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 basis of the system are the "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::opaque_types;
54 use crate::infer::{self, SuppressRegionErrors};
55 use crate::middle::region;
56 use crate::traits::error_reporting::report_object_safety_error;
58 IfExpressionCause, MatchExpressionArmCause, ObligationCause, ObligationCauseCode,
60 use crate::ty::error::TypeError;
63 subst::{Subst, SubstsRef},
64 Region, Ty, TyCtxt, TypeFoldable,
67 use rustc_hir::def_id::DefId;
70 use errors::{Applicability, DiagnosticBuilder, DiagnosticStyledString};
71 use rustc_error_codes::*;
72 use rustc_span::{Pos, Span};
73 use rustc_target::spec::abi;
79 pub use need_type_info::TypeAnnotationNeeded;
81 pub mod nice_region_error;
83 pub(super) fn note_and_explain_region(
85 region_scope_tree: ®ion::ScopeTree,
86 err: &mut DiagnosticBuilder<'_>,
88 region: ty::Region<'tcx>,
91 let (description, span) = match *region {
92 ty::ReScope(scope) => {
95 || format!("{}unknown scope: {:?}{}. Please report a bug.", prefix, scope, suffix);
96 let span = scope.span(tcx, region_scope_tree);
97 let tag = match tcx.hir().find(scope.hir_id(region_scope_tree)) {
98 Some(Node::Block(_)) => "block",
99 Some(Node::Expr(expr)) => match expr.kind {
100 hir::ExprKind::Call(..) => "call",
101 hir::ExprKind::MethodCall(..) => "method call",
102 hir::ExprKind::Match(.., hir::MatchSource::IfLetDesugar { .. }) => "if let",
103 hir::ExprKind::Match(.., hir::MatchSource::WhileLetDesugar) => "while let",
104 hir::ExprKind::Match(.., hir::MatchSource::ForLoopDesugar) => "for",
105 hir::ExprKind::Match(..) => "match",
108 Some(Node::Stmt(_)) => "statement",
109 Some(Node::Item(it)) => item_scope_tag(&it),
110 Some(Node::TraitItem(it)) => trait_item_scope_tag(&it),
111 Some(Node::ImplItem(it)) => impl_item_scope_tag(&it),
113 err.span_note(span, &unknown_scope());
117 let scope_decorated_tag = match scope.data {
118 region::ScopeData::Node => tag,
119 region::ScopeData::CallSite => "scope of call-site for function",
120 region::ScopeData::Arguments => "scope of function body",
121 region::ScopeData::Destruction => {
122 new_string = format!("destruction scope surrounding {}", tag);
125 region::ScopeData::Remainder(first_statement_index) => {
126 new_string = format!(
127 "block suffix following statement {}",
128 first_statement_index.index()
133 explain_span(tcx, scope_decorated_tag, span)
136 ty::ReEarlyBound(_) | ty::ReFree(_) | ty::ReStatic => {
137 msg_span_from_free_region(tcx, region)
140 ty::ReEmpty => ("the empty lifetime".to_owned(), None),
142 ty::RePlaceholder(_) => (format!("any other region"), None),
144 // FIXME(#13998) RePlaceholder should probably print like
145 // ReFree rather than dumping Debug output on the user.
147 // We shouldn't really be having unification failures with ReVar
148 // and ReLateBound though.
149 ty::ReVar(_) | ty::ReLateBound(..) | ty::ReErased => {
150 (format!("lifetime {:?}", region), None)
153 // We shouldn't encounter an error message with ReClosureBound.
154 ty::ReClosureBound(..) => {
155 bug!("encountered unexpected ReClosureBound: {:?}", region,);
159 emit_msg_span(err, prefix, description, span, suffix);
162 pub(super) fn note_and_explain_free_region(
164 err: &mut DiagnosticBuilder<'_>,
166 region: ty::Region<'tcx>,
169 let (description, span) = msg_span_from_free_region(tcx, region);
171 emit_msg_span(err, prefix, description, span, suffix);
174 fn msg_span_from_free_region(
176 region: ty::Region<'tcx>,
177 ) -> (String, Option<Span>) {
179 ty::ReEarlyBound(_) | ty::ReFree(_) => {
180 msg_span_from_early_bound_and_free_regions(tcx, region)
182 ty::ReStatic => ("the static lifetime".to_owned(), None),
183 ty::ReEmpty => ("an empty lifetime".to_owned(), None),
184 _ => bug!("{:?}", region),
188 fn msg_span_from_early_bound_and_free_regions(
190 region: ty::Region<'tcx>,
191 ) -> (String, Option<Span>) {
192 let cm = tcx.sess.source_map();
194 let scope = region.free_region_binding_scope(tcx);
195 let node = tcx.hir().as_local_hir_id(scope).unwrap_or(hir::DUMMY_HIR_ID);
196 let tag = match tcx.hir().find(node) {
197 Some(Node::Block(_)) | Some(Node::Expr(_)) => "body",
198 Some(Node::Item(it)) => item_scope_tag(&it),
199 Some(Node::TraitItem(it)) => trait_item_scope_tag(&it),
200 Some(Node::ImplItem(it)) => impl_item_scope_tag(&it),
203 let (prefix, span) = match *region {
204 ty::ReEarlyBound(ref br) => {
205 let mut sp = cm.def_span(tcx.hir().span(node));
207 tcx.hir().get_generics(scope).and_then(|generics| generics.get_named(br.name))
211 (format!("the lifetime `{}` as defined on", br.name), sp)
213 ty::ReFree(ty::FreeRegion { bound_region: ty::BoundRegion::BrNamed(_, name), .. }) => {
214 let mut sp = cm.def_span(tcx.hir().span(node));
216 tcx.hir().get_generics(scope).and_then(|generics| generics.get_named(name))
220 (format!("the lifetime `{}` as defined on", name), sp)
222 ty::ReFree(ref fr) => match fr.bound_region {
224 (format!("the anonymous lifetime #{} defined on", idx + 1), tcx.hir().span(node))
227 format!("the lifetime `{}` as defined on", region),
228 cm.def_span(tcx.hir().span(node)),
233 let (msg, opt_span) = explain_span(tcx, tag, span);
234 (format!("{} {}", prefix, msg), opt_span)
238 err: &mut DiagnosticBuilder<'_>,
244 let message = format!("{}{}{}", prefix, description, suffix);
246 if let Some(span) = span {
247 err.span_note(span, &message);
253 fn item_scope_tag(item: &hir::Item<'_>) -> &'static str {
255 hir::ItemKind::Impl(..) => "impl",
256 hir::ItemKind::Struct(..) => "struct",
257 hir::ItemKind::Union(..) => "union",
258 hir::ItemKind::Enum(..) => "enum",
259 hir::ItemKind::Trait(..) => "trait",
260 hir::ItemKind::Fn(..) => "function body",
265 fn trait_item_scope_tag(item: &hir::TraitItem<'_>) -> &'static str {
267 hir::TraitItemKind::Method(..) => "method body",
268 hir::TraitItemKind::Const(..) | hir::TraitItemKind::Type(..) => "associated item",
272 fn impl_item_scope_tag(item: &hir::ImplItem<'_>) -> &'static str {
274 hir::ImplItemKind::Method(..) => "method body",
275 hir::ImplItemKind::Const(..)
