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 catalogue 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 infer;
  59 use super::{InferCtxt, TypeTrace, SubregionOrigin, RegionVariableOrigin, ValuePairs};
  60 use super::region_inference::{RegionResolutionError, ConcreteFailure, SubSupConflict,
  61                               GenericBoundFailure, GenericKind};
  62
  63 use std::fmt;
  64 use hir;
  65 use hir::map as hir_map;
  66 use hir::def_id::DefId;
  67 use middle::region;
  68 use traits::{ObligationCause, ObligationCauseCode};
  69 use ty::{self, TyCtxt, TypeFoldable};
  70 use ty::{Region, Issue32330};
  71 use ty::error::TypeError;
  72 use syntax::ast::DUMMY_NODE_ID;
  73 use syntax_pos::{Pos, Span};
  74 use errors::{DiagnosticBuilder, DiagnosticStyledString};
  75
  76 mod note;
  77
  78 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
  79     pub fn note_and_explain_region(self,
  80                                    err: &mut DiagnosticBuilder,
  81                                    prefix: &str,
  82                                    region: ty::Region<'tcx>,
  83                                    suffix: &str) {
  84         fn item_scope_tag(item: &hir::Item) -> &'static str {
  85             match item.node {
  86                 hir::ItemImpl(..) => "impl",
  87                 hir::ItemStruct(..) => "struct",
  88                 hir::ItemUnion(..) => "union",
  89                 hir::ItemEnum(..) => "enum",
  90                 hir::ItemTrait(..) => "trait",
  91                 hir::ItemFn(..) => "function body",
  92                 _ => "item"
  93             }
  94         }
  95
  96         fn trait_item_scope_tag(item: &hir::TraitItem) -> &'static str {
  97             match item.node {
  98                 hir::TraitItemKind::Method(..) => "method body",
  99                 hir::TraitItemKind::Const(..) |
 100                 hir::TraitItemKind::Type(..) => "associated item"
 101             }
 102         }
 103
 104         fn impl_item_scope_tag(item: &hir::ImplItem) -> &'static str {
 105             match item.node {
 106                 hir::ImplItemKind::Method(..) => "method body",
 107                 hir::ImplItemKind::Const(..) |
 108                 hir::ImplItemKind::Type(_) => "associated item"
 109             }
 110         }
 111
 112         fn explain_span<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
 113                                         heading: &str, span: Span)
 114                                         -> (String, Option<Span>) {
 115             let lo = tcx.sess.codemap().lookup_char_pos_adj(span.lo);
 116             (format!("the {} at {}:{}", heading, lo.line, lo.col.to_usize()),
 117              Some(span))
 118         }
 119
 120         let (description, span) = match *region {
 121             ty::ReScope(scope) => {
 122                 let new_string;
 123                 let unknown_scope = || {
 124                     format!("{}unknown scope: {:?}{}.  Please report a bug.",
 125                             prefix, scope, suffix)
 126                 };
 127                 let span = match scope.span(&self.hir) {
 128                     Some(s) => s,
 129                     None => {
 130                         err.note(&unknown_scope());
 131                         return;
 132                     }
 133                 };
 134                 let tag = match self.hir.find(scope.node_id()) {
 135                     Some(hir_map::NodeBlock(_)) => "block",
 136                     Some(hir_map::NodeExpr(expr)) => match expr.node {
 137                         hir::ExprCall(..) => "call",
 138                         hir::ExprMethodCall(..) => "method call",
 139                         hir::ExprMatch(.., hir::MatchSource::IfLetDesugar { .. }) => "if let",
 140                         hir::ExprMatch(.., hir::MatchSource::WhileLetDesugar) =>  "while let",
 141                         hir::ExprMatch(.., hir::MatchSource::ForLoopDesugar) =>  "for",
 142                         hir::ExprMatch(..) => "match",
 143                         _ => "expression",
 144                     },
 145                     Some(hir_map::NodeStmt(_)) => "statement",
 146                     Some(hir_map::NodeItem(it)) => item_scope_tag(&it),
 147                     Some(hir_map::NodeTraitItem(it)) => trait_item_scope_tag(&it),
 148                     Some(hir_map::NodeImplItem(it)) => impl_item_scope_tag(&it),
 149                     Some(_) | None => {
 150                         err.span_note(span, &unknown_scope());
 151                         return;
 152                     }
 153                 };
 154                 let scope_decorated_tag = match *scope {
 155                     region::CodeExtentData::Misc(_) => tag,
 156                     region::CodeExtentData::CallSiteScope(_) => {
 157                         "scope of call-site for function"
 158                     }
 159                     region::CodeExtentData::ParameterScope(_) => {
 160                         "scope of function body"
 161                     }
 162                     region::CodeExtentData::DestructionScope(_) => {
 163                         new_string = format!("destruction scope surrounding {}", tag);
 164                         &new_string[..]
