src/librustc_mir/borrow_check/nll/region_infer/error_reporting/region_name.rs

   1 use std::fmt::{self, Display};
   2 use crate::borrow_check::nll::region_infer::RegionInferenceContext;
   3 use crate::borrow_check::nll::universal_regions::DefiningTy;
   4 use crate::borrow_check::nll::ToRegionVid;
   5 use crate::borrow_check::Upvar;
   6 use rustc::hir;
   7 use rustc::hir::def::{Res, DefKind};
   8 use rustc::hir::def_id::DefId;
   9 use rustc::infer::InferCtxt;
  10 use rustc::mir::Mir;
  11 use rustc::ty::subst::{SubstsRef, UnpackedKind};
  12 use rustc::ty::{self, RegionKind, RegionVid, Ty, TyCtxt};
  13 use rustc::ty::print::RegionHighlightMode;
  14 use rustc_errors::DiagnosticBuilder;
  15 use syntax::ast::Name;
  16 use syntax::symbol::keywords;
  17 use syntax_pos::Span;
  18 use syntax_pos::symbol::InternedString;
  19
  20 #[derive(Debug)]
  21 crate struct RegionName {
  22     crate name: InternedString,
  23     crate source: RegionNameSource,
  24 }
  25
  26 #[derive(Debug)]
  27 crate enum RegionNameSource {
  28     NamedEarlyBoundRegion(Span),
  29     NamedFreeRegion(Span),
  30     Static,
  31     SynthesizedFreeEnvRegion(Span, String),
  32     CannotMatchHirTy(Span, String),
  33     MatchedHirTy(Span),
  34     MatchedAdtAndSegment(Span),
  35     AnonRegionFromUpvar(Span, String),
  36     AnonRegionFromOutput(Span, String, String),
  37     AnonRegionFromYieldTy(Span, String),
  38 }
  39
  40 impl RegionName {
  41     #[allow(dead_code)]
  42     crate fn was_named(&self) -> bool {
  43         match self.source {
  44             RegionNameSource::NamedEarlyBoundRegion(..) |
  45             RegionNameSource::NamedFreeRegion(..) |
  46             RegionNameSource::Static => true,
  47             RegionNameSource::SynthesizedFreeEnvRegion(..) |
  48             RegionNameSource::CannotMatchHirTy(..) |
  49             RegionNameSource::MatchedHirTy(..) |
  50             RegionNameSource::MatchedAdtAndSegment(..) |
  51             RegionNameSource::AnonRegionFromUpvar(..) |
  52             RegionNameSource::AnonRegionFromOutput(..) |
  53             RegionNameSource::AnonRegionFromYieldTy(..) => false,
  54         }
  55     }
  56
  57     #[allow(dead_code)]
  58     crate fn was_synthesized(&self) -> bool {
  59         !self.was_named()
  60     }
  61
  62     #[allow(dead_code)]
  63     crate fn name(&self) -> &InternedString {
  64         &self.name
  65     }
  66
  67     crate fn highlight_region_name(
  68         &self,
  69         diag: &mut DiagnosticBuilder<'_>
  70     ) {
  71         match &self.source {
  72             RegionNameSource::NamedFreeRegion(span) |
  73             RegionNameSource::NamedEarlyBoundRegion(span) => {
  74                 diag.span_label(
  75                     *span,
  76                     format!("lifetime `{}` defined here", self),
  77                 );
  78             },
  79             RegionNameSource::SynthesizedFreeEnvRegion(span, note) => {
  80                 diag.span_label(
  81                     *span,
  82                     format!("lifetime `{}` represents this closure's body", self),
  83                 );
  84                 diag.note(&note);
  85             },
  86             RegionNameSource::CannotMatchHirTy(span, type_name) => {
  87                 diag.span_label(*span, format!("has type `{}`", type_name));
  88             },
  89             RegionNameSource::MatchedHirTy(span) => {
  90                 diag.span_label(
  91                     *span,
  92                     format!("let's call the lifetime of this reference `{}`", self),
  93                 );
  94             },
  95             RegionNameSource::MatchedAdtAndSegment(span) => {
  96                 diag.span_label(*span, format!("let's call this `{}`", self));
  97             },
  98             RegionNameSource::AnonRegionFromUpvar(span, upvar_name) => {
  99                 diag.span_label(
 100                     *span,
 101                     format!("lifetime `{}` appears in the type of `{}`", self, upvar_name),
 102                 );
 103             },
 104             RegionNameSource::AnonRegionFromOutput(span, mir_description, type_name) => {
 105                 diag.span_label(
 106                     *span,
 107                     format!("return type{} is {}", mir_description, type_name),
 108                 );
 109             },
 110             RegionNameSource::AnonRegionFromYieldTy(span, type_name) => {
 111                 diag.span_label(
 112                     *span,
 113                     format!("yield type is {}", type_name),
 114                 );
 115             }
 116             RegionNameSource::Static => {},
 117         }
 118     }
 119 }
 120
 121 impl Display for RegionName {
 122     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 123         write!(f, "{}", self.name)
 124     }
 125 }
 126
 127 impl<'tcx> RegionInferenceContext<'tcx> {
 128     /// Maps from an internal MIR region vid to something that we can
 129     /// report to the user. In some cases, the region vids will map
 130     /// directly to lifetimes that the user has a name for (e.g.,
 131     /// `'static`). But frequently they will not, in which case we
 132     /// have to find some way to identify the lifetime to the user. To
 133     /// that end, this function takes a "diagnostic" so that it can
 134     /// create auxiliary notes as needed.
 135     ///
 136     /// Example (function arguments):
 137     ///
 138     /// Suppose we are trying to give a name to the lifetime of the
 139     /// reference `x`:
 140     ///
 141     /// ```
 142     /// fn foo(x: &u32) { .. }
 143     /// ```
 144     ///
 145     /// This function would create a label like this:
 146     ///
 147     /// ```
 148     ///  | fn foo(x: &u32) { .. }
 149     ///           ------- fully elaborated type of `x` is `&'1 u32`
 150     /// ```
 151     ///
 152     /// and then return the name `'1` for us to use.
 153     crate fn give_region_a_name(
 154         &self,
 155         infcx: &InferCtxt<'_, '_, 'tcx>,
 156         mir: &Mir<'tcx>,
 157         upvars: &[Upvar],
 158         mir_def_id: DefId,
 159         fr: RegionVid,
 160         counter: &mut usize,
 161     ) -> Option<RegionName> {
 162         debug!("give_region_a_name(fr={:?}, counter={})", fr, counter);
 163
 164         assert!(self.universal_regions.is_universal_region(fr));
 165
 166         let value = self.give_name_from_error_region(infcx.tcx, mir_def_id, fr, counter)
 167             .or_else(|| {
 168                 self.give_name_if_anonymous_region_appears_in_arguments(
 169                     infcx, mir, mir_def_id, fr, counter,
 170                 )
 171             })
 172             .or_else(|| {
 173                 self.give_name_if_anonymous_region_appears_in_upvars(
 174                     infcx.tcx, upvars, fr, counter,
 175                 )
 176             })
 177             .or_else(|| {
 178                 self.give_name_if_anonymous_region_appears_in_output(
 179                     infcx, mir, mir_def_id, fr, counter,
 180                 )
 181             })
 182             .or_else(|| {
 183                 self.give_name_if_anonymous_region_appears_in_yield_ty(
 184                     infcx, mir, mir_def_id, fr, counter,
 185                 )
 186             });
 187
 188         debug!("give_region_a_name: gave name {:?}", value);
 189         value
 190     }
 191
 192     /// Checks for the case where `fr` maps to something that the
 193     /// *user* has a name for. In that case, we'll be able to map
 194     /// `fr` to a `Region<'tcx>`, and that region will be one of
 195     /// named variants.
