1 // Copyright 2014 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.
14 MismatchedProjectionTypes,
18 OutputTypeParameterMismatch,
23 ObjectSafetyViolation,
26 use errors::DiagnosticBuilder;
27 use fmt_macros::{Parser, Piece, Position};
28 use hir::{self, intravisit, Local, Pat, Body};
29 use hir::intravisit::{Visitor, NestedVisitorMap};
30 use hir::map::NodeExpr;
31 use hir::def_id::DefId;
32 use infer::{self, InferCtxt};
33 use infer::type_variable::TypeVariableOrigin;
34 use rustc::lint::builtin::EXTRA_REQUIREMENT_IN_IMPL;
36 use syntax::ast::{self, NodeId};
37 use ty::{self, AdtKind, ToPredicate, ToPolyTraitRef, Ty, TyCtxt, TypeFoldable, TyInfer, TyVar};
38 use ty::error::{ExpectedFound, TypeError};
40 use ty::fold::TypeFolder;
42 use ty::SubtypePredicate;
43 use util::nodemap::{FxHashMap, FxHashSet};
45 use syntax_pos::{DUMMY_SP, Span};
48 #[derive(Debug, PartialEq, Eq, Hash)]
49 pub struct TraitErrorKey<'tcx> {
51 predicate: ty::Predicate<'tcx>
54 impl<'a, 'gcx, 'tcx> TraitErrorKey<'tcx> {
55 fn from_error(infcx: &InferCtxt<'a, 'gcx, 'tcx>,
56 e: &FulfillmentError<'tcx>) -> Self {
58 infcx.resolve_type_vars_if_possible(&e.obligation.predicate);
60 span: e.obligation.cause.span,
61 predicate: infcx.tcx.erase_regions(&predicate)
66 struct FindLocalByTypeVisitor<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
67 infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
68 target_ty: &'a Ty<'tcx>,
69 hir_map: &'a hir::map::Map<'gcx>,
70 found_local_pattern: Option<&'gcx Pat>,
71 found_arg_pattern: Option<&'gcx Pat>,
74 impl<'a, 'gcx, 'tcx> FindLocalByTypeVisitor<'a, 'gcx, 'tcx> {
75 fn node_matches_type(&mut self, node_id: &'gcx NodeId) -> bool {
76 match self.infcx.tables.borrow().node_types.get(node_id) {
78 let ty = self.infcx.resolve_type_vars_if_possible(&ty);
79 ty.walk().any(|inner_ty| {
80 inner_ty == *self.target_ty || match (&inner_ty.sty, &self.target_ty.sty) {
81 (&TyInfer(TyVar(a_vid)), &TyInfer(TyVar(b_vid))) => {
85 .sub_unified(a_vid, b_vid)
96 impl<'a, 'gcx, 'tcx> Visitor<'gcx> for FindLocalByTypeVisitor<'a, 'gcx, 'tcx> {
97 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'gcx> {
98 NestedVisitorMap::OnlyBodies(&self.hir_map)
101 fn visit_local(&mut self, local: &'gcx Local) {
102 if self.found_local_pattern.is_none() && self.node_matches_type(&local.id) {
103 self.found_local_pattern = Some(&*local.pat);
105 intravisit::walk_local(self, local);
108 fn visit_body(&mut self, body: &'gcx Body) {
109 for argument in &body.arguments {
110 if self.found_arg_pattern.is_none() && self.node_matches_type(&argument.id) {
111 self.found_arg_pattern = Some(&*argument.pat);
114 intravisit::walk_body(self, body);
118 impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
119 pub fn report_fulfillment_errors(&self, errors: &Vec<FulfillmentError<'tcx>>) {
120 for error in errors {
121 self.report_fulfillment_error(error);
125 fn report_fulfillment_error(&self,
126 error: &FulfillmentError<'tcx>) {
127 let error_key = TraitErrorKey::from_error(self, error);
128 debug!("report_fulfillment_errors({:?}) - key={:?}",
130 if !self.reported_trait_errors.borrow_mut().insert(error_key) {
131 debug!("report_fulfillment_errors: skipping duplicate");
135 FulfillmentErrorCode::CodeSelectionError(ref e) => {
136 self.report_selection_error(&error.obligation, e);
138 FulfillmentErrorCode::CodeProjectionError(ref e) => {
139 self.report_projection_error(&error.obligation, e);
141 FulfillmentErrorCode::CodeAmbiguity => {
142 self.maybe_report_ambiguity(&error.obligation);
144 FulfillmentErrorCode::CodeSubtypeError(ref expected_found, ref err) => {
145 self.report_mismatched_types(&error.obligation.cause,
146 expected_found.expected,
147 expected_found.found,
154 fn report_projection_error(&self,
155 obligation: &PredicateObligation<'tcx>,
156 error: &MismatchedProjectionTypes<'tcx>)
159 self.resolve_type_vars_if_possible(&obligation.predicate);
161 if predicate.references_error() {
167 let mut err = &error.err;
168 let mut values = None;
170 // try to find the mismatched types to report the error with.