 165                     }
 166                     region::CodeExtentData::Remainder(r) => {
 167                         new_string = format!("block suffix following statement {}",
 168                                              r.first_statement_index);
 169                         &new_string[..]
 170                     }
 171                 };
 172                 explain_span(self, scope_decorated_tag, span)
 173             }
 174
 175             ty::ReEarlyBound(_) |
 176             ty::ReFree(_) => {
 177                 let scope = match *region {
 178                     ty::ReEarlyBound(ref br) => {
 179                         self.parent_def_id(br.def_id).unwrap()
 180                     }
 181                     ty::ReFree(ref fr) => fr.scope,
 182                     _ => bug!()
 183                 };
 184                 let prefix = match *region {
 185                     ty::ReEarlyBound(ref br) => {
 186                         format!("the lifetime {} as defined on", br.name)
 187                     }
 188                     ty::ReFree(ref fr) => {
 189                         match fr.bound_region {
 190                             ty::BrAnon(idx) => {
 191                                 format!("the anonymous lifetime #{} defined on", idx + 1)
 192                             }
 193                             ty::BrFresh(_) => "an anonymous lifetime defined on".to_owned(),
 194                             _ => {
 195                                 format!("the lifetime {} as defined on",
 196                                         fr.bound_region)
 197                             }
 198                         }
 199                     }
 200                     _ => bug!()
 201                 };
 202
 203                 let node = self.hir.as_local_node_id(scope)
 204                                    .unwrap_or(DUMMY_NODE_ID);
 205                 let unknown;
 206                 let tag = match self.hir.find(node) {
 207                     Some(hir_map::NodeBlock(_)) |
 208                     Some(hir_map::NodeExpr(_)) => "body",
 209                     Some(hir_map::NodeItem(it)) => item_scope_tag(&it),
 210                     Some(hir_map::NodeTraitItem(it)) => trait_item_scope_tag(&it),
 211                     Some(hir_map::NodeImplItem(it)) => impl_item_scope_tag(&it),
 212
 213                     // this really should not happen, but it does:
 214                     // FIXME(#27942)
 215                     Some(_) => {
 216                         unknown = format!("unexpected node ({}) for scope {:?}.  \
 217                                            Please report a bug.",
 218                                           self.hir.node_to_string(node), scope);
 219                         &unknown
 220                     }
 221                     None => {
 222                         unknown = format!("unknown node for scope {:?}.  \
 223                                            Please report a bug.", scope);
 224                         &unknown
 225                     }
 226                 };
 227                 let (msg, opt_span) = explain_span(self, tag, self.hir.span(node));
 228                 (format!("{} {}", prefix, msg), opt_span)
 229             }
 230
 231             ty::ReStatic => ("the static lifetime".to_owned(), None),
 232
 233             ty::ReEmpty => ("the empty lifetime".to_owned(), None),
 234
 235             // FIXME(#13998) ReSkolemized should probably print like
 236             // ReFree rather than dumping Debug output on the user.
 237             //
 238             // We shouldn't really be having unification failures with ReVar
 239             // and ReLateBound though.
 240             ty::ReSkolemized(..) |
 241             ty::ReVar(_) |
 242             ty::ReLateBound(..) |
 243             ty::ReErased => {
 244                 (format!("lifetime {:?}", region), None)
 245             }
 246         };
 247         let message = format!("{}{}{}", prefix, description, suffix);
 248         if let Some(span) = span {
 249             err.span_note(span, &message);
 250         } else {
 251             err.note(&message);
 252         }
 253     }
 254 }
 255
 256 impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
 257     pub fn report_region_errors(&self,
 258                                 errors: &Vec<RegionResolutionError<'tcx>>) {
 259         debug!("report_region_errors(): {} errors to start", errors.len());
 260
 261         // try to pre-process the errors, which will group some of them
 262         // together into a `ProcessedErrors` group:
 263         let errors = self.process_errors(errors);
 264
 265         debug!("report_region_errors: {} errors after preprocessing", errors.len());
 266
 267         for error in errors {
 268             debug!("report_region_errors: error = {:?}", error);
 269             match error.clone() {
 270                 ConcreteFailure(origin, sub, sup) => {
 271                     self.report_concrete_failure(origin, sub, sup).emit();
 272                 }
 273
 274                 GenericBoundFailure(kind, param_ty, sub) => {
 275                     self.report_generic_bound_failure(kind, param_ty, sub);
 276                 }
 277
 278                 SubSupConflict(var_origin,
 279                                sub_origin, sub_r,
 280                                sup_origin, sup_r) => {
 281                     self.report_sub_sup_conflict(var_origin,
 282                                                  sub_origin, sub_r,
 283                                                  sup_origin, sup_r);
 284                 }
 285             }
 286         }
 287     }
 288
 289     // This method goes through all the errors and try to group certain types
 290     // of error together, for the purpose of suggesting explicit lifetime
 291     // parameters to the user. This is done so that we can have a more
 292     // complete view of what lifetimes should be the same.
