src/librustc_trait_selection/traits/error_reporting/mod.rs

   1 pub mod on_unimplemented;
   2 pub mod suggestions;
   3
   4 use super::{
   5     ConstEvalFailure, EvaluationResult, FulfillmentError, FulfillmentErrorCode,
   6     MismatchedProjectionTypes, Obligation, ObligationCause, ObligationCauseCode,
   7     OnUnimplementedDirective, OnUnimplementedNote, OutputTypeParameterMismatch, Overflow,
   8     PredicateObligation, SelectionContext, SelectionError, TraitNotObjectSafe,
   9 };
  10
  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};
  16 use rustc_hir as hir;
  17 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
  18 use rustc_hir::Node;
  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::subst::GenericArgKind;
  23 use rustc_middle::ty::{
  24     self, fast_reject, AdtKind, SubtypePredicate, ToPolyTraitRef, ToPredicate, Ty, TyCtxt,
  25     TypeFoldable, WithConstness,
  26 };
  27 use rustc_session::DiagnosticMessageId;
  28 use rustc_span::{ExpnKind, Span, DUMMY_SP};
  29 use std::fmt;
  30
  31 use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
  32 use crate::traits::query::normalize::AtExt as _;
  33 use on_unimplemented::InferCtxtExt as _;
  34 use suggestions::InferCtxtExt as _;
  35
  36 pub use rustc_infer::traits::error_reporting::*;
  37
  38 pub trait InferCtxtExt<'tcx> {
  39     fn report_fulfillment_errors(
  40         &self,
  41         errors: &[FulfillmentError<'tcx>],
  42         body_id: Option<hir::BodyId>,
  43         fallback_has_occurred: bool,
  44     );
  45
  46     fn report_overflow_error<T>(
  47         &self,
  48         obligation: &Obligation<'tcx, T>,
  49         suggest_increasing_limit: bool,
  50     ) -> !
  51     where
  52         T: fmt::Display + TypeFoldable<'tcx>;
  53
  54     fn report_overflow_error_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> !;
  55
  56     fn report_selection_error(
  57         &self,
  58         obligation: &PredicateObligation<'tcx>,
  59         error: &SelectionError<'tcx>,
  60         fallback_has_occurred: bool,
  61         points_at_arg: bool,
  62     );
  63
  64     /// Given some node representing a fn-like thing in the HIR map,
  65     /// returns a span and `ArgKind` information that describes the
  66     /// arguments it expects. This can be supplied to
  67     /// `report_arg_count_mismatch`.
  68     fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Vec<ArgKind>)>;
  69
  70     /// Reports an error when the number of arguments needed by a
  71     /// trait match doesn't match the number that the expression
  72     /// provides.
  73     fn report_arg_count_mismatch(
  74         &self,
  75         span: Span,
  76         found_span: Option<Span>,
  77         expected_args: Vec<ArgKind>,
  78         found_args: Vec<ArgKind>,
  79         is_closure: bool,
  80     ) -> DiagnosticBuilder<'tcx>;
  81 }
  82
  83 impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
  84     fn report_fulfillment_errors(
  85         &self,
  86         errors: &[FulfillmentError<'tcx>],
  87         body_id: Option<hir::BodyId>,
  88         fallback_has_occurred: bool,
  89     ) {
  90         #[derive(Debug)]
  91         struct ErrorDescriptor<'tcx> {
  92             predicate: ty::Predicate<'tcx>,
  93             index: Option<usize>, // None if this is an old error
  94         }
  95
  96         let mut error_map: FxHashMap<_, Vec<_>> = self
  97             .reported_trait_errors
  98             .borrow()
  99             .iter()
 100             .map(|(&span, predicates)| {
 101                 (
 102                     span,
 103                     predicates
 104                         .iter()
 105                         .map(|&predicate| ErrorDescriptor { predicate, index: None })
 106                         .collect(),
 107                 )
 108             })
 109             .collect();
 110
 111         for (index, error) in errors.iter().enumerate() {
 112             // We want to ignore desugarings here: spans are equivalent even
 113             // if one is the result of a desugaring and the other is not.
 114             let mut span = error.obligation.cause.span;
 115             let expn_data = span.ctxt().outer_expn_data();
 116             if let ExpnKind::Desugaring(_) = expn_data.kind {
 117                 span = expn_data.call_site;
 118             }
 119
 120             error_map.entry(span).or_default().push(ErrorDescriptor {
 121                 predicate: error.obligation.predicate,
 122                 index: Some(index),
 123             });
 124
 125             self.reported_trait_errors
 126                 .borrow_mut()
 127                 .entry(span)
 128                 .or_default()
 129                 .push(error.obligation.predicate);
 130         }
 131
 132         // We do this in 2 passes because we want to display errors in order, though
 133         // maybe it *is* better to sort errors by span or something.
 134         let mut is_suppressed = vec![false; errors.len()];
 135         for (_, error_set) in error_map.iter() {
 136             // We want to suppress "duplicate" errors with the same span.
 137             for error in error_set {
 138                 if let Some(index) = error.index {
 139                     // Suppress errors that are either:
 140                     // 1) strictly implied by another error.
 141                     // 2) implied by an error with a smaller index.
 142                     for error2 in error_set {
 143                         if error2.index.map_or(false, |index2| is_suppressed[index2]) {
 144                             // Avoid errors being suppressed by already-suppressed
 145                             // errors, to prevent all errors from being suppressed
 146                             // at once.
 147                             continue;
 148                         }
 149
 150                         if self.error_implies(error2.predicate, error.predicate)
 151                             && !(error2.index >= error.index
 152                                 && self.error_implies(error.predicate, error2.predicate))
 153                         {
 154                             info!("skipping {:?} (implied by {:?})", error, error2);
 155                             is_suppressed[index] = true;
 156                             break;
 157                         }
 158                     }
 159                 }
 160             }
 161         }
 162
 163         for (error, suppressed) in errors.iter().zip(is_suppressed) {
 164             if !suppressed {
 165                 self.report_fulfillment_error(error, body_id, fallback_has_occurred);
 166             }
 167         }
 168     }
 169
 170     /// Reports that an overflow has occurred and halts compilation. We
 171     /// halt compilation unconditionally because it is important that
 172     /// overflows never be masked -- they basically represent computations
 173     /// whose result could not be truly determined and thus we can't say
 174     /// if the program type checks or not -- and they are unusual
 175     /// occurrences in any case.
 176     fn report_overflow_error<T>(
 177         &self,
 178         obligation: &Obligation<'tcx, T>,
 179         suggest_increasing_limit: bool,
 180     ) -> !
 181     where
 182         T: fmt::Display + TypeFoldable<'tcx>,
 183     {
 184         let predicate = self.resolve_vars_if_possible(&obligation.predicate);
 185         let mut err = struct_span_err!(
 186             self.tcx.sess,
 187             obligation.cause.span,
 188             E0275,
 189             "overflow evaluating the requirement `{}`",
 190             predicate
 191         );
 192
 193         if suggest_increasing_limit {
 194             self.suggest_new_overflow_limit(&mut err);
 195         }
 196
 197         self.note_obligation_cause_code(
 198             &mut err,
 199             &obligation.predicate,
 200             &obligation.cause.code,
 201             &mut vec![],
 202         );
 203
 204         err.emit();
 205         self.tcx.sess.abort_if_errors();
 206         bug!();
 207     }
 208
 209     /// Reports that a cycle was detected which led to overflow and halts
 210     /// compilation. This is equivalent to `report_overflow_error` except
 211     /// that we can give a more helpful error message (and, in particular,
 212     /// we do not suggest increasing the overflow limit, which is not
 213     /// going to help).