172 // this can fail if the problem was higher-ranked, in which
173 // cause I have no idea for a good error message.
174 if let ty::Predicate::Projection(ref data) = predicate {
175 let mut selcx = SelectionContext::new(self);
176 let (data, _) = self.replace_late_bound_regions_with_fresh_var(
177 obligation.cause.span,
178 infer::LateBoundRegionConversionTime::HigherRankedType,
180 let normalized = super::normalize_projection_type(
183 obligation.cause.clone(),
186 if let Err(error) = self.eq_types(
187 false, &obligation.cause,
188 data.ty, normalized.value
190 values = Some(infer::ValuePairs::Types(ExpectedFound {
191 expected: normalized.value,
199 let mut diag = struct_span_err!(
200 self.tcx.sess, obligation.cause.span, E0271,
201 "type mismatch resolving `{}`", predicate
203 self.note_type_err(&mut diag, &obligation.cause, None, values, err);
204 self.note_obligation_cause(&mut diag, obligation);
209 fn fuzzy_match_tys(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
210 /// returns the fuzzy category of a given type, or None
211 /// if the type can be equated to any type.
212 fn type_category<'tcx>(t: Ty<'tcx>) -> Option<u32> {
214 ty::TyBool => Some(0),
215 ty::TyChar => Some(1),
216 ty::TyStr => Some(2),
217 ty::TyInt(..) | ty::TyUint(..) | ty::TyInfer(ty::IntVar(..)) => Some(3),
218 ty::TyFloat(..) | ty::TyInfer(ty::FloatVar(..)) => Some(4),
219 ty::TyRef(..) | ty::TyRawPtr(..) => Some(5),
220 ty::TyArray(..) | ty::TySlice(..) => Some(6),
221 ty::TyFnDef(..) | ty::TyFnPtr(..) => Some(7),
222 ty::TyDynamic(..) => Some(8),
223 ty::TyClosure(..) => Some(9),
224 ty::TyTuple(..) => Some(10),
225 ty::TyProjection(..) => Some(11),
226 ty::TyParam(..) => Some(12),
227 ty::TyAnon(..) => Some(13),
228 ty::TyNever => Some(14),
229 ty::TyAdt(adt, ..) => match adt.adt_kind() {
230 AdtKind::Struct => Some(15),
231 AdtKind::Union => Some(16),
232 AdtKind::Enum => Some(17),
234 ty::TyInfer(..) | ty::TyError => None
238 match (type_category(a), type_category(b)) {
239 (Some(cat_a), Some(cat_b)) => match (&a.sty, &b.sty) {
240 (&ty::TyAdt(def_a, _), &ty::TyAdt(def_b, _)) => def_a == def_b,
243 // infer and error can be equated to all types
248 fn impl_similar_to(&self,
249 trait_ref: ty::PolyTraitRef<'tcx>,
250 obligation: &PredicateObligation<'tcx>)
255 let trait_ref = tcx.erase_late_bound_regions(&trait_ref);
256 let trait_self_ty = trait_ref.self_ty();
258 let mut self_match_impls = vec![];
259 let mut fuzzy_match_impls = vec![];
261 self.tcx.trait_def(trait_ref.def_id)
262 .for_each_relevant_impl(self.tcx, trait_self_ty, |def_id| {
263 let impl_substs = self.fresh_substs_for_item(obligation.cause.span, def_id);
264 let impl_trait_ref = tcx
265 .impl_trait_ref(def_id)
267 .subst(tcx, impl_substs);
269 let impl_self_ty = impl_trait_ref.self_ty();
271 if let Ok(..) = self.can_equate(&trait_self_ty, &impl_self_ty) {
272 self_match_impls.push(def_id);
274 if trait_ref.substs.types().skip(1)
275 .zip(impl_trait_ref.substs.types().skip(1))
276 .all(|(u,v)| self.fuzzy_match_tys(u, v))
278 fuzzy_match_impls.push(def_id);
283 let impl_def_id = if self_match_impls.len() == 1 {
285 } else if fuzzy_match_impls.len() == 1 {
291 if tcx.has_attr(impl_def_id, "rustc_on_unimplemented") {
298 fn on_unimplemented_note(&self,
299 trait_ref: ty::PolyTraitRef<'tcx>,
300 obligation: &PredicateObligation<'tcx>) -> Option<String> {