 293     // If the return value is an empty vector, it means that processing
 294     // failed (so the return value of this method should not be used).
 295     //
 296     // The method also attempts to weed out messages that seem like
 297     // duplicates that will be unhelpful to the end-user. But
 298     // obviously it never weeds out ALL errors.
 299     fn process_errors(&self, errors: &Vec<RegionResolutionError<'tcx>>)
 300                       -> Vec<RegionResolutionError<'tcx>> {
 301         debug!("process_errors()");
 302
 303         // We want to avoid reporting generic-bound failures if we can
 304         // avoid it: these have a very high rate of being unhelpful in
 305         // practice. This is because they are basically secondary
 306         // checks that test the state of the region graph after the
 307         // rest of inference is done, and the other kinds of errors
 308         // indicate that the region constraint graph is internally
 309         // inconsistent, so these test results are likely to be
 310         // meaningless.
 311         //
 312         // Therefore, we filter them out of the list unless they are
 313         // the only thing in the list.
 314
 315         let is_bound_failure = |e: &RegionResolutionError<'tcx>| match *e {
 316             ConcreteFailure(..) => false,
 317             SubSupConflict(..) => false,
 318             GenericBoundFailure(..) => true,
 319         };
 320
 321         if errors.iter().all(|e| is_bound_failure(e)) {
 322             errors.clone()
 323         } else {
 324             errors.iter().filter(|&e| !is_bound_failure(e)).cloned().collect()
 325         }
 326     }
 327
 328     /// Adds a note if the types come from similarly named crates
 329     fn check_and_note_conflicting_crates(&self,
 330                                          err: &mut DiagnosticBuilder,
 331                                          terr: &TypeError<'tcx>,
 332                                          sp: Span) {
 333         let report_path_match = |err: &mut DiagnosticBuilder, did1: DefId, did2: DefId| {
 334             // Only external crates, if either is from a local
 335             // module we could have false positives
 336             if !(did1.is_local() || did2.is_local()) && did1.krate != did2.krate {
 337                 let exp_path = self.tcx.item_path_str(did1);
 338                 let found_path = self.tcx.item_path_str(did2);
 339                 // We compare strings because DefPath can be different
 340                 // for imported and non-imported crates
 341                 if exp_path == found_path {
 342                     let crate_name = self.tcx.sess.cstore.crate_name(did1.krate);
 343                     err.span_note(sp, &format!("Perhaps two different versions \
 344                                                 of crate `{}` are being used?",
 345                                                crate_name));
 346                 }
 347             }
 348         };
 349         match *terr {
 350             TypeError::Sorts(ref exp_found) => {
 351                 // if they are both "path types", there's a chance of ambiguity
 352                 // due to different versions of the same crate
 353                 match (&exp_found.expected.sty, &exp_found.found.sty) {
 354                     (&ty::TyAdt(exp_adt, _), &ty::TyAdt(found_adt, _)) => {
 355                         report_path_match(err, exp_adt.did, found_adt.did);
 356                     },
 357                     _ => ()
 358                 }
 359             },
 360             TypeError::Traits(ref exp_found) => {
 361                 report_path_match(err, exp_found.expected, exp_found.found);
 362             },
 363             _ => () // FIXME(#22750) handle traits and stuff
 364         }
 365     }
 366
 367     fn note_error_origin(&self,
 368                          err: &mut DiagnosticBuilder<'tcx>,
 369                          cause: &ObligationCause<'tcx>)
 370     {
 371         match cause.code {
 372             ObligationCauseCode::MatchExpressionArm { arm_span, source } => match source {
 373                 hir::MatchSource::IfLetDesugar {..} => {
 374                     err.span_note(arm_span, "`if let` arm with an incompatible type");
 375                 }
 376                 _ => {
 377                     err.span_note(arm_span, "match arm with an incompatible type");
 378                 }
 379             },
 380             _ => ()
 381         }
 382     }
 383
 384     /// Given that `other_ty` is the same as a type argument for `name` in `sub`, populate `value`
 385     /// highlighting `name` and every type argument that isn't at `pos` (which is `other_ty`), and
 386     /// populate `other_value` with `other_ty`.