 214     fn report_overflow_error_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> ! {
 215         let cycle = self.resolve_vars_if_possible(&cycle.to_owned());
 216         assert!(!cycle.is_empty());
 217
 218         debug!("report_overflow_error_cycle: cycle={:?}", cycle);
 219
 220         self.report_overflow_error(&cycle[0], false);
 221     }
 222
 223     fn report_selection_error(
 224         &self,
 225         obligation: &PredicateObligation<'tcx>,
 226         error: &SelectionError<'tcx>,
 227         fallback_has_occurred: bool,
 228         points_at_arg: bool,
 229     ) {
 230         let tcx = self.tcx;
 231         let span = obligation.cause.span;
 232
 233         let mut err = match *error {
 234             SelectionError::Unimplemented => {
 235                 if let ObligationCauseCode::CompareImplMethodObligation {
 236                     item_name,
 237                     impl_item_def_id,
 238                     trait_item_def_id,
 239                 }
 240                 | ObligationCauseCode::CompareImplTypeObligation {
 241                     item_name,
 242                     impl_item_def_id,
 243                     trait_item_def_id,
 244                 } = obligation.cause.code
 245                 {
 246                     self.report_extra_impl_obligation(
 247                         span,
 248                         item_name,
 249                         impl_item_def_id,
 250                         trait_item_def_id,
 251                         &format!("`{}`", obligation.predicate),
 252                     )
 253                     .emit();
 254                     return;
 255                 }
 256                 match obligation.predicate.kind() {
 257                     ty::PredicateKind::Trait(ref trait_predicate, _) => {
 258                         let trait_predicate = self.resolve_vars_if_possible(trait_predicate);
 259
 260                         if self.tcx.sess.has_errors() && trait_predicate.references_error() {
 261                             return;
 262                         }
 263                         let trait_ref = trait_predicate.to_poly_trait_ref();
 264                         let (post_message, pre_message, type_def) = self
 265                             .get_parent_trait_ref(&obligation.cause.code)
 266                             .map(|(t, s)| {
 267                                 (
 268                                     format!(" in `{}`", t),
 269                                     format!("within `{}`, ", t),
 270                                     s.map(|s| (format!("within this `{}`", t), s)),
 271                                 )
 272                             })
 273                             .unwrap_or_default();
 274
 275                         let OnUnimplementedNote { message, label, note, enclosing_scope } =
 276                             self.on_unimplemented_note(trait_ref, obligation);
 277                         let have_alt_message = message.is_some() || label.is_some();
 278                         let is_try = self
 279                             .tcx
 280                             .sess
 281                             .source_map()
 282                             .span_to_snippet(span)
 283                             .map(|s| &s == "?")
 284                             .unwrap_or(false);
 285                         let is_from = format!("{}", trait_ref.print_only_trait_path())
 286                             .starts_with("std::convert::From<");
 287                         let is_unsize =
 288                             { Some(trait_ref.def_id()) == self.tcx.lang_items().unsize_trait() };
 289                         let (message, note) = if is_try && is_from {
 290                             (
 291                                 Some(format!(
 292                                     "`?` couldn't convert the error to `{}`",
 293                                     trait_ref.self_ty(),
 294                                 )),
 295                                 Some(
 296                                     "the question mark operation (`?`) implicitly performs a \
 297                                         conversion on the error value using the `From` trait"
 298                                         .to_owned(),
 299                                 ),
 300                             )
 301                         } else {
 302                             (message, note)
 303                         };
 304
 305                         let mut err = struct_span_err!(
 306                             self.tcx.sess,
 307                             span,
 308                             E0277,
 309                             "{}",
 310                             message.unwrap_or_else(|| format!(
 311                                 "the trait bound `{}` is not satisfied{}",
 312                                 trait_ref.without_const().to_predicate(tcx),
 313                                 post_message,
 314                             ))
 315                         );
 316
 317                         let should_convert_option_to_result =
 318                             format!("{}", trait_ref.print_only_trait_path())
 319                                 .starts_with("std::convert::From<std::option::NoneError");
 320                         let should_convert_result_to_option = format!("{}", trait_ref)
 321                             .starts_with("<std::option::NoneError as std::convert::From<");
 322                         if is_try && is_from {
 323                             if should_convert_option_to_result {
 324                                 err.span_suggestion_verbose(
 325                                     span.shrink_to_lo(),
 326                                     "consider converting the `Option<T>` into a `Result<T, _>` \
 327                                      using `Option::ok_or` or `Option::ok_or_else`",
 328                                     ".ok_or_else(|| /* error value */)".to_string(),
 329                                     Applicability::HasPlaceholders,
 330                                 );
 331                             } else if should_convert_result_to_option {
 332                                 err.span_suggestion_verbose(
 333                                     span.shrink_to_lo(),
 334                                     "consider converting the `Result<T, _>` into an `Option<T>` \
 335                                      using `Result::ok`",
 336                                     ".ok()".to_string(),
 337                                     Applicability::MachineApplicable,
 338                                 );
 339                             }
 340                             if let Some(ret_span) = self.return_type_span(obligation) {
 341                                 err.span_label(
 342                                     ret_span,
 343                                     &format!("expected `{}` because of this", trait_ref.self_ty()),
 344                                 );
 345                             }
 346                         }
 347
 348                         let explanation =
 349                             if obligation.cause.code == ObligationCauseCode::MainFunctionType {
 350                                 "consider using `()`, or a `Result`".to_owned()
 351                             } else {
 352                                 format!(
 353                                     "{}the trait `{}` is not implemented for `{}`",
 354                                     pre_message,
 355                                     trait_ref.print_only_trait_path(),
 356                                     trait_ref.self_ty(),
 357                                 )
 358                             };
 359
 360                         if self.suggest_add_reference_to_arg(
 361                             &obligation,
 362                             &mut err,
 363                             &trait_ref,
 364                             points_at_arg,
 365                             have_alt_message,
 366                         ) {
 367                             self.note_obligation_cause(&mut err, obligation);
 368                             err.emit();
 369                             return;
 370                         }
 371                         if let Some(ref s) = label {
 372                             // If it has a custom `#[rustc_on_unimplemented]`
 373                             // error message, let's display it as the label!
 374                             err.span_label(span, s.as_str());
 375                             err.help(&explanation);
 376                         } else {
 377                             err.span_label(span, explanation);
 378                         }
 379                         if let Some((msg, span)) = type_def {
 380                             err.span_label(span, &msg);
 381                         }
 382                         if let Some(ref s) = note {
 383                             // If it has a custom `#[rustc_on_unimplemented]` note, let's display it
 384                             err.note(s.as_str());
 385                         }
 386                         if let Some(ref s) = enclosing_scope {
 387                             let enclosing_scope_span = tcx.def_span(
 388                                 tcx.hir()
 389                                     .opt_local_def_id(obligation.cause.body_id)
 390                                     .unwrap_or_else(|| {
 391                                         tcx.hir().body_owner_def_id(hir::BodyId {
 392                                             hir_id: obligation.cause.body_id,
 393                                         })
 394                                     })
 395                                     .to_def_id(),
 396                             );
 397
 398                             err.span_label(enclosing_scope_span, s.as_str());
 399                         }
 400
 401                         self.suggest_borrow_on_unsized_slice(&obligation.cause.code, &mut err);
 402                         self.suggest_fn_call(&obligation, &mut err, &trait_ref, points_at_arg);
 403                         self.suggest_remove_reference(&obligation, &mut err, &trait_ref);
 404                         self.suggest_semicolon_removal(&obligation, &mut err, span, &trait_ref);
 405                         self.note_version_mismatch(&mut err, &trait_ref);
 406
 407                         if Some(trait_ref.def_id()) == tcx.lang_items().try_trait() {
 408                             self.suggest_await_before_try(&mut err, &obligation, &trait_ref, span);
 409                         }
 410
 411                         if self.suggest_impl_trait(&mut err, span, &obligation, &trait_ref) {
 412                             err.emit();
 413                             return;
 414                         }
 415
 416                         if is_unsize {
 417                             // If the obligation failed due to a missing implementation of the
 418                             // `Unsize` trait, give a pointer to why that might be the case
 419                             err.note(
 420                                 "all implementations of `Unsize` are provided \
 421                                 automatically by the compiler, see \
 422                                 <https://doc.rust-lang.org/stable/std/marker/trait.Unsize.html> \
 423                                 for more information",
 424                             );
 425                         }
 426
 427                         // Try to report a help message
 428                         if !trait_ref.has_infer_types_or_consts()
 429                             && self.predicate_can_apply(obligation.param_env, trait_ref)
 430                         {
 431                             // If a where-clause may be useful, remind the
 432                             // user that they can add it.
 433                             //
 434                             // don't display an on-unimplemented note, as
 435                             // these notes will often be of the form
 436                             //     "the type `T` can't be frobnicated"
 437                             // which is somewhat confusing.
 438                             self.suggest_restricting_param_bound(
 439                                 &mut err,
 440                                 trait_ref,
 441                                 obligation.cause.body_id,
 442                             );
 443                         } else {
 444                             if !have_alt_message {
 445                                 // Can't show anything else useful, try to find similar impls.
 446                                 let impl_candidates = self.find_similar_impl_candidates(trait_ref);
 447                                 self.report_similar_impl_candidates(impl_candidates, &mut err);
 448                             }
 449                             // Changing mutability doesn't make a difference to whether we have
 450                             // an `Unsize` impl (Fixes ICE in #71036)
 451                             if !is_unsize {
 452                                 self.suggest_change_mut(
 453                                     &obligation,
 454                                     &mut err,
 455                                     &trait_ref,
 456                                     points_at_arg,
 457                                 );
 458                             }
 459                         }
 460
 461                         // If this error is due to `!: Trait` not implemented but `(): Trait` is
 462                         // implemented, and fallback has occurred, then it could be due to a
 463                         // variable that used to fallback to `()` now falling back to `!`. Issue a
 464                         // note informing about the change in behaviour.
