src/librustc_mir/borrow_check/diagnostics/region_name.rs

   1 use std::fmt::{self, Display};
   2
   3 use rustc_errors::DiagnosticBuilder;
   4 use rustc_hir as hir;
   5 use rustc_hir::def::{DefKind, Res};
   6 use rustc_middle::ty::print::RegionHighlightMode;
   7 use rustc_middle::ty::subst::{GenericArgKind, SubstsRef};
   8 use rustc_middle::ty::{self, RegionVid, Ty};
   9 use rustc_span::symbol::kw;
  10 use rustc_span::{symbol::Symbol, Span, DUMMY_SP};
  11
  12 use crate::borrow_check::{nll::ToRegionVid, universal_regions::DefiningTy, MirBorrowckCtxt};
  13
  14 /// A name for a particular region used in emitting diagnostics. This name could be a generated
  15 /// name like `'1`, a name used by the user like `'a`, or a name like `'static`.
  16 #[derive(Debug, Clone)]
  17 crate struct RegionName {
  18     /// The name of the region (interned).
  19     crate name: Symbol,
  20     /// Where the region comes from.
  21     crate source: RegionNameSource,
  22 }
  23
  24 /// Denotes the source of a region that is named by a `RegionName`. For example, a free region that
  25 /// was named by the user would get `NamedFreeRegion` and `'static` lifetime would get `Static`.
  26 /// This helps to print the right kinds of diagnostics.
  27 #[derive(Debug, Clone)]
  28 crate enum RegionNameSource {
  29     /// A bound (not free) region that was substituted at the def site (not an HRTB).
  30     NamedEarlyBoundRegion(Span),
  31     /// A free region that the user has a name (`'a`) for.
  32     NamedFreeRegion(Span),
  33     /// The `'static` region.
  34     Static,
  35     /// The free region corresponding to the environment of a closure.
  36     SynthesizedFreeEnvRegion(Span, String),
  37     /// The region name corresponds to a region where the type annotation is completely missing
  38     /// from the code, e.g. in a closure arguments `|x| { ... }`, where `x` is a reference.
  39     CannotMatchHirTy(Span, String),
  40     /// The region name corresponds a reference that was found by traversing the type in the HIR.
  41     MatchedHirTy(Span),
  42     /// A region name from the generics list of a struct/enum/union.
  43     MatchedAdtAndSegment(Span),
  44     /// The region corresponding to a closure upvar.
  45     AnonRegionFromUpvar(Span, String),
  46     /// The region corresponding to the return type of a closure.
  47     AnonRegionFromOutput(Span, String, String),
  48     /// The region from a type yielded by a generator.
  49     AnonRegionFromYieldTy(Span, String),
  50     /// An anonymous region from an async fn.
  51     AnonRegionFromAsyncFn(Span),
  52 }
  53
  54 impl RegionName {
  55     crate fn was_named(&self) -> bool {
  56         match self.source {
  57             RegionNameSource::NamedEarlyBoundRegion(..)
  58             | RegionNameSource::NamedFreeRegion(..)
  59             | RegionNameSource::Static => true,
  60             RegionNameSource::SynthesizedFreeEnvRegion(..)
  61             | RegionNameSource::CannotMatchHirTy(..)
  62             | RegionNameSource::MatchedHirTy(..)
  63             | RegionNameSource::MatchedAdtAndSegment(..)
  64             | RegionNameSource::AnonRegionFromUpvar(..)
  65             | RegionNameSource::AnonRegionFromOutput(..)
  66             | RegionNameSource::AnonRegionFromYieldTy(..)
  67             | RegionNameSource::AnonRegionFromAsyncFn(..) => false,
  68         }
  69     }
  70
  71     crate fn highlight_region_name(&self, diag: &mut DiagnosticBuilder<'_>) {
  72         match &self.source {
  73             RegionNameSource::NamedFreeRegion(span)
  74             | RegionNameSource::NamedEarlyBoundRegion(span) => {
  75                 diag.span_label(*span, format!("lifetime `{}` defined here", self));
  76             }
  77             RegionNameSource::SynthesizedFreeEnvRegion(span, note) => {
  78                 diag.span_label(
  79                     *span,
  80                     format!("lifetime `{}` represents this closure's body", self),
  81                 );
  82                 diag.note(&note);
  83             }
  84             RegionNameSource::CannotMatchHirTy(span, type_name) => {
  85                 diag.span_label(*span, format!("has type `{}`", type_name));
  86             }
  87             RegionNameSource::MatchedHirTy(span)
  88             | RegionNameSource::AnonRegionFromAsyncFn(span) => {
  89                 diag.span_label(
  90                     *span,
  91                     format!("let's call the lifetime of this reference `{}`", self),
  92                 );
  93             }
  94             RegionNameSource::MatchedAdtAndSegment(span) => {
  95                 diag.span_label(*span, format!("let's call this `{}`", self));
  96             }
  97             RegionNameSource::AnonRegionFromUpvar(span, upvar_name) => {
  98                 diag.span_label(
  99                     *span,
 100                     format!("lifetime `{}` appears in the type of `{}`", self, upvar_name),
 101                 );
 102             }
 103             RegionNameSource::AnonRegionFromOutput(span, mir_description, type_name) => {
 104                 diag.span_label(*span, format!("return type{} is {}", mir_description, type_name));
 105             }
 106             RegionNameSource::AnonRegionFromYieldTy(span, type_name) => {
 107                 diag.span_label(*span, format!("yield type is {}", type_name));
 108             }
 109             RegionNameSource::Static => {}
 110         }
 111     }
 112 }
 113
 114 impl Display for RegionName {
 115     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 116         write!(f, "{}", self.name)
 117     }
 118 }
 119
 120 impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
 121     /// Generate a synthetic region named `'N`, where `N` is the next value of the counter. Then,
 122     /// increment the counter.
 123     ///
 124     /// This is _not_ idempotent. Call `give_region_a_name` when possible.
 125     fn synthesize_region_name(&self) -> Symbol {
 126         let c = self.next_region_name.replace_with(|counter| *counter + 1);
 127         Symbol::intern(&format!("'{:?}", c))
 128     }
 129
 130     /// Maps from an internal MIR region vid to something that we can
 131     /// report to the user. In some cases, the region vids will map
 132     /// directly to lifetimes that the user has a name for (e.g.,
 133     /// `'static`). But frequently they will not, in which case we
 134     /// have to find some way to identify the lifetime to the user. To
 135     /// that end, this function takes a "diagnostic" so that it can
 136     /// create auxiliary notes as needed.
 137     ///
 138     /// The names are memoized, so this is both cheap to recompute and idempotent.
 139     ///
 140     /// