src/librustc/infer/error_reporting/mod.rs

   1 // Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! Error Reporting Code for the inference engine
  12 //!
  13 //! Because of the way inference, and in particular region inference,
  14 //! works, it often happens that errors are not detected until far after
  15 //! the relevant line of code has been type-checked. Therefore, there is
  16 //! an elaborate system to track why a particular constraint in the
  17 //! inference graph arose so that we can explain to the user what gave
  18 //! rise to a particular error.
  19 //!
  20 //! The basis of the system are the "origin" types. An "origin" is the
  21 //! reason that a constraint or inference variable arose. There are
  22 //! different "origin" enums for different kinds of constraints/variables
  23 //! (e.g., `TypeOrigin`, `RegionVariableOrigin`). An origin always has
  24 //! a span, but also more information so that we can generate a meaningful
  25 //! error message.
  26 //!
  27 //! Having a catalog of all the different reasons an error can arise is
  28 //! also useful for other reasons, like cross-referencing FAQs etc, though
  29 //! we are not really taking advantage of this yet.
  30 //!
  31 //! # Region Inference
  32 //!
  33 //! Region inference is particularly tricky because it always succeeds "in
  34 //! the moment" and simply registers a constraint. Then, at the end, we
  35 //! can compute the full graph and report errors, so we need to be able to
  36 //! store and later report what gave rise to the conflicting constraints.
  37 //!
  38 //! # Subtype Trace
  39 //!
  40 //! Determining whether `T1 <: T2` often involves a number of subtypes and
  41 //! subconstraints along the way. A "TypeTrace" is an extended version
  42 //! of an origin that traces the types and other values that were being
  43 //! compared. It is not necessarily comprehensive (in fact, at the time of
  44 //! this writing it only tracks the root values being compared) but I'd
  45 //! like to extend it to include significant "waypoints". For example, if
  46 //! you are comparing `(T1, T2) <: (T3, T4)`, and the problem is that `T2
  47 //! <: T4` fails, I'd like the trace to include enough information to say
  48 //! "in the 2nd element of the tuple". Similarly, failures when comparing
  49 //! arguments or return types in fn types should be able to cite the
  50 //! specific position, etc.
  51 //!
  52 //! # Reality vs plan
  53 //!
  54 //! Of course, there is still a LOT of code in typeck that has yet to be
  55 //! ported to this system, and which relies on string concatenation at the
  56 //! time of error detection.
  57
  58 use super::lexical_region_resolve::RegionResolutionError;
  59 use super::region_constraints::GenericKind;
  60 use super::{InferCtxt, RegionVariableOrigin, SubregionOrigin, TypeTrace, ValuePairs};
  61 use infer::{self, SuppressRegionErrors};
  62
  63 use errors::{Applicability, DiagnosticBuilder, DiagnosticStyledString};
  64 use hir;
  65 use hir::def_id::DefId;
  66 use hir::Node;
  67 use middle::region;
  68 use std::{cmp, fmt};
  69 use syntax::ast::DUMMY_NODE_ID;
  70 use syntax_pos::{Pos, Span};
  71 use traits::{ObligationCause, ObligationCauseCode};
  72 use ty::error::TypeError;
  73 use ty::{self, subst::Subst, Region, Ty, TyCtxt, TyKind, TypeFoldable};
  74
  75 mod note;
  76
  77 mod need_type_info;
  78
  79 pub mod nice_region_error;
  80
  81 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
  82     pub fn note_and_explain_region(
  83         self,
  84         region_scope_tree: &region::ScopeTree,
  85         err: &mut DiagnosticBuilder<'_>,
  86         prefix: &str,
  87         region: ty::Region<'tcx>,
  88         suffix: &str,
  89     ) {
  90         let (description, span) = match *region {
  91             ty::ReScope(scope) => {
  92                 let new_string;
  93                 let unknown_scope = || {
  94                     format!(
  95                         "{}unknown scope: {:?}{}.  Please report a bug.",
  96                         prefix, scope, suffix
  97                     )
  98                 };
  99                 let span = scope.span(self, region_scope_tree);
 100                 let tag = match self.hir.find(scope.node_id(self, region_scope_tree)) {
 101                     Some(Node::Block(_)) => "block",
 102                     Some(Node::Expr(expr)) => match expr.node {
 103                         hir::ExprKind::Call(..) => "call",
 104                         hir::ExprKind::MethodCall(..) => "method call",
 105                         hir::ExprKind::Match(.., hir::MatchSource::IfLetDesugar { .. }) => "if let",
 106                         hir::ExprKind::Match(.., hir::MatchSource::WhileLetDesugar) => "while let",
 107                         hir::ExprKind::Match(.., hir::MatchSource::ForLoopDesugar) => "for",
 108                         hir::ExprKind::Match(..) => "match",
 109                         _ => "expression",
 110                     },
 111                     Some(Node::Stmt(_)) => "statement",
 112                     Some(Node::Item(it)) => Self::item_scope_tag(&it),
 113                     Some(Node::TraitItem(it)) => Self::trait_item_scope_tag(&it),
 114                     Some(Node::ImplItem(it)) => Self::impl_item_scope_tag(&it),
 115                     Some(_) | None => {
 116                         err.span_note(span, &unknown_scope());
 117                         return;
 118                     }
 119                 };
 120                 let scope_decorated_tag = match scope.data {
 121                     region::ScopeData::Node => tag,
 122                     region::ScopeData::CallSite => "scope of call-site for function",
 123                     region::ScopeData::Arguments => "scope of function body",
 124                     region::ScopeData::Destruction => {
 125                         new_string = format!("destruction scope surrounding {}", tag);
 126                         &new_string[..]
 127                     }
 128                     region::ScopeData::Remainder(first_statement_index) => {
 129                         new_string = format!(
 130                             "block suffix following statement {}",
 131                             first_statement_index.index()
 132                         );
 133                         &new_string[..]
 134                     }
 135                 };
 136                 self.explain_span(scope_decorated_tag, span)
 137             }
 138
 139             ty::ReEarlyBound(_) | ty::ReFree(_) | ty::ReStatic => {
 140                 self.msg_span_from_free_region(region)
 141             }
 142
 143             ty::ReEmpty => ("the empty lifetime".to_owned(), None),
 144
 145             // FIXME(#13998) RePlaceholder should probably print like
 146             // ReFree rather than dumping Debug output on the user.
 147             //
 148             // We shouldn't really be having unification failures with ReVar
 149             // and ReLateBound though.
 150             ty::RePlaceholder(..) | ty::ReVar(_) | ty::ReLateBound(..) | ty::ReErased => {
 151                 (format!("lifetime {:?}", region), None)
 152             }
 153
 154             // We shouldn't encounter an error message with ReClosureBound.