 465                         if trait_predicate.skip_binder().self_ty().is_never()
 466                             && fallback_has_occurred
 467                         {
 468                             let predicate = trait_predicate.map_bound(|mut trait_pred| {
 469                                 trait_pred.trait_ref.substs = self.tcx.mk_substs_trait(
 470                                     self.tcx.mk_unit(),
 471                                     &trait_pred.trait_ref.substs[1..],
 472                                 );
 473                                 trait_pred
 474                             });
 475                             let unit_obligation = Obligation {
 476                                 predicate: ty::PredicateKind::Trait(
 477                                     predicate,
 478                                     hir::Constness::NotConst,
 479                                 )
 480                                 .to_predicate(self.tcx),
 481                                 ..obligation.clone()
 482                             };
 483                             if self.predicate_may_hold(&unit_obligation) {
 484                                 err.note(
 485                                     "the trait is implemented for `()`. \
 486                                      Possibly this error has been caused by changes to \
 487                                      Rust's type-inference algorithm (see issue #48950 \
 488                                      <https://github.com/rust-lang/rust/issues/48950> \
 489                                      for more information). Consider whether you meant to use \
 490                                      the type `()` here instead.",
 491                                 );
 492                             }
 493                         }
 494
 495                         err
 496                     }
 497
 498                     ty::PredicateKind::Subtype(ref predicate) => {
 499                         // Errors for Subtype predicates show up as
 500                         // `FulfillmentErrorCode::CodeSubtypeError`,
 501                         // not selection error.
 502                         span_bug!(span, "subtype requirement gave wrong error: `{:?}`", predicate)
 503                     }
 504
 505                     ty::PredicateKind::RegionOutlives(ref predicate) => {
 506                         let predicate = self.resolve_vars_if_possible(predicate);
 507                         let err = self
 508                             .region_outlives_predicate(&obligation.cause, predicate)
 509                             .err()
 510                             .unwrap();
 511                         struct_span_err!(
 512                             self.tcx.sess,
 513                             span,
 514                             E0279,
 515                             "the requirement `{}` is not satisfied (`{}`)",
 516                             predicate,
 517                             err,
 518                         )
 519                     }
 520
 521                     ty::PredicateKind::Projection(..) | ty::PredicateKind::TypeOutlives(..) => {
 522                         let predicate = self.resolve_vars_if_possible(&obligation.predicate);
 523                         struct_span_err!(
 524                             self.tcx.sess,
 525                             span,
 526                             E0280,
 527                             "the requirement `{}` is not satisfied",
 528                             predicate
 529                         )
 530                     }
 531
 532                     &ty::PredicateKind::ObjectSafe(trait_def_id) => {
 533                         let violations = self.tcx.object_safety_violations(trait_def_id);
 534                         report_object_safety_error(self.tcx, span, trait_def_id, violations)
 535                     }
 536
 537                     &ty::PredicateKind::ClosureKind(closure_def_id, closure_substs, kind) => {
 538                         let found_kind = self.closure_kind(closure_substs).unwrap();
 539                         let closure_span =
 540                             self.tcx.sess.source_map().guess_head_span(
 541                                 self.tcx.hir().span_if_local(closure_def_id).unwrap(),
 542                             );
 543                         let hir_id = self.tcx.hir().as_local_hir_id(closure_def_id.expect_local());
 544                         let mut err = struct_span_err!(
 545                             self.tcx.sess,
 546                             closure_span,
 547                             E0525,
 548                             "expected a closure that implements the `{}` trait, \
 549                              but this closure only implements `{}`",
 550                             kind,
 551                             found_kind
 552                         );
 553
 554                         err.span_label(
 555                             closure_span,
 556                             format!("this closure implements `{}`, not `{}`", found_kind, kind),
 557                         );
 558                         err.span_label(
 559                             obligation.cause.span,
 560                             format!("the requirement to implement `{}` derives from here", kind),
 561                         );
 562
 563                         // Additional context information explaining why the closure only implements
 564                         // a particular trait.
 565                         if let Some(tables) = self.in_progress_tables {
 566                             let tables = tables.borrow();
 567                             match (found_kind, tables.closure_kind_origins().get(hir_id)) {
 568                                 (ty::ClosureKind::FnOnce, Some((span, name))) => {
 569                                     err.span_label(
 570                                         *span,
 571                                         format!(
 572                                             "closure is `FnOnce` because it moves the \
 573                                          variable `{}` out of its environment",
 574                                             name
 575                                         ),
 576                                     );
 577                                 }
 578                                 (ty::ClosureKind::FnMut, Some((span, name))) => {
 579                                     err.span_label(
 580                                         *span,
 581                                         format!(
 582                                             "closure is `FnMut` because it mutates the \
 583                                          variable `{}` here",
 584                                             name
 585                                         ),
 586                                     );
 587                                 }
 588                                 _ => {}
 589                             }
 590                         }
 591
 592                         err.emit();
 593                         return;
 594                     }
 595
 596                     ty::PredicateKind::WellFormed(ty) => {
 597                         if !self.tcx.sess.opts.debugging_opts.chalk {
 598                             // WF predicates cannot themselves make
 599                             // errors. They can only block due to
 600                             // ambiguity; otherwise, they always
 601                             // degenerate into other obligations
 602                             // (which may fail).
 603                             span_bug!(span, "WF predicate not satisfied for {:?}", ty);
 604                         } else {
 605                             // FIXME: we'll need a better message which takes into account
 606                             // which bounds actually failed to hold.
 607                             self.tcx.sess.struct_span_err(
 608                                 span,
 609                                 &format!("the type `{}` is not well-formed (chalk)", ty),
 610                             )
 611                         }
 612                     }
 613
 614                     ty::PredicateKind::ConstEvaluatable(..) => {
 615                         // Errors for `ConstEvaluatable` predicates show up as
 616                         // `SelectionError::ConstEvalFailure`,
 617                         // not `Unimplemented`.
 618                         span_bug!(
 619                             span,
 620                             "const-evaluatable requirement gave wrong error: `{:?}`",
 621                             obligation
 622                         )
 623                     }
 624
 625                     ty::PredicateKind::ConstEquate(..) => {
 626                         // Errors for `ConstEquate` predicates show up as
 627                         // `SelectionError::ConstEvalFailure`,
 628                         // not `Unimplemented`.
 629                         span_bug!(
 630                             span,
 631                             "const-equate requirement gave wrong error: `{:?}`",
 632                             obligation
 633                         )
 634                     }
 635                 }
 636             }
 637
 638             OutputTypeParameterMismatch(ref found_trait_ref, ref expected_trait_ref, _) => {
 639                 let found_trait_ref = self.resolve_vars_if_possible(&*found_trait_ref);
 640                 let expected_trait_ref = self.resolve_vars_if_possible(&*expected_trait_ref);
 641
 642                 if expected_trait_ref.self_ty().references_error() {
 643                     return;
 644                 }
 645
 646                 let found_trait_ty = found_trait_ref.self_ty();
 647
 648                 let found_did = match found_trait_ty.kind {
 649                     ty::Closure(did, _) | ty::Foreign(did) | ty::FnDef(did, _) => Some(did),
 650                     ty::Adt(def, _) => Some(def.did),
 651                     _ => None,
 652                 };
 653
 654                 let found_span = found_did
 655                     .and_then(|did| self.tcx.hir().span_if_local(did))
 656                     .map(|sp| self.tcx.sess.source_map().guess_head_span(sp)); // the sp could be an fn def
 657
 658                 if self.reported_closure_mismatch.borrow().contains(&(span, found_span)) {
 659                     // We check closures twice, with obligations flowing in different directions,
 660                     // but we want to complain about them only once.
