1 pub mod on_unimplemented;
5 ConstEvalFailure, EvaluationResult, FulfillmentError, FulfillmentErrorCode,
6 MismatchedProjectionTypes, Obligation, ObligationCause, ObligationCauseCode,
7 OnUnimplementedDirective, OnUnimplementedNote, OutputTypeParameterMismatch, Overflow,
8 PredicateObligation, SelectionContext, SelectionError, TraitNotObjectSafe,
11 use crate::infer::error_reporting::{TyCategory, TypeAnnotationNeeded as ErrorCode};
12 use crate::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
13 use crate::infer::{self, InferCtxt, TyCtxtInferExt};
14 use rustc_data_structures::fx::FxHashMap;
15 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder, ErrorReported};
17 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
19 use rustc_middle::mir::interpret::ErrorHandled;
20 use rustc_middle::ty::error::ExpectedFound;
21 use rustc_middle::ty::fold::TypeFolder;
22 use rustc_middle::ty::{
23 self, fast_reject, AdtKind, SubtypePredicate, ToPolyTraitRef, ToPredicate, Ty, TyCtxt,
24 TypeFoldable, WithConstness,
26 use rustc_session::DiagnosticMessageId;
27 use rustc_span::{ExpnKind, Span, DUMMY_SP};
30 use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
31 use crate::traits::query::normalize::AtExt as _;
32 use on_unimplemented::InferCtxtExt as _;
33 use suggestions::InferCtxtExt as _;
35 pub use rustc_infer::traits::error_reporting::*;
37 pub trait InferCtxtExt<'tcx> {
38 fn report_fulfillment_errors(
40 errors: &[FulfillmentError<'tcx>],
41 body_id: Option<hir::BodyId>,
42 fallback_has_occurred: bool,
45 fn report_overflow_error<T>(
47 obligation: &Obligation<'tcx, T>,
48 suggest_increasing_limit: bool,
51 T: fmt::Display + TypeFoldable<'tcx>;
53 fn report_overflow_error_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> !;
55 fn report_selection_error(
57 obligation: &PredicateObligation<'tcx>,
58 error: &SelectionError<'tcx>,
59 fallback_has_occurred: bool,
63 /// Given some node representing a fn-like thing in the HIR map,
64 /// returns a span and `ArgKind` information that describes the
65 /// arguments it expects. This can be supplied to
66 /// `report_arg_count_mismatch`.
67 fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Vec<ArgKind>)>;
69 /// Reports an error when the number of arguments needed by a
70 /// trait match doesn't match the number that the expression
72 fn report_arg_count_mismatch(
75 found_span: Option<Span>,
76 expected_args: Vec<ArgKind>,
77 found_args: Vec<ArgKind>,
79 ) -> DiagnosticBuilder<'tcx>;
82 impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
83 fn report_fulfillment_errors(
85 errors: &[FulfillmentError<'tcx>],
86 body_id: Option<hir::BodyId>,
87 fallback_has_occurred: bool,
90 struct ErrorDescriptor<'tcx> {
91 predicate: ty::Predicate<'tcx>,
92 index: Option<usize>, // None if this is an old error
95 let mut error_map: FxHashMap<_, Vec<_>> = self
96 .reported_trait_errors
99 .map(|(&span, predicates)| {
104 .map(|&predicate| ErrorDescriptor { predicate, index: None })
110 for (index, error) in errors.iter().enumerate() {
111 // We want to ignore desugarings here: spans are equivalent even
112 // if one is the result of a desugaring and the other is not.
113 let mut span = error.obligation.cause.span;
114 let expn_data = span.ctxt().outer_expn_data();
115 if let ExpnKind::Desugaring(_) = expn_data.kind {
116 span = expn_data.call_site;
119 error_map.entry(span).or_default().push(ErrorDescriptor {
120 predicate: error.obligation.predicate,
124 self.reported_trait_errors
128 .push(error.obligation.predicate);
131 // We do this in 2 passes because we want to display errors in order, though
132 // maybe it *is* better to sort errors by span or something.
133 let mut is_suppressed = vec![false; errors.len()];
134 for (_, error_set) in error_map.iter() {
135 // We want to suppress "duplicate" errors with the same span.
136 for error in error_set {
137 if let Some(index) = error.index {
138 // Suppress errors that are either:
139 // 1) strictly implied by another error.
140 // 2) implied by an error with a smaller index.
141 for error2 in error_set {
142 if error2.index.map_or(false, |index2| is_suppressed[index2]) {
143 // Avoid errors being suppressed by already-suppressed
144 // errors, to prevent all errors from being suppressed
149 if self.error_implies(&error2.predicate, &error.predicate)
150 && !(error2.index >= error.index
151 && self.error_implies(&error.predicate, &error2.predicate))
153 info!("skipping {:?} (implied by {:?})", error, error2);
154 is_suppressed[index] = true;
162 for (error, suppressed) in errors.iter().zip(is_suppressed) {
164 self.report_fulfillment_error(error, body_id, fallback_has_occurred);
169 /// Reports that an overflow has occurred and halts compilation. We
170 /// halt compilation unconditionally because it is important that
171 /// overflows never be masked -- they basically represent computations
172 /// whose result could not be truly determined and thus we can't say
173 /// if the program type checks or not -- and they are unusual
174 /// occurrences in any case.
