1 // Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! Error Reporting Code for the inference engine
13 //! Because of the way inference, and in particular region inference,
14 //! works, it often happens that errors are not detected until far after
15 //! the relevant line of code has been type-checked. Therefore, there is
16 //! an elaborate system to track why a particular constraint in the
17 //! inference graph arose so that we can explain to the user what gave
18 //! rise to a particular error.
20 //! The basis of the system are the "origin" types. An "origin" is the
21 //! reason that a constraint or inference variable arose. There are
22 //! different "origin" enums for different kinds of constraints/variables
23 //! (e.g., `TypeOrigin`, `RegionVariableOrigin`). An origin always has
24 //! a span, but also more information so that we can generate a meaningful
27 //! Having a catalog of all the different reasons an error can arise is
28 //! also useful for other reasons, like cross-referencing FAQs etc, though
29 //! we are not really taking advantage of this yet.
31 //! # Region Inference
33 //! Region inference is particularly tricky because it always succeeds "in
34 //! the moment" and simply registers a constraint. Then, at the end, we
35 //! can compute the full graph and report errors, so we need to be able to
36 //! store and later report what gave rise to the conflicting constraints.
40 //! Determining whether `T1 <: T2` often involves a number of subtypes and
41 //! subconstraints along the way. A "TypeTrace" is an extended version
42 //! of an origin that traces the types and other values that were being
43 //! compared. It is not necessarily comprehensive (in fact, at the time of
44 //! this writing it only tracks the root values being compared) but I'd
45 //! like to extend it to include significant "waypoints". For example, if
46 //! you are comparing `(T1, T2) <: (T3, T4)`, and the problem is that `T2
47 //! <: T4` fails, I'd like the trace to include enough information to say
48 //! "in the 2nd element of the tuple". Similarly, failures when comparing
49 //! arguments or return types in fn types should be able to cite the
50 //! specific position, etc.
54 //! Of course, there is still a LOT of code in typeck that has yet to be
55 //! ported to this system, and which relies on string concatenation at the
56 //! time of error detection.
59 use super::{InferCtxt, TypeTrace, SubregionOrigin, RegionVariableOrigin, ValuePairs};
60 use super::region_inference::{RegionResolutionError, ConcreteFailure, SubSupConflict,
61 GenericBoundFailure, GenericKind};
65 use hir::map as hir_map;
66 use hir::def_id::DefId;
68 use traits::{ObligationCause, ObligationCauseCode};
69 use ty::{self, Region, TyCtxt, TypeFoldable};
70 use ty::error::TypeError;
71 use syntax::ast::DUMMY_NODE_ID;
72 use syntax_pos::{Pos, Span};
73 use errors::{DiagnosticBuilder, DiagnosticStyledString};
79 mod named_anon_conflict;
82 mod anon_anon_conflict;
84 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
85 pub fn note_and_explain_region(self,
86 err: &mut DiagnosticBuilder,
88 region: ty::Region<'tcx>,
90 fn item_scope_tag(item: &hir::Item) -> &'static str {
92 hir::ItemImpl(..) => "impl",
93 hir::ItemStruct(..) => "struct",
94 hir::ItemUnion(..) => "union",
95 hir::ItemEnum(..) => "enum",
96 hir::ItemTrait(..) => "trait",
97 hir::ItemFn(..) => "function body",
102 fn trait_item_scope_tag(item: &hir::TraitItem) -> &'static str {
104 hir::TraitItemKind::Method(..) => "method body",
105 hir::TraitItemKind::Const(..) |
106 hir::TraitItemKind::Type(..) => "associated item"
110 fn impl_item_scope_tag(item: &hir::ImplItem) -> &'static str {
