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};
51 use infer::{self, SuppressRegionErrors};
53 use errors::{Applicability, DiagnosticBuilder, DiagnosticStyledString};
55 use hir::def_id::DefId;
59 use syntax::ast::DUMMY_NODE_ID;
60 use syntax_pos::{Pos, Span};
61 use traits::{ObligationCause, ObligationCauseCode};
62 use ty::error::TypeError;
63 use ty::{self, subst::Subst, Region, Ty, TyCtxt, TyKind, TypeFoldable};
69 pub mod nice_region_error;
71 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
72 pub fn note_and_explain_region(
74 region_scope_tree: ®ion::ScopeTree,
75 err: &mut DiagnosticBuilder<'_>,
77 region: ty::Region<'tcx>,
80 let (description, span) = match *region {
81 ty::ReScope(scope) => {
83 let unknown_scope = || {
85 "{}unknown scope: {:?}{}. Please report a bug.",
89 let span = scope.span(self, region_scope_tree);
90 let tag = match self.hir().find(scope.node_id(self, region_scope_tree)) {
91 Some(Node::Block(_)) => "block",
92 Some(Node::Expr(expr)) => match expr.node {
93 hir::ExprKind::Call(..) => "call",
94 hir::ExprKind::MethodCall(..) => "method call",
95 hir::ExprKind::Match(.., hir::MatchSource::IfLetDesugar { .. }) => "if let",
96 hir::ExprKind::Match(.., hir::MatchSource::WhileLetDesugar) => "while let",
97 hir::ExprKind::Match(.., hir::MatchSource::ForLoopDesugar) => "for",
98 hir::ExprKind::Match(..) => "match",
101 Some(Node::Stmt(_)) => "statement",
102 Some(Node::Item(it)) => Self::item_scope_tag(&it),
103 Some(Node::TraitItem(it)) => Self::trait_item_scope_tag(&it),
104 Some(Node::ImplItem(it)) => Self::impl_item_scope_tag(&it),
106 err.span_note(span, &unknown_scope());
110 let scope_decorated_tag = match scope.data {
111 region::ScopeData::Node => tag,
112 region::ScopeData::CallSite => "scope of call-site for function",
113 region::ScopeData::Arguments => "scope of function body",
114 region::ScopeData::Destruction => {
115 new_string = format!("destruction scope surrounding {}", tag);
118 region::ScopeData::Remainder(first_statement_index) => {
119 new_string = format!(
120 "block suffix following statement {}",
121 first_statement_index.index()
126 self.explain_span(scope_decorated_tag, span)
129 ty::ReEarlyBound(_) | ty::ReFree(_) | ty::ReStatic => {
130 self.msg_span_from_free_region(region)
133 ty::ReEmpty => ("the empty lifetime".to_owned(), None),
135 ty::RePlaceholder(_) => (format!("any other region"), None),
137 // FIXME(#13998) RePlaceholder should probably print like
138 // ReFree rather than dumping Debug output on the user.
140 // We shouldn't really be having unification failures with ReVar
141 // and ReLateBound though.
142 ty::ReVar(_) | ty::ReLateBound(..) | ty::ReErased => {
143 (format!("lifetime {:?}", region), None)
146 // We shouldn't encounter an error message with ReClosureBound.
147 ty::ReClosureBound(..) => {
148 bug!("encountered unexpected ReClosureBound: {:?}", region,);
152 TyCtxt::emit_msg_span(err, prefix, description, span, suffix);
155 pub fn note_and_explain_free_region(
157 err: &mut DiagnosticBuilder<'_>,
159 region: ty::Region<'tcx>,
162 let (description, span) = self.msg_span_from_free_region(region);
164 TyCtxt::emit_msg_span(err, prefix, description, span, suffix);
167 fn msg_span_from_free_region(self, region: ty::Region<'tcx>) -> (String, Option<Span>) {
169 ty::ReEarlyBound(_) | ty::ReFree(_) => {
170 self.msg_span_from_early_bound_and_free_regions(region)
172 ty::ReStatic => ("the static lifetime".to_owned(), None),
173 ty::ReEmpty => ("an empty lifetime".to_owned(), None),
174 _ => bug!("{:?}", region),
178 fn msg_span_from_early_bound_and_free_regions(
180 region: ty::Region<'tcx>,
181 ) -> (String, Option<Span>) {
182 let cm = self.sess.source_map();
184 let scope = region.free_region_binding_scope(self);
185 let node = self.hir().as_local_node_id(scope).unwrap_or(DUMMY_NODE_ID);
186 let tag = match self.hir().find(node) {
187 Some(Node::Block(_)) | Some(Node::Expr(_)) => "body",
188 Some(Node::Item(it)) => Self::item_scope_tag(&it),
189 Some(Node::TraitItem(it)) => Self::trait_item_scope_tag(&it),
190 Some(Node::ImplItem(it)) => Self::impl_item_scope_tag(&it),
193 let (prefix, span) = match *region {
194 ty::ReEarlyBound(ref br) => {
195 let mut sp = cm.def_span(self.hir().span(node));
196 if let Some(param) = self.hir()
198 .and_then(|generics| generics.get_named(&br.name))
202 (format!("the lifetime {} as defined on", br.name), sp)
204 ty::ReFree(ty::FreeRegion {
205 bound_region: ty::BoundRegion::BrNamed(_, ref name),
208 let mut sp = cm.def_span(self.hir().span(node));
209 if let Some(param) = self.hir()
211 .and_then(|generics| generics.get_named(&name))
215 (format!("the lifetime {} as defined on", name), sp)
217 ty::ReFree(ref fr) => match fr.bound_region {
219 format!("the anonymous lifetime #{} defined on", idx + 1),
220 self.hir().span(node),
223 "an anonymous lifetime defined on".to_owned(),
224 self.hir().span(node),
227 format!("the lifetime {} as defined on", fr.bound_region),
228 cm.def_span(self.hir().span(node)),
233 let (msg, opt_span) = self.explain_span(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::Existential(..)
277 | hir::ImplItemKind::Type(..) => "associated item",
281 fn explain_span(self, heading: &str, span: Span) -> (String, Option<Span>) {
282 let lo = self.sess.source_map().lookup_char_pos_adj(span.lo());
284 format!("the {} at {}:{}", heading, lo.line, lo.col.to_usize() + 1),
290 impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
291 pub fn report_region_errors(
293 region_scope_tree: ®ion::ScopeTree,
294 errors: &Vec<RegionResolutionError<'tcx>>,
295 suppress: SuppressRegionErrors,
298 "report_region_errors(): {} errors to start, suppress = {:?}",
303 if suppress.suppressed() {
307 // try to pre-process the errors, which will group some of them
308 // together into a `ProcessedErrors` group:
309 let errors = self.process_errors(errors);
312 "report_region_errors: {} errors after preprocessing",
316 for error in errors {
317 debug!("report_region_errors: error = {:?}", error);
319 if !self.try_report_nice_region_error(&error) {
320 match error.clone() {
321 // These errors could indicate all manner of different
322 // problems with many different solutions. Rather
323 // than generate a "one size fits all" error, what we
324 // attempt to do is go through a number of specific
325 // scenarios and try to find the best way to present
326 // the error. If all of these fails, we fall back to a rather
327 // general bit of code that displays the error information
328 RegionResolutionError::ConcreteFailure(origin, sub, sup) => {
329 if sub.is_placeholder() || sup.is_placeholder() {
330 self.report_placeholder_failure(region_scope_tree, origin, sub, sup)
333 self.report_concrete_failure(region_scope_tree, origin, sub, sup)
338 RegionResolutionError::GenericBoundFailure(origin, param_ty, sub) => {
339 self.report_generic_bound_failure(
348 RegionResolutionError::SubSupConflict(
356 if sub_r.is_placeholder() {
357 self.report_placeholder_failure(
364 } else if sup_r.is_placeholder() {
365 self.report_placeholder_failure(
373 self.report_sub_sup_conflict(
388 // This method goes through all the errors and try to group certain types
389 // of error together, for the purpose of suggesting explicit lifetime
390 // parameters to the user. This is done so that we can have a more
391 // complete view of what lifetimes should be the same.
392 // If the return value is an empty vector, it means that processing
393 // failed (so the return value of this method should not be used).
395 // The method also attempts to weed out messages that seem like
396 // duplicates that will be unhelpful to the end-user. But
397 // obviously it never weeds out ALL errors.
400 errors: &Vec<RegionResolutionError<'tcx>>,
401 ) -> Vec<RegionResolutionError<'tcx>> {
402 debug!("process_errors()");
404 // We want to avoid reporting generic-bound failures if we can
405 // avoid it: these have a very high rate of being unhelpful in
406 // practice. This is because they are basically secondary
407 // checks that test the state of the region graph after the
408 // rest of inference is done, and the other kinds of errors
409 // indicate that the region constraint graph is internally
410 // inconsistent, so these test results are likely to be
413 // Therefore, we filter them out of the list unless they are
414 // the only thing in the list.
416 let is_bound_failure = |e: &RegionResolutionError<'tcx>| match *e {
417 RegionResolutionError::GenericBoundFailure(..) => true,
418 RegionResolutionError::ConcreteFailure(..)
419 | RegionResolutionError::SubSupConflict(..) => false,
422 let mut errors = if errors.iter().all(|e| is_bound_failure(e)) {
427 .filter(|&e| !is_bound_failure(e))
432 // sort the errors by span, for better error message stability.
433 errors.sort_by_key(|u| match *u {
434 RegionResolutionError::ConcreteFailure(ref sro, _, _) => sro.span(),
435 RegionResolutionError::GenericBoundFailure(ref sro, _, _) => sro.span(),
436 RegionResolutionError::SubSupConflict(_, ref rvo, _, _, _, _) => rvo.span(),
441 /// Adds a note if the types come from similarly named crates
442 fn check_and_note_conflicting_crates(
444 err: &mut DiagnosticBuilder<'_>,
445 terr: &TypeError<'tcx>,
448 let report_path_match = |err: &mut DiagnosticBuilder<'_>, did1: DefId, did2: DefId| {
449 // Only external crates, if either is from a local
450 // module we could have false positives
451 if !(did1.is_local() || did2.is_local()) && did1.krate != did2.krate {
452 let exp_path = self.tcx.item_path_str(did1);
453 let found_path = self.tcx.item_path_str(did2);
454 let exp_abs_path = self.tcx.absolute_item_path_str(did1);
455 let found_abs_path = self.tcx.absolute_item_path_str(did2);
456 // We compare strings because DefPath can be different
457 // for imported and non-imported crates
458 if exp_path == found_path || exp_abs_path == found_abs_path {
459 let crate_name = self.tcx.crate_name(did1.krate);
463 "Perhaps two different versions \
464 of crate `{}` are being used?",
472 TypeError::Sorts(ref exp_found) => {
473 // if they are both "path types", there's a chance of ambiguity
474 // due to different versions of the same crate
475 if let (&ty::Adt(exp_adt, _), &ty::Adt(found_adt, _))
476 = (&exp_found.expected.sty, &exp_found.found.sty)
478 report_path_match(err, exp_adt.did, found_adt.did);
481 TypeError::Traits(ref exp_found) => {
482 report_path_match(err, exp_found.expected, exp_found.found);
484 _ => (), // FIXME(#22750) handle traits and stuff
488 fn note_error_origin(&self, err: &mut DiagnosticBuilder<'tcx>, cause: &ObligationCause<'tcx>) {
490 ObligationCauseCode::MatchExpressionArm { arm_span, source } => match source {
491 hir::MatchSource::IfLetDesugar { .. } => {
492 let msg = "`if let` arm with an incompatible type";
493 if self.tcx.sess.source_map().is_multiline(arm_span) {
494 err.span_note(arm_span, msg);
496 err.span_label(arm_span, msg);
499 hir::MatchSource::TryDesugar => {}
501 let msg = "match arm with an incompatible type";
502 if self.tcx.sess.source_map().is_multiline(arm_span) {
503 err.span_note(arm_span, msg);
505 err.span_label(arm_span, msg);
513 /// Given that `other_ty` is the same as a type argument for `name` in `sub`, populate `value`
514 /// highlighting `name` and every type argument that isn't at `pos` (which is `other_ty`), and
515 /// populate `other_value` with `other_ty`.
519 /// ^^^^--------^ this is highlighted
521 /// | this type argument is exactly the same as the other type, not highlighted
522 /// this is highlighted
524 /// -------- this type is the same as a type argument in the other type, not highlighted
528 value: &mut DiagnosticStyledString,
529 other_value: &mut DiagnosticStyledString,
531 sub: &ty::subst::Substs<'tcx>,
535 // `value` and `other_value` hold two incomplete type representation for display.
536 // `name` is the path of both types being compared. `sub`
537 value.push_highlighted(name);
540 value.push_highlighted("<");
543 // Output the lifetimes for the first type
544 let lifetimes = sub.regions()
546 let s = lifetime.to_string();
555 if !lifetimes.is_empty() {
556 if sub.regions().count() < len {
557 value.push_normal(lifetimes + &", ");
559 value.push_normal(lifetimes);
563 // Highlight all the type arguments that aren't at `pos` and compare the type argument at
564 // `pos` and `other_ty`.
565 for (i, type_arg) in sub.types().enumerate() {
567 let values = self.cmp(type_arg, other_ty);
568 value.0.extend((values.0).0);
569 other_value.0.extend((values.1).0);
571 value.push_highlighted(type_arg.to_string());
574 if len > 0 && i != len - 1 {
575 value.push_normal(", ");
577 //self.push_comma(&mut value, &mut other_value, len, i);
580 value.push_highlighted(">");
584 /// If `other_ty` is the same as a type argument present in `sub`, highlight `path` in `t1_out`,
585 /// as that is the difference to the other type.
587 /// For the following code:
590 /// let x: Foo<Bar<Qux>> = foo::<Bar<Qux>>();
593 /// The type error output will behave in the following way:
597 /// ^^^^--------^ this is highlighted
599 /// | this type argument is exactly the same as the other type, not highlighted
600 /// this is highlighted
602 /// -------- this type is the same as a type argument in the other type, not highlighted
606 mut t1_out: &mut DiagnosticStyledString,
607 mut t2_out: &mut DiagnosticStyledString,
609 sub: &ty::subst::Substs<'tcx>,
613 for (i, ta) in sub.types().enumerate() {
615 self.highlight_outer(&mut t1_out, &mut t2_out, path, sub, i, &other_ty);
618 if let &ty::Adt(def, _) = &ta.sty {
619 let path_ = self.tcx.item_path_str(def.did.clone());
620 if path_ == other_path {
621 self.highlight_outer(&mut t1_out, &mut t2_out, path, sub, i, &other_ty);
629 /// Add a `,` to the type representation only if it is appropriate.
632 value: &mut DiagnosticStyledString,
633 other_value: &mut DiagnosticStyledString,
637 if len > 0 && pos != len - 1 {
638 value.push_normal(", ");
639 other_value.push_normal(", ");
643 /// For generic types with parameters with defaults, remove the parameters corresponding to
644 /// the defaults. This repeats a lot of the logic found in `PrintContext::parameterized`.
645 fn strip_generic_default_params(
648 substs: &ty::subst::Substs<'tcx>,
649 ) -> &'tcx ty::subst::Substs<'tcx> {
650 let generics = self.tcx.generics_of(def_id);
651 let mut num_supplied_defaults = 0;
652 let mut type_params = generics
656 .filter_map(|param| match param.kind {
657 ty::GenericParamDefKind::Lifetime => None,
658 ty::GenericParamDefKind::Type { has_default, .. } => {
659 Some((param.def_id, has_default))
664 let has_default = type_params.peek().map(|(_, has_default)| has_default);
665 *has_default.unwrap_or(&false)
668 let types = substs.types().rev();
669 for ((def_id, has_default), actual) in type_params.zip(types) {
673 if self.tcx.type_of(def_id).subst(self.tcx, substs) != actual {
676 num_supplied_defaults += 1;
679 let len = generics.params.len();
680 let mut generics = generics.clone();
681 generics.params.truncate(len - num_supplied_defaults);
682 substs.truncate_to(self.tcx, &generics)
685 /// Compare two given types, eliding parts that are the same between them and highlighting
686 /// relevant differences, and return two representation of those types for highlighted printing.
687 fn cmp(&self, t1: Ty<'tcx>, t2: Ty<'tcx>) -> (DiagnosticStyledString, DiagnosticStyledString) {
688 fn equals<'tcx>(a: &Ty<'tcx>, b: &Ty<'tcx>) -> bool {
689 match (&a.sty, &b.sty) {
690 (a, b) if *a == *b => true,
691 (&ty::Int(_), &ty::Infer(ty::InferTy::IntVar(_)))
692 | (&ty::Infer(ty::InferTy::IntVar(_)), &ty::Int(_))
693 | (&ty::Infer(ty::InferTy::IntVar(_)), &ty::Infer(ty::InferTy::IntVar(_)))
694 | (&ty::Float(_), &ty::Infer(ty::InferTy::FloatVar(_)))
695 | (&ty::Infer(ty::InferTy::FloatVar(_)), &ty::Float(_))
696 | (&ty::Infer(ty::InferTy::FloatVar(_)), &ty::Infer(ty::InferTy::FloatVar(_))) => {
703 fn push_ty_ref<'tcx>(
704 r: &ty::Region<'tcx>,
706 mutbl: hir::Mutability,
707 s: &mut DiagnosticStyledString,
709 let r = &r.to_string();
710 s.push_highlighted(format!(
713 if r == "" { "" } else { " " },
714 if mutbl == hir::MutMutable { "mut " } else { "" }
716 s.push_normal(ty.to_string());
719 match (&t1.sty, &t2.sty) {
720 (&ty::Adt(def1, sub1), &ty::Adt(def2, sub2)) => {
721 let sub_no_defaults_1 = self.strip_generic_default_params(def1.did, sub1);
722 let sub_no_defaults_2 = self.strip_generic_default_params(def2.did, sub2);
723 let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new());
724 let path1 = self.tcx.item_path_str(def1.did.clone());
725 let path2 = self.tcx.item_path_str(def2.did.clone());
726 if def1.did == def2.did {
727 // Easy case. Replace same types with `_` to shorten the output and highlight
728 // the differing ones.
729 // let x: Foo<Bar, Qux> = y::<Foo<Quz, Qux>>();
732 // --- ^ type argument elided
734 // highlighted in output
735 values.0.push_normal(path1);
736 values.1.push_normal(path2);
738 // Avoid printing out default generic parameters that are common to both
740 let len1 = sub_no_defaults_1.len();
741 let len2 = sub_no_defaults_2.len();
742 let common_len = cmp::min(len1, len2);
743 let remainder1: Vec<_> = sub1.types().skip(common_len).collect();
744 let remainder2: Vec<_> = sub2.types().skip(common_len).collect();
745 let common_default_params = remainder1
748 .zip(remainder2.iter().rev())
749 .filter(|(a, b)| a == b)
751 let len = sub1.len() - common_default_params;
753 // Only draw `<...>` if there're lifetime/type arguments.
755 values.0.push_normal("<");
756 values.1.push_normal("<");
759 fn lifetime_display(lifetime: Region<'_>) -> String {
760 let s = lifetime.to_string();
767 // At one point we'd like to elide all lifetimes here, they are irrelevant for
768 // all diagnostics that use this output
772 // ^^ ^^ --- type arguments are not elided
774 // | elided as they were the same
775 // not elided, they were different, but irrelevant
776 let lifetimes = sub1.regions().zip(sub2.regions());
777 for (i, lifetimes) in lifetimes.enumerate() {
778 let l1 = lifetime_display(lifetimes.0);
779 let l2 = lifetime_display(lifetimes.1);
781 values.0.push_normal("'_");
782 values.1.push_normal("'_");
784 values.0.push_highlighted(l1);
785 values.1.push_highlighted(l2);
787 self.push_comma(&mut values.0, &mut values.1, len, i);
790 // We're comparing two types with the same path, so we compare the type
791 // arguments for both. If they are the same, do not highlight and elide from the
795 // ^ elided type as this type argument was the same in both sides
796 let type_arguments = sub1.types().zip(sub2.types());
797 let regions_len = sub1.regions().count();
798 for (i, (ta1, ta2)) in type_arguments.take(len).enumerate() {
799 let i = i + regions_len;
801 values.0.push_normal("_");
802 values.1.push_normal("_");
804 let (x1, x2) = self.cmp(ta1, ta2);
805 (values.0).0.extend(x1.0);
806 (values.1).0.extend(x2.0);
808 self.push_comma(&mut values.0, &mut values.1, len, i);
811 // Close the type argument bracket.