 661                     return;
 662                 }
 663
 664                 self.reported_closure_mismatch.borrow_mut().insert((span, found_span));
 665
 666                 let found = match found_trait_ref.skip_binder().substs.type_at(1).kind {
 667                     ty::Tuple(ref tys) => vec![ArgKind::empty(); tys.len()],
 668                     _ => vec![ArgKind::empty()],
 669                 };
 670
 671                 let expected_ty = expected_trait_ref.skip_binder().substs.type_at(1);
 672                 let expected = match expected_ty.kind {
 673                     ty::Tuple(ref tys) => tys
 674                         .iter()
 675                         .map(|t| ArgKind::from_expected_ty(t.expect_ty(), Some(span)))
 676                         .collect(),
 677                     _ => vec![ArgKind::Arg("_".to_owned(), expected_ty.to_string())],
 678                 };
 679
 680                 if found.len() == expected.len() {
 681                     self.report_closure_arg_mismatch(
 682                         span,
 683                         found_span,
 684                         found_trait_ref,
 685                         expected_trait_ref,
 686                     )
 687                 } else {
 688                     let (closure_span, found) = found_did
 689                         .and_then(|did| {
 690                             let node = self.tcx.hir().get_if_local(did)?;
 691                             let (found_span, found) = self.get_fn_like_arguments(node)?;
 692                             Some((Some(found_span), found))
 693                         })
 694                         .unwrap_or((found_span, found));
 695
 696                     self.report_arg_count_mismatch(
 697                         span,
 698                         closure_span,
 699                         expected,
 700                         found,
 701                         found_trait_ty.is_closure(),
 702                     )
 703                 }
 704             }
 705
 706             TraitNotObjectSafe(did) => {
 707                 let violations = self.tcx.object_safety_violations(did);
 708                 report_object_safety_error(self.tcx, span, did, violations)
 709             }
 710
 711             ConstEvalFailure(ErrorHandled::TooGeneric) => {
 712                 // In this instance, we have a const expression containing an unevaluated
 713                 // generic parameter. We have no idea whether this expression is valid or
 714                 // not (e.g. it might result in an error), but we don't want to just assume
 715                 // that it's okay, because that might result in post-monomorphisation time
 716                 // errors. The onus is really on the caller to provide values that it can
 717                 // prove are well-formed.
 718                 let mut err = self
 719                     .tcx
 720                     .sess
 721                     .struct_span_err(span, "constant expression depends on a generic parameter");
 722                 // FIXME(const_generics): we should suggest to the user how they can resolve this
 723                 // issue. However, this is currently not actually possible
 724                 // (see https://github.com/rust-lang/rust/issues/66962#issuecomment-575907083).
 725                 err.note("this may fail depending on what value the parameter takes");
 726                 err
 727             }
 728
 729             // Already reported in the query.
 730             ConstEvalFailure(ErrorHandled::Reported(ErrorReported)) => {
 731                 // FIXME(eddyb) remove this once `ErrorReported` becomes a proof token.
 732                 self.tcx.sess.delay_span_bug(span, "`ErrorReported` without an error");
 733                 return;
 734             }
 735
 736             // Already reported in the query, but only as a lint.
 737             // This shouldn't actually happen for constants used in types, modulo
 738             // bugs. The `delay_span_bug` here ensures it won't be ignored.
 739             ConstEvalFailure(ErrorHandled::Linted) => {
 740                 self.tcx.sess.delay_span_bug(span, "constant in type had error reported as lint");
 741                 return;
 742             }
 743
 744             Overflow => {
 745                 bug!("overflow should be handled before the `report_selection_error` path");
 746             }
 747         };
 748
 749         self.note_obligation_cause(&mut err, obligation);
 750         self.point_at_returns_when_relevant(&mut err, &obligation);
 751
 752         err.emit();
 753     }
 754
 755     /// Given some node representing a fn-like thing in the HIR map,
 756     /// returns a span and `ArgKind` information that describes the
 757     /// arguments it expects. This can be supplied to
 758     /// `report_arg_count_mismatch`.
 759     fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Vec<ArgKind>)> {
 760         let sm = self.tcx.sess.source_map();
 761         let hir = self.tcx.hir();
 762         Some(match node {
 763             Node::Expr(&hir::Expr {
 764                 kind: hir::ExprKind::Closure(_, ref _decl, id, span, _),
 765                 ..
 766             }) => (
 767                 sm.guess_head_span(span),
 768                 hir.body(id)
 769                     .params
 770                     .iter()
 771                     .map(|arg| {
 772                         if let hir::Pat { kind: hir::PatKind::Tuple(ref args, _), span, .. } =
 773                             *arg.pat
 774                         {
 775                             Some(ArgKind::Tuple(
 776                                 Some(span),
 777                                 args.iter()
 778                                     .map(|pat| {
 779                                         sm.span_to_snippet(pat.span)
 780                                             .ok()
 781                                             .map(|snippet| (snippet, "_".to_owned()))
 782                                     })
 783                                     .collect::<Option<Vec<_>>>()?,
 784                             ))
 785                         } else {
 786                             let name = sm.span_to_snippet(arg.pat.span).ok()?;
 787                             Some(ArgKind::Arg(name, "_".to_owned()))
 788                         }
 789                     })
 790                     .collect::<Option<Vec<ArgKind>>>()?,
 791             ),
 792             Node::Item(&hir::Item { span, kind: hir::ItemKind::Fn(ref sig, ..), .. })
 793             | Node::ImplItem(&hir::ImplItem {
 794                 span,
 795                 kind: hir::ImplItemKind::Fn(ref sig, _),
 796                 ..
 797             })
 798             | Node::TraitItem(&hir::TraitItem {
 799                 span,
 800                 kind: hir::TraitItemKind::Fn(ref sig, _),
 801                 ..
 802             }) => (
 803                 sm.guess_head_span(span),
 804                 sig.decl
 805                     .inputs
 806                     .iter()
 807                     .map(|arg| match arg.clone().kind {
 808                         hir::TyKind::Tup(ref tys) => ArgKind::Tuple(
 809                             Some(arg.span),
 810                             vec![("_".to_owned(), "_".to_owned()); tys.len()],
 811                         ),
 812                         _ => ArgKind::empty(),
 813                     })
 814                     .collect::<Vec<ArgKind>>(),
 815             ),
 816             Node::Ctor(ref variant_data) => {
 817                 let span = variant_data.ctor_hir_id().map(|id| hir.span(id)).unwrap_or(DUMMY_SP);
 818                 let span = sm.guess_head_span(span);
 819                 (span, vec![ArgKind::empty(); variant_data.fields().len()])
 820             }
 821             _ => panic!("non-FnLike node found: {:?}", node),
 822         })
 823     }
 824
 825     /// Reports an error when the number of arguments needed by a
 826     /// trait match doesn't match the number that the expression
 827     /// provides.
 828     fn report_arg_count_mismatch(
 829         &self,
 830         span: Span,
 831         found_span: Option<Span>,
 832         expected_args: Vec<ArgKind>,
 833         found_args: Vec<ArgKind>,
 834         is_closure: bool,
 835     ) -> DiagnosticBuilder<'tcx> {
 836         let kind = if is_closure { "closure" } else { "function" };
 837
 838         let args_str = |arguments: &[ArgKind], other: &[ArgKind]| {
 839             let arg_length = arguments.len();
 840             let distinct = match &other[..] {
 841                 &[ArgKind::Tuple(..)] => true,
 842                 _ => false,
 843             };
 844             match (arg_length, arguments.get(0)) {
 845                 (1, Some(&ArgKind::Tuple(_, ref fields))) => {
 846                     format!("a single {}-tuple as argument", fields.len())
 847                 }
 848                 _ => format!(
 849                     "{} {}argument{}",
 850                     arg_length,
 851                     if distinct && arg_length > 1 { "distinct " } else { "" },
 852                     pluralize!(arg_length)
 853                 ),
 854             }
 855         };
 856
 857         let expected_str = args_str(&expected_args, &found_args);
 858         let found_str = args_str(&found_args, &expected_args);
 859
 860         let mut err = struct_span_err!(
 861             self.tcx.sess,
 862             span,
 863             E0593,
 864             "{} is expected to take {}, but it takes {}",
 865             kind,
 866             expected_str,
 867             found_str,
 868         );
 869
 870         err.span_label(span, format!("expected {} that takes {}", kind, expected_str));
 871
 872         if let Some(found_span) = found_span {
 873             err.span_label(found_span, format!("takes {}", found_str));
 874
 875             // move |_| { ... }
 876             // ^^^^^^^^-- def_span
 877             //
 878             // move |_| { ... }
 879             // ^^^^^-- prefix
 880             let prefix_span = self.tcx.sess.source_map().span_until_non_whitespace(found_span);
 881             // move |_| { ... }
 882             //      ^^^-- pipe_span
 883             let pipe_span =
 884                 if let Some(span) = found_span.trim_start(prefix_span) { span } else { found_span };
 885
 886             // Suggest to take and ignore the arguments with expected_args_length `_`s if
 887             // found arguments is empty (assume the user just wants to ignore args in this case).
 888             // For example, if `expected_args_length` is 2, suggest `|_, _|`.