 155             ty::ReClosureBound(..) => {
 156                 bug!("encountered unexpected ReClosureBound: {:?}", region,);
 157             }
 158         };
 159
 160         TyCtxt::emit_msg_span(err, prefix, description, span, suffix);
 161     }
 162
 163     pub fn note_and_explain_free_region(
 164         self,
 165         err: &mut DiagnosticBuilder<'_>,
 166         prefix: &str,
 167         region: ty::Region<'tcx>,
 168         suffix: &str,
 169     ) {
 170         let (description, span) = self.msg_span_from_free_region(region);
 171
 172         TyCtxt::emit_msg_span(err, prefix, description, span, suffix);
 173     }
 174
 175     fn msg_span_from_free_region(self, region: ty::Region<'tcx>) -> (String, Option<Span>) {
 176         match *region {
 177             ty::ReEarlyBound(_) | ty::ReFree(_) => {
 178                 self.msg_span_from_early_bound_and_free_regions(region)
 179             }
 180             ty::ReStatic => ("the static lifetime".to_owned(), None),
 181             _ => bug!("{:?}", region),
 182         }
 183     }
 184
 185     fn msg_span_from_early_bound_and_free_regions(
 186         self,
 187         region: ty::Region<'tcx>,
 188     ) -> (String, Option<Span>) {
 189         let cm = self.sess.source_map();
 190
 191         let scope = region.free_region_binding_scope(self);
 192         let node = self.hir.as_local_node_id(scope).unwrap_or(DUMMY_NODE_ID);
 193         let tag = match self.hir.find(node) {
 194             Some(Node::Block(_)) | Some(Node::Expr(_)) => "body",
 195             Some(Node::Item(it)) => Self::item_scope_tag(&it),
 196             Some(Node::TraitItem(it)) => Self::trait_item_scope_tag(&it),
 197             Some(Node::ImplItem(it)) => Self::impl_item_scope_tag(&it),
 198             _ => unreachable!(),
 199         };
 200         let (prefix, span) = match *region {
 201             ty::ReEarlyBound(ref br) => {
 202                 let mut sp = cm.def_span(self.hir.span(node));
 203                 if let Some(param) = self.hir
 204                     .get_generics(scope)
 205                     .and_then(|generics| generics.get_named(&br.name))
 206                 {
 207                     sp = param.span;
 208                 }
 209                 (format!("the lifetime {} as defined on", br.name), sp)
 210             }
 211             ty::ReFree(ty::FreeRegion {
 212                 bound_region: ty::BoundRegion::BrNamed(_, ref name),
 213                 ..
 214             }) => {
 215                 let mut sp = cm.def_span(self.hir.span(node));
 216                 if let Some(param) = self.hir
 217                     .get_generics(scope)
 218                     .and_then(|generics| generics.get_named(&name))
 219                 {
 220                     sp = param.span;
 221                 }
 222                 (format!("the lifetime {} as defined on", name), sp)
 223             }
 224             ty::ReFree(ref fr) => match fr.bound_region {
 225                 ty::BrAnon(idx) => (
 226                     format!("the anonymous lifetime #{} defined on", idx + 1),
 227                     self.hir.span(node),
 228                 ),
 229                 ty::BrFresh(_) => (
 230                     "an anonymous lifetime defined on".to_owned(),
 231                     self.hir.span(node),
 232                 ),
 233                 _ => (
 234                     format!("the lifetime {} as defined on", fr.bound_region),
 235                     cm.def_span(self.hir.span(node)),
 236                 ),
 237             },
 238             _ => bug!(),
 239         };
 240         let (msg, opt_span) = self.explain_span(tag, span);
 241         (format!("{} {}", prefix, msg), opt_span)
 242     }
 243
 244     fn emit_msg_span(
 245         err: &mut DiagnosticBuilder<'_>,
 246         prefix: &str,
 247         description: String,
 248         span: Option<Span>,
 249         suffix: &str,
 250     ) {
 251         let message = format!("{}{}{}", prefix, description, suffix);
 252
 253         if let Some(span) = span {
 254             err.span_note(span, &message);
 255         } else {
 256             err.note(&message);
 257         }
 258     }
 259
 260     fn item_scope_tag(item: &hir::Item) -> &'static str {
 261         match item.node {
 262             hir::ItemKind::Impl(..) => "impl",
 263             hir::ItemKind::Struct(..) => "struct",
 264             hir::ItemKind::Union(..) => "union",
 265             hir::ItemKind::Enum(..) => "enum",
 266             hir::ItemKind::Trait(..) => "trait",
 267             hir::ItemKind::Fn(..) => "function body",
 268             _ => "item",
 269         }
 270     }
 271
 272     fn trait_item_scope_tag(item: &hir::TraitItem) -> &'static str {
 273         match item.node {
 274             hir::TraitItemKind::Method(..) => "method body",
 275             hir::TraitItemKind::Const(..) | hir::TraitItemKind::Type(..) => "associated item",
 276         }
 277     }
 278
 279     fn impl_item_scope_tag(item: &hir::ImplItem) -> &'static str {
 280         match item.node {
 281             hir::ImplItemKind::Method(..) => "method body",
 282             hir::ImplItemKind::Const(..)
 283             | hir::ImplItemKind::Existential(..)
 284             | hir::ImplItemKind::Type(..) => "associated item",
 285         }
 286     }
 287
 288     fn explain_span(self, heading: &str, span: Span) -> (String, Option<Span>) {
 289         let lo = self.sess.source_map().lookup_char_pos_adj(span.lo());
 290         (
 291             format!("the {} at {}:{}", heading, lo.line, lo.col.to_usize() + 1),
 292             Some(span),
 293         )
 294     }
 295 }
 296
 297 impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
 298     pub fn report_region_errors(
 299         &self,
 300         region_scope_tree: &region::ScopeTree,
 301         errors: &Vec<RegionResolutionError<'tcx>>,
 302         suppress: SuppressRegionErrors,
 303     ) {
 304         debug!(
 305             "report_region_errors(): {} errors to start, suppress = {:?}",
 306             errors.len(),
 307             suppress
 308         );
 309
 310         if suppress.suppressed() {
 311             return;
 312         }
 313
 314         // try to pre-process the errors, which will group some of them
 315         // together into a `ProcessedErrors` group:
 316         let errors = self.process_errors(errors);
 317
 318         debug!(
 319             "report_region_errors: {} errors after preprocessing",
 320             errors.len()
 321         );
 322
 323         for error in errors {
 324             debug!("report_region_errors: error = {:?}", error);
 325
 326             if !self.try_report_nice_region_error(&error) {
 327                 match error.clone() {
 328                     // These errors could indicate all manner of different
 329                     // problems with many different solutions. Rather
 330                     // than generate a "one size fits all" error, what we
 331                     // attempt to do is go through a number of specific
 332                     // scenarios and try to find the best way to present
 333                     // the error. If all of these fails, we fall back to a rather
 334                     // general bit of code that displays the error information
 335                     RegionResolutionError::ConcreteFailure(origin, sub, sup) => {
 336                         self.report_concrete_failure(region_scope_tree, origin, sub, sup)
 337                             .emit();
 338                     }
 339
 340                     RegionResolutionError::GenericBoundFailure(origin, param_ty, sub) => {
 341                         self.report_generic_bound_failure(
 342                             region_scope_tree,
 343                             origin.span(),
 344                             Some(origin),
 345                             param_ty,
 346                             sub,
 347                         );
 348                     }
 349
 350                     RegionResolutionError::SubSupConflict(
 351                         var_origin,
 352                         sub_origin,
 353                         sub_r,
 354                         sup_origin,
 355                         sup_r,
 356                     ) => {
 357                         self.report_sub_sup_conflict(
 358                             region_scope_tree,
 359                             var_origin,
 360                             sub_origin,
 361                             sub_r,
 362                             sup_origin,
 363                             sup_r,
 364                         );
 365                     }
 366                 }
 367             }
 368         }
 369     }
 370
 371     // This method goes through all the errors and try to group certain types
 372     // of error together, for the purpose of suggesting explicit lifetime
 373     // parameters to the user. This is done so that we can have a more
 374     // complete view of what lifetimes should be the same.