812 // Only draw `<...>` if there're lifetime/type arguments.
814 values.0.push_normal(">");
815 values.1.push_normal(">");
820 // let x: Foo<Bar<Qux> = foo::<Bar<Qux>>();
822 // ------- this type argument is exactly the same as the other type
824 if self.cmp_type_arg(
836 // let x: Bar<Qux> = y:<Foo<Bar<Qux>>>();
839 // ------- this type argument is exactly the same as the other type
840 if self.cmp_type_arg(
852 // We couldn't find anything in common, highlight everything.
853 // let x: Bar<Qux> = y::<Foo<Zar>>();
855 DiagnosticStyledString::highlighted(t1.to_string()),
856 DiagnosticStyledString::highlighted(t2.to_string()),
861 // When finding T != &T, highlight only the borrow
862 (&ty::Ref(r1, ref_ty1, mutbl1), _) if equals(&ref_ty1, &t2) => {
863 let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new());
864 push_ty_ref(&r1, ref_ty1, mutbl1, &mut values.0);
865 values.1.push_normal(t2.to_string());
868 (_, &ty::Ref(r2, ref_ty2, mutbl2)) if equals(&t1, &ref_ty2) => {
869 let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new());
870 values.0.push_normal(t1.to_string());
871 push_ty_ref(&r2, ref_ty2, mutbl2, &mut values.1);
875 // When encountering &T != &mut T, highlight only the borrow
876 (&ty::Ref(r1, ref_ty1, mutbl1), &ty::Ref(r2, ref_ty2, mutbl2))
877 if equals(&ref_ty1, &ref_ty2) =>
879 let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new());
880 push_ty_ref(&r1, ref_ty1, mutbl1, &mut values.0);
881 push_ty_ref(&r2, ref_ty2, mutbl2, &mut values.1);
887 // The two types are the same, elide and don't highlight.
889 DiagnosticStyledString::normal("_"),
890 DiagnosticStyledString::normal("_"),
893 // We couldn't find anything in common, highlight everything.
895 DiagnosticStyledString::highlighted(t1.to_string()),
896 DiagnosticStyledString::highlighted(t2.to_string()),
903 pub fn note_type_err(
905 diag: &mut DiagnosticBuilder<'tcx>,
906 cause: &ObligationCause<'tcx>,
907 secondary_span: Option<(Span, String)>,
908 mut values: Option<ValuePairs<'tcx>>,
909 terr: &TypeError<'tcx>,
911 // For some types of errors, expected-found does not make
912 // sense, so just ignore the values we were given.
914 TypeError::CyclicTy(_) => {
920 let (expected_found, exp_found, is_simple_error) = match values {
921 None => (None, None, false),
923 let (is_simple_error, exp_found) = match values {
924 ValuePairs::Types(exp_found) => {
926 exp_found.expected.is_primitive() && exp_found.found.is_primitive();
928 (is_simple_err, Some(exp_found))
932 let vals = match self.values_str(&values) {
933 Some((expected, found)) => Some((expected, found)),
935 // Derived error. Cancel the emitter.
936 self.tcx.sess.diagnostic().cancel(diag);
940 (vals, exp_found, is_simple_error)
944 let span = cause.span(&self.tcx);
946 diag.span_label(span, terr.to_string());
947 if let Some((sp, msg)) = secondary_span {
948 diag.span_label(sp, msg);
951 if let Some((expected, found)) = expected_found {
952 match (terr, is_simple_error, expected == found) {
953 (&TypeError::Sorts(ref values), false, true) => {
954 diag.note_expected_found_extra(
958 &format!(" ({})", values.expected.sort_string(self.tcx)),
959 &format!(" ({})", values.found.sort_string(self.tcx)),
963 if let Some(exp_found) = exp_found {
964 let (def_id, ret_ty) = match exp_found.found.sty {
965 TyKind::FnDef(def, _) => {
966 (Some(def), Some(self.tcx.fn_sig(def).output()))
971 let exp_is_struct = match exp_found.expected.sty {
972 TyKind::Adt(def, _) => def.is_struct(),
976 if let (Some(def_id), Some(ret_ty)) = (def_id, ret_ty) {
977 if exp_is_struct && &exp_found.expected == ret_ty.skip_binder() {
978 let message = format!(
979 "did you mean `{}(/* fields */)`?",
980 self.tcx.item_path_str(def_id)
982 diag.span_label(span, message);
985 self.suggest_as_ref_where_appropriate(span, &exp_found, diag);
988 diag.note_expected_found(&"type", expected, found);
994 self.check_and_note_conflicting_crates(diag, terr, span);
995 self.tcx.note_and_explain_type_err(diag, terr, span);
997 // It reads better to have the error origin as the final
999 self.note_error_origin(diag, &cause);
1002 /// When encountering a case where `.as_ref()` on a `Result` or `Option` would be appropriate,
1004 fn suggest_as_ref_where_appropriate(
