481 // Explicitly use the name instead of `sub`'s `Display` impl. The `Display` impl
2482 // for the bound is not suitable for suggestions when `-Zverbose` is set because it
2483 // uses `Debug` output, so we handle it specially here so that suggestions are
2485 binding_suggestion(&mut err, type_param_span, bound_kind, name);
2489 (ty::ReStatic, _) => {
2490 // Does the required lifetime have a nice name we can print?
2491 let mut err = struct_span_err!(
2495 "{} may not live long enough",
2498 binding_suggestion(&mut err, type_param_span, bound_kind, "'static");
2503 // If not, be less specific.
2504 let mut err = struct_span_err!(
2508 "{} may not live long enough",
2511 note_and_explain_region(
2514 &format!("{} must be valid for ", labeled_user_string),
2519 if let Some(infer::RelateParamBound(_, t, _)) = origin {
2520 let return_impl_trait = self
2521 .in_progress_typeck_results
2522 .map(|typeck_results| typeck_results.borrow().hir_owner)
2523 .and_then(|owner| self.tcx.return_type_impl_trait(owner))
2525 let t = self.resolve_vars_if_possible(t);
2528 // fn get_later<G, T>(g: G, dest: &mut T) -> impl FnOnce() + '_
2530 // fn get_later<'a, G: 'a, T>(g: G, dest: &mut T) -> impl FnOnce() + '_ + 'a
2531 ty::Closure(_, _substs) | ty::Opaque(_, _substs) if return_impl_trait => {
2532 new_binding_suggestion(&mut err, type_param_span, bound_kind);
2535 binding_suggestion(&mut err, type_param_span, bound_kind, new_lt);
2543 if let Some(origin) = origin {
2544 self.note_region_origin(&mut err, &origin);
2549 fn report_sub_sup_conflict(
2551 var_origin: RegionVariableOrigin,
2552 sub_origin: SubregionOrigin<'tcx>,
2553 sub_region: Region<'tcx>,
2554 sup_origin: SubregionOrigin<'tcx>,
2555 sup_region: Region<'tcx>,
2557 let mut err = self.report_inference_failure(var_origin);
2559 note_and_explain_region(
2562 "first, the lifetime cannot outlive ",
2568 debug!("report_sub_sup_conflict: var_origin={:?}", var_origin);
2569 debug!("report_sub_sup_conflict: sub_region={:?}", sub_region);
2570 debug!("report_sub_sup_conflict: sub_origin={:?}", sub_origin);
2571 debug!("report_sub_sup_conflict: sup_region={:?}", sup_region);
2572 debug!("report_sub_sup_conflict: sup_origin={:?}", sup_origin);
2574 if let (&infer::Subtype(ref sup_trace), &infer::Subtype(ref sub_trace)) =
2575 (&sup_origin, &sub_origin)
2577 debug!("report_sub_sup_conflict: sup_trace={:?}", sup_trace);
2578 debug!("report_sub_sup_conflict: sub_trace={:?}", sub_trace);
2579 debug!("report_sub_sup_conflict: sup_trace.values={:?}", sup_trace.values);
2580 debug!("report_sub_sup_conflict: sub_trace.values={:?}", sub_trace.values);
2582 if let (Some((sup_expected, sup_found)), Some((sub_expected, sub_found))) =
2583 (self.values_str(sup_trace.values), self.values_str(sub_trace.values))
2585 if sub_expected == sup_expected && sub_found == sup_found {
2586 note_and_explain_region(
2589 "...but the lifetime must also be valid for ",
2595 sup_trace.cause.span,
2596 &format!("...so that the {}", sup_trace.cause.as_requirement_str()),
2599 err.note_expected_found(&"", sup_expected, &"", sup_found);
2606 self.note_region_origin(&mut err, &sup_origin);
2608 note_and_explain_region(
2611 "but, the lifetime must be valid for ",
2617 self.note_region_origin(&mut err, &sub_origin);
2621 /// Determine whether an error associated with the given span and definition
2622 /// should be treated as being caused by the implicit `From` conversion
2623 /// within `?` desugaring.