276 | hir::ImplItemKind::OpaqueTy(..)
277 | hir::ImplItemKind::TyAlias(..) => "associated item",
281 fn explain_span(tcx: TyCtxt<'tcx>, heading: &str, span: Span) -> (String, Option<Span>) {
282 let lo = tcx.sess.source_map().lookup_char_pos(span.lo());
283 (format!("the {} at {}:{}", heading, lo.line, lo.col.to_usize() + 1), Some(span))
286 impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
287 pub fn report_region_errors(
289 region_scope_tree: ®ion::ScopeTree,
290 errors: &Vec<RegionResolutionError<'tcx>>,
291 suppress: SuppressRegionErrors,
294 "report_region_errors(): {} errors to start, suppress = {:?}",
299 if suppress.suppressed() {
303 // try to pre-process the errors, which will group some of them
304 // together into a `ProcessedErrors` group:
305 let errors = self.process_errors(errors);
307 debug!("report_region_errors: {} errors after preprocessing", errors.len());
309 for error in errors {
310 debug!("report_region_errors: error = {:?}", error);
312 if !self.try_report_nice_region_error(&error) {
313 match error.clone() {
314 // These errors could indicate all manner of different
315 // problems with many different solutions. Rather
316 // than generate a "one size fits all" error, what we
317 // attempt to do is go through a number of specific
318 // scenarios and try to find the best way to present
319 // the error. If all of these fails, we fall back to a rather
320 // general bit of code that displays the error information
321 RegionResolutionError::ConcreteFailure(origin, sub, sup) => {
322 if sub.is_placeholder() || sup.is_placeholder() {
323 self.report_placeholder_failure(region_scope_tree, origin, sub, sup)
326 self.report_concrete_failure(region_scope_tree, origin, sub, sup)
331 RegionResolutionError::GenericBoundFailure(origin, param_ty, sub) => {
332 self.report_generic_bound_failure(
341 RegionResolutionError::SubSupConflict(
349 if sub_r.is_placeholder() {
350 self.report_placeholder_failure(
357 } else if sup_r.is_placeholder() {
358 self.report_placeholder_failure(
366 self.report_sub_sup_conflict(
377 RegionResolutionError::MemberConstraintFailure {
384 let hidden_ty = self.resolve_vars_if_possible(&hidden_ty);
385 opaque_types::unexpected_hidden_region_diagnostic(
387 Some(region_scope_tree),
399 // This method goes through all the errors and try to group certain types
400 // of error together, for the purpose of suggesting explicit lifetime
401 // parameters to the user. This is done so that we can have a more
402 // complete view of what lifetimes should be the same.
403 // If the return value is an empty vector, it means that processing
404 // failed (so the return value of this method should not be used).
406 // The method also attempts to weed out messages that seem like
407 // duplicates that will be unhelpful to the end-user. But
408 // obviously it never weeds out ALL errors.
411 errors: &Vec<RegionResolutionError<'tcx>>,
412 ) -> Vec<RegionResolutionError<'tcx>> {
413 debug!("process_errors()");
415 // We want to avoid reporting generic-bound failures if we can
416 // avoid it: these have a very high rate of being unhelpful in
417 // practice. This is because they are basically secondary
418 // checks that test the state of the region graph after the
419 // rest of inference is done, and the other kinds of errors
420 // indicate that the region constraint graph is internally
421 // inconsistent, so these test results are likely to be
424 // Therefore, we filter them out of the list unless they are
425 // the only thing in the list.
427 let is_bound_failure = |e: &RegionResolutionError<'tcx>| match *e {
428 RegionResolutionError::GenericBoundFailure(..) => true,
429 RegionResolutionError::ConcreteFailure(..)
430 | RegionResolutionError::SubSupConflict(..)
431 | RegionResolutionError::MemberConstraintFailure { .. } => false,
434 let mut errors = if errors.iter().all(|e| is_bound_failure(e)) {
437 errors.iter().filter(|&e| !is_bound_failure(e)).cloned().collect()
440 // sort the errors by span, for better error message stability.
441 errors.sort_by_key(|u| match *u {
442 RegionResolutionError::ConcreteFailure(ref sro, _, _) => sro.span(),
443 RegionResolutionError::GenericBoundFailure(ref sro, _, _) => sro.span(),
444 RegionResolutionError::SubSupConflict(_, ref rvo, _, _, _, _) => rvo.span(),
445 RegionResolutionError::MemberConstraintFailure { span, .. } => span,
450 /// Adds a note if the types come from similarly named crates
451 fn check_and_note_conflicting_crates(
453 err: &mut DiagnosticBuilder<'_>,
454 terr: &TypeError<'tcx>,
456 use hir::def_id::CrateNum;
457 use map::DisambiguatedDefPathData;
458 use ty::print::Printer;
459 use ty::subst::GenericArg;
461 struct AbsolutePathPrinter<'tcx> {
465 struct NonTrivialPath;
467 impl<'tcx> Printer<'tcx> for AbsolutePathPrinter<'tcx> {
468 type Error = NonTrivialPath;
470 type Path = Vec<String>;
473 type DynExistential = !;
476 fn tcx<'a>(&'a self) -> TyCtxt<'tcx> {
480 fn print_region(self, _region: ty::Region<'_>) -> Result<Self::Region, Self::Error> {
484 fn print_type(self, _ty: Ty<'tcx>) -> Result<Self::Type, Self::Error> {
488 fn print_dyn_existential(
490 _predicates: &'tcx ty::List<ty::ExistentialPredicate<'tcx>>,
491 ) -> Result<Self::DynExistential, Self::Error> {
495 fn print_const(self, _ct: &'tcx ty::Const<'tcx>) -> Result<Self::Const, Self::Error> {
499 fn path_crate(self, cnum: CrateNum) -> Result<Self::Path, Self::Error> {
500 Ok(vec![self.tcx.original_crate_name(cnum).to_string()])
505 _trait_ref: Option<ty::TraitRef<'tcx>>,
506 ) -> Result<Self::Path, Self::Error> {
512 _print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
513 _disambiguated_data: &DisambiguatedDefPathData,
515 _trait_ref: Option<ty::TraitRef<'tcx>>,
516 ) -> Result<Self::Path, Self::Error> {
521 print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
522 disambiguated_data: &DisambiguatedDefPathData,
523 ) -> Result<Self::Path, Self::Error> {
524 let mut path = print_prefix(self)?;
525 path.push(disambiguated_data.data.as_symbol().to_string());
528 fn path_generic_args(
530 print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
531 _args: &[GenericArg<'tcx>],
532 ) -> Result<Self::Path, Self::Error> {
537 let report_path_match = |err: &mut DiagnosticBuilder<'_>, did1: DefId, did2: DefId| {
538 // Only external crates, if either is from a local
539 // module we could have false positives
540 if !(did1.is_local() || did2.is_local()) && did1.krate != did2.krate {
542 |def_id| AbsolutePathPrinter { tcx: self.tcx }.print_def_path(def_id, &[]);
544 // We compare strings because DefPath can be different
545 // for imported and non-imported crates
546 let same_path = || -> Result<_, NonTrivialPath> {
547 Ok(self.tcx.def_path_str(did1) == self.tcx.def_path_str(did2)
548 || abs_path(did1)? == abs_path(did2)?)