1007 exp_found: &ty::error::ExpectedFound<Ty<'tcx>>,
1008 diag: &mut DiagnosticBuilder<'tcx>,
1010 match (&exp_found.expected.sty, &exp_found.found.sty) {
1011 (TyKind::Adt(exp_def, exp_substs), TyKind::Ref(_, found_ty, _)) => {
1012 if let TyKind::Adt(found_def, found_substs) = found_ty.sty {
1013 let path_str = format!("{:?}", exp_def);
1014 if exp_def == &found_def {
1015 let opt_msg = "you can convert from `&Option<T>` to `Option<&T>` using \
1017 let result_msg = "you can convert from `&Result<T, E>` to \
1018 `Result<&T, &E>` using `.as_ref()`";
1019 let have_as_ref = &[
1020 ("std::option::Option", opt_msg),
1021 ("core::option::Option", opt_msg),
1022 ("std::result::Result", result_msg),
1023 ("core::result::Result", result_msg),
1025 if let Some(msg) = have_as_ref.iter()
1026 .filter_map(|(path, msg)| if &path_str == path {
1032 let mut show_suggestion = true;
1033 for (exp_ty, found_ty) in exp_substs.types().zip(found_substs.types()) {
1035 TyKind::Ref(_, exp_ty, _) => {
1036 match (&exp_ty.sty, &found_ty.sty) {
1037 (_, TyKind::Param(_)) |
1038 (_, TyKind::Infer(_)) |
1039 (TyKind::Param(_), _) |
1040 (TyKind::Infer(_), _) => {}
1041 _ if ty::TyS::same_type(exp_ty, found_ty) => {}
1042 _ => show_suggestion = false,
1045 TyKind::Param(_) | TyKind::Infer(_) => {}
1046 _ => show_suggestion = false,
1049 if let (Ok(snippet), true) = (
1050 self.tcx.sess.source_map().span_to_snippet(span),
1053 diag.span_suggestion_with_applicability(
1056 format!("{}.as_ref()", snippet),
1057 Applicability::MachineApplicable,
1068 pub fn report_and_explain_type_error(
1070 trace: TypeTrace<'tcx>,
1071 terr: &TypeError<'tcx>,
1072 ) -> DiagnosticBuilder<'tcx> {
1074 "report_and_explain_type_error(trace={:?}, terr={:?})",
1078 let span = trace.cause.span(&self.tcx);
1079 let failure_code = trace.cause.as_failure_code(terr);
1080 let mut diag = match failure_code {
1081 FailureCode::Error0317(failure_str) => {
1082 struct_span_err!(self.tcx.sess, span, E0317, "{}", failure_str)
1084 FailureCode::Error0580(failure_str) => {
1085 struct_span_err!(self.tcx.sess, span, E0580, "{}", failure_str)
1087 FailureCode::Error0308(failure_str) => {
1088 struct_span_err!(self.tcx.sess, span, E0308, "{}", failure_str)
1090 FailureCode::Error0644(failure_str) => {
1091 struct_span_err!(self.tcx.sess, span, E0644, "{}", failure_str)
1094 self.note_type_err(&mut diag, &trace.cause, None, Some(trace.values), terr);
1100 values: &ValuePairs<'tcx>,
1101 ) -> Option<(DiagnosticStyledString, DiagnosticStyledString)> {
1103 infer::Types(ref exp_found) => self.expected_found_str_ty(exp_found),
1104 infer::Regions(ref exp_found) => self.expected_found_str(exp_found),
1105 infer::TraitRefs(ref exp_found) => self.expected_found_str(exp_found),
1106 infer::PolyTraitRefs(ref exp_found) => self.expected_found_str(exp_found),
1110 fn expected_found_str_ty(
1112 exp_found: &ty::error::ExpectedFound<Ty<'tcx>>,
1113 ) -> Option<(DiagnosticStyledString, DiagnosticStyledString)> {
1114 let exp_found = self.resolve_type_vars_if_possible(exp_found);
1115 if exp_found.references_error() {
1119 Some(self.cmp(exp_found.expected, exp_found.found))
1122 /// Returns a string of the form "expected `{}`, found `{}`".
1123 fn expected_found_str<T: fmt::Display + TypeFoldable<'tcx>>(
1125 exp_found: &ty::error::ExpectedFound<T>,
1126 ) -> Option<(DiagnosticStyledString, DiagnosticStyledString)> {
1127 let exp_found = self.resolve_type_vars_if_possible(exp_found);
1128 if exp_found.references_error() {
1133 DiagnosticStyledString::highlighted(exp_found.expected.to_string()),
1134 DiagnosticStyledString::highlighted(exp_found.found.to_string()),
1138 pub fn report_generic_bound_failure(
1140 region_scope_tree: ®ion::ScopeTree,
1142 origin: Option<SubregionOrigin<'tcx>>,
1143 bound_kind: GenericKind<'tcx>,
1146 self.construct_generic_bound_failure(region_scope_tree, span, origin, bound_kind, sub)
1150 pub fn construct_generic_bound_failure(
1152 region_scope_tree: ®ion::ScopeTree,
1154 origin: Option<SubregionOrigin<'tcx>>,
1155 bound_kind: GenericKind<'tcx>,
1157 ) -> DiagnosticBuilder<'a> {
1158 // Attempt to obtain the span of the parameter so we can
1159 // suggest adding an explicit lifetime bound to it.