 375     // If the return value is an empty vector, it means that processing
 376     // failed (so the return value of this method should not be used).
 377     //
 378     // The method also attempts to weed out messages that seem like
 379     // duplicates that will be unhelpful to the end-user. But
 380     // obviously it never weeds out ALL errors.
 381     fn process_errors(
 382         &self,
 383         errors: &Vec<RegionResolutionError<'tcx>>,
 384     ) -> Vec<RegionResolutionError<'tcx>> {
 385         debug!("process_errors()");
 386
 387         // We want to avoid reporting generic-bound failures if we can
 388         // avoid it: these have a very high rate of being unhelpful in
 389         // practice. This is because they are basically secondary
 390         // checks that test the state of the region graph after the
 391         // rest of inference is done, and the other kinds of errors
 392         // indicate that the region constraint graph is internally
 393         // inconsistent, so these test results are likely to be
 394         // meaningless.
 395         //
 396         // Therefore, we filter them out of the list unless they are
 397         // the only thing in the list.
 398
 399         let is_bound_failure = |e: &RegionResolutionError<'tcx>| match *e {
 400             RegionResolutionError::GenericBoundFailure(..) => true,
 401             RegionResolutionError::ConcreteFailure(..)
 402             | RegionResolutionError::SubSupConflict(..) => false,
 403         };
 404
 405         let mut errors = if errors.iter().all(|e| is_bound_failure(e)) {
 406             errors.clone()
 407         } else {
 408             errors
 409             .iter()
 410             .filter(|&e| !is_bound_failure(e))
 411             .cloned()
 412             .collect()
 413         };
 414
 415         // sort the errors by span, for better error message stability.
 416         errors.sort_by_key(|u| match *u {
 417             RegionResolutionError::ConcreteFailure(ref sro, _, _) => sro.span(),
 418             RegionResolutionError::GenericBoundFailure(ref sro, _, _) => sro.span(),
 419             RegionResolutionError::SubSupConflict(ref rvo, _, _, _, _) => rvo.span(),
 420         });
 421         errors
 422     }
 423
 424     /// Adds a note if the types come from similarly named crates
 425     fn check_and_note_conflicting_crates(
 426         &self,
 427         err: &mut DiagnosticBuilder<'_>,
 428         terr: &TypeError<'tcx>,
 429         sp: Span,
 430     ) {
 431         let report_path_match = |err: &mut DiagnosticBuilder<'_>, did1: DefId, did2: DefId| {
 432             // Only external crates, if either is from a local
 433             // module we could have false positives
 434             if !(did1.is_local() || did2.is_local()) && did1.krate != did2.krate {
 435                 let exp_path = self.tcx.item_path_str(did1);
 436                 let found_path = self.tcx.item_path_str(did2);
 437                 let exp_abs_path = self.tcx.absolute_item_path_str(did1);
 438                 let found_abs_path = self.tcx.absolute_item_path_str(did2);
 439                 // We compare strings because DefPath can be different
 440                 // for imported and non-imported crates
 441                 if exp_path == found_path || exp_abs_path == found_abs_path {
 442                     let crate_name = self.tcx.crate_name(did1.krate);
 443                     err.span_note(
 444                         sp,
 445                         &format!(
 446                             "Perhaps two different versions \
 447                              of crate `{}` are being used?",
 448                             crate_name
 449                         ),
 450                     );
 451                 }
 452             }
 453         };
 454         match *terr {
 455             TypeError::Sorts(ref exp_found) => {
 456                 // if they are both "path types", there's a chance of ambiguity
 457                 // due to different versions of the same crate
 458                 if let (&ty::Adt(exp_adt, _), &ty::Adt(found_adt, _))
 459                      = (&exp_found.expected.sty, &exp_found.found.sty)
 460                 {
 461                     report_path_match(err, exp_adt.did, found_adt.did);
 462                 }
 463             }
 464             TypeError::Traits(ref exp_found) => {
 465                 report_path_match(err, exp_found.expected, exp_found.found);
 466             }
 467             _ => (), // FIXME(#22750) handle traits and stuff
 468         }
 469     }
 470
 471     fn note_error_origin(&self, err: &mut DiagnosticBuilder<'tcx>, cause: &ObligationCause<'tcx>) {
 472         match cause.code {
 473             ObligationCauseCode::MatchExpressionArm { arm_span, source } => match source {
 474                 hir::MatchSource::IfLetDesugar { .. } => {
 475                     let msg = "`if let` arm with an incompatible type";
 476                     if self.tcx.sess.source_map().is_multiline(arm_span) {
 477                         err.span_note(arm_span, msg);
 478                     } else {
 479                         err.span_label(arm_span, msg);
 480                     }
 481                 }
 482                 hir::MatchSource::TryDesugar => {}
 483                 _ => {
 484                     let msg = "match arm with an incompatible type";
 485                     if self.tcx.sess.source_map().is_multiline(arm_span) {
 486                         err.span_note(arm_span, msg);
 487                     } else {
 488                         err.span_label(arm_span, msg);
 489                     }
 490                 }
 491             },
 492             _ => (),
 493         }
 494     }
 495
 496     /// Given that `other_ty` is the same as a type argument for `name` in `sub`, populate `value`
 497     /// highlighting `name` and every type argument that isn't at `pos` (which is `other_ty`), and
 498     /// populate `other_value` with `other_ty`.
 499     ///
 500     /// ```text
 501     /// Foo<Bar<Qux>>
 502     /// ^^^^--------^ this is highlighted
 503     /// |   |
 504     /// |   this type argument is exactly the same as the other type, not highlighted
 505     /// this is highlighted
 506     /// Bar<Qux>
 507     /// -------- this type is the same as a type argument in the other type, not highlighted
 508     /// ```
 509     fn highlight_outer(
 510         &self,
 511         value: &mut DiagnosticStyledString,
 512         other_value: &mut DiagnosticStyledString,
 513         name: String,
 514         sub: &ty::subst::Substs<'tcx>,
 515         pos: usize,
 516         other_ty: &Ty<'tcx>,
 517     ) {
 518         // `value` and `other_value` hold two incomplete type representation for display.