550 if same_path().unwrap_or(false) {
551 let crate_name = self.tcx.crate_name(did1.krate);
553 "perhaps two different versions of crate `{}` are being used?",
560 TypeError::Sorts(ref exp_found) => {
561 // if they are both "path types", there's a chance of ambiguity
562 // due to different versions of the same crate
563 if let (&ty::Adt(exp_adt, _), &ty::Adt(found_adt, _)) =
564 (&exp_found.expected.kind, &exp_found.found.kind)
566 report_path_match(err, exp_adt.did, found_adt.did);
569 TypeError::Traits(ref exp_found) => {
570 report_path_match(err, exp_found.expected, exp_found.found);
572 _ => (), // FIXME(#22750) handle traits and stuff
576 fn note_error_origin(
578 err: &mut DiagnosticBuilder<'tcx>,
579 cause: &ObligationCause<'tcx>,
580 exp_found: Option<ty::error::ExpectedFound<Ty<'tcx>>>,
583 ObligationCauseCode::Pattern { origin_expr: true, span: Some(span), root_ty } => {
584 let ty = self.resolve_vars_if_possible(&root_ty);
585 if ty.is_suggestable() {
586 // don't show type `_`
587 err.span_label(span, format!("this expression has type `{}`", ty));
589 if let Some(ty::error::ExpectedFound { found, .. }) = exp_found {
590 if ty.is_box() && ty.boxed_ty() == found {
591 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
594 "consider dereferencing the boxed value",
595 format!("*{}", snippet),
596 Applicability::MachineApplicable,
602 ObligationCauseCode::Pattern { origin_expr: false, span: Some(span), .. } => {
603 err.span_label(span, "expected due to this");
605 ObligationCauseCode::MatchExpressionArm(box MatchExpressionArmCause {
612 hir::MatchSource::IfLetDesugar { .. } => {
613 let msg = "`if let` arms have incompatible types";
614 err.span_label(cause.span, msg);
616 hir::MatchSource::TryDesugar => {
617 if let Some(ty::error::ExpectedFound { expected, .. }) = exp_found {
618 let scrut_expr = self.tcx.hir().expect_expr(scrut_hir_id);
619 let scrut_ty = if let hir::ExprKind::Call(_, args) = &scrut_expr.kind {
620 let arg_expr = args.first().expect("try desugaring call w/out arg");
621 self.in_progress_tables
622 .and_then(|tables| tables.borrow().expr_ty_opt(arg_expr))
624 bug!("try desugaring w/out call expr as scrutinee");
628 Some(ty) if expected == ty => {
629 let source_map = self.tcx.sess.source_map();
631 source_map.end_point(cause.span),
632 "try removing this `?`",
634 Applicability::MachineApplicable,
642 // `last_ty` can be `!`, `expected` will have better info when present.
643 let t = self.resolve_vars_if_possible(&match exp_found {
644 Some(ty::error::ExpectedFound { expected, .. }) => expected,
647 let msg = "`match` arms have incompatible types";
648 err.span_label(cause.span, msg);
649 if prior_arms.len() <= 4 {
650 for sp in prior_arms {
651 err.span_label(*sp, format!("this is found to be of type `{}`", t));
653 } else if let Some(sp) = prior_arms.last() {
656 format!("this and all prior arms are found to be of type `{}`", t),
661 ObligationCauseCode::IfExpression(box IfExpressionCause { then, outer, semicolon }) => {
662 err.span_label(then, "expected because of this");
663 outer.map(|sp| err.span_label(sp, "`if` and `else` have incompatible types"));
664 if let Some(sp) = semicolon {
665 err.span_suggestion_short(
667 "consider removing this semicolon",
669 Applicability::MachineApplicable,
677 /// Given that `other_ty` is the same as a type argument for `name` in `sub`, populate `value`
678 /// highlighting `name` and every type argument that isn't at `pos` (which is `other_ty`), and
679 /// populate `other_value` with `other_ty`.
683 /// ^^^^--------^ this is highlighted
685 /// | this type argument is exactly the same as the other type, not highlighted
686 /// this is highlighted
688 /// -------- this type is the same as a type argument in the other type, not highlighted
692 value: &mut DiagnosticStyledString,
693 other_value: &mut DiagnosticStyledString,
695 sub: ty::subst::SubstsRef<'tcx>,
699 // `value` and `other_value` hold two incomplete type representation for display.
700 // `name` is the path of both types being compared. `sub`
701 value.push_highlighted(name);
704 value.push_highlighted("<");
707 // Output the lifetimes for the first type
711 let s = lifetime.to_string();
712 if s.is_empty() { "'_".to_string() } else { s }
716 if !lifetimes.is_empty() {
717 if sub.regions().count() < len {
718 value.push_normal(lifetimes + &", ");
720 value.push_normal(lifetimes);
724 // Highlight all the type arguments that aren't at `pos` and compare the type argument at
725 // `pos` and `other_ty`.
726 for (i, type_arg) in sub.types().enumerate() {
728 let values = self.cmp(type_arg, other_ty);
729 value.0.extend((values.0).0);
730 other_value.0.extend((values.1).0);
732 value.push_highlighted(type_arg.to_string());
735 if len > 0 && i != len - 1 {
736 value.push_normal(", ");
740 value.push_highlighted(">");
744 /// If `other_ty` is the same as a type argument present in `sub`, highlight `path` in `t1_out`,
745 /// as that is the difference to the other type.
747 /// For the following code:
750 /// let x: Foo<Bar<Qux>> = foo::<Bar<Qux>>();
753 /// The type error output will behave in the following way:
757 /// ^^^^--------^ this is highlighted
759 /// | this type argument is exactly the same as the other type, not highlighted
760 /// this is highlighted
762 /// -------- this type is the same as a type argument in the other type, not highlighted
766 mut t1_out: &mut DiagnosticStyledString,
767 mut t2_out: &mut DiagnosticStyledString,
769 sub: ty::subst::SubstsRef<'tcx>,
773 for (i, ta) in sub.types().enumerate() {
775 self.highlight_outer(&mut t1_out, &mut t2_out, path, sub, i, &other_ty);
778 if let &ty::Adt(def, _) = &ta.kind {
779 let path_ = self.tcx.def_path_str(def.did.clone());
780 if path_ == other_path {
781 self.highlight_outer(&mut t1_out, &mut t2_out, path, sub, i, &other_ty);
789 /// Adds a `,` to the type representation only if it is appropriate.
792 value: &mut DiagnosticStyledString,
793 other_value: &mut DiagnosticStyledString,
797 if len > 0 && pos != len - 1 {
798 value.push_normal(", ");
799 other_value.push_normal(", ");
803 /// For generic types with parameters with defaults, remove the parameters corresponding to
804 /// the defaults. This repeats a lot of the logic found in `ty::print::pretty`.