 387     ///
 388     /// ```text
 389     /// Foo<Bar<Qux>>
 390     /// ^^^^--------^ this is highlighted
 391     /// |   |
 392     /// |   this type argument is exactly the same as the other type, not highlighted
 393     /// this is highlighted
 394     /// Bar<Qux>
 395     /// -------- this type is the same as a type argument in the other type, not highlighted
 396     /// ```
 397     fn highlight_outer(&self,
 398                        mut value: &mut DiagnosticStyledString,
 399                        mut other_value: &mut DiagnosticStyledString,
 400                        name: String,
 401                        sub: &ty::subst::Substs<'tcx>,
 402                        pos: usize,
 403                        other_ty: &ty::Ty<'tcx>) {
 404         // `value` and `other_value` hold two incomplete type representation for display.
 405         // `name` is the path of both types being compared. `sub`
 406         value.push_highlighted(name);
 407         let len = sub.len();
 408         if len > 0 {
 409             value.push_highlighted("<");
 410         }
 411
 412         // Output the lifetimes fot the first type
 413         let lifetimes = sub.regions().map(|lifetime| {
 414             let s = format!("{}", lifetime);
 415             if s.is_empty() {
 416                 "'_".to_string()
 417             } else {
 418                 s
 419             }
 420         }).collect::<Vec<_>>().join(", ");
 421         if !lifetimes.is_empty() {
 422             if sub.regions().count() < len {
 423                 value.push_normal(lifetimes + &", ");
 424             } else {
 425                 value.push_normal(lifetimes);
 426             }
 427         }
 428
 429         // Highlight all the type arguments that aren't at `pos` and compare the type argument at
 430         // `pos` and `other_ty`.
 431         for (i, type_arg) in sub.types().enumerate() {
 432             if i == pos {
 433                 let values = self.cmp(type_arg, other_ty);
 434                 value.0.extend((values.0).0);
 435                 other_value.0.extend((values.1).0);
 436             } else {
 437                 value.push_highlighted(format!("{}", type_arg));
 438             }
 439
 440             if len > 0 && i != len - 1 {
 441                 value.push_normal(", ");
 442             }
 443             //self.push_comma(&mut value, &mut other_value, len, i);
 444         }
 445         if len > 0 {
 446             value.push_highlighted(">");
 447         }
 448     }
 449
 450     /// If `other_ty` is the same as a type argument present in `sub`, highlight `path` in `t1_out`,
 451     /// as that is the difference to the other type.
 452     ///
 453     /// For the following code:
 454     ///
 455     /// ```norun
 456     /// let x: Foo<Bar<Qux>> = foo::<Bar<Qux>>();
 457     /// ```
 458     ///
 459     /// The type error output will behave in the following way:
 460     ///
 461     /// ```text
 462     /// Foo<Bar<Qux>>
 463     /// ^^^^--------^ this is highlighted
 464     /// |   |
 465     /// |   this type argument is exactly the same as the other type, not highlighted
 466     /// this is highlighted
 467     /// Bar<Qux>
 468     /// -------- this type is the same as a type argument in the other type, not highlighted
 469     /// ```
 470     fn cmp_type_arg(&self,
 471                     mut t1_out: &mut DiagnosticStyledString,
 472                     mut t2_out: &mut DiagnosticStyledString,
 473                     path: String,
 474                     sub: &ty::subst::Substs<'tcx>,
 475                     other_path: String,
 476                     other_ty: &ty::Ty<'tcx>) -> Option<()> {
 477         for (i, ta) in sub.types().enumerate() {
 478             if &ta == other_ty {
 479                 self.highlight_outer(&mut t1_out, &mut t2_out, path, sub, i, &other_ty);
 480                 return Some(());
 481             }
 482             if let &ty::TyAdt(def, _) = &ta.sty {
 483                 let path_ = self.tcx.item_path_str(def.did.clone());
 484                 if path_ == other_path {
 485                     self.highlight_outer(&mut t1_out, &mut t2_out, path, sub, i, &other_ty);
 486                     return Some(());
 487                 }
 488             }
 489         }
 490         None
 491     }
 492
 493     /// Add a `,` to the type representation only if it is appropriate.
 494     fn push_comma(&self,
 495                   value: &mut DiagnosticStyledString,
 496                   other_value: &mut DiagnosticStyledString,
 497                   len: usize,
 498                   pos: usize) {
 499         if len > 0 && pos != len - 1 {
 500             value.push_normal(", ");
 501             other_value.push_normal(", ");
 502         }
 503     }
 504
 505     /// Compare two given types, eliding parts that are the same between them and highlighting
 506     /// relevant differences, and return two representation of those types for highlighted printing.
 507     fn cmp(&self, t1: ty::Ty<'tcx>, t2: ty::Ty<'tcx>)
 508         -> (DiagnosticStyledString, DiagnosticStyledString)
 509     {
 510         match (&t1.sty, &t2.sty) {
 511             (&ty::TyAdt(def1, sub1), &ty::TyAdt(def2, sub2)) => {
 512                 let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new());
 513                 let path1 = self.tcx.item_path_str(def1.did.clone());
 514                 let path2 = self.tcx.item_path_str(def2.did.clone());
 515                 if def1.did == def2.did {
 516                     // Easy case. Replace same types with `_` to shorten the output and highlight
 517                     // the differing ones.