 519         // `name` is the path of both types being compared. `sub`
 520         value.push_highlighted(name);
 521         let len = sub.len();
 522         if len > 0 {
 523             value.push_highlighted("<");
 524         }
 525
 526         // Output the lifetimes for the first type
 527         let lifetimes = sub.regions()
 528             .map(|lifetime| {
 529                 let s = lifetime.to_string();
 530                 if s.is_empty() {
 531                     "'_".to_string()
 532                 } else {
 533                     s
 534                 }
 535             })
 536             .collect::<Vec<_>>()
 537             .join(", ");
 538         if !lifetimes.is_empty() {
 539             if sub.regions().count() < len {
 540                 value.push_normal(lifetimes + &", ");
 541             } else {
 542                 value.push_normal(lifetimes);
 543             }
 544         }
 545
 546         // Highlight all the type arguments that aren't at `pos` and compare the type argument at
 547         // `pos` and `other_ty`.
 548         for (i, type_arg) in sub.types().enumerate() {
 549             if i == pos {
 550                 let values = self.cmp(type_arg, other_ty);
 551                 value.0.extend((values.0).0);
 552                 other_value.0.extend((values.1).0);
 553             } else {
 554                 value.push_highlighted(type_arg.to_string());
 555             }
 556
 557             if len > 0 && i != len - 1 {
 558                 value.push_normal(", ");
 559             }
 560             //self.push_comma(&mut value, &mut other_value, len, i);
 561         }
 562         if len > 0 {
 563             value.push_highlighted(">");
 564         }
 565     }
 566
 567     /// If `other_ty` is the same as a type argument present in `sub`, highlight `path` in `t1_out`,
 568     /// as that is the difference to the other type.
 569     ///
 570     /// For the following code:
 571     ///
 572     /// ```norun
 573     /// let x: Foo<Bar<Qux>> = foo::<Bar<Qux>>();
 574     /// ```
 575     ///
 576     /// The type error output will behave in the following way:
 577     ///
 578     /// ```text
 579     /// Foo<Bar<Qux>>
 580     /// ^^^^--------^ this is highlighted
 581     /// |   |
 582     /// |   this type argument is exactly the same as the other type, not highlighted
 583     /// this is highlighted
 584     /// Bar<Qux>
 585     /// -------- this type is the same as a type argument in the other type, not highlighted
 586     /// ```
 587     fn cmp_type_arg(
 588         &self,
 589         mut t1_out: &mut DiagnosticStyledString,
 590         mut t2_out: &mut DiagnosticStyledString,
 591         path: String,
 592         sub: &ty::subst::Substs<'tcx>,
 593         other_path: String,
 594         other_ty: &Ty<'tcx>,
 595     ) -> Option<()> {
 596         for (i, ta) in sub.types().enumerate() {
 597             if &ta == other_ty {
 598                 self.highlight_outer(&mut t1_out, &mut t2_out, path, sub, i, &other_ty);
 599                 return Some(());
 600             }
 601             if let &ty::Adt(def, _) = &ta.sty {
 602                 let path_ = self.tcx.item_path_str(def.did.clone());
 603                 if path_ == other_path {
 604                     self.highlight_outer(&mut t1_out, &mut t2_out, path, sub, i, &other_ty);
 605                     return Some(());
 606                 }
 607             }
 608         }
 609         None
 610     }
 611
 612     /// Add a `,` to the type representation only if it is appropriate.
 613     fn push_comma(
 614         &self,
 615         value: &mut DiagnosticStyledString,
 616         other_value: &mut DiagnosticStyledString,
 617         len: usize,
 618         pos: usize,
 619     ) {
 620         if len > 0 && pos != len - 1 {
 621             value.push_normal(", ");
 622             other_value.push_normal(", ");
 623         }
 624     }
 625
 626     /// For generic types with parameters with defaults, remove the parameters corresponding to
 627     /// the defaults. This repeats a lot of the logic found in `PrintContext::parameterized`.
 628     fn strip_generic_default_params(
 629         &self,
 630         def_id: DefId,
 631         substs: &ty::subst::Substs<'tcx>,
 632     ) -> &'tcx ty::subst::Substs<'tcx> {
 633         let generics = self.tcx.generics_of(def_id);
 634         let mut num_supplied_defaults = 0;
 635         let mut type_params = generics
 636             .params
 637             .iter()
 638             .rev()
 639             .filter_map(|param| match param.kind {
 640                 ty::GenericParamDefKind::Lifetime => None,
 641                 ty::GenericParamDefKind::Type { has_default, .. } => {
 642                     Some((param.def_id, has_default))
 643                 }
 644             })
 645             .peekable();
 646         let has_default = {
 647             let has_default = type_params.peek().map(|(_, has_default)| has_default);
 648             *has_default.unwrap_or(&false)
 649         };
 650         if has_default {
 651             let types = substs.types().rev();
 652             for ((def_id, has_default), actual) in type_params.zip(types) {
 653                 if !has_default {
 654                     break;
 655                 }
 656                 if self.tcx.type_of(def_id).subst(self.tcx, substs) != actual {
 657                     break;
 658                 }
 659                 num_supplied_defaults += 1;
 660             }
 661         }
 662         let len = generics.params.len();
 663         let mut generics = generics.clone();
 664         generics.params.truncate(len - num_supplied_defaults);
 665         substs.truncate_to(self.tcx, &generics)
 666     }
 667
 668     /// Compare two given types, eliding parts that are the same between them and highlighting
 669     /// relevant differences, and return two representation of those types for highlighted printing.
 670     fn cmp(&self, t1: Ty<'tcx>, t2: Ty<'tcx>) -> (DiagnosticStyledString, DiagnosticStyledString) {
 671         fn equals<'tcx>(a: &Ty<'tcx>, b: &Ty<'tcx>) -> bool {
 672             match (&a.sty, &b.sty) {
 673                 (a, b) if *a == *b => true,
 674                 (&ty::Int(_), &ty::Infer(ty::InferTy::IntVar(_)))
 675                 | (&ty::Infer(ty::InferTy::IntVar(_)), &ty::Int(_))
 676                 | (&ty::Infer(ty::InferTy::IntVar(_)), &ty::Infer(ty::InferTy::IntVar(_)))
 677                 | (&ty::Float(_), &ty::Infer(ty::InferTy::FloatVar(_)))
 678                 | (&ty::Infer(ty::InferTy::FloatVar(_)), &ty::Float(_))
 679                 | (&ty::Infer(ty::InferTy::FloatVar(_)), &ty::Infer(ty::InferTy::FloatVar(_))) => {
 680                     true
 681                 }
 682                 _ => false,
 683             }
 684         }
 685
 686         fn push_ty_ref<'tcx>(
 687             r: &ty::Region<'tcx>,
 688             ty: Ty<'tcx>,
 689             mutbl: hir::Mutability,
 690             s: &mut DiagnosticStyledString,
 691         ) {
 692             let r = &r.to_string();
 693             s.push_highlighted(format!(
 694                 "&{}{}{}",
 695                 r,
 696                 if r == "" { "" } else { " " },
 697                 if mutbl == hir::MutMutable { "mut " } else { "" }
 698             ));
 699             s.push_normal(ty.to_string());
 700         }
 701
 702         match (&t1.sty, &t2.sty) {
 703             (&ty::Adt(def1, sub1), &ty::Adt(def2, sub2)) => {
 704                 let sub_no_defaults_1 = self.strip_generic_default_params(def1.did, sub1);
 705                 let sub_no_defaults_2 = self.strip_generic_default_params(def2.did, sub2);
 706                 let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new());
 707                 let path1 = self.tcx.item_path_str(def1.did.clone());
 708                 let path2 = self.tcx.item_path_str(def2.did.clone());
 709                 if def1.did == def2.did {
 710                     // Easy case. Replace same types with `_` to shorten the output and highlight
 711                     // the differing ones.