805 fn strip_generic_default_params(
808 substs: ty::subst::SubstsRef<'tcx>,
809 ) -> SubstsRef<'tcx> {
810 let generics = self.tcx.generics_of(def_id);
811 let mut num_supplied_defaults = 0;
812 let mut type_params = generics
816 .filter_map(|param| match param.kind {
817 ty::GenericParamDefKind::Lifetime => None,
818 ty::GenericParamDefKind::Type { has_default, .. } => {
819 Some((param.def_id, has_default))
821 ty::GenericParamDefKind::Const => None, // FIXME(const_generics:defaults)
825 let has_default = type_params.peek().map(|(_, has_default)| has_default);
826 *has_default.unwrap_or(&false)
829 let types = substs.types().rev();
830 for ((def_id, has_default), actual) in type_params.zip(types) {
834 if self.tcx.type_of(def_id).subst(self.tcx, substs) != actual {
837 num_supplied_defaults += 1;
840 let len = generics.params.len();
841 let mut generics = generics.clone();
842 generics.params.truncate(len - num_supplied_defaults);
843 substs.truncate_to(self.tcx, &generics)
846 /// Given two `fn` signatures highlight only sub-parts that are different.
849 sig1: &ty::PolyFnSig<'tcx>,
850 sig2: &ty::PolyFnSig<'tcx>,
851 ) -> (DiagnosticStyledString, DiagnosticStyledString) {
852 let get_lifetimes = |sig| {
853 use rustc_hir::def::Namespace;
854 let mut s = String::new();
855 let (_, (sig, reg)) = ty::print::FmtPrinter::new(self.tcx, &mut s, Namespace::TypeNS)
856 .name_all_regions(sig)
858 let lts: Vec<String> = reg.into_iter().map(|(_, kind)| kind.to_string()).collect();
859 (if lts.is_empty() { String::new() } else { format!("for<{}> ", lts.join(", ")) }, sig)
862 let (lt1, sig1) = get_lifetimes(sig1);
863 let (lt2, sig2) = get_lifetimes(sig2);
865 // unsafe extern "C" for<'a> fn(&'a T) -> &'a T
867 DiagnosticStyledString::normal("".to_string()),
868 DiagnosticStyledString::normal("".to_string()),
871 // unsafe extern "C" for<'a> fn(&'a T) -> &'a T
873 values.0.push(sig1.unsafety.prefix_str(), sig1.unsafety != sig2.unsafety);
874 values.1.push(sig2.unsafety.prefix_str(), sig1.unsafety != sig2.unsafety);
876 // unsafe extern "C" for<'a> fn(&'a T) -> &'a T
878 if sig1.abi != abi::Abi::Rust {
879 values.0.push(format!("extern {} ", sig1.abi), sig1.abi != sig2.abi);
881 if sig2.abi != abi::Abi::Rust {
882 values.1.push(format!("extern {} ", sig2.abi), sig1.abi != sig2.abi);
885 // unsafe extern "C" for<'a> fn(&'a T) -> &'a T
887 let lifetime_diff = lt1 != lt2;
888 values.0.push(lt1, lifetime_diff);
889 values.1.push(lt2, lifetime_diff);
891 // unsafe extern "C" for<'a> fn(&'a T) -> &'a T
893 values.0.push_normal("fn(");
894 values.1.push_normal("fn(");
896 // unsafe extern "C" for<'a> fn(&'a T) -> &'a T
898 let len1 = sig1.inputs().len();
899 let len2 = sig2.inputs().len();
901 for (i, (l, r)) in sig1.inputs().iter().zip(sig2.inputs().iter()).enumerate() {
902 let (x1, x2) = self.cmp(l, r);
903 (values.0).0.extend(x1.0);
904 (values.1).0.extend(x2.0);
905 self.push_comma(&mut values.0, &mut values.1, len1, i);
908 for (i, l) in sig1.inputs().iter().enumerate() {
909 values.0.push_highlighted(l.to_string());
911 values.0.push_highlighted(", ");
914 for (i, r) in sig2.inputs().iter().enumerate() {
915 values.1.push_highlighted(r.to_string());
917 values.1.push_highlighted(", ");
924 values.0.push_normal(", ");
926 values.0.push("...", !sig2.c_variadic);
930 values.1.push_normal(", ");
932 values.1.push("...", !sig1.c_variadic);
935 // unsafe extern "C" for<'a> fn(&'a T) -> &'a T
937 values.0.push_normal(")");
938 values.1.push_normal(")");
940 // unsafe extern "C" for<'a> fn(&'a T) -> &'a T
942 let output1 = sig1.output();
943 let output2 = sig2.output();
944 let (x1, x2) = self.cmp(output1, output2);
945 if !output1.is_unit() {
946 values.0.push_normal(" -> ");
947 (values.0).0.extend(x1.0);
949 if !output2.is_unit() {
950 values.1.push_normal(" -> ");
951 (values.1).0.extend(x2.0);
956 /// Compares two given types, eliding parts that are the same between them and highlighting
957 /// relevant differences, and return two representation of those types for highlighted printing.
958 fn cmp(&self, t1: Ty<'tcx>, t2: Ty<'tcx>) -> (DiagnosticStyledString, DiagnosticStyledString) {
959 debug!("cmp(t1={}, t1.kind={:?}, t2={}, t2.kind={:?})", t1, t1.kind, t2, t2.kind);
962 fn equals<'tcx>(a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
963 match (&a.kind, &b.kind) {
964 (a, b) if *a == *b => true,
965 (&ty::Int(_), &ty::Infer(ty::InferTy::IntVar(_)))
966 | (&ty::Infer(ty::InferTy::IntVar(_)), &ty::Int(_))
967 | (&ty::Infer(ty::InferTy::IntVar(_)), &ty::Infer(ty::InferTy::IntVar(_)))
968 | (&ty::Float(_), &ty::Infer(ty::InferTy::FloatVar(_)))
969 | (&ty::Infer(ty::InferTy::FloatVar(_)), &ty::Float(_))
970 | (&ty::Infer(ty::InferTy::FloatVar(_)), &ty::Infer(ty::InferTy::FloatVar(_))) => {
977 fn push_ty_ref<'tcx>(
978 r: &ty::Region<'tcx>,
980 mutbl: hir::Mutability,
981 s: &mut DiagnosticStyledString,
983 let mut r = r.to_string();
989 s.push_highlighted(format!("&{}{}", r, mutbl.prefix_str()));
990 s.push_normal(ty.to_string());
993 // process starts here
994 match (&t1.kind, &t2.kind) {
995 (&ty::Adt(def1, sub1), &ty::Adt(def2, sub2)) => {
996 let sub_no_defaults_1 = self.strip_generic_default_params(def1.did, sub1);
997 let sub_no_defaults_2 = self.strip_generic_default_params(def2.did, sub2);
998 let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new());
999 let path1 = self.tcx.def_path_str(def1.did.clone());
1000 let path2 = self.tcx.def_path_str(def2.did.clone());
1001 if def1.did == def2.did {
1002 // Easy case. Replace same types with `_` to shorten the output and highlight
1003 // the differing ones.
1004 // let x: Foo<Bar, Qux> = y::<Foo<Quz, Qux>>();
1007 // --- ^ type argument elided
1009 // highlighted in output
1010 values.0.push_normal(path1);
1011 values.1.push_normal(path2);
1013 // Avoid printing out default generic parameters that are common to both
1015 let len1 = sub_no_defaults_1.len();
1016 let len2 = sub_no_defaults_2.len();
1017 let common_len = cmp::min(len1, len2);
1018 let remainder1: Vec<_> = sub1.types().skip(common_len).collect();
1019 let remainder2: Vec<_> = sub2.types().skip(common_len).collect();
1020 let common_default_params = remainder1
1023 .zip(remainder2.iter().rev())
1024 .filter(|(a, b)| a == b)
1026 let len = sub1.len() - common_default_params;
1027 let consts_offset = len - sub1.consts().count();
1029 // Only draw `<...>` if there're lifetime/type arguments.