1160 let type_param_span = match (self.in_progress_tables, bound_kind) {
1161 (Some(ref table), GenericKind::Param(ref param)) => {
1162 let table = table.borrow();
1163 table.local_id_root.and_then(|did| {
1164 let generics = self.tcx.generics_of(did);
1165 // Account for the case where `did` corresponds to `Self`, which doesn't have
1166 // the expected type argument.
1167 if !param.is_self() {
1168 let type_param = generics.type_param(param, self.tcx);
1169 let hir = &self.tcx.hir();
1170 hir.as_local_node_id(type_param.def_id).map(|id| {
1171 // Get the `hir::Param` to verify whether it already has any bounds.
1172 // We do this to avoid suggesting code that ends up as `T: 'a'b`,
1173 // instead we suggest `T: 'a + 'b` in that case.
1174 let mut has_bounds = false;
1175 if let Node::GenericParam(ref param) = hir.get(id) {
1176 has_bounds = !param.bounds.is_empty();
1178 let sp = hir.span(id);
1179 // `sp` only covers `T`, change it so that it covers
1180 // `T:` when appropriate
1181 let is_impl_trait = bound_kind.to_string().starts_with("impl ");
1182 let sp = if has_bounds && !is_impl_trait {
1186 .next_point(self.tcx.sess.source_map().next_point(sp)))
1190 (sp, has_bounds, is_impl_trait)
1200 let labeled_user_string = match bound_kind {
1201 GenericKind::Param(ref p) => format!("the parameter type `{}`", p),
1202 GenericKind::Projection(ref p) => format!("the associated type `{}`", p),
1205 if let Some(SubregionOrigin::CompareImplMethodObligation {
1212 return self.report_extra_impl_obligation(
1217 &format!("`{}: {}`", bound_kind, sub),
1221 fn binding_suggestion<'tcx, S: fmt::Display>(
1222 err: &mut DiagnosticBuilder<'tcx>,
1223 type_param_span: Option<(Span, bool, bool)>,
1224 bound_kind: GenericKind<'tcx>,
1227 let consider = format!(
1228 "consider adding an explicit lifetime bound {}",
1229 if type_param_span.map(|(_, _, is_impl_trait)| is_impl_trait).unwrap_or(false) {
1230 format!(" `{}` to `{}`...", sub, bound_kind)
1232 format!("`{}: {}`...", bound_kind, sub)
1235 if let Some((sp, has_lifetimes, is_impl_trait)) = type_param_span {
1236 let suggestion = if is_impl_trait {
1237 format!("{} + {}", bound_kind, sub)
1239 let tail = if has_lifetimes { " + " } else { "" };
1240 format!("{}: {}{}", bound_kind, sub, tail)
1242 err.span_suggestion_short_with_applicability(
1246 Applicability::MaybeIncorrect, // Issue #41966
1249 err.help(&consider);
1253 let mut err = match *sub {
1255 | ty::ReFree(ty::FreeRegion {
1256 bound_region: ty::BrNamed(..),
1259 // Does the required lifetime have a nice name we can print?
1260 let mut err = struct_span_err!(
1264 "{} may not live long enough",
1267 binding_suggestion(&mut err, type_param_span, bound_kind, sub);
1272 // Does the required lifetime have a nice name we can print?
1273 let mut err = struct_span_err!(
1277 "{} may not live long enough",
1280 binding_suggestion(&mut err, type_param_span, bound_kind, "'static");
1285 // If not, be less specific.
1286 let mut err = struct_span_err!(
1290 "{} may not live long enough",
1294 "consider adding an explicit lifetime bound for `{}`",
1297 self.tcx.note_and_explain_region(
1300 &format!("{} must be valid for ", labeled_user_string),
1308 if let Some(origin) = origin {
1309 self.note_region_origin(&mut err, &origin);
1314 fn report_sub_sup_conflict(
1316 region_scope_tree: ®ion::ScopeTree,
1317 var_origin: RegionVariableOrigin,
1318 sub_origin: SubregionOrigin<'tcx>,
1319 sub_region: Region<'tcx>,
1320 sup_origin: SubregionOrigin<'tcx>,
1321 sup_region: Region<'tcx>,
1323 let mut err = self.report_inference_failure(var_origin);
1325 self.tcx.note_and_explain_region(
1328 "first, the lifetime cannot outlive ",
1333 match (&sup_origin, &sub_origin) {
1334 (&infer::Subtype(ref sup_trace), &infer::Subtype(ref sub_trace)) => {
1335 debug!("report_sub_sup_conflict: var_origin={:?}", var_origin);
1336 debug!("report_sub_sup_conflict: sub_region={:?}", sub_region);
1337 debug!("report_sub_sup_conflict: sub_origin={:?}", sub_origin);
1338 debug!("report_sub_sup_conflict: sup_region={:?}", sup_region);
1339 debug!("report_sub_sup_conflict: sup_origin={:?}", sup_origin);
1340 debug!("report_sub_sup_conflict: sup_trace={:?}", sup_trace);
1341 debug!("report_sub_sup_conflict: sub_trace={:?}", sub_trace);
1342 debug!("report_sub_sup_conflict: sup_trace.values={:?}", sup_trace.values);
1343 debug!("report_sub_sup_conflict: sub_trace.values={:?}", sub_trace.values);
1345 if let (Some((sup_expected, sup_found)), Some((sub_expected, sub_found))) = (