112 hir::ImplItemKind::Method(..) => "method body",
113 hir::ImplItemKind::Const(..) |
114 hir::ImplItemKind::Type(_) => "associated item"
118 fn explain_span<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
119 heading: &str, span: Span)
120 -> (String, Option<Span>) {
121 let lo = tcx.sess.codemap().lookup_char_pos_adj(span.lo());
122 (format!("the {} at {}:{}", heading, lo.line, lo.col.to_usize() + 1),
126 let (description, span) = match *region {
127 ty::ReScope(scope) => {
129 let unknown_scope = || {
130 format!("{}unknown scope: {:?}{}. Please report a bug.",
131 prefix, scope, suffix)
133 let span = match scope.span(&self.hir) {
136 err.note(&unknown_scope());
140 let tag = match self.hir.find(scope.node_id()) {
141 Some(hir_map::NodeBlock(_)) => "block",
142 Some(hir_map::NodeExpr(expr)) => match expr.node {
143 hir::ExprCall(..) => "call",
144 hir::ExprMethodCall(..) => "method call",
145 hir::ExprMatch(.., hir::MatchSource::IfLetDesugar { .. }) => "if let",
146 hir::ExprMatch(.., hir::MatchSource::WhileLetDesugar) => "while let",
147 hir::ExprMatch(.., hir::MatchSource::ForLoopDesugar) => "for",
148 hir::ExprMatch(..) => "match",
151 Some(hir_map::NodeStmt(_)) => "statement",
152 Some(hir_map::NodeItem(it)) => item_scope_tag(&it),
153 Some(hir_map::NodeTraitItem(it)) => trait_item_scope_tag(&it),
154 Some(hir_map::NodeImplItem(it)) => impl_item_scope_tag(&it),
156 err.span_note(span, &unknown_scope());
160 let scope_decorated_tag = match scope {
161 region::CodeExtent::Misc(_) => tag,
162 region::CodeExtent::CallSiteScope(_) => {
163 "scope of call-site for function"
165 region::CodeExtent::ParameterScope(_) => {
166 "scope of function body"
168 region::CodeExtent::DestructionScope(_) => {
169 new_string = format!("destruction scope surrounding {}", tag);
172 region::CodeExtent::Remainder(r) => {
173 new_string = format!("block suffix following statement {}",
174 r.first_statement_index);
178 explain_span(self, scope_decorated_tag, span)
181 ty::ReEarlyBound(_) |
183 let scope = match *region {
184 ty::ReEarlyBound(ref br) => {
185 self.parent_def_id(br.def_id).unwrap()
187 ty::ReFree(ref fr) => fr.scope,
190 let prefix = match *region {
191 ty::ReEarlyBound(ref br) => {
192 format!("the lifetime {} as defined on", br.name)
194 ty::ReFree(ref fr) => {
195 match fr.bound_region {
197 format!("the anonymous lifetime #{} defined on", idx + 1)
199 ty::BrFresh(_) => "an anonymous lifetime defined on".to_owned(),
201 format!("the lifetime {} as defined on",
209 let node = self.hir.as_local_node_id(scope)
210 .unwrap_or(DUMMY_NODE_ID);
212 let tag = match self.hir.find(node) {
213 Some(hir_map::NodeBlock(_)) |
214 Some(hir_map::NodeExpr(_)) => "body",
215 Some(hir_map::NodeItem(it)) => item_scope_tag(&it),
216 Some(hir_map::NodeTraitItem(it)) => trait_item_scope_tag(&it),
217 Some(hir_map::NodeImplItem(it)) => impl_item_scope_tag(&it),
219 // this really should not happen, but it does:
222 unknown = format!("unexpected node ({}) for scope {:?}. \
223 Please report a bug.",
224 self.hir.node_to_string(node), scope);
228 unknown = format!("unknown node for scope {:?}. \
229 Please report a bug.", scope);
233 let (msg, opt_span) = explain_span(self, tag, self.hir.span(node));
234 (format!("{} {}", prefix, msg), opt_span)
237 ty::ReStatic => ("the static lifetime".to_owned(), None),
239 ty::ReEmpty => ("the empty lifetime".to_owned(), None),
241 // FIXME(#13998) ReSkolemized should probably print like
242 // ReFree rather than dumping Debug output on the user.
244 // We shouldn't really be having unification failures with ReVar
245 // and ReLateBound though.