 518                     //     let x: Foo<Bar, Qux> = y::<Foo<Quz, Qux>>();
 519                     //     Foo<Bar, _>
 520                     //     Foo<Quz, _>
 521                     //         ---  ^ type argument elided
 522                     //         |
 523                     //         highlighted in output
 524                     values.0.push_normal(path1);
 525                     values.1.push_normal(path2);
 526
 527                     // Only draw `<...>` if there're lifetime/type arguments.
 528                     let len = sub1.len();
 529                     if len > 0 {
 530                         values.0.push_normal("<");
 531                         values.1.push_normal("<");
 532                     }
 533
 534                     fn lifetime_display(lifetime: Region) -> String {
 535                         let s = format!("{}", lifetime);
 536                         if s.is_empty() {
 537                             "'_".to_string()
 538                         } else {
 539                             s
 540                         }
 541                     }
 542                     // At one point we'd like to elide all lifetimes here, they are irrelevant for
 543                     // all diagnostics that use this output
 544                     //
 545                     //     Foo<'x, '_, Bar>
 546                     //     Foo<'y, '_, Qux>
 547                     //         ^^  ^^  --- type arguments are not elided
 548                     //         |   |
 549                     //         |   elided as they were the same
 550                     //         not elided, they were different, but irrelevant
 551                     let lifetimes = sub1.regions().zip(sub2.regions());
 552                     for (i, lifetimes) in lifetimes.enumerate() {
 553                         let l1 = lifetime_display(lifetimes.0);
 554                         let l2 = lifetime_display(lifetimes.1);
 555                         if l1 == l2 {
 556                             values.0.push_normal("'_");
 557                             values.1.push_normal("'_");
 558                         } else {
 559                             values.0.push_highlighted(l1);
 560                             values.1.push_highlighted(l2);
 561                         }
 562                         self.push_comma(&mut values.0, &mut values.1, len, i);
 563                     }
 564
 565                     // We're comparing two types with the same path, so we compare the type
 566                     // arguments for both. If they are the same, do not highlight and elide from the
 567                     // output.
 568                     //     Foo<_, Bar>
 569                     //     Foo<_, Qux>
 570                     //         ^ elided type as this type argument was the same in both sides
 571                     let type_arguments = sub1.types().zip(sub2.types());
 572                     let regions_len = sub1.regions().collect::<Vec<_>>().len();
 573                     for (i, (ta1, ta2)) in type_arguments.enumerate() {
 574                         let i = i + regions_len;
 575                         if ta1 == ta2 {
 576                             values.0.push_normal("_");
 577                             values.1.push_normal("_");
 578                         } else {
 579                             let (x1, x2) = self.cmp(ta1, ta2);
 580                             (values.0).0.extend(x1.0);
 581                             (values.1).0.extend(x2.0);
 582                         }
 583                         self.push_comma(&mut values.0, &mut values.1, len, i);
 584                     }
 585
 586                     // Close the type argument bracket.
 587                     // Only draw `<...>` if there're lifetime/type arguments.
 588                     if len > 0 {
 589                         values.0.push_normal(">");
 590                         values.1.push_normal(">");
 591                     }
 592                     values
 593                 } else {
 594                     // Check for case:
 595                     //     let x: Foo<Bar<Qux> = foo::<Bar<Qux>>();
 596                     //     Foo<Bar<Qux>
 597                     //         ------- this type argument is exactly the same as the other type
 598                     //     Bar<Qux>
 599                     if self.cmp_type_arg(&mut values.0,
 600                                          &mut values.1,
 601                                          path1.clone(),
 602                                          sub1,
 603                                          path2.clone(),
 604                                          &t2).is_some() {
 605                         return values;
 606                     }
 607                     // Check for case:
 608                     //     let x: Bar<Qux> = y:<Foo<Bar<Qux>>>();
 609                     //     Bar<Qux>
 610                     //     Foo<Bar<Qux>>
 611                     //         ------- this type argument is exactly the same as the other type
 612                     if self.cmp_type_arg(&mut values.1,
 613                                          &mut values.0,
 614                                          path2,
 615                                          sub2,
 616                                          path1,
 617                                          &t1).is_some() {
 618                         return values;
 619                     }
 620
 621                     // We couldn't find anything in common, highlight everything.
 622                     //     let x: Bar<Qux> = y::<Foo<Zar>>();
 623                     (DiagnosticStyledString::highlighted(format!("{}", t1)),
 624                      DiagnosticStyledString::highlighted(format!("{}", t2)))
 625                 }
 626             }
 627             _ => {
 628                 if t1 == t2 {
 629                     // The two types are the same, elide and don't highlight.