175 fn report_overflow_error<T>(
177 obligation: &Obligation<'tcx, T>,
178 suggest_increasing_limit: bool,
181 T: fmt::Display + TypeFoldable<'tcx>,
183 let predicate = self.resolve_vars_if_possible(&obligation.predicate);
184 let mut err = struct_span_err!(
186 obligation.cause.span,
188 "overflow evaluating the requirement `{}`",
192 if suggest_increasing_limit {
193 self.suggest_new_overflow_limit(&mut err);
196 self.note_obligation_cause_code(
198 &obligation.predicate,
199 &obligation.cause.code,
204 self.tcx.sess.abort_if_errors();
208 /// Reports that a cycle was detected which led to overflow and halts
209 /// compilation. This is equivalent to `report_overflow_error` except
210 /// that we can give a more helpful error message (and, in particular,
211 /// we do not suggest increasing the overflow limit, which is not
213 fn report_overflow_error_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> ! {
214 let cycle = self.resolve_vars_if_possible(&cycle.to_owned());
215 assert!(!cycle.is_empty());
217 debug!("report_overflow_error_cycle: cycle={:?}", cycle);
219 self.report_overflow_error(&cycle[0], false);
222 fn report_selection_error(
224 obligation: &PredicateObligation<'tcx>,
225 error: &SelectionError<'tcx>,
226 fallback_has_occurred: bool,
230 let span = obligation.cause.span;
232 let mut err = match *error {
233 SelectionError::Unimplemented => {
234 if let ObligationCauseCode::CompareImplMethodObligation {
239 | ObligationCauseCode::CompareImplTypeObligation {
243 } = obligation.cause.code
245 self.report_extra_impl_obligation(
250 &format!("`{}`", obligation.predicate),
255 match obligation.predicate {
256 ty::Predicate::Trait(ref trait_predicate, _) => {
257 let trait_predicate = self.resolve_vars_if_possible(trait_predicate);
259 if self.tcx.sess.has_errors() && trait_predicate.references_error() {
262 let trait_ref = trait_predicate.to_poly_trait_ref();
263 let (post_message, pre_message, type_def) = self
264 .get_parent_trait_ref(&obligation.cause.code)
267 format!(" in `{}`", t),
268 format!("within `{}`, ", t),
269 s.map(|s| (format!("within this `{}`", t), s)),
272 .unwrap_or_default();
274 let OnUnimplementedNote { message, label, note, enclosing_scope } =
275 self.on_unimplemented_note(trait_ref, obligation);
276 let have_alt_message = message.is_some() || label.is_some();
281 .span_to_snippet(span)
284 let is_from = format!("{}", trait_ref.print_only_trait_path())
285 .starts_with("std::convert::From<");
286 let (message, note) = if is_try && is_from {
289 "`?` couldn't convert the error to `{}`",
293 "the question mark operation (`?`) implicitly performs a \
294 conversion on the error value using the `From` trait"
302 let mut err = struct_span_err!(
307 message.unwrap_or_else(|| format!(
308 "the trait bound `{}` is not satisfied{}",
309 trait_ref.without_const().to_predicate(),
314 let should_convert_option_to_result =
315 format!("{}", trait_ref.print_only_trait_path())
316 .starts_with("std::convert::From<std::option::NoneError");
317 let should_convert_result_to_option = format!("{}", trait_ref)
318 .starts_with("<std::option::NoneError as std::convert::From<");
319 if is_try && is_from {
320 if should_convert_option_to_result {
321 err.span_suggestion_verbose(
323 "consider converting the `Option<T>` into a `Result<T, _>` \
324 using `Option::ok_or` or `Option::ok_or_else`",
325 ".ok_or_else(|| /* error value */)".to_string(),
326 Applicability::HasPlaceholders,
328 } else if should_convert_result_to_option {
329 err.span_suggestion_verbose(
331 "consider converting the `Result<T, _>` into an `Option<T>` \
334 Applicability::MachineApplicable,
337 if let Some(ret_span) = self.return_type_span(obligation) {
340 &format!("expected `{}` because of this", trait_ref.self_ty()),
346 if obligation.cause.code == ObligationCauseCode::MainFunctionType {
347 "consider using `()`, or a `Result`".to_owned()
350 "{}the trait `{}` is not implemented for `{}`",
352 trait_ref.print_only_trait_path(),
357 if self.suggest_add_reference_to_arg(
364 self.note_obligation_cause(&mut err, obligation);
368 if let Some(ref s) = label {
369 // If it has a custom `#[rustc_on_unimplemented]`
370 // error message, let's display it as the label!
371 err.span_label(span, s.as_str());
372 err.help(&explanation);
374 err.span_label(span, explanation);
376 if let Some((msg, span)) = type_def {
377 err.span_label(span, &msg);
379 if let Some(ref s) = note {
380 // If it has a custom `#[rustc_on_unimplemented]` note, let's display it
381 err.note(s.as_str());
383 if let Some(ref s) = enclosing_scope {
384 let enclosing_scope_span = tcx.def_span(
386 .opt_local_def_id(obligation.cause.body_id)
388 tcx.hir().body_owner_def_id(hir::BodyId {
389 hir_id: obligation.cause.body_id,
395 err.span_label(enclosing_scope_span, s.as_str());
398 self.suggest_borrow_on_unsized_slice(&obligation.cause.code, &mut err);
399 self.suggest_fn_call(&obligation, &mut err, &trait_ref, points_at_arg);
400 self.suggest_remove_reference(&obligation, &mut err, &trait_ref);
401 self.suggest_semicolon_removal(&obligation, &mut err, span, &trait_ref);
402 self.note_version_mismatch(&mut err, &trait_ref);
403 if self.suggest_impl_trait(&mut err, span, &obligation, &trait_ref) {
408 // Try to report a help message
409 if !trait_ref.has_infer_types_or_consts()
410 && self.predicate_can_apply(obligation.param_env, trait_ref)
412 // If a where-clause may be useful, remind the
413 // user that they can add it.
415 // don't display an on-unimplemented note, as
416 // these notes will often be of the form
417 // "the type `T` can't be frobnicated"
418 // which is somewhat confusing.
419 self.suggest_restricting_param_bound(
422 obligation.cause.body_id,
425 if !have_alt_message {
426 // Can't show anything else useful, try to find similar impls.
427 let impl_candidates = self.find_similar_impl_candidates(trait_ref);
428 self.report_similar_impl_candidates(impl_candidates, &mut err);
430 self.suggest_change_mut(
438 // If this error is due to `!: Trait` not implemented but `(): Trait` is
439 // implemented, and fallback has occurred, then it could be due to a
440 // variable that used to fallback to `()` now falling back to `!`. Issue a
441 // note informing about the change in behaviour.
442 if trait_predicate.skip_binder().self_ty().is_never()
443 && fallback_has_occurred
445 let predicate = trait_predicate.map_bound(|mut trait_pred| {
446 trait_pred.trait_ref.substs = self.tcx.mk_substs_trait(
448 &trait_pred.trait_ref.substs[1..],
452 let unit_obligation = Obligation {
453 predicate: ty::Predicate::Trait(
455 hir::Constness::NotConst,
459 if self.predicate_may_hold(&unit_obligation) {
461 "the trait is implemented for `()`. \
462 Possibly this error has been caused by changes to \
463 Rust's type-inference algorithm (see issue #48950 \
464 <https://github.com/rust-lang/rust/issues/48950> \
465 for more information). Consider whether you meant to use \
466 the type `()` here instead.",
474 ty::Predicate::Subtype(ref predicate) => {
475 // Errors for Subtype predicates show up as
476 // `FulfillmentErrorCode::CodeSubtypeError`,
477 // not selection error.
478 span_bug!(span, "subtype requirement gave wrong error: `{:?}`", predicate)
481 ty::Predicate::RegionOutlives(ref predicate) => {
482 let predicate = self.resolve_vars_if_possible(predicate);
484 .region_outlives_predicate(&obligation.cause, &predicate)
491 "the requirement `{}` is not satisfied (`{}`)",
497 ty::Predicate::Projection(..) | ty::Predicate::TypeOutlives(..) => {
498 let predicate = self.resolve_vars_if_possible(&obligation.predicate);
503 "the requirement `{}` is not satisfied",
508 ty::Predicate::ObjectSafe(trait_def_id) => {
509 let violations = self.tcx.object_safety_violations(trait_def_id);
510 report_object_safety_error(self.tcx, span, trait_def_id, violations)
513 ty::Predicate::ClosureKind(closure_def_id, closure_substs, kind) => {
514 let found_kind = self.closure_kind(closure_substs).unwrap();
516 self.tcx.sess.source_map().guess_head_span(
517 self.tcx.hir().span_if_local(closure_def_id).unwrap(),
519 let hir_id = self.tcx.hir().as_local_hir_id(closure_def_id.expect_local());
520 let mut err = struct_span_err!(
524 "expected a closure that implements the `{}` trait, \
525 but this closure only implements `{}`",
532 format!("this closure implements `{}`, not `{}`", found_kind, kind),
535 obligation.cause.span,
536 format!("the requirement to implement `{}` derives from here", kind),
539 // Additional context information explaining why the closure only implements
540 // a particular trait.
541 if let Some(tables) = self.in_progress_tables {
542 let tables = tables.borrow();
543 match (found_kind, tables.closure_kind_origins().get(hir_id)) {
544 (ty::ClosureKind::FnOnce, Some((span, name))) => {
548 "closure is `FnOnce` because it moves the \
549 variable `{}` out of its environment",
554 (ty::ClosureKind::FnMut, Some((span, name))) => {
558 "closure is `FnMut` because it mutates the \
572 ty::Predicate::WellFormed(ty) => {
573 if !self.tcx.sess.opts.debugging_opts.chalk {
574 // WF predicates cannot themselves make
575 // errors. They can only block due to
576 // ambiguity; otherwise, they always
577 // degenerate into other obligations
579 span_bug!(span, "WF predicate not satisfied for {:?}", ty);
581 // FIXME: we'll need a better message which takes into account
582 // which bounds actually failed to hold.
583 self.tcx.sess.struct_span_err(
585 &format!("the type `{}` is not well-formed (chalk)", ty),
590 ty::Predicate::ConstEvaluatable(..) => {
591 // Errors for `ConstEvaluatable` predicates show up as
592 // `SelectionError::ConstEvalFailure`,
593 // not `Unimplemented`.
596 "const-evaluatable requirement gave wrong error: `{:?}`",
603 OutputTypeParameterMismatch(ref found_trait_ref, ref expected_trait_ref, _) => {
604 let found_trait_ref = self.resolve_vars_if_possible(&*found_trait_ref);
605 let expected_trait_ref = self.resolve_vars_if_possible(&*expected_trait_ref);
607 if expected_trait_ref.self_ty().references_error() {
611 let found_trait_ty = found_trait_ref.self_ty();
613 let found_did = match found_trait_ty.kind {
614 ty::Closure(did, _) | ty::Foreign(did) | ty::FnDef(did, _) => Some(did),
615 ty::Adt(def, _) => Some(def.did),
619 let found_span = found_did
620 .and_then(|did| self.tcx.hir().span_if_local(did))
621 .map(|sp| self.tcx.sess.source_map().guess_head_span(sp)); // the sp could be an fn def
623 if self.reported_closure_mismatch.borrow().contains(&(span, found_span)) {
624 // We check closures twice, with obligations flowing in different directions,
625 // but we want to complain about them only once.
629 self.reported_closure_mismatch.borrow_mut().insert((span, found_span));
631 let found = match found_trait_ref.skip_binder().substs.type_at(1).kind {
632 ty::Tuple(ref tys) => vec![ArgKind::empty(); tys.len()],
633 _ => vec![ArgKind::empty()],
636 let expected_ty = expected_trait_ref.skip_binder().substs.type_at(1);
637 let expected = match expected_ty.kind {
638 ty::Tuple(ref tys) => tys
640 .map(|t| ArgKind::from_expected_ty(t.expect_ty(), Some(span)))
642 _ => vec![ArgKind::Arg("_".to_owned(), expected_ty.to_string())],
645 if found.len() == expected.len() {
646 self.report_closure_arg_mismatch(
653 let (closure_span, found) = found_did
655 let node = self.tcx.hir().get_if_local(did)?;
656 let (found_span, found) = self.get_fn_like_arguments(node)?;
657 Some((Some(found_span), found))
659 .unwrap_or((found_span, found));
661 self.report_arg_count_mismatch(
666 found_trait_ty.is_closure(),
671 TraitNotObjectSafe(did) => {
672 let violations = self.tcx.object_safety_violations(did);
673 report_object_safety_error(self.tcx, span, did, violations)
676 ConstEvalFailure(ErrorHandled::TooGeneric) => {
677 // In this instance, we have a const expression containing an unevaluated
678 // generic parameter. We have no idea whether this expression is valid or
679 // not (e.g. it might result in an error), but we don't want to just assume
680 // that it's okay, because that might result in post-monomorphisation time
681 // errors. The onus is really on the caller to provide values that it can
682 // prove are well-formed.
686 .struct_span_err(span, "constant expression depends on a generic parameter");
687 // FIXME(const_generics): we should suggest to the user how they can resolve this
688 // issue. However, this is currently not actually possible
689 // (see https://github.com/rust-lang/rust/issues/66962#issuecomment-575907083).
690 err.note("this may fail depending on what value the parameter takes");
694 // Already reported in the query.
695 ConstEvalFailure(ErrorHandled::Reported(ErrorReported)) => {
696 // FIXME(eddyb) remove this once `ErrorReported` becomes a proof token.
697 self.tcx.sess.delay_span_bug(span, "`ErrorReported` without an error");
701 // Already reported in the query, but only as a lint.
702 // This shouldn't actually happen for constants used in types, modulo
703 // bugs. The `delay_span_bug` here ensures it won't be ignored.
704 ConstEvalFailure(ErrorHandled::Linted) => {
705 self.tcx.sess.delay_span_bug(span, "constant in type had error reported as lint");
710 bug!("overflow should be handled before the `report_selection_error` path");
714 self.note_obligation_cause(&mut err, obligation);
715 self.point_at_returns_when_relevant(&mut err, &obligation);
720 /// Given some node representing a fn-like thing in the HIR map,
721 /// returns a span and `ArgKind` information that describes the
722 /// arguments it expects. This can be supplied to
723 /// `report_arg_count_mismatch`.
724 fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Vec<ArgKind>)> {
725 let sm = self.tcx.sess.source_map();
726 let hir = self.tcx.hir();
728 Node::Expr(&hir::Expr {
729 kind: hir::ExprKind::Closure(_, ref _decl, id, span, _),
732 sm.guess_head_span(span),
737 if let hir::Pat { kind: hir::PatKind::Tuple(ref args, _), span, .. } =
744 sm.span_to_snippet(pat.span)
746 .map(|snippet| (snippet, "_".to_owned()))
748 .collect::<Option<Vec<_>>>()?,
751 let name = sm.span_to_snippet(arg.pat.span).ok()?;
752 Some(ArgKind::Arg(name, "_".to_owned()))
755 .collect::<Option<Vec<ArgKind>>>()?,
757 Node::Item(&hir::Item { span, kind: hir::ItemKind::Fn(ref sig, ..), .. })
758 | Node::ImplItem(&hir::ImplItem {
760 kind: hir::ImplItemKind::Fn(ref sig, _),
763 | Node::TraitItem(&hir::TraitItem {
765 kind: hir::TraitItemKind::Fn(ref sig, _),
768 sm.guess_head_span(span),
772 .map(|arg| match arg.clone().kind {
773 hir::TyKind::Tup(ref tys) => ArgKind::Tuple(
775 vec![("_".to_owned(), "_".to_owned()); tys.len()],
777 _ => ArgKind::empty(),
779 .collect::<Vec<ArgKind>>(),
781 Node::Ctor(ref variant_data) => {
782 let span = variant_data.ctor_hir_id().map(|id| hir.span(id)).unwrap_or(DUMMY_SP);
783 let span = sm.guess_head_span(span);
784 (span, vec![ArgKind::empty(); variant_data.fields().len()])
786 _ => panic!("non-FnLike node found: {:?}", node),
790 /// Reports an error when the number of arguments needed by a
791 /// trait match doesn't match the number that the expression
793 fn report_arg_count_mismatch(
796 found_span: Option<Span>,
797 expected_args: Vec<ArgKind>,
798 found_args: Vec<ArgKind>,
800 ) -> DiagnosticBuilder<'tcx> {
801 let kind = if is_closure { "closure" } else { "function" };
803 let args_str = |arguments: &[ArgKind], other: &[ArgKind]| {
804 let arg_length = arguments.len();
805 let distinct = match &other[..] {
806 &[ArgKind::Tuple(..)] => true,
809 match (arg_length, arguments.get(0)) {
810 (1, Some(&ArgKind::Tuple(_, ref fields))) => {
811 format!("a single {}-tuple as argument", fields.len())
816 if distinct && arg_length > 1 { "distinct " } else { "" },
817 pluralize!(arg_length)
822 let expected_str = args_str(&expected_args, &found_args);
823 let found_str = args_str(&found_args, &expected_args);
825 let mut err = struct_span_err!(
829 "{} is expected to take {}, but it takes {}",
835 err.span_label(span, format!("expected {} that takes {}", kind, expected_str));
837 if let Some(found_span) = found_span {
838 err.span_label(found_span, format!("takes {}", found_str));
841 // ^^^^^^^^-- def_span
845 let prefix_span = self.tcx.sess.source_map().span_until_non_whitespace(found_span);
849 if let Some(span) = found_span.trim_start(prefix_span) { span } else { found_span };
851 // Suggest to take and ignore the arguments with expected_args_length `_`s if
852 // found arguments is empty (assume the user just wants to ignore args in this case).
853 // For example, if `expected_args_length` is 2, suggest `|_, _|`.
854 if found_args.is_empty() && is_closure {
855 let underscores = vec!["_"; expected_args.len()].join(", ");
856 err.span_suggestion_verbose(
859 "consider changing the closure to take and ignore the expected argument{}",
860 pluralize!(expected_args.len())
862 format!("|{}|", underscores),
863 Applicability::MachineApplicable,
867 if let &[ArgKind::Tuple(_, ref fields)] = &found_args[..] {
868 if fields.len() == expected_args.len() {
871 .map(|(name, _)| name.to_owned())
872 .collect::<Vec<String>>()
874 err.span_suggestion_verbose(
876 "change the closure to take multiple arguments instead of a single tuple",
877 format!("|{}|", sugg),
878 Applicability::MachineApplicable,
882 if let &[ArgKind::Tuple(_, ref fields)] = &expected_args[..] {
883 if fields.len() == found_args.len() && is_closure {
888 .map(|arg| match arg {
889 ArgKind::Arg(name, _) => name.to_owned(),
892 .collect::<Vec<String>>()
894 // add type annotations if available
895 if found_args.iter().any(|arg| match arg {
896 ArgKind::Arg(_, ty) => ty != "_",
903 .map(|(_, ty)| ty.to_owned())
904 .collect::<Vec<String>>()
911 err.span_suggestion_verbose(
913 "change the closure to accept a tuple instead of individual arguments",
915 Applicability::MachineApplicable,
925 trait InferCtxtPrivExt<'tcx> {
926 // returns if `cond` not occurring implies that `error` does not occur - i.e., that
927 // `error` occurring implies that `cond` occurs.
928 fn error_implies(&self, cond: &ty::Predicate<'tcx>, error: &ty::Predicate<'tcx>) -> bool;
930 fn report_fulfillment_error(
932 error: &FulfillmentError<'tcx>,
933 body_id: Option<hir::BodyId>,
934 fallback_has_occurred: bool,
937 fn report_projection_error(
939 obligation: &PredicateObligation<'tcx>,
940 error: &MismatchedProjectionTypes<'tcx>,
943 fn fuzzy_match_tys(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> bool;
945 fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str>;
947 fn find_similar_impl_candidates(
949 trait_ref: ty::PolyTraitRef<'tcx>,
950 ) -> Vec<ty::TraitRef<'tcx>>;
952 fn report_similar_impl_candidates(
954 impl_candidates: Vec<ty::TraitRef<'tcx>>,
955 err: &mut DiagnosticBuilder<'_>,
958 /// Gets the parent trait chain start
959 fn get_parent_trait_ref(
961 code: &ObligationCauseCode<'tcx>,
962 ) -> Option<(String, Option<Span>)>;
964 /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
965 /// with the same path as `trait_ref`, a help message about
966 /// a probable version mismatch is added to `err`
967 fn note_version_mismatch(
969 err: &mut DiagnosticBuilder<'_>,
970 trait_ref: &ty::PolyTraitRef<'tcx>,
973 fn mk_obligation_for_def_id(
977 cause: ObligationCause<'tcx>,
978 param_env: ty::ParamEnv<'tcx>,
979 ) -> PredicateObligation<'tcx>;
981 fn maybe_report_ambiguity(
983 obligation: &PredicateObligation<'tcx>,
984 body_id: Option<hir::BodyId>,
987 fn predicate_can_apply(
989 param_env: ty::ParamEnv<'tcx>,
990 pred: ty::PolyTraitRef<'tcx>,
993 fn note_obligation_cause(
995 err: &mut DiagnosticBuilder<'_>,
996 obligation: &PredicateObligation<'tcx>,
999 fn suggest_unsized_bound_if_applicable(
1001 err: &mut DiagnosticBuilder<'_>,
1002 obligation: &PredicateObligation<'tcx>,
1005 fn is_recursive_obligation(
1007 obligated_types: &mut Vec<&ty::TyS<'tcx>>,
1008 cause_code: &ObligationCauseCode<'tcx>,
1012 impl<'a, 'tcx> InferCtxtPrivExt<'tcx> for InferCtxt<'a, 'tcx> {
1013 // returns if `cond` not occurring implies that `error` does not occur - i.e., that
1014 // `error` occurring implies that `cond` occurs.
1015 fn error_implies(&self, cond: &ty::Predicate<'tcx>, error: &ty::Predicate<'tcx>) -> bool {
1020 let (cond, error) = match (cond, error) {
1021 (&ty::Predicate::Trait(..), &ty::Predicate::Trait(ref error, _)) => (cond, error),
1023 // FIXME: make this work in other cases too.
1028 for obligation in super::elaborate_predicates(self.tcx, std::iter::once(*cond)) {
1029 if let ty::Predicate::Trait(implication, _) = obligation.predicate {
1030 let error = error.to_poly_trait_ref();
1031 let implication = implication.to_poly_trait_ref();
1032 // FIXME: I'm just not taking associated types at all here.
1033 // Eventually I'll need to implement param-env-aware
1034 // `Γ₁ ⊦ φ₁ => Γ₂ ⊦ φ₂` logic.
1035 let param_env = ty::ParamEnv::empty();
1036 if self.can_sub(param_env, error, implication).is_ok() {
1037 debug!("error_implies: {:?} -> {:?} -> {:?}", cond, error, implication);
1046 fn report_fulfillment_error(
1048 error: &FulfillmentError<'tcx>,
1049 body_id: Option<hir::BodyId>,
1050 fallback_has_occurred: bool,
1052 debug!("report_fulfillment_error({:?})", error);
1054 FulfillmentErrorCode::CodeSelectionError(ref selection_error) => {
1055 self.report_selection_error(
1058 fallback_has_occurred,
1059 error.points_at_arg_span,
1062 FulfillmentErrorCode::CodeProjectionError(ref e) => {
1063 self.report_projection_error(&error.obligation, e);
1065 FulfillmentErrorCode::CodeAmbiguity => {
1066 self.maybe_report_ambiguity(&error.obligation, body_id);
1068 FulfillmentErrorCode::CodeSubtypeError(ref expected_found, ref err) => {
1069 self.report_mismatched_types(
1070 &error.obligation.cause,
1071 expected_found.expected,
1072 expected_found.found,
1080 fn report_projection_error(
1082 obligation: &PredicateObligation<'tcx>,
1083 error: &MismatchedProjectionTypes<'tcx>,
1085 let predicate = self.resolve_vars_if_possible(&obligation.predicate);
1087 if predicate.references_error() {
1093 let mut err = &error.err;
1094 let mut values = None;
1096 // try to find the mismatched types to report the error with.
1098 // this can fail if the problem was higher-ranked, in which
1099 // cause I have no idea for a good error message.
1100 if let ty::Predicate::Projection(ref data) = predicate {
1101 let mut selcx = SelectionContext::new(self);
1102 let (data, _) = self.replace_bound_vars_with_fresh_vars(
1103 obligation.cause.span,
1104 infer::LateBoundRegionConversionTime::HigherRankedType,
1107 let mut obligations = vec![];
1108 let normalized_ty = super::normalize_projection_type(
1110 obligation.param_env,
1112 obligation.cause.clone(),
1118 "report_projection_error obligation.cause={:?} obligation.param_env={:?}",
1119 obligation.cause, obligation.param_env
1123 "report_projection_error normalized_ty={:?} data.ty={:?}",
1124 normalized_ty, data.ty
1127 let is_normalized_ty_expected = match &obligation.cause.code {
1128 ObligationCauseCode::ItemObligation(_)
1129 | ObligationCauseCode::BindingObligation(_, _)
1130 | ObligationCauseCode::ObjectCastObligation(_) => false,
1134 if let Err(error) = self.at(&obligation.cause, obligation.param_env).eq_exp(
1135 is_normalized_ty_expected,
1139 values = Some(infer::ValuePairs::Types(ExpectedFound::new(
1140 is_normalized_ty_expected,
1150 let msg = format!("type mismatch resolving `{}`", predicate);
1151 let error_id = (DiagnosticMessageId::ErrorId(271), Some(obligation.cause.span), msg);
1152 let fresh = self.tcx.sess.one_time_diagnostics.borrow_mut().insert(error_id);
1154 let mut diag = struct_span_err!(
1156 obligation.cause.span,
1158 "type mismatch resolving `{}`",
1161 self.note_type_err(&mut diag, &obligation.cause, None, values, err);
1162 self.note_obligation_cause(&mut diag, obligation);
1168 fn fuzzy_match_tys(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
1169 /// returns the fuzzy category of a given type, or None
1170 /// if the type can be equated to any type.