246 ty::ReSkolemized(..) |
248 ty::ReLateBound(..) |
250 (format!("lifetime {:?}", region), None)
253 let message = format!("{}{}{}", prefix, description, suffix);
254 if let Some(span) = span {
255 err.span_note(span, &message);
262 impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
264 pub fn report_region_errors(&self, errors: &Vec<RegionResolutionError<'tcx>>) {
265 debug!("report_region_errors(): {} errors to start", errors.len());
267 // try to pre-process the errors, which will group some of them
268 // together into a `ProcessedErrors` group:
269 let errors = self.process_errors(errors);
271 debug!("report_region_errors: {} errors after preprocessing", errors.len());
273 for error in errors {
274 debug!("report_region_errors: error = {:?}", error);
276 if !self.try_report_named_anon_conflict(&error) &&
277 !self.try_report_anon_anon_conflict(&error) {
279 match error.clone() {
280 // These errors could indicate all manner of different
281 // problems with many different solutions. Rather
282 // than generate a "one size fits all" error, what we
283 // attempt to do is go through a number of specific
284 // scenarios and try to find the best way to present
285 // the error. If all of these fails, we fall back to a rather
286 // general bit of code that displays the error information
287 ConcreteFailure(origin, sub, sup) => {
289 self.report_concrete_failure(origin, sub, sup).emit();
292 GenericBoundFailure(kind, param_ty, sub) => {
293 self.report_generic_bound_failure(kind, param_ty, sub);
296 SubSupConflict(var_origin, sub_origin, sub_r, sup_origin, sup_r) => {
297 self.report_sub_sup_conflict(var_origin,
308 // This method goes through all the errors and try to group certain types
309 // of error together, for the purpose of suggesting explicit lifetime
310 // parameters to the user. This is done so that we can have a more
311 // complete view of what lifetimes should be the same.
312 // If the return value is an empty vector, it means that processing
313 // failed (so the return value of this method should not be used).
315 // The method also attempts to weed out messages that seem like
316 // duplicates that will be unhelpful to the end-user. But
317 // obviously it never weeds out ALL errors.
318 fn process_errors(&self, errors: &Vec<RegionResolutionError<'tcx>>)
319 -> Vec<RegionResolutionError<'tcx>> {
320 debug!("process_errors()");
322 // We want to avoid reporting generic-bound failures if we can
323 // avoid it: these have a very high rate of being unhelpful in
324 // practice. This is because they are basically secondary
325 // checks that test the state of the region graph after the
326 // rest of inference is done, and the other kinds of errors
327 // indicate that the region constraint graph is internally
328 // inconsistent, so these test results are likely to be
331 // Therefore, we filter them out of the list unless they are
332 // the only thing in the list.
334 let is_bound_failure = |e: &RegionResolutionError<'tcx>| match *e {
335 ConcreteFailure(..) => false,
336 SubSupConflict(..) => false,
337 GenericBoundFailure(..) => true,
340 if errors.iter().all(|e| is_bound_failure(e)) {
343 errors.iter().filter(|&e| !is_bound_failure(e)).cloned().collect()
347 /// Adds a note if the types come from similarly named crates
348 fn check_and_note_conflicting_crates(&self,
349 err: &mut DiagnosticBuilder,
350 terr: &TypeError<'tcx>,
352 let report_path_match = |err: &mut DiagnosticBuilder, did1: DefId, did2: DefId| {
353 // Only external crates, if either is from a local
354 // module we could have false positives
355 if !(did1.is_local() || did2.is_local()) && did1.krate != did2.krate {
356 let exp_path = self.tcx.item_path_str(did1);
357 let found_path = self.tcx.item_path_str(did2);
358 let exp_abs_path = self.tcx.absolute_item_path_str(did1);
359 let found_abs_path = self.tcx.absolute_item_path_str(did2);
360 // We compare strings because DefPath can be different
361 // for imported and non-imported crates
362 if exp_path == found_path
363 || exp_abs_path == found_abs_path {
364 let crate_name = self.tcx.sess.cstore.crate_name(did1.krate);
365 err.span_note(sp, &format!("Perhaps two different versions \
366 of crate `{}` are being used?",
372 TypeError::Sorts(ref exp_found) => {
373 // if they are both "path types", there's a chance of ambiguity
374 // due to different versions of the same crate
375 match (&exp_found.expected.sty, &exp_found.found.sty) {
376 (&ty::TyAdt(exp_adt, _), &ty::TyAdt(found_adt, _)) => {
377 report_path_match(err, exp_adt.did, found_adt.did);
382 TypeError::Traits(ref exp_found) => {
383 report_path_match(err, exp_found.expected, exp_found.found);
385 _ => () // FIXME(#22750) handle traits and stuff
389 fn note_error_origin(&self,
390 err: &mut DiagnosticBuilder<'tcx>,
391 cause: &ObligationCause<'tcx>)
394 ObligationCauseCode::MatchExpressionArm { arm_span, source } => match source {
395 hir::MatchSource::IfLetDesugar {..} => {
396 err.span_note(arm_span, "`if let` arm with an incompatible type");
399 err.span_note(arm_span, "match arm with an incompatible type");
406 /// Given that `other_ty` is the same as a type argument for `name` in `sub`, populate `value`
407 /// highlighting `name` and every type argument that isn't at `pos` (which is `other_ty`), and
408 /// populate `other_value` with `other_ty`.