 889             if found_args.is_empty() && is_closure {
 890                 let underscores = vec!["_"; expected_args.len()].join(", ");
 891                 err.span_suggestion_verbose(
 892                     pipe_span,
 893                     &format!(
 894                         "consider changing the closure to take and ignore the expected argument{}",
 895                         pluralize!(expected_args.len())
 896                     ),
 897                     format!("|{}|", underscores),
 898                     Applicability::MachineApplicable,
 899                 );
 900             }
 901
 902             if let &[ArgKind::Tuple(_, ref fields)] = &found_args[..] {
 903                 if fields.len() == expected_args.len() {
 904                     let sugg = fields
 905                         .iter()
 906                         .map(|(name, _)| name.to_owned())
 907                         .collect::<Vec<String>>()
 908                         .join(", ");
 909                     err.span_suggestion_verbose(
 910                         found_span,
 911                         "change the closure to take multiple arguments instead of a single tuple",
 912                         format!("|{}|", sugg),
 913                         Applicability::MachineApplicable,
 914                     );
 915                 }
 916             }
 917             if let &[ArgKind::Tuple(_, ref fields)] = &expected_args[..] {
 918                 if fields.len() == found_args.len() && is_closure {
 919                     let sugg = format!(
 920                         "|({}){}|",
 921                         found_args
 922                             .iter()
 923                             .map(|arg| match arg {
 924                                 ArgKind::Arg(name, _) => name.to_owned(),
 925                                 _ => "_".to_owned(),
 926                             })
 927                             .collect::<Vec<String>>()
 928                             .join(", "),
 929                         // add type annotations if available
 930                         if found_args.iter().any(|arg| match arg {
 931                             ArgKind::Arg(_, ty) => ty != "_",
 932                             _ => false,
 933                         }) {
 934                             format!(
 935                                 ": ({})",
 936                                 fields
 937                                     .iter()
 938                                     .map(|(_, ty)| ty.to_owned())
 939                                     .collect::<Vec<String>>()
 940                                     .join(", ")
 941                             )
 942                         } else {
 943                             String::new()
 944                         },
 945                     );
 946                     err.span_suggestion_verbose(
 947                         found_span,
 948                         "change the closure to accept a tuple instead of individual arguments",
 949                         sugg,
 950                         Applicability::MachineApplicable,
 951                     );
 952                 }
 953             }
 954         }
 955
 956         err
 957     }
 958 }
 959
 960 trait InferCtxtPrivExt<'tcx> {
 961     // returns if `cond` not occurring implies that `error` does not occur - i.e., that
 962     // `error` occurring implies that `cond` occurs.
 963     fn error_implies(&self, cond: ty::Predicate<'tcx>, error: ty::Predicate<'tcx>) -> bool;
 964
 965     fn report_fulfillment_error(
 966         &self,
 967         error: &FulfillmentError<'tcx>,
 968         body_id: Option<hir::BodyId>,
 969         fallback_has_occurred: bool,
 970     );
 971
 972     fn report_projection_error(
 973         &self,
 974         obligation: &PredicateObligation<'tcx>,
 975         error: &MismatchedProjectionTypes<'tcx>,
 976     );
 977
 978     fn fuzzy_match_tys(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> bool;
 979
 980     fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str>;
 981
 982     fn find_similar_impl_candidates(
 983         &self,
 984         trait_ref: ty::PolyTraitRef<'tcx>,
 985     ) -> Vec<ty::TraitRef<'tcx>>;
 986
 987     fn report_similar_impl_candidates(
 988         &self,
 989         impl_candidates: Vec<ty::TraitRef<'tcx>>,
 990         err: &mut DiagnosticBuilder<'_>,
 991     );
 992
 993     /// Gets the parent trait chain start
 994     fn get_parent_trait_ref(
 995         &self,
 996         code: &ObligationCauseCode<'tcx>,
 997     ) -> Option<(String, Option<Span>)>;
 998
 999     /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
1000     /// with the same path as `trait_ref`, a help message about
1001     /// a probable version mismatch is added to `err`
1002     fn note_version_mismatch(
1003         &self,
1004         err: &mut DiagnosticBuilder<'_>,
1005         trait_ref: &ty::PolyTraitRef<'tcx>,
1006     );
1007
1008     /// Creates a `PredicateObligation` with `new_self_ty` replacing the existing type in the
1009     /// `trait_ref`.
1010     ///
1011     /// For this to work, `new_self_ty` must have no escaping bound variables.
1012     fn mk_trait_obligation_with_new_self_ty(
1013         &self,
1014         param_env: ty::ParamEnv<'tcx>,
1015         trait_ref: &ty::PolyTraitRef<'tcx>,
1016         new_self_ty: Ty<'tcx>,
1017     ) -> PredicateObligation<'tcx>;
1018
1019     fn maybe_report_ambiguity(
1020         &self,
1021         obligation: &PredicateObligation<'tcx>,
1022         body_id: Option<hir::BodyId>,
1023     );
1024
1025     fn predicate_can_apply(
1026         &self,
1027         param_env: ty::ParamEnv<'tcx>,
1028         pred: ty::PolyTraitRef<'tcx>,
1029     ) -> bool;
1030
1031     fn note_obligation_cause(
1032         &self,
1033         err: &mut DiagnosticBuilder<'tcx>,
1034         obligation: &PredicateObligation<'tcx>,
1035     );
1036
1037     fn suggest_unsized_bound_if_applicable(
1038         &self,
1039         err: &mut DiagnosticBuilder<'tcx>,
1040         obligation: &PredicateObligation<'tcx>,
1041     );
1042
1043     fn is_recursive_obligation(
1044         &self,
1045         obligated_types: &mut Vec<&ty::TyS<'tcx>>,
1046         cause_code: &ObligationCauseCode<'tcx>,
1047     ) -> bool;
1048 }
1049
1050 impl<'a, 'tcx> InferCtxtPrivExt<'tcx> for InferCtxt<'a, 'tcx> {
1051     // returns if `cond` not occurring implies that `error` does not occur - i.e., that
1052     // `error` occurring implies that `cond` occurs.
1053     fn error_implies(&self, cond: ty::Predicate<'tcx>, error: ty::Predicate<'tcx>) -> bool {
1054         if cond == error {
1055             return true;
1056         }
1057
1058         let (cond, error) = match (cond.kind(), error.kind()) {
1059             (ty::PredicateKind::Trait(..), ty::PredicateKind::Trait(error, _)) => (cond, error),
1060             _ => {
1061                 // FIXME: make this work in other cases too.
1062                 return false;
1063             }
1064         };
1065
1066         for obligation in super::elaborate_predicates(self.tcx, std::iter::once(cond)) {
1067             if let ty::PredicateKind::Trait(implication, _) = obligation.predicate.kind() {
1068                 let error = error.to_poly_trait_ref();
1069                 let implication = implication.to_poly_trait_ref();
1070                 // FIXME: I'm just not taking associated types at all here.
1071                 // Eventually I'll need to implement param-env-aware
1072                 // `Γ₁ ⊦ φ₁ => Γ₂ ⊦ φ₂` logic.
1073                 let param_env = ty::ParamEnv::empty();
1074                 if self.can_sub(param_env, error, implication).is_ok() {
1075                     debug!("error_implies: {:?} -> {:?} -> {:?}", cond, error, implication);
1076                     return true;
1077                 }
1078             }
1079         }
1080
1081         false
1082     }
1083
1084     fn report_fulfillment_error(
1085         &self,
1086         error: &FulfillmentError<'tcx>,
1087         body_id: Option<hir::BodyId>,
1088         fallback_has_occurred: bool,
1089     ) {
1090         debug!("report_fulfillment_error({:?})", error);
1091         match error.code {
1092             FulfillmentErrorCode::CodeSelectionError(ref selection_error) => {
1093                 self.report_selection_error(
1094                     &error.obligation,
1095                     selection_error,
1096                     fallback_has_occurred,
1097                     error.points_at_arg_span,
1098                 );
1099             }
1100             FulfillmentErrorCode::CodeProjectionError(ref e) => {
1101                 self.report_projection_error(&error.obligation, e);
1102             }
1103             FulfillmentErrorCode::CodeAmbiguity => {
1104                 self.maybe_report_ambiguity(&error.obligation, body_id);
1105             }
1106             FulfillmentErrorCode::CodeSubtypeError(ref expected_found, ref err) => {
1107                 self.report_mismatched_types(
1108                     &error.obligation.cause,
1109                     expected_found.expected,
1110                     expected_found.found,
1111                     err.clone(),
1112                 )
1113                 .emit();
1114             }
1115             FulfillmentErrorCode::CodeConstEquateError(ref expected_found, ref err) => {
1116                 self.report_mismatched_consts(
1117                     &error.obligation.cause,
1118                     expected_found.expected,
1119                     expected_found.found,
1120                     err.clone(),
1121                 )
1122                 .emit();
1123             }
1124         }
1125     }
1126
1127     fn report_projection_error(
1128         &self,
1129         obligation: &PredicateObligation<'tcx>,
1130         error: &MismatchedProjectionTypes<'tcx>,
1131     ) {
1132         let predicate = self.resolve_vars_if_possible(&obligation.predicate);
1133
1134         if predicate.references_error() {
1135             return;
1136         }
1137
1138         self.probe(|_| {
1139             let err_buf;
1140             let mut err = &error.err;
1141             let mut values = None;
1142
1143             // try to find the mismatched types to report the error with.
1144             //
1145             // this can fail if the problem was higher-ranked, in which
1146             // cause I have no idea for a good error message.