 196     fn give_name_from_error_region(
 197         &self,
 198         tcx: TyCtxt<'_, '_, 'tcx>,
 199         mir_def_id: DefId,
 200         fr: RegionVid,
 201         counter: &mut usize,
 202     ) -> Option<RegionName> {
 203         let error_region = self.to_error_region(fr)?;
 204
 205         debug!("give_region_a_name: error_region = {:?}", error_region);
 206         match error_region {
 207             ty::ReEarlyBound(ebr) => {
 208                 if ebr.has_name() {
 209                     let span = self.get_named_span(tcx, error_region, &ebr.name);
 210                     Some(RegionName {
 211                         name: ebr.name,
 212                         source: RegionNameSource::NamedEarlyBoundRegion(span)
 213                     })
 214                 } else {
 215                     None
 216                 }
 217             }
 218
 219             ty::ReStatic => Some(RegionName {
 220                 name: keywords::StaticLifetime.name().as_interned_str(),
 221                 source: RegionNameSource::Static
 222             }),
 223
 224             ty::ReFree(free_region) => match free_region.bound_region {
 225                 ty::BoundRegion::BrNamed(_, name) => {
 226                     let span = self.get_named_span(tcx, error_region, &name);
 227                     Some(RegionName {
 228                         name,
 229                         source: RegionNameSource::NamedFreeRegion(span),
 230                     })
 231                 },
 232
 233                 ty::BoundRegion::BrEnv => {
 234                     let mir_node_id = tcx.hir()
 235                                          .as_local_node_id(mir_def_id)
 236                                          .expect("non-local mir");
 237                     let def_ty = self.universal_regions.defining_ty;
 238
 239                     if let DefiningTy::Closure(def_id, substs) = def_ty {
 240                         let args_span = if let hir::ExprKind::Closure(_, _, _, span, _) =
 241                             tcx.hir().expect_expr(mir_node_id).node
 242                         {
 243                             span
 244                         } else {
 245                             bug!("Closure is not defined by a closure expr");
 246                         };
 247                         let region_name = self.synthesize_region_name(counter);
 248
 249                         let closure_kind_ty = substs.closure_kind_ty(def_id, tcx);
 250                         let note = match closure_kind_ty.to_opt_closure_kind() {
 251                             Some(ty::ClosureKind::Fn) => {
 252                                 "closure implements `Fn`, so references to captured variables \
 253                                  can't escape the closure"
 254                             }
 255                             Some(ty::ClosureKind::FnMut) => {
 256                                 "closure implements `FnMut`, so references to captured variables \
 257                                  can't escape the closure"
 258                             }
 259                             Some(ty::ClosureKind::FnOnce) => {
 260                                 bug!("BrEnv in a `FnOnce` closure");
 261                             }
 262                             None => bug!("Closure kind not inferred in borrow check"),
 263                         };
 264
 265                         Some(RegionName {
 266                             name: region_name,
 267                             source: RegionNameSource::SynthesizedFreeEnvRegion(
 268                                 args_span,
 269                                 note.to_string()
 270                             ),
 271                         })
 272                     } else {
 273                         // Can't have BrEnv in functions, constants or generators.
 274                         bug!("BrEnv outside of closure.");
 275                     }
 276                 }
 277
 278                 ty::BoundRegion::BrAnon(_) | ty::BoundRegion::BrFresh(_) => None,
 279             },
 280
 281             ty::ReLateBound(..)
 282             | ty::ReScope(..)
 283             | ty::ReVar(..)
 284             | ty::RePlaceholder(..)