412 /// ^^^^--------^ this is highlighted
414 /// | this type argument is exactly the same as the other type, not highlighted
415 /// this is highlighted
417 /// -------- this type is the same as a type argument in the other type, not highlighted
419 fn highlight_outer(&self,
420 value: &mut DiagnosticStyledString,
421 other_value: &mut DiagnosticStyledString,
423 sub: &ty::subst::Substs<'tcx>,
425 other_ty: &ty::Ty<'tcx>) {
426 // `value` and `other_value` hold two incomplete type representation for display.
427 // `name` is the path of both types being compared. `sub`
428 value.push_highlighted(name);
431 value.push_highlighted("<");
434 // Output the lifetimes fot the first type
435 let lifetimes = sub.regions().map(|lifetime| {
436 let s = format!("{}", lifetime);
442 }).collect::<Vec<_>>().join(", ");
443 if !lifetimes.is_empty() {
444 if sub.regions().count() < len {
445 value.push_normal(lifetimes + &", ");
447 value.push_normal(lifetimes);
451 // Highlight all the type arguments that aren't at `pos` and compare the type argument at
452 // `pos` and `other_ty`.
453 for (i, type_arg) in sub.types().enumerate() {
455 let values = self.cmp(type_arg, other_ty);
456 value.0.extend((values.0).0);
457 other_value.0.extend((values.1).0);
459 value.push_highlighted(format!("{}", type_arg));
462 if len > 0 && i != len - 1 {
463 value.push_normal(", ");
465 //self.push_comma(&mut value, &mut other_value, len, i);
468 value.push_highlighted(">");
472 /// If `other_ty` is the same as a type argument present in `sub`, highlight `path` in `t1_out`,
473 /// as that is the difference to the other type.
475 /// For the following code:
478 /// let x: Foo<Bar<Qux>> = foo::<Bar<Qux>>();
481 /// The type error output will behave in the following way:
485 /// ^^^^--------^ this is highlighted
487 /// | this type argument is exactly the same as the other type, not highlighted
488 /// this is highlighted
490 /// -------- this type is the same as a type argument in the other type, not highlighted
492 fn cmp_type_arg(&self,
493 mut t1_out: &mut DiagnosticStyledString,
494 mut t2_out: &mut DiagnosticStyledString,
496 sub: &ty::subst::Substs<'tcx>,
498 other_ty: &ty::Ty<'tcx>) -> Option<()> {
499 for (i, ta) in sub.types().enumerate() {
501 self.highlight_outer(&mut t1_out, &mut t2_out, path, sub, i, &other_ty);
504 if let &ty::TyAdt(def, _) = &ta.sty {
505 let path_ = self.tcx.item_path_str(def.did.clone());
506 if path_ == other_path {
507 self.highlight_outer(&mut t1_out, &mut t2_out, path, sub, i, &other_ty);
515 /// Add a `,` to the type representation only if it is appropriate.
517 value: &mut DiagnosticStyledString,
518 other_value: &mut DiagnosticStyledString,
521 if len > 0 && pos != len - 1 {
522 value.push_normal(", ");
523 other_value.push_normal(", ");
527 /// Compare two given types, eliding parts that are the same between them and highlighting
528 /// relevant differences, and return two representation of those types for highlighted printing.
529 fn cmp(&self, t1: ty::Ty<'tcx>, t2: ty::Ty<'tcx>)
530 -> (DiagnosticStyledString, DiagnosticStyledString)
532 match (&t1.sty, &t2.sty) {
533 (&ty::TyAdt(def1, sub1), &ty::TyAdt(def2, sub2)) => {
534 let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new());
535 let path1 = self.tcx.item_path_str(def1.did.clone());
536 let path2 = self.tcx.item_path_str(def2.did.clone());
537 if def1.did == def2.did {
538 // Easy case. Replace same types with `_` to shorten the output and highlight
539 // the differing ones.