1147             if let ty::PredicateKind::Projection(ref data) = predicate.kind() {
1148                 let mut selcx = SelectionContext::new(self);
1149                 let (data, _) = self.replace_bound_vars_with_fresh_vars(
1150                     obligation.cause.span,
1151                     infer::LateBoundRegionConversionTime::HigherRankedType,
1152                     data,
1153                 );
1154                 let mut obligations = vec![];
1155                 let normalized_ty = super::normalize_projection_type(
1156                     &mut selcx,
1157                     obligation.param_env,
1158                     data.projection_ty,
1159                     obligation.cause.clone(),
1160                     0,
1161                     &mut obligations,
1162                 );
1163
1164                 debug!(
1165                     "report_projection_error obligation.cause={:?} obligation.param_env={:?}",
1166                     obligation.cause, obligation.param_env
1167                 );
1168
1169                 debug!(
1170                     "report_projection_error normalized_ty={:?} data.ty={:?}",
1171                     normalized_ty, data.ty
1172                 );
1173
1174                 let is_normalized_ty_expected = match &obligation.cause.code {
1175                     ObligationCauseCode::ItemObligation(_)
1176                     | ObligationCauseCode::BindingObligation(_, _)
1177                     | ObligationCauseCode::ObjectCastObligation(_) => false,
1178                     _ => true,
1179                 };
1180
1181                 if let Err(error) = self.at(&obligation.cause, obligation.param_env).eq_exp(
1182                     is_normalized_ty_expected,
1183                     normalized_ty,
1184                     data.ty,
1185                 ) {
1186                     values = Some(infer::ValuePairs::Types(ExpectedFound::new(
1187                         is_normalized_ty_expected,
1188                         normalized_ty,
1189                         data.ty,
1190                     )));
1191
1192                     err_buf = error;
1193                     err = &err_buf;
1194                 }
1195             }
1196
1197             let msg = format!("type mismatch resolving `{}`", predicate);
1198             let error_id = (DiagnosticMessageId::ErrorId(271), Some(obligation.cause.span), msg);
1199             let fresh = self.tcx.sess.one_time_diagnostics.borrow_mut().insert(error_id);
1200             if fresh {
1201                 let mut diag = struct_span_err!(
1202                     self.tcx.sess,
1203                     obligation.cause.span,
1204                     E0271,
1205                     "type mismatch resolving `{}`",
1206                     predicate
1207                 );
1208                 self.note_type_err(&mut diag, &obligation.cause, None, values, err);
1209                 self.note_obligation_cause(&mut diag, obligation);
1210                 diag.emit();
1211             }
1212         });
1213     }
1214
1215     fn fuzzy_match_tys(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
1216         /// returns the fuzzy category of a given type, or None
1217         /// if the type can be equated to any type.
1218         fn type_category(t: Ty<'_>) -> Option<u32> {
1219             match t.kind {
1220                 ty::Bool => Some(0),
1221                 ty::Char => Some(1),
1222                 ty::Str => Some(2),
1223                 ty::Int(..) | ty::Uint(..) | ty::Infer(ty::IntVar(..)) => Some(3),
1224                 ty::Float(..) | ty::Infer(ty::FloatVar(..)) => Some(4),
1225                 ty::Ref(..) | ty::RawPtr(..) => Some(5),
1226                 ty::Array(..) | ty::Slice(..) => Some(6),
1227                 ty::FnDef(..) | ty::FnPtr(..) => Some(7),
1228                 ty::Dynamic(..) => Some(8),
1229                 ty::Closure(..) => Some(9),
1230                 ty::Tuple(..) => Some(10),
1231                 ty::Projection(..) => Some(11),
1232                 ty::Param(..) => Some(12),
1233                 ty::Opaque(..) => Some(13),
1234                 ty::Never => Some(14),
1235                 ty::Adt(adt, ..) => match adt.adt_kind() {
1236                     AdtKind::Struct => Some(15),
1237                     AdtKind::Union => Some(16),
1238                     AdtKind::Enum => Some(17),
1239                 },
1240                 ty::Generator(..) => Some(18),
1241                 ty::Foreign(..) => Some(19),
1242                 ty::GeneratorWitness(..) => Some(20),
1243                 ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) | ty::Error => None,
1244             }
1245         }
1246
1247         match (type_category(a), type_category(b)) {
1248             (Some(cat_a), Some(cat_b)) => match (&a.kind, &b.kind) {
1249                 (&ty::Adt(def_a, _), &ty::Adt(def_b, _)) => def_a == def_b,
1250                 _ => cat_a == cat_b,
1251             },
1252             // infer and error can be equated to all types
1253             _ => true,
1254         }
1255     }
1256
1257     fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str> {
1258         self.tcx.hir().body(body_id).generator_kind.map(|gen_kind| match gen_kind {
1259             hir::GeneratorKind::Gen => "a generator",
1260             hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Block) => "an async block",
1261             hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Fn) => "an async function",
1262             hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Closure) => "an async closure",
1263         })
1264     }
1265
1266     fn find_similar_impl_candidates(
1267         &self,
1268         trait_ref: ty::PolyTraitRef<'tcx>,
1269     ) -> Vec<ty::TraitRef<'tcx>> {
1270         let simp = fast_reject::simplify_type(self.tcx, trait_ref.skip_binder().self_ty(), true);
1271         let all_impls = self.tcx.all_impls(trait_ref.def_id());
1272
1273         match simp {
1274             Some(simp) => all_impls
1275                 .filter_map(|def_id| {
1276                     let imp = self.tcx.impl_trait_ref(def_id).unwrap();
1277                     let imp_simp = fast_reject::simplify_type(self.tcx, imp.self_ty(), true);
1278                     if let Some(imp_simp) = imp_simp {
1279                         if simp != imp_simp {
1280                             return None;
1281                         }
1282                     }
1283                     Some(imp)
1284                 })
1285                 .collect(),
1286             None => all_impls.map(|def_id| self.tcx.impl_trait_ref(def_id).unwrap()).collect(),
1287         }
1288     }
1289
1290     fn report_similar_impl_candidates(
1291         &self,
1292         impl_candidates: Vec<ty::TraitRef<'tcx>>,
1293         err: &mut DiagnosticBuilder<'_>,
1294     ) {
1295         if impl_candidates.is_empty() {
1296             return;
1297         }
1298
1299         let len = impl_candidates.len();
1300         let end = if impl_candidates.len() <= 5 { impl_candidates.len() } else { 4 };
1301
1302         let normalize = |candidate| {
1303             self.tcx.infer_ctxt().enter(|ref infcx| {
1304                 let normalized = infcx
1305                     .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
1306                     .normalize(candidate)
1307                     .ok();
1308                 match normalized {
1309                     Some(normalized) => format!("\n  {:?}", normalized.value),
1310                     None => format!("\n  {:?}", candidate),
1311                 }
1312             })
1313         };
1314
1315         // Sort impl candidates so that ordering is consistent for UI tests.