 712                     //     let x: Foo<Bar, Qux> = y::<Foo<Quz, Qux>>();
 713                     //     Foo<Bar, _>
 714                     //     Foo<Quz, _>
 715                     //         ---  ^ type argument elided
 716                     //         |
 717                     //         highlighted in output
 718                     values.0.push_normal(path1);
 719                     values.1.push_normal(path2);
 720
 721                     // Avoid printing out default generic parameters that are common to both
 722                     // types.
 723                     let len1 = sub_no_defaults_1.len();
 724                     let len2 = sub_no_defaults_2.len();
 725                     let common_len = cmp::min(len1, len2);
 726                     let remainder1: Vec<_> = sub1.types().skip(common_len).collect();
 727                     let remainder2: Vec<_> = sub2.types().skip(common_len).collect();
 728                     let common_default_params = remainder1
 729                         .iter()
 730                         .rev()
 731                         .zip(remainder2.iter().rev())
 732                         .filter(|(a, b)| a == b)
 733                         .count();
 734                     let len = sub1.len() - common_default_params;
 735
 736                     // Only draw `<...>` if there're lifetime/type arguments.
 737                     if len > 0 {
 738                         values.0.push_normal("<");
 739                         values.1.push_normal("<");
 740                     }
 741
 742                     fn lifetime_display(lifetime: Region<'_>) -> String {
 743                         let s = lifetime.to_string();
 744                         if s.is_empty() {
 745                             "'_".to_string()
 746                         } else {
 747                             s
 748                         }
 749                     }
 750                     // At one point we'd like to elide all lifetimes here, they are irrelevant for
 751                     // all diagnostics that use this output
 752                     //
 753                     //     Foo<'x, '_, Bar>
 754                     //     Foo<'y, '_, Qux>
 755                     //         ^^  ^^  --- type arguments are not elided
 756                     //         |   |
 757                     //         |   elided as they were the same
 758                     //         not elided, they were different, but irrelevant
 759                     let lifetimes = sub1.regions().zip(sub2.regions());
 760                     for (i, lifetimes) in lifetimes.enumerate() {
 761                         let l1 = lifetime_display(lifetimes.0);
 762                         let l2 = lifetime_display(lifetimes.1);
 763                         if l1 == l2 {
 764                             values.0.push_normal("'_");
 765                             values.1.push_normal("'_");
 766                         } else {
 767                             values.0.push_highlighted(l1);
 768                             values.1.push_highlighted(l2);
 769                         }
 770                         self.push_comma(&mut values.0, &mut values.1, len, i);
 771                     }
 772
 773                     // We're comparing two types with the same path, so we compare the type
 774                     // arguments for both. If they are the same, do not highlight and elide from the
 775                     // output.
 776                     //     Foo<_, Bar>
 777                     //     Foo<_, Qux>
 778                     //         ^ elided type as this type argument was the same in both sides
 779                     let type_arguments = sub1.types().zip(sub2.types());
 780                     let regions_len = sub1.regions().count();
 781                     for (i, (ta1, ta2)) in type_arguments.take(len).enumerate() {
 782                         let i = i + regions_len;
 783                         if ta1 == ta2 {
 784                             values.0.push_normal("_");
 785                             values.1.push_normal("_");
 786                         } else {
 787                             let (x1, x2) = self.cmp(ta1, ta2);
 788                             (values.0).0.extend(x1.0);
 789                             (values.1).0.extend(x2.0);
 790                         }
 791                         self.push_comma(&mut values.0, &mut values.1, len, i);
 792                     }
 793
 794                     // Close the type argument bracket.
 795                     // Only draw `<...>` if there're lifetime/type arguments.
 796                     if len > 0 {
 797                         values.0.push_normal(">");
 798                         values.1.push_normal(">");
 799                     }
 800                     values
 801                 } else {
 802                     // Check for case:
 803                     //     let x: Foo<Bar<Qux> = foo::<Bar<Qux>>();
 804                     //     Foo<Bar<Qux>
 805                     //         ------- this type argument is exactly the same as the other type
 806                     //     Bar<Qux>
 807                     if self.cmp_type_arg(
 808                         &mut values.0,
 809                         &mut values.1,
 810                         path1.clone(),
 811                         sub_no_defaults_1,
 812                         path2.clone(),
 813                         &t2,
 814                     ).is_some()
 815                     {
 816                         return values;
 817                     }
 818                     // Check for case:
 819                     //     let x: Bar<Qux> = y:<Foo<Bar<Qux>>>();
 820                     //     Bar<Qux>
 821                     //     Foo<Bar<Qux>>
 822                     //         ------- this type argument is exactly the same as the other type
 823                     if self.cmp_type_arg(
 824                         &mut values.1,
 825                         &mut values.0,
 826                         path2,
 827                         sub_no_defaults_2,
 828                         path1,
 829                         &t1,
 830                     ).is_some()
 831                     {
 832                         return values;
 833                     }
 834
 835                     // We couldn't find anything in common, highlight everything.
 836                     //     let x: Bar<Qux> = y::<Foo<Zar>>();
 837                     (
 838                         DiagnosticStyledString::highlighted(t1.to_string()),
 839                         DiagnosticStyledString::highlighted(t2.to_string()),
 840                     )
 841                 }
 842             }
 843
 844             // When finding T != &T, highlight only the borrow
 845             (&ty::Ref(r1, ref_ty1, mutbl1), _) if equals(&ref_ty1, &t2) => {
 846                 let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new());
 847                 push_ty_ref(&r1, ref_ty1, mutbl1, &mut values.0);
 848                 values.1.push_normal(t2.to_string());
 849                 values
 850             }
 851             (_, &ty::Ref(r2, ref_ty2, mutbl2)) if equals(&t1, &ref_ty2) => {
 852                 let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new());
 853                 values.0.push_normal(t1.to_string());
 854                 push_ty_ref(&r2, ref_ty2, mutbl2, &mut values.1);
 855                 values
 856             }
 857
 858             // When encountering &T != &mut T, highlight only the borrow
 859             (&ty::Ref(r1, ref_ty1, mutbl1), &ty::Ref(r2, ref_ty2, mutbl2))
 860                 if equals(&ref_ty1, &ref_ty2) =>
 861             {
 862                 let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new());
 863                 push_ty_ref(&r1, ref_ty1, mutbl1, &mut values.0);
 864                 push_ty_ref(&r2, ref_ty2, mutbl2, &mut values.1);
 865                 values
 866             }
 867
 868             _ => {
 869                 if t1 == t2 {
 870                     // The two types are the same, elide and don't highlight.