540 // let x: Foo<Bar, Qux> = y::<Foo<Quz, Qux>>();
543 // --- ^ type argument elided
545 // highlighted in output
546 values.0.push_normal(path1);
547 values.1.push_normal(path2);
549 // Only draw `<...>` if there're lifetime/type arguments.
550 let len = sub1.len();
552 values.0.push_normal("<");
553 values.1.push_normal("<");
556 fn lifetime_display(lifetime: Region) -> String {
557 let s = format!("{}", lifetime);
564 // At one point we'd like to elide all lifetimes here, they are irrelevant for
565 // all diagnostics that use this output
569 // ^^ ^^ --- type arguments are not elided
571 // | elided as they were the same
572 // not elided, they were different, but irrelevant
573 let lifetimes = sub1.regions().zip(sub2.regions());
574 for (i, lifetimes) in lifetimes.enumerate() {
575 let l1 = lifetime_display(lifetimes.0);
576 let l2 = lifetime_display(lifetimes.1);
578 values.0.push_normal("'_");
579 values.1.push_normal("'_");
581 values.0.push_highlighted(l1);
582 values.1.push_highlighted(l2);
584 self.push_comma(&mut values.0, &mut values.1, len, i);
587 // We're comparing two types with the same path, so we compare the type
588 // arguments for both. If they are the same, do not highlight and elide from the
592 // ^ elided type as this type argument was the same in both sides
593 let type_arguments = sub1.types().zip(sub2.types());
594 let regions_len = sub1.regions().collect::<Vec<_>>().len();
595 for (i, (ta1, ta2)) in type_arguments.enumerate() {
596 let i = i + regions_len;
598 values.0.push_normal("_");
599 values.1.push_normal("_");
601 let (x1, x2) = self.cmp(ta1, ta2);
602 (values.0).0.extend(x1.0);
603 (values.1).0.extend(x2.0);
605 self.push_comma(&mut values.0, &mut values.1, len, i);
608 // Close the type argument bracket.
609 // Only draw `<...>` if there're lifetime/type arguments.
611 values.0.push_normal(">");
612 values.1.push_normal(">");
617 // let x: Foo<Bar<Qux> = foo::<Bar<Qux>>();
619 // ------- this type argument is exactly the same as the other type
621 if self.cmp_type_arg(&mut values.0,
630 // let x: Bar<Qux> = y:<Foo<Bar<Qux>>>();
633 // ------- this type argument is exactly the same as the other type
634 if self.cmp_type_arg(&mut values.1,
643 // We couldn't find anything in common, highlight everything.
644 // let x: Bar<Qux> = y::<Foo<Zar>>();
645 (DiagnosticStyledString::highlighted(format!("{}", t1)),
646 DiagnosticStyledString::highlighted(format!("{}", t2)))
651 // The two types are the same, elide and don't highlight.
652 (DiagnosticStyledString::normal("_"), DiagnosticStyledString::normal("_"))
654 // We couldn't find anything in common, highlight everything.
655 (DiagnosticStyledString::highlighted(format!("{}", t1)),
656 DiagnosticStyledString::highlighted(format!("{}", t2)))
662 pub fn note_type_err(&self,
663 diag: &mut DiagnosticBuilder<'tcx>,
664 cause: &ObligationCause<'tcx>,
665 secondary_span: Option<(Span, String)>,
666 values: Option<ValuePairs<'tcx>>,
667 terr: &TypeError<'tcx>)
669 let (expected_found, is_simple_error) = match values {
670 None => (None, false),
672 let is_simple_error = match values {
673 ValuePairs::Types(exp_found) => {
674 exp_found.expected.is_primitive() && exp_found.found.is_primitive()
678 let vals = match self.values_str(&values) {
679 Some((expected, found)) => Some((expected, found)),
681 // Derived error. Cancel the emitter.