301 let def_id = self.impl_similar_to(trait_ref, obligation)
302 .unwrap_or(trait_ref.def_id());
303 let trait_ref = trait_ref.skip_binder();
305 let span = obligation.cause.span;
306 let mut report = None;
307 if let Some(item) = self.tcx
310 .filter(|a| a.check_name("rustc_on_unimplemented"))
313 let err_sp = item.span.substitute_dummy(span);
314 let trait_str = self.tcx.item_path_str(trait_ref.def_id);
315 if let Some(istring) = item.value_str() {
316 let istring = &*istring.as_str();
317 let generics = self.tcx.generics_of(trait_ref.def_id);
318 let generic_map = generics.types.iter().map(|param| {
319 (param.name.as_str().to_string(),
320 trait_ref.substs.type_for_def(param).to_string())
321 }).collect::<FxHashMap<String, String>>();
322 let parser = Parser::new(istring);
323 let mut errored = false;
324 let err: String = parser.filter_map(|p| {
326 Piece::String(s) => Some(s),
327 Piece::NextArgument(a) => match a.position {
328 Position::ArgumentNamed(s) => match generic_map.get(s) {
329 Some(val) => Some(val),
331 span_err!(self.tcx.sess, err_sp, E0272,
332 "the #[rustc_on_unimplemented] attribute on trait \
333 definition for {} refers to non-existent type \
341 span_err!(self.tcx.sess, err_sp, E0273,
342 "the #[rustc_on_unimplemented] attribute on trait \
343 definition for {} must have named format arguments, eg \
344 `#[rustc_on_unimplemented = \"foo {{T}}\"]`",
352 // Report only if the format string checks out
357 span_err!(self.tcx.sess, err_sp, E0274,
358 "the #[rustc_on_unimplemented] attribute on \
359 trait definition for {} must have a value, \
360 eg `#[rustc_on_unimplemented = \"foo\"]`",
367 fn find_similar_impl_candidates(&self,
368 trait_ref: ty::PolyTraitRef<'tcx>)
369 -> Vec<ty::TraitRef<'tcx>>
371 let simp = fast_reject::simplify_type(self.tcx,
372 trait_ref.skip_binder().self_ty(),
374 let mut impl_candidates = Vec::new();
375 let trait_def = self.tcx.trait_def(trait_ref.def_id());
378 Some(simp) => trait_def.for_each_impl(self.tcx, |def_id| {
379 let imp = self.tcx.impl_trait_ref(def_id).unwrap();
380 let imp_simp = fast_reject::simplify_type(self.tcx,
383 if let Some(imp_simp) = imp_simp {
384 if simp != imp_simp {
388 impl_candidates.push(imp);
390 None => trait_def.for_each_impl(self.tcx, |def_id| {
391 impl_candidates.push(
392 self.tcx.impl_trait_ref(def_id).unwrap());
398 fn report_similar_impl_candidates(&self,
399 impl_candidates: Vec<ty::TraitRef<'tcx>>,
400 err: &mut DiagnosticBuilder)
402 if impl_candidates.is_empty() {
406 let end = if impl_candidates.len() <= 5 {
407 impl_candidates.len()
411 err.help(&format!("the following implementations were found:{}{}",
412 &impl_candidates[0..end].iter().map(|candidate| {
413 format!("\n {:?}", candidate)
414 }).collect::<String>(),
415 if impl_candidates.len() > 5 {
416 format!("\nand {} others", impl_candidates.len() - 4)
423 /// Reports that an overflow has occurred and halts compilation. We
424 /// halt compilation unconditionally because it is important that
425 /// overflows never be masked -- they basically represent computations
426 /// whose result could not be truly determined and thus we can't say
427 /// if the program type checks or not -- and they are unusual
428 /// occurrences in any case.
429 pub fn report_overflow_error<T>(&self,
430 obligation: &Obligation<'tcx, T>,
431 suggest_increasing_limit: bool) -> !