1316         let mut normalized_impl_candidates =
1317             impl_candidates.iter().map(normalize).collect::<Vec<String>>();
1318
1319         // Sort before taking the `..end` range,
1320         // because the ordering of `impl_candidates` may not be deterministic:
1321         // https://github.com/rust-lang/rust/pull/57475#issuecomment-455519507
1322         normalized_impl_candidates.sort();
1323
1324         err.help(&format!(
1325             "the following implementations were found:{}{}",
1326             normalized_impl_candidates[..end].join(""),
1327             if len > 5 { format!("\nand {} others", len - 4) } else { String::new() }
1328         ));
1329     }
1330
1331     /// Gets the parent trait chain start
1332     fn get_parent_trait_ref(
1333         &self,
1334         code: &ObligationCauseCode<'tcx>,
1335     ) -> Option<(String, Option<Span>)> {
1336         match code {
1337             &ObligationCauseCode::BuiltinDerivedObligation(ref data) => {
1338                 let parent_trait_ref = self.resolve_vars_if_possible(&data.parent_trait_ref);
1339                 match self.get_parent_trait_ref(&data.parent_code) {
1340                     Some(t) => Some(t),
1341                     None => {
1342                         let ty = parent_trait_ref.skip_binder().self_ty();
1343                         let span =
1344                             TyCategory::from_ty(ty).map(|(_, def_id)| self.tcx.def_span(def_id));
1345                         Some((ty.to_string(), span))
1346                     }
1347                 }
1348             }
1349             _ => None,
1350         }
1351     }
1352
1353     /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
1354     /// with the same path as `trait_ref`, a help message about
1355     /// a probable version mismatch is added to `err`
1356     fn note_version_mismatch(
1357         &self,
1358         err: &mut DiagnosticBuilder<'_>,
1359         trait_ref: &ty::PolyTraitRef<'tcx>,
1360     ) {
1361         let get_trait_impl = |trait_def_id| {
1362             let mut trait_impl = None;
1363             self.tcx.for_each_relevant_impl(trait_def_id, trait_ref.self_ty(), |impl_def_id| {
1364                 if trait_impl.is_none() {
1365                     trait_impl = Some(impl_def_id);
1366                 }
1367             });
1368             trait_impl
1369         };
1370         let required_trait_path = self.tcx.def_path_str(trait_ref.def_id());
1371         let all_traits = self.tcx.all_traits(LOCAL_CRATE);
1372         let traits_with_same_path: std::collections::BTreeSet<_> = all_traits
1373             .iter()
1374             .filter(|trait_def_id| **trait_def_id != trait_ref.def_id())
1375             .filter(|trait_def_id| self.tcx.def_path_str(**trait_def_id) == required_trait_path)
1376             .collect();
1377         for trait_with_same_path in traits_with_same_path {
1378             if let Some(impl_def_id) = get_trait_impl(*trait_with_same_path) {
1379                 let impl_span = self.tcx.def_span(impl_def_id);
1380                 err.span_help(impl_span, "trait impl with same name found");
1381                 let trait_crate = self.tcx.crate_name(trait_with_same_path.krate);
1382                 let crate_msg = format!(
1383                     "perhaps two different versions of crate `{}` are being used?",
1384                     trait_crate
1385                 );
1386                 err.note(&crate_msg);
1387             }
1388         }
1389     }
1390
1391     fn mk_trait_obligation_with_new_self_ty(
1392         &self,
1393         param_env: ty::ParamEnv<'tcx>,
1394         trait_ref: &ty::PolyTraitRef<'tcx>,
1395         new_self_ty: Ty<'tcx>,
1396     ) -> PredicateObligation<'tcx> {
1397         assert!(!new_self_ty.has_escaping_bound_vars());
1398
1399         let trait_ref = trait_ref.map_bound_ref(|tr| ty::TraitRef {
1400             substs: self.tcx.mk_substs_trait(new_self_ty, &tr.substs[1..]),
1401             ..*tr
1402         });
1403
1404         Obligation::new(
1405             ObligationCause::dummy(),
1406             param_env,
1407             trait_ref.without_const().to_predicate(self.tcx),
1408         )
1409     }
1410
1411     fn maybe_report_ambiguity(
1412         &self,
1413         obligation: &PredicateObligation<'tcx>,
1414         body_id: Option<hir::BodyId>,
1415     ) {
1416         // Unable to successfully determine, probably means
1417         // insufficient type information, but could mean
1418         // ambiguous impls. The latter *ought* to be a
1419         // coherence violation, so we don't report it here.
1420
1421         let predicate = self.resolve_vars_if_possible(&obligation.predicate);
1422         let span = obligation.cause.span;
1423
1424         debug!(
1425             "maybe_report_ambiguity(predicate={:?}, obligation={:?} body_id={:?}, code={:?})",
1426             predicate, obligation, body_id, obligation.cause.code,
1427         );
1428
1429         // Ambiguity errors are often caused as fallout from earlier
1430         // errors. So just ignore them if this infcx is tainted.
1431         if self.is_tainted_by_errors() {
1432             return;
1433         }
1434
1435         let mut err = match predicate.kind() {
1436             ty::PredicateKind::Trait(ref data, _) => {
1437                 let trait_ref = data.to_poly_trait_ref();
1438                 let self_ty = trait_ref.self_ty();
1439                 debug!("self_ty {:?} {:?} trait_ref {:?}", self_ty, self_ty.kind, trait_ref);
1440
1441                 if predicate.references_error() {
1442                     return;
1443                 }
1444                 // Typically, this ambiguity should only happen if
1445                 // there are unresolved type inference variables
1446                 // (otherwise it would suggest a coherence
1447                 // failure). But given #21974 that is not necessarily
1448                 // the case -- we can have multiple where clauses that
1449                 // are only distinguished by a region, which results
1450                 // in an ambiguity even when all types are fully
1451                 // known, since we don't dispatch based on region
1452                 // relationships.
1453
1454                 // This is kind of a hack: it frequently happens that some earlier
1455                 // error prevents types from being fully inferred, and then we get
1456                 // a bunch of uninteresting errors saying something like "<generic
1457                 // #0> doesn't implement Sized".  It may even be true that we
1458                 // could just skip over all checks where the self-ty is an
1459                 // inference variable, but I was afraid that there might be an
1460                 // inference variable created, registered as an obligation, and
1461                 // then never forced by writeback, and hence by skipping here we'd
1462                 // be ignoring the fact that we don't KNOW the type works
1463                 // out. Though even that would probably be harmless, given that
1464                 // we're only talking about builtin traits, which are known to be
1465                 // inhabited. We used to check for `self.tcx.sess.has_errors()` to
1466                 // avoid inundating the user with unnecessary errors, but we now
1467                 // check upstream for type errors and don't add the obligations to
1468                 // begin with in those cases.
1469                 if self
1470                     .tcx
1471                     .lang_items()
1472                     .sized_trait()
1473                     .map_or(false, |sized_id| sized_id == trait_ref.def_id())
1474                 {
1475                     self.need_type_info_err(body_id, span, self_ty, ErrorCode::E0282).emit();
1476                     return;
1477                 }
1478                 let mut err = self.need_type_info_err(body_id, span, self_ty, ErrorCode::E0283);
1479                 err.note(&format!("cannot satisfy `{}`", predicate));
1480                 if let ObligationCauseCode::ItemObligation(def_id) = obligation.cause.code {
1481                     self.suggest_fully_qualified_path(&mut err, def_id, span, trait_ref.def_id());
1482                 } else if let (
1483                     Ok(ref snippet),
1484                     ObligationCauseCode::BindingObligation(ref def_id, _),
1485                 ) =
1486                     (self.tcx.sess.source_map().span_to_snippet(span), &obligation.cause.code)
1487                 {
1488                     let generics = self.tcx.generics_of(*def_id);
1489                     if generics.params.iter().any(|p| p.name.as_str() != "Self")
1490                         && !snippet.ends_with('>')
1491                     {
1492                         // FIXME: To avoid spurious suggestions in functions where type arguments
1493                         // where already supplied, we check the snippet to make sure it doesn't
1494                         // end with a turbofish. Ideally we would have access to a `PathSegment`
1495                         // instead. Otherwise we would produce the following output:
1496                         //
1497                         // error[E0283]: type annotations needed
1498                         //   --> $DIR/issue-54954.rs:3:24
1499                         //    |
1500                         // LL | const ARR_LEN: usize = Tt::const_val::<[i8; 123]>();
1501                         //    |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^
1502                         //    |                        |
1503                         //    |                        cannot infer type
1504                         //    |                        help: consider specifying the type argument
1505                         //    |                        in the function call:
1506                         //    |                        `Tt::const_val::<[i8; 123]>::<T>`
1507                         // ...
1508                         // LL |     const fn const_val<T: Sized>() -> usize {
1509                         //    |                        - required by this bound in `Tt::const_val`
1510                         //    |
1511                         //    = note: cannot satisfy `_: Tt`
1512
1513                         err.span_suggestion_verbose(
1514                             span.shrink_to_hi(),
1515                             &format!(
1516                                 "consider specifying the type argument{} in the function call",
1517                                 pluralize!(generics.params.len()),
1518                             ),
1519                             format!(
1520                                 "::<{}>",
1521                                 generics
1522                                     .params
1523                                     .iter()
1524                                     .map(|p| p.name.to_string())
1525                                     .collect::<Vec<String>>()
1526                                     .join(", ")
1527                             ),
1528                             Applicability::HasPlaceholders,
1529                         );
1530                     }
1531                 }
1532                 err
1533             }
1534
1535             ty::PredicateKind::WellFormed(arg) => {
1536                 // Same hacky approach as above to avoid deluging user
1537                 // with error messages.
1538                 if arg.references_error() || self.tcx.sess.has_errors() {
1539                     return;
1540                 }
1541
1542                 match arg.unpack() {
1543                     GenericArgKind::Lifetime(lt) => {
1544                         span_bug!(span, "unexpected well formed predicate: {:?}", lt)
1545                     }
1546                     GenericArgKind::Type(ty) => {
1547                         self.need_type_info_err(body_id, span, ty, ErrorCode::E0282)
1548                     }
1549                     GenericArgKind::Const(ct) => {
1550                         self.need_type_info_err_const(body_id, span, ct, ErrorCode::E0282)
1551                     }
1552                 }
1553             }
1554
1555             ty::PredicateKind::Subtype(ref data) => {
1556                 if data.references_error() || self.tcx.sess.has_errors() {
1557                     // no need to overload user in such cases
1558                     return;
1559                 }
1560                 let &SubtypePredicate { a_is_expected: _, a, b } = data.skip_binder();
1561                 // both must be type variables, or the other would've been instantiated
1562                 assert!(a.is_ty_var() && b.is_ty_var());
1563                 self.need_type_info_err(body_id, span, a, ErrorCode::E0282)
1564             }
1565             ty::PredicateKind::Projection(ref data) => {
1566                 let trait_ref = data.to_poly_trait_ref(self.tcx);
1567                 let self_ty = trait_ref.self_ty();
1568                 let ty = data.skip_binder().ty;
1569                 if predicate.references_error() {
1570                     return;
1571                 }
1572                 if self_ty.needs_infer() && ty.needs_infer() {
1573                     // We do this for the `foo.collect()?` case to produce a suggestion.