 285             | ty::ReEmpty
 286             | ty::ReErased
 287             | ty::ReClosureBound(..) => None,
 288         }
 289     }
 290
 291     /// Gets a span of a named region to provide context for error messages that
 292     /// mention that span, for example:
 293     ///
 294     /// ```
 295     ///  |
 296     ///  | fn two_regions<'a, 'b, T>(cell: Cell<&'a ()>, t: T)
 297     ///  |                --  -- lifetime `'b` defined here
 298     ///  |                |
 299     ///  |                lifetime `'a` defined here
 300     ///  |
 301     ///  |     with_signature(cell, t, |cell, t| require(cell, t));
 302     ///  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ argument requires that `'b` must
 303     ///  |                                                         outlive `'a`
 304     /// ```
 305     fn get_named_span(
 306         &self,
 307         tcx: TyCtxt<'_, '_, 'tcx>,
 308         error_region: &RegionKind,
 309         name: &InternedString,
 310     ) -> Span {
 311         let scope = error_region.free_region_binding_scope(tcx);
 312         let node = tcx.hir().as_local_hir_id(scope).unwrap_or(hir::DUMMY_HIR_ID);
 313
 314         let span = tcx.sess.source_map().def_span(tcx.hir().span_by_hir_id(node));
 315         if let Some(param) = tcx.hir()
 316             .get_generics(scope)
 317             .and_then(|generics| generics.get_named(name))
 318         {
 319             param.span
 320         } else {
 321             span
 322         }
 323     }
 324
 325     /// Finds an argument that contains `fr` and label it with a fully
 326     /// elaborated type, returning something like `'1`. Result looks
 327     /// like:
 328     ///
 329     /// ```
 330     ///  | fn foo(x: &u32) { .. }
 331     ///           ------- fully elaborated type of `x` is `&'1 u32`
 332     /// ```
 333     fn give_name_if_anonymous_region_appears_in_arguments(
 334         &self,
 335         infcx: &InferCtxt<'_, '_, 'tcx>,
 336         mir: &Mir<'tcx>,
 337         mir_def_id: DefId,
 338         fr: RegionVid,
 339         counter: &mut usize,
 340     ) -> Option<RegionName> {
 341         let implicit_inputs = self.universal_regions.defining_ty.implicit_inputs();
 342         let argument_index = self.get_argument_index_for_region(infcx.tcx, fr)?;
 343
 344         let arg_ty =
 345             self.universal_regions.unnormalized_input_tys[implicit_inputs + argument_index];
 346         if let Some(region_name) = self.give_name_if_we_can_match_hir_ty_from_argument(
 347             infcx,
 348             mir,
 349             mir_def_id,
 350             fr,
 351             arg_ty,
 352             argument_index,
 353             counter,
 354         ) {
 355             return Some(region_name);
 356         }
 357
 358         self.give_name_if_we_cannot_match_hir_ty(infcx, mir, fr, arg_ty, counter)
 359     }
 360
 361     fn give_name_if_we_can_match_hir_ty_from_argument(
 362         &self,
 363         infcx: &InferCtxt<'_, '_, 'tcx>,
 364         mir: &Mir<'tcx>,
 365         mir_def_id: DefId,
 366         needle_fr: RegionVid,
 367         argument_ty: Ty<'tcx>,
 368         argument_index: usize,
 369         counter: &mut usize,
 370     ) -> Option<RegionName> {
 371         let mir_node_id = infcx.tcx.hir().as_local_node_id(mir_def_id)?;
 372         let fn_decl = infcx.tcx.hir().fn_decl(mir_node_id)?;
 373         let argument_hir_ty: &hir::Ty = &fn_decl.inputs[argument_index];
 374         match argument_hir_ty.node {
 375             // This indicates a variable with no type annotation, like
 376             // `|x|`... in that case, we can't highlight the type but
 377             // must highlight the variable.
 378             hir::TyKind::Infer => self.give_name_if_we_cannot_match_hir_ty(
 379                 infcx,
 380                 mir,
 381                 needle_fr,
 382                 argument_ty,
 383                 counter,
 384             ),
 385
 386             _ => self.give_name_if_we_can_match_hir_ty(
 387                 infcx.tcx,
 388                 needle_fr,
 389                 argument_ty,
 390                 argument_hir_ty,
 391                 counter,
 392             ),
 393         }
 394     }
 395
 396     /// Attempts to highlight the specific part of a type in an argument
 397     /// that has no type annotation.