432 where T: fmt::Display + TypeFoldable<'tcx>
435 self.resolve_type_vars_if_possible(&obligation.predicate);
436 let mut err = struct_span_err!(self.tcx.sess, obligation.cause.span, E0275,
437 "overflow evaluating the requirement `{}`",
440 if suggest_increasing_limit {
441 self.suggest_new_overflow_limit(&mut err);
444 self.note_obligation_cause(&mut err, obligation);
447 self.tcx.sess.abort_if_errors();
451 /// Reports that a cycle was detected which led to overflow and halts
452 /// compilation. This is equivalent to `report_overflow_error` except
453 /// that we can give a more helpful error message (and, in particular,
454 /// we do not suggest increasing the overflow limit, which is not
456 pub fn report_overflow_error_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> ! {
457 let cycle = self.resolve_type_vars_if_possible(&cycle.to_owned());
458 assert!(cycle.len() > 0);
460 debug!("report_overflow_error_cycle: cycle={:?}", cycle);
462 self.report_overflow_error(&cycle[0], false);
465 pub fn report_extra_impl_obligation(&self,
467 item_name: ast::Name,
468 _impl_item_def_id: DefId,
469 trait_item_def_id: DefId,
470 requirement: &fmt::Display,
471 lint_id: Option<ast::NodeId>) // (*)
472 -> DiagnosticBuilder<'tcx>
474 // (*) This parameter is temporary and used only for phasing
475 // in the bug fix to #18937. If it is `Some`, it has a kind of
476 // weird effect -- the diagnostic is reported as a lint, and
477 // the builder which is returned is marked as canceled.
480 struct_span_err!(self.tcx.sess,
483 "impl has stricter requirements than trait");
485 if let Some(trait_item_span) = self.tcx.hir.span_if_local(trait_item_def_id) {
486 let span = self.tcx.sess.codemap().def_span(trait_item_span);
487 err.span_label(span, format!("definition of `{}` from trait", item_name));
492 format!("impl has extra requirement {}", requirement));
494 if let Some(node_id) = lint_id {
495 self.tcx.sess.add_lint_diagnostic(EXTRA_REQUIREMENT_IN_IMPL,
505 /// Get the parent trait chain start
506 fn get_parent_trait_ref(&self, code: &ObligationCauseCode<'tcx>) -> Option<String> {
508 &ObligationCauseCode::BuiltinDerivedObligation(ref data) => {
509 let parent_trait_ref = self.resolve_type_vars_if_possible(
510 &data.parent_trait_ref);
511 match self.get_parent_trait_ref(&data.parent_code) {
513 None => Some(format!("{}", parent_trait_ref.0.self_ty())),
520 pub fn report_selection_error(&self,
521 obligation: &PredicateObligation<'tcx>,
522 error: &SelectionError<'tcx>)
524 let span = obligation.cause.span;
526 let mut err = match *error {
527 SelectionError::Unimplemented => {
528 if let ObligationCauseCode::CompareImplMethodObligation {
529 item_name, impl_item_def_id, trait_item_def_id, lint_id
530 } = obligation.cause.code {
531 self.report_extra_impl_obligation(
536 &format!("`{}`", obligation.predicate),
541 match obligation.predicate {
542 ty::Predicate::Trait(ref trait_predicate) => {
543 let trait_predicate =
544 self.resolve_type_vars_if_possible(trait_predicate);
546 if self.tcx.sess.has_errors() && trait_predicate.references_error() {
549 let trait_ref = trait_predicate.to_poly_trait_ref();
550 let (post_message, pre_message) =
551 self.get_parent_trait_ref(&obligation.cause.code)
552 .map(|t| (format!(" in `{}`", t), format!("within `{}`, ", t)))
553 .unwrap_or((String::new(), String::new()));
554 let mut err = struct_span_err!(
558 "the trait bound `{}` is not satisfied{}",
559 trait_ref.to_predicate(),
562 // Try to report a help message
563 if !trait_ref.has_infer_types() &&
564 self.predicate_can_apply(trait_ref) {
565 // If a where-clause may be useful, remind the
566 // user that they can add it.
568 // don't display an on-unimplemented note, as
569 // these notes will often be of the form
570 // "the type `T` can't be frobnicated"
571 // which is somewhat confusing.
572 err.help(&format!("consider adding a `where {}` bound",
573 trait_ref.to_predicate()));
574 } else if let Some(s) = self.on_unimplemented_note(trait_ref, obligation) {
575 // If it has a custom "#[rustc_on_unimplemented]"
576 // error message, let's display it!
579 // Can't show anything else useful, try to find similar impls.
580 let impl_candidates = self.find_similar_impl_candidates(trait_ref);
581 self.report_similar_impl_candidates(impl_candidates, &mut err);
585 format!("{}the trait `{}` is not implemented for `{}`",
588 trait_ref.self_ty()));
592 ty::Predicate::Subtype(ref predicate) => {
593 // Errors for Subtype predicates show up as
594 // `FulfillmentErrorCode::CodeSubtypeError`,
595 // not selection error.