682 self.tcx.sess.diagnostic().cancel(diag);
686 (vals, is_simple_error)
690 let span = cause.span;
692 if let Some((expected, found)) = expected_found {
693 match (terr, is_simple_error, expected == found) {
694 (&TypeError::Sorts(ref values), false, true) => {
695 diag.note_expected_found_extra(
696 &"type", expected, found,
697 &format!(" ({})", values.expected.sort_string(self.tcx)),
698 &format!(" ({})", values.found.sort_string(self.tcx)));
701 diag.note_expected_found(&"type", expected, found);
707 diag.span_label(span, terr.to_string());
708 if let Some((sp, msg)) = secondary_span {
709 diag.span_label(sp, msg);
712 self.note_error_origin(diag, &cause);
713 self.check_and_note_conflicting_crates(diag, terr, span);
714 self.tcx.note_and_explain_type_err(diag, terr, span);
717 pub fn report_and_explain_type_error(&self,
718 trace: TypeTrace<'tcx>,
719 terr: &TypeError<'tcx>)
720 -> DiagnosticBuilder<'tcx>
722 let span = trace.cause.span;
723 let failure_str = trace.cause.as_failure_str();
724 let mut diag = match trace.cause.code {
725 ObligationCauseCode::IfExpressionWithNoElse => {
726 struct_span_err!(self.tcx.sess, span, E0317, "{}", failure_str)
728 ObligationCauseCode::MainFunctionType => {
729 struct_span_err!(self.tcx.sess, span, E0580, "{}", failure_str)
732 struct_span_err!(self.tcx.sess, span, E0308, "{}", failure_str)
735 self.note_type_err(&mut diag, &trace.cause, None, Some(trace.values), terr);
739 fn values_str(&self, values: &ValuePairs<'tcx>)
740 -> Option<(DiagnosticStyledString, DiagnosticStyledString)>
743 infer::Types(ref exp_found) => self.expected_found_str_ty(exp_found),
744 infer::TraitRefs(ref exp_found) => self.expected_found_str(exp_found),
745 infer::PolyTraitRefs(ref exp_found) => self.expected_found_str(exp_found),
749 fn expected_found_str_ty(&self,
750 exp_found: &ty::error::ExpectedFound<ty::Ty<'tcx>>)
751 -> Option<(DiagnosticStyledString, DiagnosticStyledString)> {
752 let exp_found = self.resolve_type_vars_if_possible(exp_found);
753 if exp_found.references_error() {
757 Some(self.cmp(exp_found.expected, exp_found.found))
760 /// Returns a string of the form "expected `{}`, found `{}`".
761 fn expected_found_str<T: fmt::Display + TypeFoldable<'tcx>>(
763 exp_found: &ty::error::ExpectedFound<T>)
764 -> Option<(DiagnosticStyledString, DiagnosticStyledString)>
766 let exp_found = self.resolve_type_vars_if_possible(exp_found);
767 if exp_found.references_error() {
771 Some((DiagnosticStyledString::highlighted(format!("{}", exp_found.expected)),
772 DiagnosticStyledString::highlighted(format!("{}", exp_found.found))))
775 fn report_generic_bound_failure(&self,
776 origin: SubregionOrigin<'tcx>,
777 bound_kind: GenericKind<'tcx>,
780 // FIXME: it would be better to report the first error message
781 // with the span of the parameter itself, rather than the span
782 // where the error was detected. But that span is not readily
785 let labeled_user_string = match bound_kind {
786 GenericKind::Param(ref p) =>
787 format!("the parameter type `{}`", p),
788 GenericKind::Projection(ref p) =>
789 format!("the associated type `{}`", p),
792 if let SubregionOrigin::CompareImplMethodObligation {
793 span, item_name, impl_item_def_id, trait_item_def_id, lint_id
795 self.report_extra_impl_obligation(span,
799 &format!("`{}: {}`", bound_kind, sub),
805 let mut err = match *sub {
806 ty::ReEarlyBound(_) |
807 ty::ReFree(ty::FreeRegion {bound_region: ty::BrNamed(..), ..}) => {
808 // Does the required lifetime have a nice name we can print?
809 let mut err = struct_span_err!(self.tcx.sess,
812 "{} may not live long enough",
813 labeled_user_string);
814 err.help(&format!("consider adding an explicit lifetime bound `{}: {}`...",
821 // Does the required lifetime have a nice name we can print?
822 let mut err = struct_span_err!(self.tcx.sess,
825 "{} may not live long enough",
826 labeled_user_string);
827 err.help(&format!("consider adding an explicit lifetime \
828 bound `{}: 'static`...",
834 // If not, be less specific.