 630                     (DiagnosticStyledString::normal("_"), DiagnosticStyledString::normal("_"))
 631                 } else {
 632                     // We couldn't find anything in common, highlight everything.
 633                     (DiagnosticStyledString::highlighted(format!("{}", t1)),
 634                      DiagnosticStyledString::highlighted(format!("{}", t2)))
 635                 }
 636             }
 637         }
 638     }
 639
 640     pub fn note_type_err(&self,
 641                          diag: &mut DiagnosticBuilder<'tcx>,
 642                          cause: &ObligationCause<'tcx>,
 643                          secondary_span: Option<(Span, String)>,
 644                          values: Option<ValuePairs<'tcx>>,
 645                          terr: &TypeError<'tcx>)
 646     {
 647         let (expected_found, is_simple_error) = match values {
 648             None => (None, false),
 649             Some(values) => {
 650                 let is_simple_error = match values {
 651                     ValuePairs::Types(exp_found) => {
 652                         exp_found.expected.is_primitive() && exp_found.found.is_primitive()
 653                     }
 654                     _ => false,
 655                 };
 656                 let vals = match self.values_str(&values) {
 657                     Some((expected, found)) => Some((expected, found)),
 658                     None => {
 659                         // Derived error. Cancel the emitter.
 660                         self.tcx.sess.diagnostic().cancel(diag);
 661                         return
 662                     }
 663                 };
 664                 (vals, is_simple_error)
 665             }
 666         };
 667
 668         let span = cause.span;
 669
 670         if let Some((expected, found)) = expected_found {
 671             match (terr, is_simple_error, expected == found) {
 672                 (&TypeError::Sorts(ref values), false, true) => {
 673                     diag.note_expected_found_extra(
 674                         &"type", expected, found,
 675                         &format!(" ({})", values.expected.sort_string(self.tcx)),
 676                         &format!(" ({})", values.found.sort_string(self.tcx)));
 677                 }
 678                 (_, false,  _) => {
 679                     diag.note_expected_found(&"type", expected, found);
 680                 }
 681                 _ => (),
 682             }
 683         }
 684
 685         diag.span_label(span, terr.to_string());
 686         if let Some((sp, msg)) = secondary_span {
 687             diag.span_label(sp, msg);
 688         }
 689
 690         self.note_error_origin(diag, &cause);
 691         self.check_and_note_conflicting_crates(diag, terr, span);
 692         self.tcx.note_and_explain_type_err(diag, terr, span);
 693     }
 694
 695     pub fn note_issue_32330(&self,
 696                             diag: &mut DiagnosticBuilder<'tcx>,
 697                             terr: &TypeError<'tcx>)
 698     {
 699         debug!("note_issue_32330: terr={:?}", terr);
 700         match *terr {
 701             TypeError::RegionsInsufficientlyPolymorphic(_, _, Some(box Issue32330 {
 702                 fn_def_id, region_name
 703             })) |
 704             TypeError::RegionsOverlyPolymorphic(_, _, Some(box Issue32330 {
 705                 fn_def_id, region_name
 706             })) => {
 707                 diag.note(
 708                     &format!("lifetime parameter `{0}` declared on fn `{1}` \
 709                               appears only in the return type, \
 710                               but here is required to be higher-ranked, \
 711                               which means that `{0}` must appear in both \
 712                               argument and return types",
 713                              region_name,
 714                              self.tcx.item_path_str(fn_def_id)));
 715                 diag.note(
 716                     &format!("this error is the result of a recent bug fix; \
 717                               for more information, see issue #33685 \
 718                               <https://github.com/rust-lang/rust/issues/33685>"));
 719             }
 720             _ => {}
 721         }
 722     }
 723
 724     pub fn report_and_explain_type_error(&self,
 725                                          trace: TypeTrace<'tcx>,
 726                                          terr: &TypeError<'tcx>)
 727                                          -> DiagnosticBuilder<'tcx>
 728     {
 729         let span = trace.cause.span;
 730         let failure_str = trace.cause.as_failure_str();
 731         let mut diag = match trace.cause.code {
 732             ObligationCauseCode::IfExpressionWithNoElse => {
 733                 struct_span_err!(self.tcx.sess, span, E0317, "{}", failure_str)
 734             }
 735             ObligationCauseCode::MainFunctionType => {
 736                 struct_span_err!(self.tcx.sess, span, E0580, "{}", failure_str)
 737             }
 738             _ => {
 739                 struct_span_err!(self.tcx.sess, span, E0308, "{}", failure_str)
 740             }
 741         };
 742         self.note_type_err(&mut diag, &trace.cause, None, Some(trace.values), terr);
 743         self.note_issue_32330(&mut diag, terr);
 744         diag
 745     }
 746
 747     fn values_str(&self, values: &ValuePairs<'tcx>)
 748         -> Option<(DiagnosticStyledString, DiagnosticStyledString)>
 749     {
 750         match *values {
 751             infer::Types(ref exp_found) => self.expected_found_str_ty(exp_found),
 752             infer::TraitRefs(ref exp_found) => self.expected_found_str(exp_found),
 753             infer::PolyTraitRefs(ref exp_found) => self.expected_found_str(exp_found),
 754         }
 755     }
 756
 757     fn expected_found_str_ty(&self,
 758                              exp_found: &ty::error::ExpectedFound<ty::Ty<'tcx>>)
 759                              -> Option<(DiagnosticStyledString, DiagnosticStyledString)> {
 760         let exp_found = self.resolve_type_vars_if_possible(exp_found);
 761         if exp_found.references_error() {
 762             return None;
 763         }
 764
 765         Some(self.cmp(exp_found.expected, exp_found.found))
 766     }
 767
 768     /// Returns a string of the form "expected `{}`, found `{}`".