596 span_bug!(span, "subtype requirement gave wrong error: `{:?}`", predicate)
599 ty::Predicate::Equate(ref predicate) => {
600 let predicate = self.resolve_type_vars_if_possible(predicate);
601 let err = self.equality_predicate(&obligation.cause,
602 &predicate).err().unwrap();
603 struct_span_err!(self.tcx.sess, span, E0278,
604 "the requirement `{}` is not satisfied (`{}`)",
608 ty::Predicate::RegionOutlives(ref predicate) => {
609 let predicate = self.resolve_type_vars_if_possible(predicate);
610 let err = self.region_outlives_predicate(&obligation.cause,
611 &predicate).err().unwrap();
612 struct_span_err!(self.tcx.sess, span, E0279,
613 "the requirement `{}` is not satisfied (`{}`)",
617 ty::Predicate::Projection(..) | ty::Predicate::TypeOutlives(..) => {
619 self.resolve_type_vars_if_possible(&obligation.predicate);
620 struct_span_err!(self.tcx.sess, span, E0280,
621 "the requirement `{}` is not satisfied",
625 ty::Predicate::ObjectSafe(trait_def_id) => {
626 let violations = self.tcx.object_safety_violations(trait_def_id);
627 self.tcx.report_object_safety_error(span,
632 ty::Predicate::ClosureKind(closure_def_id, kind) => {
633 let found_kind = self.closure_kind(closure_def_id).unwrap();
634 let closure_span = self.tcx.hir.span_if_local(closure_def_id).unwrap();
635 let mut err = struct_span_err!(
636 self.tcx.sess, closure_span, E0525,
637 "expected a closure that implements the `{}` trait, \
638 but this closure only implements `{}`",
642 obligation.cause.span,
643 &format!("the requirement to implement \
644 `{}` derives from here", kind));
649 ty::Predicate::WellFormed(ty) => {
650 // WF predicates cannot themselves make
651 // errors. They can only block due to
652 // ambiguity; otherwise, they always
653 // degenerate into other obligations
655 span_bug!(span, "WF predicate not satisfied for {:?}", ty);
660 OutputTypeParameterMismatch(ref expected_trait_ref, ref actual_trait_ref, ref e) => {
661 let expected_trait_ref = self.resolve_type_vars_if_possible(&*expected_trait_ref);
662 let actual_trait_ref = self.resolve_type_vars_if_possible(&*actual_trait_ref);
663 if actual_trait_ref.self_ty().references_error() {
666 let expected_trait_ty = expected_trait_ref.self_ty();
667 let found_span = expected_trait_ty.ty_to_def_id().and_then(|did| {
668 self.tcx.hir.span_if_local(did)
671 if let &TypeError::TupleSize(ref expected_found) = e {
672 // Expected `|x| { }`, found `|x, y| { }`
673 self.report_arg_count_mismatch(span,
675 expected_found.expected,
676 expected_found.found,
677 expected_trait_ty.is_closure())
678 } else if let &TypeError::Sorts(ref expected_found) = e {
679 let expected = if let ty::TyTuple(tys, _) = expected_found.expected.sty {
684 let found = if let ty::TyTuple(tys, _) = expected_found.found.sty {
690 if expected != found {
691 // Expected `|| { }`, found `|x, y| { }`
692 // Expected `fn(x) -> ()`, found `|| { }`
693 self.report_arg_count_mismatch(span,
697 expected_trait_ty.is_closure())
699 self.report_type_argument_mismatch(span,
707 self.report_type_argument_mismatch(span,
716 TraitNotObjectSafe(did) => {
717 let violations = self.tcx.object_safety_violations(did);
718 self.tcx.report_object_safety_error(span, did,
722 self.note_obligation_cause(&mut err, obligation);
726 fn report_type_argument_mismatch(&self,
728 found_span: Option<Span>,
729 expected_ty: Ty<'tcx>,
730 expected_ref: ty::PolyTraitRef<'tcx>,
731 found_ref: ty::PolyTraitRef<'tcx>,
732 type_error: &TypeError<'tcx>)
733 -> DiagnosticBuilder<'tcx>
735 let mut err = struct_span_err!(self.tcx.sess, span, E0281,
736 "type mismatch: `{}` implements the trait `{}`, but the trait `{}` is required",
741 err.span_label(span, format!("{}", type_error));
743 if let Some(sp) = found_span {
744 err.span_label(span, format!("requires `{}`", found_ref));
745 err.span_label(sp, format!("implements `{}`", expected_ref));
751 fn report_arg_count_mismatch(&self,
753 found_span: Option<Span>,
757 -> DiagnosticBuilder<'tcx>
759 let mut err = struct_span_err!(self.tcx.sess, span, E0593,
760 "{} takes {} argument{} but {} argument{} {} required",