 871                     (
 872                         DiagnosticStyledString::normal("_"),
 873                         DiagnosticStyledString::normal("_"),
 874                     )
 875                 } else {
 876                     // We couldn't find anything in common, highlight everything.
 877                     (
 878                         DiagnosticStyledString::highlighted(t1.to_string()),
 879                         DiagnosticStyledString::highlighted(t2.to_string()),
 880                     )
 881                 }
 882             }
 883         }
 884     }
 885
 886     pub fn note_type_err(
 887         &self,
 888         diag: &mut DiagnosticBuilder<'tcx>,
 889         cause: &ObligationCause<'tcx>,
 890         secondary_span: Option<(Span, String)>,
 891         mut values: Option<ValuePairs<'tcx>>,
 892         terr: &TypeError<'tcx>,
 893     ) {
 894         // For some types of errors, expected-found does not make
 895         // sense, so just ignore the values we were given.
 896         match terr {
 897             TypeError::CyclicTy(_) => {
 898                 values = None;
 899             }
 900             _ => {}
 901         }
 902
 903         let (expected_found, exp_found, is_simple_error) = match values {
 904             None => (None, None, false),
 905             Some(values) => {
 906                 let (is_simple_error, exp_found) = match values {
 907                     ValuePairs::Types(exp_found) => {
 908                         let is_simple_err =
 909                             exp_found.expected.is_primitive() && exp_found.found.is_primitive();
 910
 911                         (is_simple_err, Some(exp_found))
 912                     }
 913                     _ => (false, None),
 914                 };
 915                 let vals = match self.values_str(&values) {
 916                     Some((expected, found)) => Some((expected, found)),
 917                     None => {
 918                         // Derived error. Cancel the emitter.
 919                         self.tcx.sess.diagnostic().cancel(diag);
 920                         return;
 921                     }
 922                 };
 923                 (vals, exp_found, is_simple_error)
 924             }
 925         };
 926
 927         let span = cause.span(&self.tcx);
 928
 929         diag.span_label(span, terr.to_string());
 930         if let Some((sp, msg)) = secondary_span {
 931             diag.span_label(sp, msg);
 932         }
 933
 934         if let Some((expected, found)) = expected_found {
 935             match (terr, is_simple_error, expected == found) {
 936                 (&TypeError::Sorts(ref values), false, true) => {
 937                     diag.note_expected_found_extra(
 938                         &"type",
 939                         expected,
 940                         found,
 941                         &format!(" ({})", values.expected.sort_string(self.tcx)),
 942                         &format!(" ({})", values.found.sort_string(self.tcx)),
 943                     );
 944                 }
 945                 (_, false, _) => {
 946                     if let Some(exp_found) = exp_found {
 947                         let (def_id, ret_ty) = match exp_found.found.sty {
 948                             TyKind::FnDef(def, _) => {
 949                                 (Some(def), Some(self.tcx.fn_sig(def).output()))
 950                             }
 951                             _ => (None, None),
 952                         };
 953
 954                         let exp_is_struct = match exp_found.expected.sty {
 955                             TyKind::Adt(def, _) => def.is_struct(),
 956                             _ => false,
 957                         };
 958
 959                         if let (Some(def_id), Some(ret_ty)) = (def_id, ret_ty) {
 960                             if exp_is_struct && &exp_found.expected == ret_ty.skip_binder() {
 961                                 let message = format!(
 962                                     "did you mean `{}(/* fields */)`?",
 963                                     self.tcx.item_path_str(def_id)
 964                                 );
 965                                 diag.span_label(span, message);
 966                             }
 967                         }
 968                     }
 969
 970                     diag.note_expected_found(&"type", expected, found);
 971                 }
 972                 _ => (),
 973             }
 974         }
 975
 976         self.check_and_note_conflicting_crates(diag, terr, span);
 977         self.tcx.note_and_explain_type_err(diag, terr, span);
 978
 979         // It reads better to have the error origin as the final
 980         // thing.
 981         self.note_error_origin(diag, &cause);
 982     }
 983
 984     pub fn report_and_explain_type_error(
 985         &self,
 986         trace: TypeTrace<'tcx>,
 987         terr: &TypeError<'tcx>,
 988     ) -> DiagnosticBuilder<'tcx> {
 989         debug!(
 990             "report_and_explain_type_error(trace={:?}, terr={:?})",
 991             trace, terr
 992         );
 993
 994         let span = trace.cause.span(&self.tcx);
 995         let failure_code = trace.cause.as_failure_code(terr);
 996         let mut diag = match failure_code {
 997             FailureCode::Error0317(failure_str) => {
 998                 struct_span_err!(self.tcx.sess, span, E0317, "{}", failure_str)
 999             }
1000             FailureCode::Error0580(failure_str) => {
1001                 struct_span_err!(self.tcx.sess, span, E0580, "{}", failure_str)
1002             }
1003             FailureCode::Error0308(failure_str) => {
1004                 struct_span_err!(self.tcx.sess, span, E0308, "{}", failure_str)
1005             }
1006             FailureCode::Error0644(failure_str) => {
1007                 struct_span_err!(self.tcx.sess, span, E0644, "{}", failure_str)
1008             }
1009         };
1010         self.note_type_err(&mut diag, &trace.cause, None, Some(trace.values), terr);
1011         diag
1012     }
1013
1014     fn values_str(
1015         &self,
1016         values: &ValuePairs<'tcx>,
1017     ) -> Option<(DiagnosticStyledString, DiagnosticStyledString)> {
1018         match *values {
1019             infer::Types(ref exp_found) => self.expected_found_str_ty(exp_found),
1020             infer::Regions(ref exp_found) => self.expected_found_str(exp_found),
1021             infer::TraitRefs(ref exp_found) => self.expected_found_str(exp_found),
1022             infer::PolyTraitRefs(ref exp_found) => self.expected_found_str(exp_found),
1023         }
1024     }
1025
1026     fn expected_found_str_ty(
1027         &self,
1028         exp_found: &ty::error::ExpectedFound<Ty<'tcx>>,
1029     ) -> Option<(DiagnosticStyledString, DiagnosticStyledString)> {
1030         let exp_found = self.resolve_type_vars_if_possible(exp_found);
1031         if exp_found.references_error() {
1032             return None;
1033         }
1034
1035         Some(self.cmp(exp_found.expected, exp_found.found))
1036     }
1037
1038     /// Returns a string of the form "expected `{}`, found `{}`".