 769     fn expected_found_str<T: fmt::Display + TypeFoldable<'tcx>>(
 770         &self,
 771         exp_found: &ty::error::ExpectedFound<T>)
 772         -> Option<(DiagnosticStyledString, DiagnosticStyledString)>
 773     {
 774         let exp_found = self.resolve_type_vars_if_possible(exp_found);
 775         if exp_found.references_error() {
 776             return None;
 777         }
 778
 779         Some((DiagnosticStyledString::highlighted(format!("{}", exp_found.expected)),
 780               DiagnosticStyledString::highlighted(format!("{}", exp_found.found))))
 781     }
 782
 783     fn report_generic_bound_failure(&self,
 784                                     origin: SubregionOrigin<'tcx>,
 785                                     bound_kind: GenericKind<'tcx>,
 786                                     sub: Region<'tcx>)
 787     {
 788         // FIXME: it would be better to report the first error message
 789         // with the span of the parameter itself, rather than the span
 790         // where the error was detected. But that span is not readily
 791         // accessible.
 792
 793         let labeled_user_string = match bound_kind {
 794             GenericKind::Param(ref p) =>
 795                 format!("the parameter type `{}`", p),
 796             GenericKind::Projection(ref p) =>
 797                 format!("the associated type `{}`", p),
 798         };
 799
 800         if let SubregionOrigin::CompareImplMethodObligation {
 801             span, item_name, impl_item_def_id, trait_item_def_id, lint_id
 802         } = origin {
 803             self.report_extra_impl_obligation(span,
 804                                               item_name,
 805                                               impl_item_def_id,
 806                                               trait_item_def_id,
 807                                               &format!("`{}: {}`", bound_kind, sub),
 808                                               lint_id)
 809                 .emit();
 810             return;
 811         }
 812
 813         let mut err = match *sub {
 814             ty::ReEarlyBound(_) |
 815             ty::ReFree(ty::FreeRegion {bound_region: ty::BrNamed(..), ..}) => {
 816                 // Does the required lifetime have a nice name we can print?
 817                 let mut err = struct_span_err!(self.tcx.sess,
 818                                                origin.span(),
 819                                                E0309,
 820                                                "{} may not live long enough",
 821                                                labeled_user_string);
 822                 err.help(&format!("consider adding an explicit lifetime bound `{}: {}`...",
 823                          bound_kind,
 824                          sub));
 825                 err
 826             }
 827
 828             ty::ReStatic => {
 829                 // Does the required lifetime have a nice name we can print?
 830                 let mut err = struct_span_err!(self.tcx.sess,
 831                                                origin.span(),
 832                                                E0310,
 833                                                "{} may not live long enough",
 834                                                labeled_user_string);
 835                 err.help(&format!("consider adding an explicit lifetime \
 836                                    bound `{}: 'static`...",
 837                                   bound_kind));
 838                 err
 839             }
 840
 841             _ => {
 842                 // If not, be less specific.