1031 values.0.push_normal("<");
1032 values.1.push_normal("<");
1035 fn lifetime_display(lifetime: Region<'_>) -> String {
1036 let s = lifetime.to_string();
1037 if s.is_empty() { "'_".to_string() } else { s }
1039 // At one point we'd like to elide all lifetimes here, they are irrelevant for
1040 // all diagnostics that use this output
1044 // ^^ ^^ --- type arguments are not elided
1046 // | elided as they were the same
1047 // not elided, they were different, but irrelevant
1048 let lifetimes = sub1.regions().zip(sub2.regions());
1049 for (i, lifetimes) in lifetimes.enumerate() {
1050 let l1 = lifetime_display(lifetimes.0);
1051 let l2 = lifetime_display(lifetimes.1);
1052 if lifetimes.0 == lifetimes.1 {
1053 values.0.push_normal("'_");
1054 values.1.push_normal("'_");
1056 values.0.push_highlighted(l1);
1057 values.1.push_highlighted(l2);
1059 self.push_comma(&mut values.0, &mut values.1, len, i);
1062 // We're comparing two types with the same path, so we compare the type
1063 // arguments for both. If they are the same, do not highlight and elide from the
1067 // ^ elided type as this type argument was the same in both sides
1068 let type_arguments = sub1.types().zip(sub2.types());
1069 let regions_len = sub1.regions().count();
1070 let num_display_types = consts_offset - regions_len;
1071 for (i, (ta1, ta2)) in type_arguments.take(num_display_types).enumerate() {
1072 let i = i + regions_len;
1074 values.0.push_normal("_");
1075 values.1.push_normal("_");
1077 let (x1, x2) = self.cmp(ta1, ta2);
1078 (values.0).0.extend(x1.0);
1079 (values.1).0.extend(x2.0);
1081 self.push_comma(&mut values.0, &mut values.1, len, i);
1084 // Do the same for const arguments, if they are equal, do not highlight and
1085 // elide them from the output.
1086 let const_arguments = sub1.consts().zip(sub2.consts());
1087 for (i, (ca1, ca2)) in const_arguments.enumerate() {
1088 let i = i + consts_offset;
1090 values.0.push_normal("_");
1091 values.1.push_normal("_");
1093 values.0.push_highlighted(ca1.to_string());
1094 values.1.push_highlighted(ca2.to_string());
1096 self.push_comma(&mut values.0, &mut values.1, len, i);
1099 // Close the type argument bracket.
1100 // Only draw `<...>` if there're lifetime/type arguments.
1102 values.0.push_normal(">");
1103 values.1.push_normal(">");
1108 // let x: Foo<Bar<Qux> = foo::<Bar<Qux>>();
1110 // ------- this type argument is exactly the same as the other type
1126 // let x: Bar<Qux> = y:<Foo<Bar<Qux>>>();
1129 // ------- this type argument is exactly the same as the other type
1144 // We can't find anything in common, highlight relevant part of type path.
1145 // let x: foo::bar::Baz<Qux> = y:<foo::bar::Bar<Zar>>();
1146 // foo::bar::Baz<Qux>
1147 // foo::bar::Bar<Zar>
1148 // -------- this part of the path is different
1150 let t1_str = t1.to_string();
1151 let t2_str = t2.to_string();
1152 let min_len = t1_str.len().min(t2_str.len());
1154 const SEPARATOR: &str = "::";
1155 let separator_len = SEPARATOR.len();
1156 let split_idx: usize = t1_str
1158 .zip(t2_str.split(SEPARATOR))
1159 .take_while(|(mod1_str, mod2_str)| mod1_str == mod2_str)
1160 .map(|(mod_str, _)| mod_str.len() + separator_len)
1164 "cmp: separator_len={}, split_idx={}, min_len={}",
1165 separator_len, split_idx, min_len
1168 if split_idx >= min_len {
1169 // paths are identical, highlight everything
1171 DiagnosticStyledString::highlighted(t1_str),
1172 DiagnosticStyledString::highlighted(t2_str),
1175 let (common, uniq1) = t1_str.split_at(split_idx);
1176 let (_, uniq2) = t2_str.split_at(split_idx);
1177 debug!("cmp: common={}, uniq1={}, uniq2={}", common, uniq1, uniq2);
1179 values.0.push_normal(common);
1180 values.0.push_highlighted(uniq1);
1181 values.1.push_normal(common);
1182 values.1.push_highlighted(uniq2);
1189 // When finding T != &T, highlight only the borrow
1190 (&ty::Ref(r1, ref_ty1, mutbl1), _) if equals(&ref_ty1, &t2) => {
1191 let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new());
1192 push_ty_ref(&r1, ref_ty1, mutbl1, &mut values.0);
1193 values.1.push_normal(t2.to_string());
1196 (_, &ty::Ref(r2, ref_ty2, mutbl2)) if equals(&t1, &ref_ty2) => {
1197 let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new());
1198 values.0.push_normal(t1.to_string());
1199 push_ty_ref(&r2, ref_ty2, mutbl2, &mut values.1);
1203 // When encountering &T != &mut T, highlight only the borrow
1204 (&ty::Ref(r1, ref_ty1, mutbl1), &ty::Ref(r2, ref_ty2, mutbl2))
1205 if equals(&ref_ty1, &ref_ty2) =>
1207 let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new());
1208 push_ty_ref(&r1, ref_ty1, mutbl1, &mut values.0);
1209 push_ty_ref(&r2, ref_ty2, mutbl2, &mut values.1);
1213 // When encountering tuples of the same size, highlight only the differing types
1214 (&ty::Tuple(substs1), &ty::Tuple(substs2)) if substs1.len() == substs2.len() => {
1216 (DiagnosticStyledString::normal("("), DiagnosticStyledString::normal("("));
1217 let len = substs1.len();
1218 for (i, (left, right)) in substs1.types().zip(substs2.types()).enumerate() {
1219 let (x1, x2) = self.cmp(left, right);
1220 (values.0).0.extend(x1.0);
1221 (values.1).0.extend(x2.0);
1222 self.push_comma(&mut values.0, &mut values.1, len, i);
1225 // Keep the output for single element tuples as `(ty,)`.
1226 values.0.push_normal(",");
1227 values.1.push_normal(",");
1229 values.0.push_normal(")");
1230 values.1.push_normal(")");
1234 (ty::FnDef(did1, substs1), ty::FnDef(did2, substs2)) => {
1235 let sig1 = self.tcx.fn_sig(*did1).subst(self.tcx, substs1);
1236 let sig2 = self.tcx.fn_sig(*did2).subst(self.tcx, substs2);
1237 let mut values = self.cmp_fn_sig(&sig1, &sig2);
1238 let path1 = format!(" {{{}}}", self.tcx.def_path_str_with_substs(*did1, substs1));
1239 let path2 = format!(" {{{}}}", self.tcx.def_path_str_with_substs(*did2, substs2));
1240 let same_path = path1 == path2;
1241 values.0.push(path1, !same_path);
1242 values.1.push(path2, !same_path);
1246 (ty::FnDef(did1, substs1), ty::FnPtr(sig2)) => {
1247 let sig1 = self.tcx.fn_sig(*did1).subst(self.tcx, substs1);
1248 let mut values = self.cmp_fn_sig(&sig1, sig2);
1249 values.0.push_normal(format!(
1251 self.tcx.def_path_str_with_substs(*did1, substs1)
1256 (ty::FnPtr(sig1), ty::FnDef(did2, substs2)) => {
1257 let sig2 = self.tcx.fn_sig(*did2).subst(self.tcx, substs2);
1258 let mut values = self.cmp_fn_sig(sig1, &sig2);
1259 values.1.push_normal(format!(
1261 self.tcx.def_path_str_with_substs(*did2, substs2)
1266 (ty::FnPtr(sig1), ty::FnPtr(sig2)) => self.cmp_fn_sig(sig1, sig2),
1270 // The two types are the same, elide and don't highlight.