1171 fn type_category(t: Ty<'_>) -> Option<u32> {
1173 ty::Bool => Some(0),
1174 ty::Char => Some(1),
1176 ty::Int(..) | ty::Uint(..) | ty::Infer(ty::IntVar(..)) => Some(3),
1177 ty::Float(..) | ty::Infer(ty::FloatVar(..)) => Some(4),
1178 ty::Ref(..) | ty::RawPtr(..) => Some(5),
1179 ty::Array(..) | ty::Slice(..) => Some(6),
1180 ty::FnDef(..) | ty::FnPtr(..) => Some(7),
1181 ty::Dynamic(..) => Some(8),
1182 ty::Closure(..) => Some(9),
1183 ty::Tuple(..) => Some(10),
1184 ty::Projection(..) => Some(11),
1185 ty::Param(..) => Some(12),
1186 ty::Opaque(..) => Some(13),
1187 ty::Never => Some(14),
1188 ty::Adt(adt, ..) => match adt.adt_kind() {
1189 AdtKind::Struct => Some(15),
1190 AdtKind::Union => Some(16),
1191 AdtKind::Enum => Some(17),
1193 ty::Generator(..) => Some(18),
1194 ty::Foreign(..) => Some(19),
1195 ty::GeneratorWitness(..) => Some(20),
1196 ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) | ty::Error => None,
1197 ty::UnnormalizedProjection(..) => bug!("only used with chalk-engine"),
1201 match (type_category(a), type_category(b)) {
1202 (Some(cat_a), Some(cat_b)) => match (&a.kind, &b.kind) {
1203 (&ty::Adt(def_a, _), &ty::Adt(def_b, _)) => def_a == def_b,
1204 _ => cat_a == cat_b,
1206 // infer and error can be equated to all types
1211 fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str> {
1212 self.tcx.hir().body(body_id).generator_kind.map(|gen_kind| match gen_kind {
1213 hir::GeneratorKind::Gen => "a generator",
1214 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Block) => "an async block",
1215 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Fn) => "an async function",
1216 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Closure) => "an async closure",
1220 fn find_similar_impl_candidates(
1222 trait_ref: ty::PolyTraitRef<'tcx>,
1223 ) -> Vec<ty::TraitRef<'tcx>> {
1224 let simp = fast_reject::simplify_type(self.tcx, trait_ref.skip_binder().self_ty(), true);
1225 let all_impls = self.tcx.all_impls(trait_ref.def_id());
1228 Some(simp) => all_impls
1229 .filter_map(|def_id| {
1230 let imp = self.tcx.impl_trait_ref(def_id).unwrap();
1231 let imp_simp = fast_reject::simplify_type(self.tcx, imp.self_ty(), true);
1232 if let Some(imp_simp) = imp_simp {
1233 if simp != imp_simp {
1240 None => all_impls.map(|def_id| self.tcx.impl_trait_ref(def_id).unwrap()).collect(),
1244 fn report_similar_impl_candidates(
1246 impl_candidates: Vec<ty::TraitRef<'tcx>>,
1247 err: &mut DiagnosticBuilder<'_>,
1249 if impl_candidates.is_empty() {
1253 let len = impl_candidates.len();
1254 let end = if impl_candidates.len() <= 5 { impl_candidates.len() } else { 4 };
1256 let normalize = |candidate| {
1257 self.tcx.infer_ctxt().enter(|ref infcx| {
1258 let normalized = infcx
1259 .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
1260 .normalize(candidate)
1263 Some(normalized) => format!("\n {:?}", normalized.value),
1264 None => format!("\n {:?}", candidate),
1269 // Sort impl candidates so that ordering is consistent for UI tests.
1270 let mut normalized_impl_candidates =
1271 impl_candidates.iter().map(normalize).collect::<Vec<String>>();
1273 // Sort before taking the `..end` range,
1274 // because the ordering of `impl_candidates` may not be deterministic:
1275 // https://github.com/rust-lang/rust/pull/57475#issuecomment-455519507
1276 normalized_impl_candidates.sort();
1279 "the following implementations were found:{}{}",
1280 normalized_impl_candidates[..end].join(""),
1281 if len > 5 { format!("\nand {} others", len - 4) } else { String::new() }
1285 /// Gets the parent trait chain start
1286 fn get_parent_trait_ref(
1288 code: &ObligationCauseCode<'tcx>,
1289 ) -> Option<(String, Option<Span>)> {
1291 &ObligationCauseCode::BuiltinDerivedObligation(ref data) => {
1292 let parent_trait_ref = self.resolve_vars_if_possible(&data.parent_trait_ref);
1293 match self.get_parent_trait_ref(&data.parent_code) {
1296 let ty = parent_trait_ref.skip_binder().self_ty();
1298 TyCategory::from_ty(ty).map(|(_, def_id)| self.tcx.def_span(def_id));
1299 Some((ty.to_string(), span))
1307 /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
1308 /// with the same path as `trait_ref`, a help message about
1309 /// a probable version mismatch is added to `err`
1310 fn note_version_mismatch(
1312 err: &mut DiagnosticBuilder<'_>,
1313 trait_ref: &ty::PolyTraitRef<'tcx>,
1315 let get_trait_impl = |trait_def_id| {
1316 let mut trait_impl = None;
1317 self.tcx.for_each_relevant_impl(trait_def_id, trait_ref.self_ty(), |impl_def_id| {
1318 if trait_impl.is_none() {
1319 trait_impl = Some(impl_def_id);
1324 let required_trait_path = self.tcx.def_path_str(trait_ref.def_id());
1325 let all_traits = self.tcx.all_traits(LOCAL_CRATE);
1326 let traits_with_same_path: std::collections::BTreeSet<_> = all_traits
1328 .filter(|trait_def_id| **trait_def_id != trait_ref.def_id())
1329 .filter(|trait_def_id| self.tcx.def_path_str(**trait_def_id) == required_trait_path)
1331 for trait_with_same_path in traits_with_same_path {
1332 if let Some(impl_def_id) = get_trait_impl(*trait_with_same_path) {
1333 let impl_span = self.tcx.def_span(impl_def_id);
1334 err.span_help(impl_span, "trait impl with same name found");
1335 let trait_crate = self.tcx.crate_name(trait_with_same_path.krate);
1336 let crate_msg = format!(
1337 "perhaps two different versions of crate `{}` are being used?",
1340 err.note(&crate_msg);
1345 fn mk_obligation_for_def_id(
1348 output_ty: Ty<'tcx>,
1349 cause: ObligationCause<'tcx>,
1350 param_env: ty::ParamEnv<'tcx>,
1351 ) -> PredicateObligation<'tcx> {
1353 ty::TraitRef { def_id, substs: self.tcx.mk_substs_trait(output_ty, &[]) };
1354 Obligation::new(cause, param_env, new_trait_ref.without_const().to_predicate())
1357 fn maybe_report_ambiguity(
1359 obligation: &PredicateObligation<'tcx>,
1360 body_id: Option<hir::BodyId>,
1362 // Unable to successfully determine, probably means
1363 // insufficient type information, but could mean
1364 // ambiguous impls. The latter *ought* to be a
1365 // coherence violation, so we don't report it here.