1039     fn expected_found_str<T: fmt::Display + TypeFoldable<'tcx>>(
1040         &self,
1041         exp_found: &ty::error::ExpectedFound<T>,
1042     ) -> Option<(DiagnosticStyledString, DiagnosticStyledString)> {
1043         let exp_found = self.resolve_type_vars_if_possible(exp_found);
1044         if exp_found.references_error() {
1045             return None;
1046         }
1047
1048         Some((
1049             DiagnosticStyledString::highlighted(exp_found.expected.to_string()),
1050             DiagnosticStyledString::highlighted(exp_found.found.to_string()),
1051         ))
1052     }
1053
1054     pub fn report_generic_bound_failure(
1055         &self,
1056         region_scope_tree: &region::ScopeTree,
1057         span: Span,
1058         origin: Option<SubregionOrigin<'tcx>>,
1059         bound_kind: GenericKind<'tcx>,
1060         sub: Region<'tcx>,
1061     ) {
1062         self.construct_generic_bound_failure(region_scope_tree, span, origin, bound_kind, sub)
1063             .emit()
1064     }
1065
1066     pub fn construct_generic_bound_failure(
1067         &self,
1068         region_scope_tree: &region::ScopeTree,
1069         span: Span,
1070         origin: Option<SubregionOrigin<'tcx>>,
1071         bound_kind: GenericKind<'tcx>,
1072         sub: Region<'tcx>,
1073     ) -> DiagnosticBuilder<'a> {
1074         // Attempt to obtain the span of the parameter so we can
1075         // suggest adding an explicit lifetime bound to it.
1076         let type_param_span = match (self.in_progress_tables, bound_kind) {
1077             (Some(ref table), GenericKind::Param(ref param)) => {
1078                 let table = table.borrow();
1079                 table.local_id_root.and_then(|did| {
1080                     let generics = self.tcx.generics_of(did);
1081                     // Account for the case where `did` corresponds to `Self`, which doesn't have
1082                     // the expected type argument.
1083                     if !param.is_self() {
1084                         let type_param = generics.type_param(param, self.tcx);
1085                         let hir = &self.tcx.hir;
1086                         hir.as_local_node_id(type_param.def_id).map(|id| {
1087                             // Get the `hir::Param` to verify whether it already has any bounds.
1088                             // We do this to avoid suggesting code that ends up as `T: 'a'b`,
1089                             // instead we suggest `T: 'a + 'b` in that case.
1090                             let mut has_bounds = false;
1091                             if let Node::GenericParam(ref param) = hir.get(id) {
1092                                 has_bounds = !param.bounds.is_empty();
1093                             }
1094                             let sp = hir.span(id);
1095                             // `sp` only covers `T`, change it so that it covers
1096                             // `T:` when appropriate
1097                             let sp = if has_bounds {
1098                                 sp.to(self.tcx
1099                                     .sess
1100                                     .source_map()
1101                                     .next_point(self.tcx.sess.source_map().next_point(sp)))
1102                             } else {
1103                                 sp
1104                             };
1105                             (sp, has_bounds)
1106                         })
1107                     } else {
1108                         None
1109                     }
1110                 })
1111             }
1112             _ => None,
1113         };
1114
1115         let labeled_user_string = match bound_kind {
1116             GenericKind::Param(ref p) => format!("the parameter type `{}`", p),
1117             GenericKind::Projection(ref p) => format!("the associated type `{}`", p),
1118         };
1119
1120         if let Some(SubregionOrigin::CompareImplMethodObligation {
1121             span,
1122             item_name,
1123             impl_item_def_id,
1124             trait_item_def_id,
1125         }) = origin
1126         {
1127             return self.report_extra_impl_obligation(
1128                 span,
1129                 item_name,
1130                 impl_item_def_id,
1131                 trait_item_def_id,
1132                 &format!("`{}: {}`", bound_kind, sub),
1133             );
1134         }
1135
1136         fn binding_suggestion<'tcx, S: fmt::Display>(
1137             err: &mut DiagnosticBuilder<'tcx>,
1138             type_param_span: Option<(Span, bool)>,
1139             bound_kind: GenericKind<'tcx>,
1140             sub: S,
1141         ) {
1142             let consider = &format!(
1143                 "consider adding an explicit lifetime bound `{}: {}`...",
1144                 bound_kind, sub
1145             );
1146             if let Some((sp, has_lifetimes)) = type_param_span {
1147                 let tail = if has_lifetimes { " + " } else { "" };
1148                 let suggestion = format!("{}: {}{}", bound_kind, sub, tail);
1149                 err.span_suggestion_short_with_applicability(
1150                     sp,
1151                     consider,
1152                     suggestion,
1153                     Applicability::MaybeIncorrect, // Issue #41966
1154                 );
1155             } else {
1156                 err.help(consider);
1157             }
1158         }
1159
1160         let mut err = match *sub {
1161             ty::ReEarlyBound(_)
1162             | ty::ReFree(ty::FreeRegion {
1163                 bound_region: ty::BrNamed(..),
1164                 ..
1165             }) => {
1166                 // Does the required lifetime have a nice name we can print?
1167                 let mut err = struct_span_err!(
1168                     self.tcx.sess,
1169                     span,
1170                     E0309,
1171                     "{} may not live long enough",
1172                     labeled_user_string
1173                 );
1174                 binding_suggestion(&mut err, type_param_span, bound_kind, sub);
1175                 err
1176             }
1177
1178             ty::ReStatic => {
1179                 // Does the required lifetime have a nice name we can print?
1180                 let mut err = struct_span_err!(
1181                     self.tcx.sess,
1182                     span,
1183                     E0310,
1184                     "{} may not live long enough",
1185                     labeled_user_string
1186                 );
1187                 binding_suggestion(&mut err, type_param_span, bound_kind, "'static");
1188                 err
1189             }
1190
1191             _ => {
1192                 // If not, be less specific.