1271 (DiagnosticStyledString::normal("_"), DiagnosticStyledString::normal("_"))
1273 // We couldn't find anything in common, highlight everything.
1275 DiagnosticStyledString::highlighted(t1.to_string()),
1276 DiagnosticStyledString::highlighted(t2.to_string()),
1283 pub fn note_type_err(
1285 diag: &mut DiagnosticBuilder<'tcx>,
1286 cause: &ObligationCause<'tcx>,
1287 secondary_span: Option<(Span, String)>,
1288 mut values: Option<ValuePairs<'tcx>>,
1289 terr: &TypeError<'tcx>,
1291 // For some types of errors, expected-found does not make
1292 // sense, so just ignore the values we were given.
1294 TypeError::CyclicTy(_) => {
1300 debug!("note_type_err(diag={:?})", diag);
1301 let (expected_found, exp_found, is_simple_error) = match values {
1302 None => (None, None, false),
1304 let (is_simple_error, exp_found) = match values {
1305 ValuePairs::Types(exp_found) => {
1307 exp_found.expected.is_simple_text() && exp_found.found.is_simple_text();
1309 (is_simple_err, Some(exp_found))
1313 let vals = match self.values_str(&values) {
1314 Some((expected, found)) => Some((expected, found)),
1316 // Derived error. Cancel the emitter.
1321 (vals, exp_found, is_simple_error)
1325 let span = cause.span(self.tcx);
1327 // Ignore msg for object safe coercion
1328 // since E0038 message will be printed
1330 TypeError::ObjectUnsafeCoercion(_) => {}
1332 diag.span_label(span, terr.to_string());
1333 if let Some((sp, msg)) = secondary_span {
1334 diag.span_label(sp, msg);
1339 if let Some((expected, found)) = expected_found {
1340 let expected_label = exp_found.map_or("type".into(), |ef| ef.expected.prefix_string());
1341 let found_label = exp_found.map_or("type".into(), |ef| ef.found.prefix_string());
1342 match (&terr, expected == found) {
1343 (TypeError::Sorts(values), extra) => {
1344 let sort_string = |ty: Ty<'tcx>| match (extra, &ty.kind) {
1345 (true, ty::Opaque(def_id, _)) => format!(
1346 " (opaque type at {})",
1350 .mk_substr_filename(self.tcx.def_span(*def_id)),
1352 (true, _) => format!(" ({})", ty.sort_string(self.tcx)),
1353 (false, _) => "".to_string(),
1355 if !(values.expected.is_simple_text() && values.found.is_simple_text())
1356 || (exp_found.map_or(false, |ef| {
1357 // This happens when the type error is a subset of the expectation,
1358 // like when you have two references but one is `usize` and the other
1359 // is `f32`. In those cases we still want to show the `note`. If the
1360 // value from `ef` is `Infer(_)`, then we ignore it.
1361 if !ef.expected.is_ty_infer() {
1362 ef.expected != values.expected
1363 } else if !ef.found.is_ty_infer() {
1364 ef.found != values.found
1370 diag.note_expected_found_extra(
1375 &sort_string(values.expected),
1376 &sort_string(values.found),
1380 (TypeError::ObjectUnsafeCoercion(_), _) => {
1381 diag.note_unsuccessfull_coercion(found, expected);
1385 "note_type_err: exp_found={:?}, expected={:?} found={:?}",
1386 exp_found, expected, found
1388 if !is_simple_error || terr.must_include_note() {
1389 diag.note_expected_found(&expected_label, expected, &found_label, found);
1394 if let Some(exp_found) = exp_found {
1395 self.suggest_as_ref_where_appropriate(span, &exp_found, diag);
1398 // In some (most?) cases cause.body_id points to actual body, but in some cases
1399 // it's a actual definition. According to the comments (e.g. in
1400 // librustc_typeck/check/compare_method.rs:compare_predicate_entailment) the latter
1401 // is relied upon by some other code. This might (or might not) need cleanup.
1402 let body_owner_def_id =
1403 self.tcx.hir().opt_local_def_id(cause.body_id).unwrap_or_else(|| {
1404 self.tcx.hir().body_owner_def_id(hir::BodyId { hir_id: cause.body_id })
1406 self.check_and_note_conflicting_crates(diag, terr);
1407 self.tcx.note_and_explain_type_err(diag, terr, span, body_owner_def_id);
1409 // It reads better to have the error origin as the final
1411 self.note_error_origin(diag, &cause, exp_found);
1414 /// When encountering a case where `.as_ref()` on a `Result` or `Option` would be appropriate,
1416 fn suggest_as_ref_where_appropriate(
1419 exp_found: &ty::error::ExpectedFound<Ty<'tcx>>,
1420 diag: &mut DiagnosticBuilder<'tcx>,
1422 match (&exp_found.expected.kind, &exp_found.found.kind) {
1423 (ty::Adt(exp_def, exp_substs), ty::Ref(_, found_ty, _)) => {
1424 if let ty::Adt(found_def, found_substs) = found_ty.kind {
1425 let path_str = format!("{:?}", exp_def);
1426 if exp_def == &found_def {
1427 let opt_msg = "you can convert from `&Option<T>` to `Option<&T>` using \
1429 let result_msg = "you can convert from `&Result<T, E>` to \
1430 `Result<&T, &E>` using `.as_ref()`";
1431 let have_as_ref = &[
1432 ("std::option::Option", opt_msg),
1433 ("core::option::Option", opt_msg),
1434 ("std::result::Result", result_msg),
1435 ("core::result::Result", result_msg),
1437 if let Some(msg) = have_as_ref
1440 |(path, msg)| if &path_str == path { Some(msg) } else { None },
1444 let mut show_suggestion = true;
1445 for (exp_ty, found_ty) in exp_substs.types().zip(found_substs.types()) {
1447 ty::Ref(_, exp_ty, _) => {
1448 match (&exp_ty.kind, &found_ty.kind) {
1452 | (ty::Infer(_), _) => {}
1453 _ if ty::TyS::same_type(exp_ty, found_ty) => {}
1454 _ => show_suggestion = false,
1457 ty::Param(_) | ty::Infer(_) => {}
1458 _ => show_suggestion = false,
1461 if let (Ok(snippet), true) =
1462 (self.tcx.sess.source_map().span_to_snippet(span), show_suggestion)
1464 diag.span_suggestion(
1467 format!("{}.as_ref()", snippet),
1468 Applicability::MachineApplicable,
1479 pub fn report_and_explain_type_error(
1481 trace: TypeTrace<'tcx>,
1482 terr: &TypeError<'tcx>,
1483 ) -> DiagnosticBuilder<'tcx> {
1484 debug!("report_and_explain_type_error(trace={:?}, terr={:?})", trace, terr);
1486 let span = trace.cause.span(self.tcx);
1487 let failure_code = trace.cause.as_failure_code(terr);
1488 let mut diag = match failure_code {