 398     /// For example, we might produce an annotation like this:
 399     ///
 400     /// ```
 401     ///  |     foo(|a, b| b)
 402     ///  |          -  -
 403     ///  |          |  |
 404     ///  |          |  has type `&'1 u32`
 405     ///  |          has type `&'2 u32`
 406     /// ```
 407     fn give_name_if_we_cannot_match_hir_ty(
 408         &self,
 409         infcx: &InferCtxt<'_, '_, 'tcx>,
 410         mir: &Mir<'tcx>,
 411         needle_fr: RegionVid,
 412         argument_ty: Ty<'tcx>,
 413         counter: &mut usize,
 414     ) -> Option<RegionName> {
 415         let mut highlight = RegionHighlightMode::default();
 416         highlight.highlighting_region_vid(needle_fr, *counter);
 417         let type_name = infcx.extract_type_name(&argument_ty, Some(highlight));
 418
 419         debug!(
 420             "give_name_if_we_cannot_match_hir_ty: type_name={:?} needle_fr={:?}",
 421             type_name, needle_fr
 422         );
 423         let assigned_region_name = if type_name.find(&format!("'{}", counter)).is_some() {
 424             // Only add a label if we can confirm that a region was labelled.
 425             let argument_index = self.get_argument_index_for_region(infcx.tcx, needle_fr)?;
 426             let (_, span) = self.get_argument_name_and_span_for_region(mir, argument_index);
 427
 428             Some(RegionName {
 429                 // This counter value will already have been used, so this function will increment
 430                 // it so the next value will be used next and return the region name that would
 431                 // have been used.
 432                 name: self.synthesize_region_name(counter),
 433                 source: RegionNameSource::CannotMatchHirTy(span, type_name),
 434             })
 435         } else {
 436             None
 437         };
 438
 439         assigned_region_name
 440     }
 441
 442     /// Attempts to highlight the specific part of a type annotation
 443     /// that contains the anonymous reference we want to give a name
 444     /// to. For example, we might produce an annotation like this:
 445     ///
 446     /// ```
 447     ///  | fn a<T>(items: &[T]) -> Box<dyn Iterator<Item = &T>> {
 448     ///  |                - let's call the lifetime of this reference `'1`
 449     /// ```
 450     ///
 451     /// the way this works is that we match up `argument_ty`, which is
 452     /// a `Ty<'tcx>` (the internal form of the type) with
 453     /// `argument_hir_ty`, a `hir::Ty` (the syntax of the type
 454     /// annotation). We are descending through the types stepwise,
 455     /// looking in to find the region `needle_fr` in the internal
 456     /// type. Once we find that, we can use the span of the `hir::Ty`
 457     /// to add the highlight.
 458     ///
 459     /// This is a somewhat imperfect process, so long the way we also
 460     /// keep track of the **closest** type we've found. If we fail to
 461     /// find the exact `&` or `'_` to highlight, then we may fall back
 462     /// to highlighting that closest type instead.
 463     fn give_name_if_we_can_match_hir_ty(
 464         &self,
 465         tcx: TyCtxt<'_, '_, 'tcx>,
 466         needle_fr: RegionVid,
 467         argument_ty: Ty<'tcx>,
 468         argument_hir_ty: &hir::Ty,
 469         counter: &mut usize,
 470     ) -> Option<RegionName> {
 471         let search_stack: &mut Vec<(Ty<'tcx>, &hir::Ty)> =
 472             &mut vec![(argument_ty, argument_hir_ty)];
 473
 474         while let Some((ty, hir_ty)) = search_stack.pop() {
 475             match (&ty.sty, &hir_ty.node) {
 476                 // Check if the `argument_ty` is `&'X ..` where `'X`
 477                 // is the region we are looking for -- if so, and we have a `&T`
 478                 // on the RHS, then we want to highlight the `&` like so:
 479                 //
 480                 //     &
 481                 //     - let's call the lifetime of this reference `'1`
 482                 (
 483                     ty::Ref(region, referent_ty, _),
 484                     hir::TyKind::Rptr(_lifetime, referent_hir_ty),
 485                 ) => {
 486                     if region.to_region_vid() == needle_fr {
 487                         let region_name = self.synthesize_region_name(counter);
 488
 489                         // Just grab the first character, the `&`.
 490                         let source_map = tcx.sess.source_map();
 491                         let ampersand_span = source_map.start_point(hir_ty.span);
 492
 493                         return Some(RegionName {
 494                             name: region_name,
 495                             source: RegionNameSource::MatchedHirTy(ampersand_span),
 496                         });
 497                     }
 498
 499                     // Otherwise, let's descend into the referent types.