835 let mut err = struct_span_err!(self.tcx.sess,
838 "{} may not live long enough",
839 labeled_user_string);
840 err.help(&format!("consider adding an explicit lifetime bound for `{}`",
842 self.tcx.note_and_explain_region(
844 &format!("{} must be valid for ", labeled_user_string),
851 self.note_region_origin(&mut err, &origin);
855 fn report_sub_sup_conflict(&self,
856 var_origin: RegionVariableOrigin,
857 sub_origin: SubregionOrigin<'tcx>,
858 sub_region: Region<'tcx>,
859 sup_origin: SubregionOrigin<'tcx>,
860 sup_region: Region<'tcx>) {
861 let mut err = self.report_inference_failure(var_origin);
863 self.tcx.note_and_explain_region(&mut err,
864 "first, the lifetime cannot outlive ",
868 self.note_region_origin(&mut err, &sup_origin);
870 self.tcx.note_and_explain_region(&mut err,
871 "but, the lifetime must be valid for ",
875 self.note_region_origin(&mut err, &sub_origin);
880 impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
881 fn report_inference_failure(&self,
882 var_origin: RegionVariableOrigin)
883 -> DiagnosticBuilder<'tcx> {
884 let br_string = |br: ty::BoundRegion| {
885 let mut s = br.to_string();
891 let var_description = match var_origin {
892 infer::MiscVariable(_) => "".to_string(),
893 infer::PatternRegion(_) => " for pattern".to_string(),
894 infer::AddrOfRegion(_) => " for borrow expression".to_string(),
895 infer::Autoref(_) => " for autoref".to_string(),
896 infer::Coercion(_) => " for automatic coercion".to_string(),
897 infer::LateBoundRegion(_, br, infer::FnCall) => {
898 format!(" for lifetime parameter {}in function call",
901 infer::LateBoundRegion(_, br, infer::HigherRankedType) => {
902 format!(" for lifetime parameter {}in generic type", br_string(br))
904 infer::LateBoundRegion(_, br, infer::AssocTypeProjection(def_id)) => {
905 format!(" for lifetime parameter {}in trait containing associated type `{}`",
906 br_string(br), self.tcx.associated_item(def_id).name)
908 infer::EarlyBoundRegion(_, name) => {
909 format!(" for lifetime parameter `{}`",
912 infer::BoundRegionInCoherence(name) => {
913 format!(" for lifetime parameter `{}` in coherence check",
916 infer::UpvarRegion(ref upvar_id, _) => {
917 format!(" for capture of `{}` by closure",
918 self.tcx.local_var_name_str_def_index(upvar_id.var_id))
922 struct_span_err!(self.tcx.sess, var_origin.span(), E0495,
923 "cannot infer an appropriate lifetime{} \
924 due to conflicting requirements",
929 impl<'tcx> ObligationCause<'tcx> {
930 fn as_failure_str(&self) -> &'static str {
931 use traits::ObligationCauseCode::*;
933 CompareImplMethodObligation { .. } => "method not compatible with trait",
934 MatchExpressionArm { source, .. } => match source {
935 hir::MatchSource::IfLetDesugar{..} => "`if let` arms have incompatible types",
936 _ => "match arms have incompatible types",
938 IfExpression => "if and else have incompatible types",
939 IfExpressionWithNoElse => "if may be missing an else clause",
940 EquatePredicate => "equality predicate not satisfied",
941 MainFunctionType => "main function has wrong type",
942 StartFunctionType => "start function has wrong type",
943 IntrinsicType => "intrinsic has wrong type",
944 MethodReceiver => "mismatched method receiver",
945 _ => "mismatched types",
949 fn as_requirement_str(&self) -> &'static str {
950 use traits::ObligationCauseCode::*;
952 CompareImplMethodObligation { .. } => "method type is compatible with trait",
953 ExprAssignable => "expression is assignable",
954 MatchExpressionArm { source, .. } => match source {
955 hir::MatchSource::IfLetDesugar{..} => "`if let` arms have compatible types",
956 _ => "match arms have compatible types",
958 IfExpression => "if and else have compatible types",
959 IfExpressionWithNoElse => "if missing an else returns ()",
960 EquatePredicate => "equality where clause is satisfied",
961 MainFunctionType => "`main` function has the correct type",
962 StartFunctionType => "`start` function has the correct type",
963 IntrinsicType => "intrinsic has the correct type",
964 MethodReceiver => "method receiver has the correct type",
965 _ => "types are compatible",