2624 pub fn is_try_conversion(&self, span: Span, trait_def_id: DefId) -> bool {
2625 span.is_desugaring(DesugaringKind::QuestionMark)
2626 && self.tcx.is_diagnostic_item(sym::From, trait_def_id)
2630 impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
2631 fn report_inference_failure(
2633 var_origin: RegionVariableOrigin,
2634 ) -> DiagnosticBuilder<'tcx> {
2635 let br_string = |br: ty::BoundRegionKind| {
2636 let mut s = match br {
2637 ty::BrNamed(_, name) => name.to_string(),
2645 let var_description = match var_origin {
2646 infer::MiscVariable(_) => String::new(),
2647 infer::PatternRegion(_) => " for pattern".to_string(),
2648 infer::AddrOfRegion(_) => " for borrow expression".to_string(),
2649 infer::Autoref(_) => " for autoref".to_string(),
2650 infer::Coercion(_) => " for automatic coercion".to_string(),
2651 infer::LateBoundRegion(_, br, infer::FnCall) => {
2652 format!(" for lifetime parameter {}in function call", br_string(br))
2654 infer::LateBoundRegion(_, br, infer::HigherRankedType) => {
2655 format!(" for lifetime parameter {}in generic type", br_string(br))
2657 infer::LateBoundRegion(_, br, infer::AssocTypeProjection(def_id)) => format!(
2658 " for lifetime parameter {}in trait containing associated type `{}`",
2660 self.tcx.associated_item(def_id).ident
2662 infer::EarlyBoundRegion(_, name) => format!(" for lifetime parameter `{}`", name),
2663 infer::UpvarRegion(ref upvar_id, _) => {
2664 let var_name = self.tcx.hir().name(upvar_id.var_path.hir_id);
2665 format!(" for capture of `{}` by closure", var_name)
2667 infer::Nll(..) => bug!("NLL variable found in lexical phase"),
2674 "cannot infer an appropriate lifetime{} due to conflicting requirements",
2682 Error0317(&'static str),
2683 Error0580(&'static str),
2684 Error0308(&'static str),
2685 Error0644(&'static str),
2688 trait ObligationCauseExt<'tcx> {
2689 fn as_failure_code(&self, terr: &TypeError<'tcx>) -> FailureCode;
2690 fn as_requirement_str(&self) -> &'static str;
2693 impl<'tcx> ObligationCauseExt<'tcx> for ObligationCause<'tcx> {
2694 fn as_failure_code(&self, terr: &TypeError<'tcx>) -> FailureCode {
2695 use self::FailureCode::*;
2696 use crate::traits::ObligationCauseCode::*;
2698 CompareImplMethodObligation { .. } => Error0308("method not compatible with trait"),
2699 CompareImplTypeObligation { .. } => Error0308("type not compatible with trait"),
2700 MatchExpressionArm(box MatchExpressionArmCause { source, .. }) => {
2701 Error0308(match source {
2702 hir::MatchSource::TryDesugar => "`?` operator has incompatible types",
2703 _ => "`match` arms have incompatible types",
2706 IfExpression { .. } => Error0308("`if` and `else` have incompatible types"),
2707 IfExpressionWithNoElse => Error0317("`if` may be missing an `else` clause"),
2708 LetElse => Error0308("`else` clause of `let...else` does not diverge"),
2709 MainFunctionType => Error0580("`main` function has wrong type"),
2710 StartFunctionType => Error0308("`#[start]` function has wrong type"),
2711 IntrinsicType => Error0308("intrinsic has wrong type"),
2712 MethodReceiver => Error0308("mismatched `self` parameter type"),
2714 // In the case where we have no more specific thing to
2715 // say, also take a look at the error code, maybe we can
2718 TypeError::CyclicTy(ty) if ty.is_closure() || ty.is_generator() => {
2719 Error0644("closure/generator type that references itself")
2721 TypeError::IntrinsicCast => {
2722 Error0308("cannot coerce intrinsics to function pointers")
2724 TypeError::ObjectUnsafeCoercion(did) => Error0038(*did),
2725 _ => Error0308("mismatched types"),
2730 fn as_requirement_str(&self) -> &'static str {
2731 use crate::traits::ObligationCauseCode::*;
2733 CompareImplMethodObligation { .. } => "method type is compatible with trait",
2734 CompareImplTypeObligation { .. } => "associated type is compatible with trait",
2735 ExprAssignable => "expression is assignable",
2736 IfExpression { .. } => "`if` and `else` have incompatible types",
2737 IfExpressionWithNoElse => "`if` missing an `else` returns `()`",
2738 MainFunctionType => "`main` function has the correct type",
2739 StartFunctionType => "`#[start]` function has the correct type",
2740 IntrinsicType => "intrinsic has the correct type",
2741 MethodReceiver => "method receiver has the correct type",
2742 _ => "types are compatible",
2747 /// This is a bare signal of what kind of type we're dealing with. `ty::TyKind` tracks
2748 /// extra information about each type, but we only care about the category.
2749 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
2750 pub enum TyCategory {
2753 Generator(hir::GeneratorKind),
2758 fn descr(&self) -> &'static str {
2760 Self::Closure => "closure",
2761 Self::Opaque => "opaque type",
2762 Self::Generator(gk) => gk.descr(),
2763 Self::Foreign => "foreign type",
2767 pub fn from_ty(tcx: TyCtxt<'_>, ty: Ty<'_>) -> Option<(Self, DefId)> {
2769 ty::Closure(def_id, _) => Some((Self::Closure, def_id)),
2770 ty::Opaque(def_id, _) => Some((Self::Opaque, def_id)),
2771 ty::Generator(def_id, ..) => {
2772 Some((Self::Generator(tcx.generator_kind(def_id).unwrap()), def_id))
2774 ty::Foreign(def_id) => Some((Self::Foreign, def_id)),