1346 self.values_str(&sup_trace.values),
1347 self.values_str(&sub_trace.values),
1349 if sub_expected == sup_expected && sub_found == sup_found {
1350 self.tcx.note_and_explain_region(
1353 "...but the lifetime must also be valid for ",
1358 "...so that the {}:\nexpected {}\n found {}",
1359 sup_trace.cause.as_requirement_str(),
1360 sup_expected.content(),
1371 self.note_region_origin(&mut err, &sup_origin);
1373 self.tcx.note_and_explain_region(
1376 "but, the lifetime must be valid for ",
1381 self.note_region_origin(&mut err, &sub_origin);
1386 impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
1387 fn report_inference_failure(
1389 var_origin: RegionVariableOrigin,
1390 ) -> DiagnosticBuilder<'tcx> {
1391 let br_string = |br: ty::BoundRegion| {
1392 let mut s = br.to_string();
1398 let var_description = match var_origin {
1399 infer::MiscVariable(_) => String::new(),
1400 infer::PatternRegion(_) => " for pattern".to_string(),
1401 infer::AddrOfRegion(_) => " for borrow expression".to_string(),
1402 infer::Autoref(_) => " for autoref".to_string(),
1403 infer::Coercion(_) => " for automatic coercion".to_string(),
1404 infer::LateBoundRegion(_, br, infer::FnCall) => {
1405 format!(" for lifetime parameter {}in function call", br_string(br))
1407 infer::LateBoundRegion(_, br, infer::HigherRankedType) => {
1408 format!(" for lifetime parameter {}in generic type", br_string(br))
1410 infer::LateBoundRegion(_, br, infer::AssocTypeProjection(def_id)) => format!(
1411 " for lifetime parameter {}in trait containing associated type `{}`",
1413 self.tcx.associated_item(def_id).ident
1415 infer::EarlyBoundRegion(_, name) => format!(" for lifetime parameter `{}`", name),
1416 infer::BoundRegionInCoherence(name) => {
1417 format!(" for lifetime parameter `{}` in coherence check", name)
1419 infer::UpvarRegion(ref upvar_id, _) => {
1420 let var_node_id = self.tcx.hir().hir_to_node_id(upvar_id.var_path.hir_id);
1421 let var_name = self.tcx.hir().name(var_node_id);
1422 format!(" for capture of `{}` by closure", var_name)
1424 infer::NLL(..) => bug!("NLL variable found in lexical phase"),
1431 "cannot infer an appropriate lifetime{} \
1432 due to conflicting requirements",
1439 Error0317(&'static str),
1440 Error0580(&'static str),
1441 Error0308(&'static str),
1442 Error0644(&'static str),
1445 impl<'tcx> ObligationCause<'tcx> {
1446 fn as_failure_code(&self, terr: &TypeError<'tcx>) -> FailureCode {
1447 use self::FailureCode::*;
1448 use traits::ObligationCauseCode::*;
1450 CompareImplMethodObligation { .. } => Error0308("method not compatible with trait"),
1451 MatchExpressionArm { source, .. } => Error0308(match source {
1452 hir::MatchSource::IfLetDesugar { .. } => "`if let` arms have incompatible types",
1453 hir::MatchSource::TryDesugar => {
1454 "try expression alternatives have incompatible types"
1456 _ => "match arms have incompatible types",
1458 IfExpression => Error0308("if and else have incompatible types"),
1459 IfExpressionWithNoElse => Error0317("if may be missing an else clause"),
1460 MainFunctionType => Error0580("main function has wrong type"),
1461 StartFunctionType => Error0308("start function has wrong type"),
1462 IntrinsicType => Error0308("intrinsic has wrong type"),
1463 MethodReceiver => Error0308("mismatched method receiver"),
1465 // In the case where we have no more specific thing to
1466 // say, also take a look at the error code, maybe we can
1469 TypeError::CyclicTy(ty) if ty.is_closure() || ty.is_generator() => {
1470 Error0644("closure/generator type that references itself")
1472 _ => Error0308("mismatched types"),
1477 fn as_requirement_str(&self) -> &'static str {
1478 use traits::ObligationCauseCode::*;
1480 CompareImplMethodObligation { .. } => "method type is compatible with trait",
1481 ExprAssignable => "expression is assignable",
1482 MatchExpressionArm { source, .. } => match source {
1483 hir::MatchSource::IfLetDesugar { .. } => "`if let` arms have compatible types",
1484 _ => "match arms have compatible types",
1486 IfExpression => "if and else have compatible types",
1487 IfExpressionWithNoElse => "if missing an else returns ()",
1488 MainFunctionType => "`main` function has the correct type",
1489 StartFunctionType => "`start` function has the correct type",
1490 IntrinsicType => "intrinsic has the correct type",
1491 MethodReceiver => "method receiver has the correct type",
1492 _ => "types are compatible",