761 if is_closure { "closure" } else { "function" },
763 if found == 1 { "" } else { "s" },
765 if expected == 1 { "" } else { "s" },
766 if expected == 1 { "is" } else { "are" });
768 err.span_label(span, format!("expected {} that takes {} argument{}",
769 if is_closure { "closure" } else { "function" },
771 if expected == 1 { "" } else { "s" }));
772 if let Some(span) = found_span {
773 err.span_label(span, format!("takes {} argument{}",
775 if found == 1 { "" } else { "s" }));
781 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
782 pub fn recursive_type_with_infinite_size_error(self,
784 -> DiagnosticBuilder<'tcx>
786 assert!(type_def_id.is_local());
787 let span = self.hir.span_if_local(type_def_id).unwrap();
788 let span = self.sess.codemap().def_span(span);
789 let mut err = struct_span_err!(self.sess, span, E0072,
790 "recursive type `{}` has infinite size",
791 self.item_path_str(type_def_id));
792 err.span_label(span, "recursive type has infinite size");
793 err.help(&format!("insert indirection (e.g., a `Box`, `Rc`, or `&`) \
794 at some point to make `{}` representable",
795 self.item_path_str(type_def_id)));
799 pub fn report_object_safety_error(self,
802 violations: Vec<ObjectSafetyViolation>)
803 -> DiagnosticBuilder<'tcx>
805 let trait_str = self.item_path_str(trait_def_id);
806 let span = self.sess.codemap().def_span(span);
807 let mut err = struct_span_err!(
808 self.sess, span, E0038,
809 "the trait `{}` cannot be made into an object",
811 err.span_label(span, format!("the trait `{}` cannot be made into an object", trait_str));
813 let mut reported_violations = FxHashSet();
814 for violation in violations {
815 if !reported_violations.insert(violation.clone()) {
818 err.note(&violation.error_msg());
824 impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
825 fn maybe_report_ambiguity(&self, obligation: &PredicateObligation<'tcx>) {
826 // Unable to successfully determine, probably means
827 // insufficient type information, but could mean
828 // ambiguous impls. The latter *ought* to be a
829 // coherence violation, so we don't report it here.
831 let predicate = self.resolve_type_vars_if_possible(&obligation.predicate);
832 let body_id = hir::BodyId { node_id: obligation.cause.body_id };
833 let span = obligation.cause.span;
835 debug!("maybe_report_ambiguity(predicate={:?}, obligation={:?})",
839 // Ambiguity errors are often caused as fallout from earlier
840 // errors. So just ignore them if this infcx is tainted.
841 if self.is_tainted_by_errors() {
846 ty::Predicate::Trait(ref data) => {
847 let trait_ref = data.to_poly_trait_ref();
848 let self_ty = trait_ref.self_ty();
849 if predicate.references_error() {
852 // Typically, this ambiguity should only happen if
853 // there are unresolved type inference variables
854 // (otherwise it would suggest a coherence
855 // failure). But given #21974 that is not necessarily
856 // the case -- we can have multiple where clauses that
857 // are only distinguished by a region, which results
858 // in an ambiguity even when all types are fully
859 // known, since we don't dispatch based on region
862 // This is kind of a hack: it frequently happens that some earlier
863 // error prevents types from being fully inferred, and then we get
864 // a bunch of uninteresting errors saying something like "<generic
865 // #0> doesn't implement Sized". It may even be true that we
866 // could just skip over all checks where the self-ty is an
867 // inference variable, but I was afraid that there might be an
868 // inference variable created, registered as an obligation, and
869 // then never forced by writeback, and hence by skipping here we'd
870 // be ignoring the fact that we don't KNOW the type works
871 // out. Though even that would probably be harmless, given that
872 // we're only talking about builtin traits, which are known to be
873 // inhabited. But in any case I just threw in this check for
874 // has_errors() to be sure that compilation isn't happening
875 // anyway. In that case, why inundate the user.