 500                     search_stack.push((referent_ty, &referent_hir_ty.ty));
 501                 }
 502
 503                 // Match up something like `Foo<'1>`
 504                 (
 505                     ty::Adt(_adt_def, substs),
 506                     hir::TyKind::Path(hir::QPath::Resolved(None, path)),
 507                 ) => {
 508                     match path.res {
 509                         // Type parameters of the type alias have no reason to
 510                         // be the same as those of the ADT.
 511                         // FIXME: We should be able to do something similar to
 512                         // match_adt_and_segment in this case.
 513                         Res::Def(DefKind::TyAlias, _) => (),
 514                         _ => if let Some(last_segment) = path.segments.last() {
 515                             if let Some(name) = self.match_adt_and_segment(
 516                                 substs,
 517                                 needle_fr,
 518                                 last_segment,
 519                                 counter,
 520                                 search_stack,
 521                             ) {
 522                                 return Some(name);
 523                             }
 524                         }
 525                     }
 526                 }
 527
 528                 // The following cases don't have lifetimes, so we
 529                 // just worry about trying to match up the rustc type
 530                 // with the HIR types:
 531                 (ty::Tuple(elem_tys), hir::TyKind::Tup(elem_hir_tys)) => {
 532                     search_stack.extend(elem_tys.iter().map(|k| k.expect_ty()).zip(elem_hir_tys));
 533                 }
 534
 535                 (ty::Slice(elem_ty), hir::TyKind::Slice(elem_hir_ty))
 536                 | (ty::Array(elem_ty, _), hir::TyKind::Array(elem_hir_ty, _)) => {
 537                     search_stack.push((elem_ty, elem_hir_ty));
 538                 }
 539
 540                 (ty::RawPtr(mut_ty), hir::TyKind::Ptr(mut_hir_ty)) => {
 541                     search_stack.push((mut_ty.ty, &mut_hir_ty.ty));
 542                 }
 543
 544                 _ => {
 545                     // FIXME there are other cases that we could trace
 546                 }
 547             }
 548         }
 549
 550         return None;
 551     }
 552
 553     /// We've found an enum/struct/union type with the substitutions
 554     /// `substs` and -- in the HIR -- a path type with the final
 555     /// segment `last_segment`. Try to find a `'_` to highlight in
 556     /// the generic args (or, if not, to produce new zipped pairs of
 557     /// types+hir to search through).
 558     fn match_adt_and_segment<'hir>(
 559         &self,
 560         substs: SubstsRef<'tcx>,
 561         needle_fr: RegionVid,
 562         last_segment: &'hir hir::PathSegment,
 563         counter: &mut usize,
 564         search_stack: &mut Vec<(Ty<'tcx>, &'hir hir::Ty)>,
 565     ) -> Option<RegionName> {
 566         // Did the user give explicit arguments? (e.g., `Foo<..>`)
 567         let args = last_segment.args.as_ref()?;
 568         let lifetime = self.try_match_adt_and_generic_args(substs, needle_fr, args, search_stack)?;
 569         match lifetime.name {
 570             hir::LifetimeName::Param(_)
 571             | hir::LifetimeName::Error
 572             | hir::LifetimeName::Static
 573             | hir::LifetimeName::Underscore => {
 574                 let region_name = self.synthesize_region_name(counter);
 575                 let ampersand_span = lifetime.span;
 576                 Some(RegionName {
 577                     name: region_name,
 578                     source: RegionNameSource::MatchedAdtAndSegment(ampersand_span),
 579                 })
 580             }
 581
 582             hir::LifetimeName::Implicit => {
 583                 // In this case, the user left off the lifetime; so
 584                 // they wrote something like:
 585                 //
 586                 // ```
 587                 // x: Foo<T>
 588                 // ```
 589                 //
 590                 // where the fully elaborated form is `Foo<'_, '1,
 591                 // T>`. We don't consider this a match; instead we let
 592                 // the "fully elaborated" type fallback above handle
 593                 // it.