1193                 let mut err = struct_span_err!(
1194                     self.tcx.sess,
1195                     span,
1196                     E0311,
1197                     "{} may not live long enough",
1198                     labeled_user_string
1199                 );
1200                 err.help(&format!(
1201                     "consider adding an explicit lifetime bound for `{}`",
1202                     bound_kind
1203                 ));
1204                 self.tcx.note_and_explain_region(
1205                     region_scope_tree,
1206                     &mut err,
1207                     &format!("{} must be valid for ", labeled_user_string),
1208                     sub,
1209                     "...",
1210                 );
1211                 err
1212             }
1213         };
1214
1215         if let Some(origin) = origin {
1216             self.note_region_origin(&mut err, &origin);
1217         }
1218         err
1219     }
1220
1221     fn report_sub_sup_conflict(
1222         &self,
1223         region_scope_tree: &region::ScopeTree,
1224         var_origin: RegionVariableOrigin,
1225         sub_origin: SubregionOrigin<'tcx>,
1226         sub_region: Region<'tcx>,
1227         sup_origin: SubregionOrigin<'tcx>,
1228         sup_region: Region<'tcx>,
1229     ) {
1230         let mut err = self.report_inference_failure(var_origin);
1231
1232         self.tcx.note_and_explain_region(
1233             region_scope_tree,
1234             &mut err,
1235             "first, the lifetime cannot outlive ",
1236             sup_region,
1237             "...",
1238         );
1239
1240         match (&sup_origin, &sub_origin) {
1241             (&infer::Subtype(ref sup_trace), &infer::Subtype(ref sub_trace)) => {
1242                 if let (Some((sup_expected, sup_found)), Some((sub_expected, sub_found))) = (
1243                     self.values_str(&sup_trace.values),
1244                     self.values_str(&sub_trace.values),
1245                 ) {
1246                     if sub_expected == sup_expected && sub_found == sup_found {
1247                         self.tcx.note_and_explain_region(
1248                             region_scope_tree,
1249                             &mut err,
1250                             "...but the lifetime must also be valid for ",
1251                             sub_region,
1252                             "...",
1253                         );
1254                         err.note(&format!(
1255                             "...so that the {}:\nexpected {}\n   found {}",
1256                             sup_trace.cause.as_requirement_str(),
1257                             sup_expected.content(),
1258                             sup_found.content()
1259                         ));
1260                         err.emit();
1261                         return;
1262                     }
1263                 }
1264             }
1265             _ => {}
1266         }
1267
1268         self.note_region_origin(&mut err, &sup_origin);
1269
1270         self.tcx.note_and_explain_region(
1271             region_scope_tree,
1272             &mut err,
1273             "but, the lifetime must be valid for ",
1274             sub_region,
1275             "...",
1276         );
1277
1278         self.note_region_origin(&mut err, &sub_origin);
1279         err.emit();
1280     }
1281 }
1282
1283 impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
1284     fn report_inference_failure(
1285         &self,
1286         var_origin: RegionVariableOrigin,
1287     ) -> DiagnosticBuilder<'tcx> {
1288         let br_string = |br: ty::BoundRegion| {
1289             let mut s = br.to_string();
1290             if !s.is_empty() {
1291                 s.push_str(" ");
1292             }
1293             s
1294         };
1295         let var_description = match var_origin {
1296             infer::MiscVariable(_) => String::new(),
1297             infer::PatternRegion(_) => " for pattern".to_string(),
1298             infer::AddrOfRegion(_) => " for borrow expression".to_string(),
1299             infer::Autoref(_) => " for autoref".to_string(),
1300             infer::Coercion(_) => " for automatic coercion".to_string(),
1301             infer::LateBoundRegion(_, br, infer::FnCall) => {
1302                 format!(" for lifetime parameter {}in function call", br_string(br))
1303             }
1304             infer::LateBoundRegion(_, br, infer::HigherRankedType) => {
1305                 format!(" for lifetime parameter {}in generic type", br_string(br))
1306             }
1307             infer::LateBoundRegion(_, br, infer::AssocTypeProjection(def_id)) => format!(
1308                 " for lifetime parameter {}in trait containing associated type `{}`",
1309                 br_string(br),
1310                 self.tcx.associated_item(def_id).ident
1311             ),
1312             infer::EarlyBoundRegion(_, name) => format!(" for lifetime parameter `{}`", name),
1313             infer::BoundRegionInCoherence(name) => {
1314                 format!(" for lifetime parameter `{}` in coherence check", name)
1315             }
1316             infer::UpvarRegion(ref upvar_id, _) => {
1317                 let var_node_id = self.tcx.hir.hir_to_node_id(upvar_id.var_id);
1318                 let var_name = self.tcx.hir.name(var_node_id);
1319                 format!(" for capture of `{}` by closure", var_name)
1320             }
1321             infer::NLL(..) => bug!("NLL variable found in lexical phase"),
1322         };
1323
1324         struct_span_err!(
1325             self.tcx.sess,
1326             var_origin.span(),
1327             E0495,
1328             "cannot infer an appropriate lifetime{} \
1329              due to conflicting requirements",
1330             var_description
1331         )
1332     }
1333 }
1334
1335 enum FailureCode {
1336     Error0317(&'static str),
1337     Error0580(&'static str),
1338     Error0308(&'static str),
1339     Error0644(&'static str),
1340 }
1341
1342 impl<'tcx> ObligationCause<'tcx> {
1343     fn as_failure_code(&self, terr: &TypeError<'tcx>) -> FailureCode {
1344         use self::FailureCode::*;
1345         use traits::ObligationCauseCode::*;
1346         match self.code {
1347             CompareImplMethodObligation { .. } => Error0308("method not compatible with trait"),
1348             MatchExpressionArm { source, .. } => Error0308(match source {
1349                 hir::MatchSource::IfLetDesugar { .. } => "`if let` arms have incompatible types",
1350                 hir::MatchSource::TryDesugar => {
1351                     "try expression alternatives have incompatible types"
1352                 }
1353                 _ => "match arms have incompatible types",
1354             }),
1355             IfExpression => Error0308("if and else have incompatible types"),
1356             IfExpressionWithNoElse => Error0317("if may be missing an else clause"),
1357             MainFunctionType => Error0580("main function has wrong type"),
1358             StartFunctionType => Error0308("start function has wrong type"),
1359             IntrinsicType => Error0308("intrinsic has wrong type"),
1360             MethodReceiver => Error0308("mismatched method receiver"),
1361
1362             // In the case where we have no more specific thing to
1363             // say, also take a look at the error code, maybe we can
1364             // tailor to that.
1365             _ => match terr {
1366                 TypeError::CyclicTy(ty) if ty.is_closure() || ty.is_generator() => {
1367                     Error0644("closure/generator type that references itself")
1368                 }
1369                 _ => Error0308("mismatched types"),
1370             },
1371         }
1372     }
1373
1374     fn as_requirement_str(&self) -> &'static str {
1375         use traits::ObligationCauseCode::*;
1376         match self.code {
1377             CompareImplMethodObligation { .. } => "method type is compatible with trait",
1378             ExprAssignable => "expression is assignable",
1379             MatchExpressionArm { source, .. } => match source {
1380                 hir::MatchSource::IfLetDesugar { .. } => "`if let` arms have compatible types",
1381                 _ => "match arms have compatible types",
1382             },
1383             IfExpression => "if and else have compatible types",
1384             IfExpressionWithNoElse => "if missing an else returns ()",
1385             MainFunctionType => "`main` function has the correct type",
1386             StartFunctionType => "`start` function has the correct type",
1387             IntrinsicType => "intrinsic has the correct type",
1388             MethodReceiver => "method receiver has the correct type",
1389             _ => "types are compatible",
1390         }
1391     }
1392 }