876 if !self.tcx.sess.has_errors() {
878 self.tcx.lang_items.sized_trait()
879 .map_or(false, |sized_id| sized_id == trait_ref.def_id())
881 self.need_type_info(body_id, span, self_ty);
883 let mut err = struct_span_err!(self.tcx.sess,
885 "type annotations required: \
886 cannot resolve `{}`",
888 self.note_obligation_cause(&mut err, obligation);
894 ty::Predicate::WellFormed(ty) => {
895 // Same hacky approach as above to avoid deluging user
896 // with error messages.
897 if !ty.references_error() && !self.tcx.sess.has_errors() {
898 self.need_type_info(body_id, span, ty);
902 ty::Predicate::Subtype(ref data) => {
903 if data.references_error() || self.tcx.sess.has_errors() {
904 // no need to overload user in such cases
906 let &SubtypePredicate { a_is_expected: _, a, b } = data.skip_binder();
907 // both must be type variables, or the other would've been instantiated
908 assert!(a.is_ty_var() && b.is_ty_var());
909 self.need_type_info(hir::BodyId { node_id: obligation.cause.body_id },
910 obligation.cause.span,
916 if !self.tcx.sess.has_errors() {
917 let mut err = struct_span_err!(self.tcx.sess,
918 obligation.cause.span, E0284,
919 "type annotations required: \
920 cannot resolve `{}`",
922 self.note_obligation_cause(&mut err, obligation);
929 /// Returns whether the trait predicate may apply for *some* assignment
930 /// to the type parameters.
931 fn predicate_can_apply(&self, pred: ty::PolyTraitRef<'tcx>) -> bool {
932 struct ParamToVarFolder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
933 infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
934 var_map: FxHashMap<Ty<'tcx>, Ty<'tcx>>
937 impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for ParamToVarFolder<'a, 'gcx, 'tcx> {
938 fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.infcx.tcx }
940 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
941 if let ty::TyParam(ty::ParamTy {name, ..}) = ty.sty {
942 let infcx = self.infcx;
943 self.var_map.entry(ty).or_insert_with(||
945 TypeVariableOrigin::TypeParameterDefinition(DUMMY_SP, name)))
947 ty.super_fold_with(self)
953 let mut selcx = SelectionContext::new(self);
955 let cleaned_pred = pred.fold_with(&mut ParamToVarFolder {
960 let cleaned_pred = super::project::normalize(
962 ObligationCause::dummy(),
966 let obligation = Obligation::new(
967 ObligationCause::dummy(),
968 cleaned_pred.to_predicate()
971 selcx.evaluate_obligation(&obligation)
975 fn extract_type_name(&self, ty: &'a Ty<'tcx>) -> String {
976 if let ty::TyInfer(ty::TyVar(ty_vid)) = (*ty).sty {
977 let ty_vars = self.type_variables.borrow();
978 if let TypeVariableOrigin::TypeParameterDefinition(_, name) =
979 *ty_vars.var_origin(ty_vid) {
989 pub fn need_type_info(&self, body_id: hir::BodyId, span: Span, ty: Ty<'tcx>) {
990 let ty = self.resolve_type_vars_if_possible(&ty);
991 let name = self.extract_type_name(&ty);
993 let mut err_span = span;
994 let mut labels = vec![(span, format!("cannot infer type for `{}`", name))];
996 let mut local_visitor = FindLocalByTypeVisitor {
999 hir_map: &self.tcx.hir,
1000 found_local_pattern: None,
1001 found_arg_pattern: None,
1004 // #40294: cause.body_id can also be a fn declaration.
1005 // Currently, if it's anything other than NodeExpr, we just ignore it
1006 match self.tcx.hir.find(body_id.node_id) {
1007 Some(NodeExpr(expr)) => local_visitor.visit_expr(expr),
1011 if let Some(pattern) = local_visitor.found_arg_pattern {
1012 err_span = pattern.span;
1013 // We don't want to show the default label for closures.