1367 let predicate = self.resolve_vars_if_possible(&obligation.predicate);
1368 let span = obligation.cause.span;
1371 "maybe_report_ambiguity(predicate={:?}, obligation={:?} body_id={:?}, code={:?})",
1372 predicate, obligation, body_id, obligation.cause.code,
1375 // Ambiguity errors are often caused as fallout from earlier
1376 // errors. So just ignore them if this infcx is tainted.
1377 if self.is_tainted_by_errors() {
1381 let mut err = match predicate {
1382 ty::Predicate::Trait(ref data, _) => {
1383 let trait_ref = data.to_poly_trait_ref();
1384 let self_ty = trait_ref.self_ty();
1385 debug!("self_ty {:?} {:?} trait_ref {:?}", self_ty, self_ty.kind, trait_ref);
1387 if predicate.references_error() {
1390 // Typically, this ambiguity should only happen if
1391 // there are unresolved type inference variables
1392 // (otherwise it would suggest a coherence
1393 // failure). But given #21974 that is not necessarily
1394 // the case -- we can have multiple where clauses that
1395 // are only distinguished by a region, which results
1396 // in an ambiguity even when all types are fully
1397 // known, since we don't dispatch based on region
1400 // This is kind of a hack: it frequently happens that some earlier
1401 // error prevents types from being fully inferred, and then we get
1402 // a bunch of uninteresting errors saying something like "<generic
1403 // #0> doesn't implement Sized". It may even be true that we
1404 // could just skip over all checks where the self-ty is an
1405 // inference variable, but I was afraid that there might be an
1406 // inference variable created, registered as an obligation, and
1407 // then never forced by writeback, and hence by skipping here we'd
1408 // be ignoring the fact that we don't KNOW the type works
1409 // out. Though even that would probably be harmless, given that
1410 // we're only talking about builtin traits, which are known to be
1411 // inhabited. We used to check for `self.tcx.sess.has_errors()` to
1412 // avoid inundating the user with unnecessary errors, but we now
1413 // check upstream for type errors and don't add the obligations to
1414 // begin with in those cases.
1419 .map_or(false, |sized_id| sized_id == trait_ref.def_id())
1421 self.need_type_info_err(body_id, span, self_ty, ErrorCode::E0282).emit();
1424 let mut err = self.need_type_info_err(body_id, span, self_ty, ErrorCode::E0283);
1425 err.note(&format!("cannot satisfy `{}`", predicate));
1426 if let ObligationCauseCode::ItemObligation(def_id) = obligation.cause.code {
1427 self.suggest_fully_qualified_path(&mut err, def_id, span, trait_ref.def_id());
1430 ObligationCauseCode::BindingObligation(ref def_id, _),
1432 (self.tcx.sess.source_map().span_to_snippet(span), &obligation.cause.code)
1434 let generics = self.tcx.generics_of(*def_id);
1435 if generics.params.iter().any(|p| p.name.as_str() != "Self")
1436 && !snippet.ends_with('>')
1438 // FIXME: To avoid spurious suggestions in functions where type arguments
1439 // where already supplied, we check the snippet to make sure it doesn't
1440 // end with a turbofish. Ideally we would have access to a `PathSegment`
1441 // instead. Otherwise we would produce the following output:
1443 // error[E0283]: type annotations needed
1444 // --> $DIR/issue-54954.rs:3:24
1446 // LL | const ARR_LEN: usize = Tt::const_val::<[i8; 123]>();
1447 // | ^^^^^^^^^^^^^^^^^^^^^^^^^^
1449 // | cannot infer type
1450 // | help: consider specifying the type argument
1451 // | in the function call:
1452 // | `Tt::const_val::<[i8; 123]>::<T>`
1454 // LL | const fn const_val<T: Sized>() -> usize {
1455 // | - required by this bound in `Tt::const_val`
1457 // = note: cannot satisfy `_: Tt`
1459 err.span_suggestion_verbose(
1460 span.shrink_to_hi(),
1462 "consider specifying the type argument{} in the function call",
1463 pluralize!(generics.params.len()),
1470 .map(|p| p.name.to_string())
1471 .collect::<Vec<String>>()
1474 Applicability::HasPlaceholders,
1481 ty::Predicate::WellFormed(ty) => {
1482 // Same hacky approach as above to avoid deluging user
1483 // with error messages.
1484 if ty.references_error() || self.tcx.sess.has_errors() {
1487 self.need_type_info_err(body_id, span, ty, ErrorCode::E0282)
1490 ty::Predicate::Subtype(ref data) => {
1491 if data.references_error() || self.tcx.sess.has_errors() {
1492 // no need to overload user in such cases
1495 let &SubtypePredicate { a_is_expected: _, a, b } = data.skip_binder();
1496 // both must be type variables, or the other would've been instantiated
1497 assert!(a.is_ty_var() && b.is_ty_var());
1498 self.need_type_info_err(body_id, span, a, ErrorCode::E0282)
1500 ty::Predicate::Projection(ref data) => {
1501 let trait_ref = data.to_poly_trait_ref(self.tcx);
1502 let self_ty = trait_ref.self_ty();
1503 let ty = data.skip_binder().ty;
1504 if predicate.references_error() {
1507 if self_ty.needs_infer() && ty.needs_infer() {
1508 // We do this for the `foo.collect()?` case to produce a suggestion.