 594                 None
 595             }
 596         }
 597     }
 598
 599     /// We've found an enum/struct/union type with the substitutions
 600     /// `substs` and -- in the HIR -- a path with the generic
 601     /// arguments `args`. If `needle_fr` appears in the args, return
 602     /// the `hir::Lifetime` that corresponds to it. If not, push onto
 603     /// `search_stack` the types+hir to search through.
 604     fn try_match_adt_and_generic_args<'hir>(
 605         &self,
 606         substs: SubstsRef<'tcx>,
 607         needle_fr: RegionVid,
 608         args: &'hir hir::GenericArgs,
 609         search_stack: &mut Vec<(Ty<'tcx>, &'hir hir::Ty)>,
 610     ) -> Option<&'hir hir::Lifetime> {
 611         for (kind, hir_arg) in substs.iter().zip(&args.args) {
 612             match (kind.unpack(), hir_arg) {
 613                 (UnpackedKind::Lifetime(r), hir::GenericArg::Lifetime(lt)) => {
 614                     if r.to_region_vid() == needle_fr {
 615                         return Some(lt);
 616                     }
 617                 }
 618
 619                 (UnpackedKind::Type(ty), hir::GenericArg::Type(hir_ty)) => {
 620                     search_stack.push((ty, hir_ty));
 621                 }
 622
 623                 (UnpackedKind::Const(_ct), hir::GenericArg::Const(_hir_ct)) => {
 624                     // Lifetimes cannot be found in consts, so we don't need
 625                     // to search anything here.
 626                 }
 627
 628                 (UnpackedKind::Lifetime(_), _)
 629                 | (UnpackedKind::Type(_), _)
 630                 | (UnpackedKind::Const(_), _) => {
 631                     // I *think* that HIR lowering should ensure this
 632                     // doesn't happen, even in erroneous
 633                     // programs. Else we should use delay-span-bug.
 634                     span_bug!(
 635                         hir_arg.span(),
 636                         "unmatched subst and hir arg: found {:?} vs {:?}",
 637                         kind,
 638                         hir_arg,
 639                     );
 640                 }
 641             }
 642         }
 643
 644         None
 645     }
 646
 647     /// Finds a closure upvar that contains `fr` and label it with a
 648     /// fully elaborated type, returning something like `'1`. Result
 649     /// looks like:
 650     ///
 651     /// ```
 652     ///  | let x = Some(&22);
 653     ///        - fully elaborated type of `x` is `Option<&'1 u32>`
 654     /// ```
 655     fn give_name_if_anonymous_region_appears_in_upvars(
 656         &self,
 657         tcx: TyCtxt<'_, '_, 'tcx>,
 658         upvars: &[Upvar],
 659         fr: RegionVid,
 660         counter: &mut usize,
 661     ) -> Option<RegionName> {
 662         let upvar_index = self.get_upvar_index_for_region(tcx, fr)?;
 663         let (upvar_name, upvar_span) =
 664             self.get_upvar_name_and_span_for_region(tcx, upvars, upvar_index);
 665         let region_name = self.synthesize_region_name(counter);
 666
 667         Some(RegionName {
 668             name: region_name,
 669             source: RegionNameSource::AnonRegionFromUpvar(upvar_span, upvar_name.to_string()),
 670         })
 671     }
 672
 673     /// Checks for arguments appearing in the (closure) return type. It
 674     /// must be a closure since, in a free fn, such an argument would
 675     /// have to either also appear in an argument (if using elision)
 676     /// or be early bound (named, not in argument).