 843                 let mut err = struct_span_err!(self.tcx.sess,
 844                                                origin.span(),
 845                                                E0311,
 846                                                "{} may not live long enough",
 847                                                labeled_user_string);
 848                 err.help(&format!("consider adding an explicit lifetime bound for `{}`",
 849                                   bound_kind));
 850                 self.tcx.note_and_explain_region(
 851                     &mut err,
 852                     &format!("{} must be valid for ", labeled_user_string),
 853                     sub,
 854                     "...");
 855                 err
 856             }
 857         };
 858
 859         self.note_region_origin(&mut err, &origin);
 860         err.emit();
 861     }
 862
 863     fn report_sub_sup_conflict(&self,
 864                                var_origin: RegionVariableOrigin,
 865                                sub_origin: SubregionOrigin<'tcx>,
 866                                sub_region: Region<'tcx>,
 867                                sup_origin: SubregionOrigin<'tcx>,
 868                                sup_region: Region<'tcx>) {
 869         let mut err = self.report_inference_failure(var_origin);
 870
 871         self.tcx.note_and_explain_region(&mut err,
 872             "first, the lifetime cannot outlive ",
 873             sup_region,
 874             "...");
 875
 876         self.note_region_origin(&mut err, &sup_origin);
 877
 878         self.tcx.note_and_explain_region(&mut err,
 879             "but, the lifetime must be valid for ",
 880             sub_region,
 881             "...");
 882
 883         self.note_region_origin(&mut err, &sub_origin);
 884         err.emit();
 885     }
 886 }
 887
 888 impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
 889     fn report_inference_failure(&self,
 890                                 var_origin: RegionVariableOrigin)
 891                                 -> DiagnosticBuilder<'tcx> {
 892         let br_string = |br: ty::BoundRegion| {
 893             let mut s = br.to_string();
 894             if !s.is_empty() {
 895                 s.push_str(" ");
 896             }
 897             s
 898         };
 899         let var_description = match var_origin {
 900             infer::MiscVariable(_) => "".to_string(),
 901             infer::PatternRegion(_) => " for pattern".to_string(),
 902             infer::AddrOfRegion(_) => " for borrow expression".to_string(),
 903             infer::Autoref(_) => " for autoref".to_string(),
 904             infer::Coercion(_) => " for automatic coercion".to_string(),
 905             infer::LateBoundRegion(_, br, infer::FnCall) => {
 906                 format!(" for lifetime parameter {}in function call",
 907                         br_string(br))
 908             }
 909             infer::LateBoundRegion(_, br, infer::HigherRankedType) => {
 910                 format!(" for lifetime parameter {}in generic type", br_string(br))
 911             }
 912             infer::LateBoundRegion(_, br, infer::AssocTypeProjection(type_name)) => {
 913                 format!(" for lifetime parameter {}in trait containing associated type `{}`",
 914                         br_string(br), type_name)
 915             }
 916             infer::EarlyBoundRegion(_, name, _) => {
 917                 format!(" for lifetime parameter `{}`",
 918                         name)
 919             }
 920             infer::BoundRegionInCoherence(name) => {
 921                 format!(" for lifetime parameter `{}` in coherence check",
 922                         name)
 923             }
 924             infer::UpvarRegion(ref upvar_id, _) => {
 925                 format!(" for capture of `{}` by closure",
 926                         self.tcx.local_var_name_str(upvar_id.var_id).to_string())
 927             }
 928         };
 929
 930         struct_span_err!(self.tcx.sess, var_origin.span(), E0495,
 931                   "cannot infer an appropriate lifetime{} \
 932                    due to conflicting requirements",
 933                   var_description)
 934     }
 935 }
 936
 937 impl<'tcx> ObligationCause<'tcx> {
 938     fn as_failure_str(&self) -> &'static str {
 939         use traits::ObligationCauseCode::*;
 940         match self.code {
 941             CompareImplMethodObligation { .. } => "method not compatible with trait",
 942             MatchExpressionArm { source, .. } => match source {
 943                 hir::MatchSource::IfLetDesugar{..} => "`if let` arms have incompatible types",
 944                 _ => "match arms have incompatible types",
 945             },
 946             IfExpression => "if and else have incompatible types",
 947             IfExpressionWithNoElse => "if may be missing an else clause",
 948             EquatePredicate => "equality predicate not satisfied",
 949             MainFunctionType => "main function has wrong type",
 950             StartFunctionType => "start function has wrong type",
 951             IntrinsicType => "intrinsic has wrong type",
 952             MethodReceiver => "mismatched method receiver",
 953             _ => "mismatched types",
 954         }
 955     }
 956
 957     fn as_requirement_str(&self) -> &'static str {
 958         use traits::ObligationCauseCode::*;
 959         match self.code {
 960             CompareImplMethodObligation { .. } => "method type is compatible with trait",
 961             ExprAssignable => "expression is assignable",
 962             MatchExpressionArm { source, .. } => match source {
 963                 hir::MatchSource::IfLetDesugar{..} => "`if let` arms have compatible types",
 964                 _ => "match arms have compatible types",
 965             },
 966             IfExpression => "if and else have compatible types",
 967             IfExpressionWithNoElse => "if missing an else returns ()",
 968             EquatePredicate => "equality where clause is satisfied",
 969             MainFunctionType => "`main` function has the correct type",
 970             StartFunctionType => "`start` function has the correct type",
 971             IntrinsicType => "intrinsic has the correct type",
 972             MethodReceiver => "method receiver has the correct type",
 973             _ => "types are compatible",
 974         }
 975     }
 976 }