1489 FailureCode::Error0038(did) => {
1490 let violations = self.tcx.object_safety_violations(did);
1491 report_object_safety_error(self.tcx, span, did, violations)
1493 FailureCode::Error0317(failure_str) => {
1494 struct_span_err!(self.tcx.sess, span, E0317, "{}", failure_str)
1496 FailureCode::Error0580(failure_str) => {
1497 struct_span_err!(self.tcx.sess, span, E0580, "{}", failure_str)
1499 FailureCode::Error0308(failure_str) => {
1500 struct_span_err!(self.tcx.sess, span, E0308, "{}", failure_str)
1502 FailureCode::Error0644(failure_str) => {
1503 struct_span_err!(self.tcx.sess, span, E0644, "{}", failure_str)
1506 self.note_type_err(&mut diag, &trace.cause, None, Some(trace.values), terr);
1512 values: &ValuePairs<'tcx>,
1513 ) -> Option<(DiagnosticStyledString, DiagnosticStyledString)> {
1515 infer::Types(ref exp_found) => self.expected_found_str_ty(exp_found),
1516 infer::Regions(ref exp_found) => self.expected_found_str(exp_found),
1517 infer::Consts(ref exp_found) => self.expected_found_str(exp_found),
1518 infer::TraitRefs(ref exp_found) => {
1519 let pretty_exp_found = ty::error::ExpectedFound {
1520 expected: exp_found.expected.print_only_trait_path(),
1521 found: exp_found.found.print_only_trait_path(),
1523 self.expected_found_str(&pretty_exp_found)
1525 infer::PolyTraitRefs(ref exp_found) => {
1526 let pretty_exp_found = ty::error::ExpectedFound {
1527 expected: exp_found.expected.print_only_trait_path(),
1528 found: exp_found.found.print_only_trait_path(),
1530 self.expected_found_str(&pretty_exp_found)
1535 fn expected_found_str_ty(
1537 exp_found: &ty::error::ExpectedFound<Ty<'tcx>>,
1538 ) -> Option<(DiagnosticStyledString, DiagnosticStyledString)> {
1539 let exp_found = self.resolve_vars_if_possible(exp_found);
1540 if exp_found.references_error() {
1544 Some(self.cmp(exp_found.expected, exp_found.found))
1547 /// Returns a string of the form "expected `{}`, found `{}`".
1548 fn expected_found_str<T: fmt::Display + TypeFoldable<'tcx>>(
1550 exp_found: &ty::error::ExpectedFound<T>,
1551 ) -> Option<(DiagnosticStyledString, DiagnosticStyledString)> {
1552 let exp_found = self.resolve_vars_if_possible(exp_found);
1553 if exp_found.references_error() {
1558 DiagnosticStyledString::highlighted(exp_found.expected.to_string()),
1559 DiagnosticStyledString::highlighted(exp_found.found.to_string()),
1563 pub fn report_generic_bound_failure(
1565 region_scope_tree: ®ion::ScopeTree,
1567 origin: Option<SubregionOrigin<'tcx>>,
1568 bound_kind: GenericKind<'tcx>,
1571 self.construct_generic_bound_failure(region_scope_tree, span, origin, bound_kind, sub)
1575 pub fn construct_generic_bound_failure(
1577 region_scope_tree: ®ion::ScopeTree,
1579 origin: Option<SubregionOrigin<'tcx>>,
1580 bound_kind: GenericKind<'tcx>,
1582 ) -> DiagnosticBuilder<'a> {
1583 // Attempt to obtain the span of the parameter so we can
1584 // suggest adding an explicit lifetime bound to it.
1585 let type_param_span = match (self.in_progress_tables, bound_kind) {
1586 (Some(ref table), GenericKind::Param(ref param)) => {
1587 let table = table.borrow();
1588 table.local_id_root.and_then(|did| {
1589 let generics = self.tcx.generics_of(did);
1590 // Account for the case where `did` corresponds to `Self`, which doesn't have
1591 // the expected type argument.
1592 if !(generics.has_self && param.index == 0) {
1593 let type_param = generics.type_param(param, self.tcx);
1594 let hir = &self.tcx.hir();
1595 hir.as_local_hir_id(type_param.def_id).map(|id| {
1596 // Get the `hir::Param` to verify whether it already has any bounds.
1597 // We do this to avoid suggesting code that ends up as `T: 'a'b`,
1598 // instead we suggest `T: 'a + 'b` in that case.
1599 let mut has_bounds = false;
1600 if let Node::GenericParam(param) = hir.get(id) {
1601 has_bounds = !param.bounds.is_empty();
1603 let sp = hir.span(id);
1604 // `sp` only covers `T`, change it so that it covers
1605 // `T:` when appropriate
1606 let is_impl_trait = bound_kind.to_string().starts_with("impl ");
1607 let sp = if has_bounds && !is_impl_trait {
1612 .next_point(self.tcx.sess.source_map().next_point(sp)))
1616 (sp, has_bounds, is_impl_trait)
1626 let labeled_user_string = match bound_kind {
1627 GenericKind::Param(ref p) => format!("the parameter type `{}`", p),
1628 GenericKind::Projection(ref p) => format!("the associated type `{}`", p),
1631 if let Some(SubregionOrigin::CompareImplMethodObligation {
1638 return self.report_extra_impl_obligation(
1643 &format!("`{}: {}`", bound_kind, sub),
1647 fn binding_suggestion<'tcx, S: fmt::Display>(
1648 err: &mut DiagnosticBuilder<'tcx>,
1649 type_param_span: Option<(Span, bool, bool)>,
1650 bound_kind: GenericKind<'tcx>,
1653 let consider = format!(
1654 "consider adding an explicit lifetime bound {}",
1655 if type_param_span.map(|(_, _, is_impl_trait)| is_impl_trait).unwrap_or(false) {
1656 format!(" `{}` to `{}`...", sub, bound_kind)
1658 format!("`{}: {}`...", bound_kind, sub)
1661 if let Some((sp, has_lifetimes, is_impl_trait)) = type_param_span {
1662 let suggestion = if is_impl_trait {
1663 format!("{} + {}", bound_kind, sub)
1665 let tail = if has_lifetimes { " + " } else { "" };
1666 format!("{}: {}{}", bound_kind, sub, tail)
1668 err.span_suggestion_short(
1672 Applicability::MaybeIncorrect, // Issue #41966
1675 err.help(&consider);
1679 let mut err = match *sub {
1681 | ty::ReFree(ty::FreeRegion { bound_region: ty::BrNamed(..), .. }) => {
1682 // Does the required lifetime have a nice name we can print?
1683 let mut err = struct_span_err!(
1687 "{} may not live long enough",
1690 binding_suggestion(&mut err, type_param_span, bound_kind, sub);
1695 // Does the required lifetime have a nice name we can print?
1696 let mut err = struct_span_err!(
1700 "{} may not live long enough",
1703 binding_suggestion(&mut err, type_param_span, bound_kind, "'static");
1708 // If not, be less specific.