1509 let mut err = self.need_type_info_err(body_id, span, self_ty, ErrorCode::E0284);
1510 err.note(&format!("cannot satisfy `{}`", predicate));
1513 let mut err = struct_span_err!(
1517 "type annotations needed: cannot satisfy `{}`",
1520 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
1526 if self.tcx.sess.has_errors() {
1529 let mut err = struct_span_err!(
1533 "type annotations needed: cannot satisfy `{}`",
1536 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
1540 self.note_obligation_cause(&mut err, obligation);
1544 /// Returns `true` if the trait predicate may apply for *some* assignment
1545 /// to the type parameters.
1546 fn predicate_can_apply(
1548 param_env: ty::ParamEnv<'tcx>,
1549 pred: ty::PolyTraitRef<'tcx>,
1551 struct ParamToVarFolder<'a, 'tcx> {
1552 infcx: &'a InferCtxt<'a, 'tcx>,
1553 var_map: FxHashMap<Ty<'tcx>, Ty<'tcx>>,
1556 impl<'a, 'tcx> TypeFolder<'tcx> for ParamToVarFolder<'a, 'tcx> {
1557 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
1561 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
1562 if let ty::Param(ty::ParamTy { name, .. }) = ty.kind {
1563 let infcx = self.infcx;
1564 self.var_map.entry(ty).or_insert_with(|| {
1565 infcx.next_ty_var(TypeVariableOrigin {
1566 kind: TypeVariableOriginKind::TypeParameterDefinition(name, None),
1571 ty.super_fold_with(self)
1577 let mut selcx = SelectionContext::new(self);
1580 pred.fold_with(&mut ParamToVarFolder { infcx: self, var_map: Default::default() });
1582 let cleaned_pred = super::project::normalize(
1585 ObligationCause::dummy(),
1590 let obligation = Obligation::new(
1591 ObligationCause::dummy(),
1593 cleaned_pred.without_const().to_predicate(),
1596 self.predicate_may_hold(&obligation)
1600 fn note_obligation_cause(
1602 err: &mut DiagnosticBuilder<'_>,
1603 obligation: &PredicateObligation<'tcx>,
1605 // First, attempt to add note to this error with an async-await-specific
1606 // message, and fall back to regular note otherwise.
1607 if !self.maybe_note_obligation_cause_for_async_await(err, obligation) {
1608 self.note_obligation_cause_code(
1610 &obligation.predicate,
1611 &obligation.cause.code,
1614 self.suggest_unsized_bound_if_applicable(err, obligation);
1618 fn suggest_unsized_bound_if_applicable(
1620 err: &mut DiagnosticBuilder<'_>,
1621 obligation: &PredicateObligation<'tcx>,
1624 ty::Predicate::Trait(pred, _),
1625 ObligationCauseCode::BindingObligation(item_def_id, span),
1626 ) = (&obligation.predicate, &obligation.cause.code)
1628 if let (Some(generics), true) = (
1629 self.tcx.hir().get_if_local(*item_def_id).as_ref().and_then(|n| n.generics()),
1630 Some(pred.def_id()) == self.tcx.lang_items().sized_trait(),
1632 for param in generics.params {
1633 if param.span == *span
1634 && !param.bounds.iter().any(|bound| {
1635 bound.trait_ref().and_then(|trait_ref| trait_ref.trait_def_id())
1636 == self.tcx.lang_items().sized_trait()
1639 let (span, separator) = match param.bounds {
1640 [] => (span.shrink_to_hi(), ":"),
1641 [.., bound] => (bound.span().shrink_to_hi(), " + "),
1643 err.span_suggestion_verbose(
1645 "consider relaxing the implicit `Sized` restriction",
1646 format!("{} ?Sized", separator),
1647 Applicability::MachineApplicable,
1656 fn is_recursive_obligation(
1658 obligated_types: &mut Vec<&ty::TyS<'tcx>>,
1659 cause_code: &ObligationCauseCode<'tcx>,
1661 if let ObligationCauseCode::BuiltinDerivedObligation(ref data) = cause_code {
1662 let parent_trait_ref = self.resolve_vars_if_possible(&data.parent_trait_ref);
1664 if obligated_types.iter().any(|ot| ot == &parent_trait_ref.skip_binder().self_ty()) {
1672 pub fn recursive_type_with_infinite_size_error(
1675 ) -> DiagnosticBuilder<'tcx> {
1676 assert!(type_def_id.is_local());
1677 let span = tcx.hir().span_if_local(type_def_id).unwrap();
1678 let span = tcx.sess.source_map().guess_head_span(span);
1679 let mut err = struct_span_err!(
1683 "recursive type `{}` has infinite size",
1684 tcx.def_path_str(type_def_id)
1686 err.span_label(span, "recursive type has infinite size");
1688 "insert indirection (e.g., a `Box`, `Rc`, or `&`) \
1689 at some point to make `{}` representable",
1690 tcx.def_path_str(type_def_id)
1695 /// Summarizes information
1698 /// An argument of non-tuple type. Parameters are (name, ty)
1699 Arg(String, String),
1701 /// An argument of tuple type. For a "found" argument, the span is
1702 /// the locationo in the source of the pattern. For a "expected"
1703 /// argument, it will be None. The vector is a list of (name, ty)
1704 /// strings for the components of the tuple.
1705 Tuple(Option<Span>, Vec<(String, String)>),
1709 fn empty() -> ArgKind {
1710 ArgKind::Arg("_".to_owned(), "_".to_owned())
1713 /// Creates an `ArgKind` from the expected type of an
1714 /// argument. It has no name (`_`) and an optional source span.
1715 pub fn from_expected_ty(t: Ty<'_>, span: Option<Span>) -> ArgKind {
1717 ty::Tuple(ref tys) => ArgKind::Tuple(
1719 tys.iter().map(|ty| ("_".to_owned(), ty.to_string())).collect::<Vec<_>>(),
1721 _ => ArgKind::Arg("_".to_owned(), t.to_string()),