1015 // So, before clearing, the output would look something like this:
1018 // - ^^^^ cannot infer type for `[_; 0]`
1020 // consider giving this closure parameter a type
1023 // After clearing, it looks something like this:
1026 // ^ consider giving this closure parameter a type
1029 labels.push((pattern.span, format!("consider giving this closure parameter a type")));
1032 if let Some(pattern) = local_visitor.found_local_pattern {
1033 if let Some(simple_name) = pattern.simple_name() {
1034 labels.push((pattern.span, format!("consider giving `{}` a type", simple_name)));
1036 labels.push((pattern.span, format!("consider giving the pattern a type")));
1040 let mut err = struct_span_err!(self.tcx.sess,
1043 "type annotations needed");
1045 for (target_span, label_message) in labels {
1046 err.span_label(target_span, label_message);
1052 fn note_obligation_cause<T>(&self,
1053 err: &mut DiagnosticBuilder,
1054 obligation: &Obligation<'tcx, T>)
1055 where T: fmt::Display
1057 self.note_obligation_cause_code(err,
1058 &obligation.predicate,
1059 &obligation.cause.code);
1062 fn note_obligation_cause_code<T>(&self,
1063 err: &mut DiagnosticBuilder,
1065 cause_code: &ObligationCauseCode<'tcx>)
1066 where T: fmt::Display
1070 ObligationCauseCode::ExprAssignable |
1071 ObligationCauseCode::MatchExpressionArm { .. } |
1072 ObligationCauseCode::IfExpression |
1073 ObligationCauseCode::IfExpressionWithNoElse |
1074 ObligationCauseCode::EquatePredicate |
1075 ObligationCauseCode::MainFunctionType |
1076 ObligationCauseCode::StartFunctionType |
1077 ObligationCauseCode::IntrinsicType |
1078 ObligationCauseCode::MethodReceiver |
1079 ObligationCauseCode::ReturnNoExpression |
1080 ObligationCauseCode::MiscObligation => {
1082 ObligationCauseCode::SliceOrArrayElem => {
1083 err.note("slice and array elements must have `Sized` type");
1085 ObligationCauseCode::TupleElem => {
1086 err.note("tuple elements must have `Sized` type");
1088 ObligationCauseCode::ProjectionWf(data) => {
1089 err.note(&format!("required so that the projection `{}` is well-formed",
1092 ObligationCauseCode::ReferenceOutlivesReferent(ref_ty) => {
1093 err.note(&format!("required so that reference `{}` does not outlive its referent",
1096 ObligationCauseCode::ObjectTypeBound(object_ty, region) => {
1097 err.note(&format!("required so that the lifetime bound of `{}` for `{}` \
1099 region, object_ty));
1101 ObligationCauseCode::ItemObligation(item_def_id) => {
1102 let item_name = tcx.item_path_str(item_def_id);
1103 err.note(&format!("required by `{}`", item_name));
1105 ObligationCauseCode::ObjectCastObligation(object_ty) => {
1106 err.note(&format!("required for the cast to the object type `{}`",
1107 self.ty_to_string(object_ty)));
1109 ObligationCauseCode::RepeatVec => {
1110 err.note("the `Copy` trait is required because the \
1111 repeated element will be copied");
1113 ObligationCauseCode::VariableType(_) => {
1114 err.note("all local variables must have a statically known size");
1116 ObligationCauseCode::ReturnType => {
1117 err.note("the return type of a function must have a \
1118 statically known size");
1120 ObligationCauseCode::AssignmentLhsSized => {
1121 err.note("the left-hand-side of an assignment must have a statically known size");
1123 ObligationCauseCode::StructInitializerSized => {
1124 err.note("structs must have a statically known size to be initialized");
1126 ObligationCauseCode::FieldSized => {
1127 err.note("only the last field of a struct may have a dynamically sized type");
1129 ObligationCauseCode::ConstSized => {
1130 err.note("constant expressions must have a statically known size");
1132 ObligationCauseCode::SharedStatic => {
1133 err.note("shared static variables must have a type that implements `Sync`");
1135 ObligationCauseCode::BuiltinDerivedObligation(ref data) => {
1136 let parent_trait_ref = self.resolve_type_vars_if_possible(&data.parent_trait_ref);
1137 err.note(&format!("required because it appears within the type `{}`",
1138 parent_trait_ref.0.self_ty()));
1139 let parent_predicate = parent_trait_ref.to_predicate();
1140 self.note_obligation_cause_code(err,
1144 ObligationCauseCode::ImplDerivedObligation(ref data) => {
1145 let parent_trait_ref = self.resolve_type_vars_if_possible(&data.parent_trait_ref);
1147 &format!("required because of the requirements on the impl of `{}` for `{}`",
1149 parent_trait_ref.0.self_ty()));
1150 let parent_predicate = parent_trait_ref.to_predicate();
1151 self.note_obligation_cause_code(err,
1155 ObligationCauseCode::CompareImplMethodObligation { .. } => {
1157 &format!("the requirement `{}` appears on the impl method \
1158 but not on the corresponding trait method",
1164 fn suggest_new_overflow_limit(&self, err: &mut DiagnosticBuilder) {
1165 let current_limit = self.tcx.sess.recursion_limit.get();
1166 let suggested_limit = current_limit * 2;
1168 "consider adding a `#![recursion_limit=\"{}\"]` attribute to your crate",