1709 let mut err = struct_span_err!(
1713 "{} may not live long enough",
1717 "consider adding an explicit lifetime bound for `{}`",
1720 note_and_explain_region(
1724 &format!("{} must be valid for ", labeled_user_string),
1732 if let Some(origin) = origin {
1733 self.note_region_origin(&mut err, &origin);
1738 fn report_sub_sup_conflict(
1740 region_scope_tree: ®ion::ScopeTree,
1741 var_origin: RegionVariableOrigin,
1742 sub_origin: SubregionOrigin<'tcx>,
1743 sub_region: Region<'tcx>,
1744 sup_origin: SubregionOrigin<'tcx>,
1745 sup_region: Region<'tcx>,
1747 let mut err = self.report_inference_failure(var_origin);
1749 note_and_explain_region(
1753 "first, the lifetime cannot outlive ",
1758 match (&sup_origin, &sub_origin) {
1759 (&infer::Subtype(ref sup_trace), &infer::Subtype(ref sub_trace)) => {
1760 debug!("report_sub_sup_conflict: var_origin={:?}", var_origin);
1761 debug!("report_sub_sup_conflict: sub_region={:?}", sub_region);
1762 debug!("report_sub_sup_conflict: sub_origin={:?}", sub_origin);
1763 debug!("report_sub_sup_conflict: sup_region={:?}", sup_region);
1764 debug!("report_sub_sup_conflict: sup_origin={:?}", sup_origin);
1765 debug!("report_sub_sup_conflict: sup_trace={:?}", sup_trace);
1766 debug!("report_sub_sup_conflict: sub_trace={:?}", sub_trace);
1767 debug!("report_sub_sup_conflict: sup_trace.values={:?}", sup_trace.values);
1768 debug!("report_sub_sup_conflict: sub_trace.values={:?}", sub_trace.values);
1770 if let (Some((sup_expected, sup_found)), Some((sub_expected, sub_found))) =
1771 (self.values_str(&sup_trace.values), self.values_str(&sub_trace.values))
1773 if sub_expected == sup_expected && sub_found == sup_found {
1774 note_and_explain_region(
1778 "...but the lifetime must also be valid for ",
1783 sup_trace.cause.span,
1784 &format!("...so that the {}", sup_trace.cause.as_requirement_str()),
1787 err.note_expected_found(&"", sup_expected, &"", sup_found);
1796 self.note_region_origin(&mut err, &sup_origin);
1798 note_and_explain_region(
1802 "but, the lifetime must be valid for ",
1807 self.note_region_origin(&mut err, &sub_origin);
1812 impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
1813 fn report_inference_failure(
1815 var_origin: RegionVariableOrigin,
1816 ) -> DiagnosticBuilder<'tcx> {
1817 let br_string = |br: ty::BoundRegion| {
1818 let mut s = match br {
1819 ty::BrNamed(_, name) => name.to_string(),
1827 let var_description = match var_origin {
1828 infer::MiscVariable(_) => String::new(),
1829 infer::PatternRegion(_) => " for pattern".to_string(),
1830 infer::AddrOfRegion(_) => " for borrow expression".to_string(),
1831 infer::Autoref(_) => " for autoref".to_string(),
1832 infer::Coercion(_) => " for automatic coercion".to_string(),
1833 infer::LateBoundRegion(_, br, infer::FnCall) => {
1834 format!(" for lifetime parameter {}in function call", br_string(br))
1836 infer::LateBoundRegion(_, br, infer::HigherRankedType) => {
1837 format!(" for lifetime parameter {}in generic type", br_string(br))
1839 infer::LateBoundRegion(_, br, infer::AssocTypeProjection(def_id)) => format!(
1840 " for lifetime parameter {}in trait containing associated type `{}`",
1842 self.tcx.associated_item(def_id).ident
1844 infer::EarlyBoundRegion(_, name) => format!(" for lifetime parameter `{}`", name),
1845 infer::BoundRegionInCoherence(name) => {
1846 format!(" for lifetime parameter `{}` in coherence check", name)
1848 infer::UpvarRegion(ref upvar_id, _) => {
1849 let var_name = self.tcx.hir().name(upvar_id.var_path.hir_id);
1850 format!(" for capture of `{}` by closure", var_name)
1852 infer::NLL(..) => bug!("NLL variable found in lexical phase"),
1859 "cannot infer an appropriate lifetime{} \
1860 due to conflicting requirements",
1868 Error0317(&'static str),
1869 Error0580(&'static str),
1870 Error0308(&'static str),
1871 Error0644(&'static str),
1874 impl<'tcx> ObligationCause<'tcx> {
1875 fn as_failure_code(&self, terr: &TypeError<'tcx>) -> FailureCode {
1876 use self::FailureCode::*;
1877 use crate::traits::ObligationCauseCode::*;
1879 CompareImplMethodObligation { .. } => Error0308("method not compatible with trait"),
1880 CompareImplTypeObligation { .. } => Error0308("type not compatible with trait"),
1881 MatchExpressionArm(box MatchExpressionArmCause { source, .. }) => {
1882 Error0308(match source {
1883 hir::MatchSource::IfLetDesugar { .. } => {
1884 "`if let` arms have incompatible types"
1886 hir::MatchSource::TryDesugar => {
1887 "try expression alternatives have incompatible types"
1889 _ => "`match` arms have incompatible types",
1892 IfExpression { .. } => Error0308("`if` and `else` have incompatible types"),
1893 IfExpressionWithNoElse => Error0317("`if` may be missing an `else` clause"),
1894 MainFunctionType => Error0580("`main` function has wrong type"),
1895 StartFunctionType => Error0308("`#[start]` function has wrong type"),
1896 IntrinsicType => Error0308("intrinsic has wrong type"),
1897 MethodReceiver => Error0308("mismatched `self` parameter type"),
1899 // In the case where we have no more specific thing to
1900 // say, also take a look at the error code, maybe we can
1903 TypeError::CyclicTy(ty) if ty.is_closure() || ty.is_generator() => {
1904 Error0644("closure/generator type that references itself")
1906 TypeError::IntrinsicCast => {
1907 Error0308("cannot coerce intrinsics to function pointers")
1909 TypeError::ObjectUnsafeCoercion(did) => Error0038(did.clone()),
1910 _ => Error0308("mismatched types"),
1915 fn as_requirement_str(&self) -> &'static str {
1916 use crate::traits::ObligationCauseCode::*;
1918 CompareImplMethodObligation { .. } => "method type is compatible with trait",
1919 CompareImplTypeObligation { .. } => "associated type is compatible with trait",
1920 ExprAssignable => "expression is assignable",
1921 MatchExpressionArm(box MatchExpressionArmCause { source, .. }) => match source {
1922 hir::MatchSource::IfLetDesugar { .. } => "`if let` arms have compatible types",
1923 _ => "`match` arms have compatible types",
1925 IfExpression { .. } => "`if` and `else` have incompatible types",
1926 IfExpressionWithNoElse => "`if` missing an `else` returns `()`",
1927 MainFunctionType => "`main` function has the correct type",
1928 StartFunctionType => "`#[start]` function has the correct type",
1929 IntrinsicType => "intrinsic has the correct type",
1930 MethodReceiver => "method receiver has the correct type",
1931 _ => "types are compatible",