 677     fn give_name_if_anonymous_region_appears_in_output(
 678         &self,
 679         infcx: &InferCtxt<'_, '_, 'tcx>,
 680         mir: &Mir<'tcx>,
 681         mir_def_id: DefId,
 682         fr: RegionVid,
 683         counter: &mut usize,
 684     ) -> Option<RegionName> {
 685         let tcx = infcx.tcx;
 686
 687         let return_ty = self.universal_regions.unnormalized_output_ty;
 688         debug!(
 689             "give_name_if_anonymous_region_appears_in_output: return_ty = {:?}",
 690             return_ty
 691         );
 692         if !tcx.any_free_region_meets(&return_ty, |r| r.to_region_vid() == fr) {
 693             return None;
 694         }
 695
 696         let mut highlight = RegionHighlightMode::default();
 697         highlight.highlighting_region_vid(fr, *counter);
 698         let type_name = infcx.extract_type_name(&return_ty, Some(highlight));
 699
 700         let mir_node_id = tcx.hir().as_local_node_id(mir_def_id).expect("non-local mir");
 701
 702         let (return_span, mir_description) = match tcx.hir().get(mir_node_id) {
 703             hir::Node::Expr(hir::Expr {
 704                 node: hir::ExprKind::Closure(_, return_ty, _, span, gen_move),
 705                 ..
 706             }) => (
 707                 match return_ty.output {
 708                     hir::FunctionRetTy::DefaultReturn(_) => tcx.sess.source_map().end_point(*span),
 709                     hir::FunctionRetTy::Return(_) => return_ty.output.span(),
 710                 },
 711                 if gen_move.is_some() {
 712                     " of generator"
 713                 } else {
 714                     " of closure"
 715                 },
 716             ),
 717             hir::Node::ImplItem(hir::ImplItem {
 718                 node: hir::ImplItemKind::Method(method_sig, _),
 719                 ..
 720             }) => (method_sig.decl.output.span(), ""),
 721             _ => (mir.span, ""),
 722         };
 723
 724         Some(RegionName {
 725             // This counter value will already have been used, so this function will increment it
 726             // so the next value will be used next and return the region name that would have been
 727             // used.
 728             name: self.synthesize_region_name(counter),
 729             source: RegionNameSource::AnonRegionFromOutput(
 730                 return_span,
 731                 mir_description.to_string(),
 732                 type_name
 733             ),
 734         })
 735     }
 736
 737     fn give_name_if_anonymous_region_appears_in_yield_ty(
 738         &self,
 739         infcx: &InferCtxt<'_, '_, 'tcx>,
 740         mir: &Mir<'tcx>,
 741         mir_def_id: DefId,
 742         fr: RegionVid,
 743         counter: &mut usize,
 744     ) -> Option<RegionName> {
 745         // Note: generators from `async fn` yield `()`, so we don't have to
 746         // worry about them here.
 747         let yield_ty = self.universal_regions.yield_ty?;
 748         debug!(
 749             "give_name_if_anonymous_region_appears_in_yield_ty: yield_ty = {:?}",
 750             yield_ty,
 751         );
 752
 753         let tcx = infcx.tcx;
 754
 755         if !tcx.any_free_region_meets(&yield_ty, |r| r.to_region_vid() == fr) {
 756             return None;
 757         }
 758
 759         let mut highlight = RegionHighlightMode::default();
 760         highlight.highlighting_region_vid(fr, *counter);
 761         let type_name = infcx.extract_type_name(&yield_ty, Some(highlight));
 762
 763         let mir_node_id = tcx.hir().as_local_node_id(mir_def_id).expect("non-local mir");
 764
 765         let yield_span = match tcx.hir().get(mir_node_id) {
 766             hir::Node::Expr(hir::Expr {
 767                 node: hir::ExprKind::Closure(_, _, _, span, _),
 768                 ..
 769             }) => (
 770                 tcx.sess.source_map().end_point(*span)
 771             ),
 772             _ => mir.span,
 773         };
 774
 775         debug!(
 776             "give_name_if_anonymous_region_appears_in_yield_ty: \
 777              type_name = {:?}, yield_span = {:?}",
 778             yield_span,
 779             type_name,
 780         );
 781
 782         Some(RegionName {
 783             name: self.synthesize_region_name(counter),
 784             source: RegionNameSource::AnonRegionFromYieldTy(yield_span, type_name),
 785         })
 786     }
 787
 788     /// Creates a synthetic region named `'1`, incrementing the
 789     /// counter.
 790     fn synthesize_region_name(&self, counter: &mut usize) -> InternedString {
 791         let c = *counter;
 792         *counter += 1;
 793
 794         Name::intern(&format!("'{:?}", c)).as_interned_str()
 795     }
 796 }