1574                     let mut err = self.need_type_info_err(body_id, span, self_ty, ErrorCode::E0284);
1575                     err.note(&format!("cannot satisfy `{}`", predicate));
1576                     err
1577                 } else {
1578                     let mut err = struct_span_err!(
1579                         self.tcx.sess,
1580                         span,
1581                         E0284,
1582                         "type annotations needed: cannot satisfy `{}`",
1583                         predicate,
1584                     );
1585                     err.span_label(span, &format!("cannot satisfy `{}`", predicate));
1586                     err
1587                 }
1588             }
1589
1590             _ => {
1591                 if self.tcx.sess.has_errors() {
1592                     return;
1593                 }
1594                 let mut err = struct_span_err!(
1595                     self.tcx.sess,
1596                     span,
1597                     E0284,
1598                     "type annotations needed: cannot satisfy `{}`",
1599                     predicate,
1600                 );
1601                 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
1602                 err
1603             }
1604         };
1605         self.note_obligation_cause(&mut err, obligation);
1606         err.emit();
1607     }
1608
1609     /// Returns `true` if the trait predicate may apply for *some* assignment
1610     /// to the type parameters.
1611     fn predicate_can_apply(
1612         &self,
1613         param_env: ty::ParamEnv<'tcx>,
1614         pred: ty::PolyTraitRef<'tcx>,
1615     ) -> bool {
1616         struct ParamToVarFolder<'a, 'tcx> {
1617             infcx: &'a InferCtxt<'a, 'tcx>,
1618             var_map: FxHashMap<Ty<'tcx>, Ty<'tcx>>,
1619         }
1620
1621         impl<'a, 'tcx> TypeFolder<'tcx> for ParamToVarFolder<'a, 'tcx> {
1622             fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
1623                 self.infcx.tcx
1624             }
1625
1626             fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
1627                 if let ty::Param(ty::ParamTy { name, .. }) = ty.kind {
1628                     let infcx = self.infcx;
1629                     self.var_map.entry(ty).or_insert_with(|| {
1630                         infcx.next_ty_var(TypeVariableOrigin {
1631                             kind: TypeVariableOriginKind::TypeParameterDefinition(name, None),
1632                             span: DUMMY_SP,
1633                         })
1634                     })
1635                 } else {
1636                     ty.super_fold_with(self)
1637                 }
1638             }
1639         }
1640
1641         self.probe(|_| {
1642             let mut selcx = SelectionContext::new(self);
1643
1644             let cleaned_pred =
1645                 pred.fold_with(&mut ParamToVarFolder { infcx: self, var_map: Default::default() });
1646
1647             let cleaned_pred = super::project::normalize(
1648                 &mut selcx,
1649                 param_env,
1650                 ObligationCause::dummy(),
1651                 &cleaned_pred,
1652             )
1653             .value;
1654
1655             let obligation = Obligation::new(
1656                 ObligationCause::dummy(),
1657                 param_env,
1658                 cleaned_pred.without_const().to_predicate(selcx.tcx()),
1659             );
1660
1661             self.predicate_may_hold(&obligation)
1662         })
1663     }
1664
1665     fn note_obligation_cause(
1666         &self,
1667         err: &mut DiagnosticBuilder<'tcx>,
1668         obligation: &PredicateObligation<'tcx>,
1669     ) {
1670         // First, attempt to add note to this error with an async-await-specific
1671         // message, and fall back to regular note otherwise.
1672         if !self.maybe_note_obligation_cause_for_async_await(err, obligation) {
1673             self.note_obligation_cause_code(
1674                 err,
1675                 &obligation.predicate,
1676                 &obligation.cause.code,
1677                 &mut vec![],
1678             );
1679             self.suggest_unsized_bound_if_applicable(err, obligation);
1680         }
1681     }
1682
1683     fn suggest_unsized_bound_if_applicable(
1684         &self,
1685         err: &mut DiagnosticBuilder<'tcx>,
1686         obligation: &PredicateObligation<'tcx>,
1687     ) {
1688         if let (
1689             ty::PredicateKind::Trait(pred, _),
1690             ObligationCauseCode::BindingObligation(item_def_id, span),
1691         ) = (obligation.predicate.kind(), &obligation.cause.code)
1692         {
1693             if let (Some(generics), true) = (
1694                 self.tcx.hir().get_if_local(*item_def_id).as_ref().and_then(|n| n.generics()),
1695                 Some(pred.def_id()) == self.tcx.lang_items().sized_trait(),
1696             ) {
1697                 for param in generics.params {
1698                     if param.span == *span
1699                         && !param.bounds.iter().any(|bound| {
1700                             bound.trait_ref().and_then(|trait_ref| trait_ref.trait_def_id())
1701                                 == self.tcx.lang_items().sized_trait()
1702                         })
1703                     {
1704                         let (span, separator) = match param.bounds {
1705                             [] => (span.shrink_to_hi(), ":"),
1706                             [.., bound] => (bound.span().shrink_to_hi(), " +"),
1707                         };
1708                         err.span_suggestion_verbose(
1709                             span,
1710                             "consider relaxing the implicit `Sized` restriction",
1711                             format!("{} ?Sized", separator),
1712                             Applicability::MachineApplicable,
1713                         );
1714                         return;
1715                     }
1716                 }
1717             }
1718         }
1719     }
1720
1721     fn is_recursive_obligation(
1722         &self,
1723         obligated_types: &mut Vec<&ty::TyS<'tcx>>,
1724         cause_code: &ObligationCauseCode<'tcx>,
1725     ) -> bool {
1726         if let ObligationCauseCode::BuiltinDerivedObligation(ref data) = cause_code {
1727             let parent_trait_ref = self.resolve_vars_if_possible(&data.parent_trait_ref);
1728
1729             if obligated_types.iter().any(|ot| ot == &parent_trait_ref.skip_binder().self_ty()) {
1730                 return true;
1731             }
1732         }
1733         false
1734     }
1735 }
1736
1737 pub fn recursive_type_with_infinite_size_error(
1738     tcx: TyCtxt<'tcx>,
1739     type_def_id: DefId,
1740 ) -> DiagnosticBuilder<'tcx> {
1741     assert!(type_def_id.is_local());
1742     let span = tcx.hir().span_if_local(type_def_id).unwrap();
1743     let span = tcx.sess.source_map().guess_head_span(span);
1744     let mut err = struct_span_err!(
1745         tcx.sess,
1746         span,
1747         E0072,
1748         "recursive type `{}` has infinite size",
1749         tcx.def_path_str(type_def_id)
1750     );
1751     err.span_label(span, "recursive type has infinite size");
1752     err.help(&format!(
1753         "insert indirection (e.g., a `Box`, `Rc`, or `&`) \
1754                            at some point to make `{}` representable",
1755         tcx.def_path_str(type_def_id)
1756     ));
1757     err
1758 }
1759
1760 /// Summarizes information
1761 #[derive(Clone)]
1762 pub enum ArgKind {
1763     /// An argument of non-tuple type. Parameters are (name, ty)
1764     Arg(String, String),
1765
1766     /// An argument of tuple type. For a "found" argument, the span is
1767     /// the locationo in the source of the pattern. For a "expected"
1768     /// argument, it will be None. The vector is a list of (name, ty)
1769     /// strings for the components of the tuple.
1770     Tuple(Option<Span>, Vec<(String, String)>),
1771 }
1772
1773 impl ArgKind {
1774     fn empty() -> ArgKind {
1775         ArgKind::Arg("_".to_owned(), "_".to_owned())
1776     }
1777
1778     /// Creates an `ArgKind` from the expected type of an
1779     /// argument. It has no name (`_`) and an optional source span.
1780     pub fn from_expected_ty(t: Ty<'_>, span: Option<Span>) -> ArgKind {
1781         match t.kind {
1782             ty::Tuple(ref tys) => ArgKind::Tuple(
1783                 span,
1784                 tys.iter().map(|ty| ("_".to_owned(), ty.to_string())).collect::<Vec<_>>(),
1785             ),
1786             _ => ArgKind::Arg("_".to_owned(), t.to_string()),
1787         }
1788     }
1789 }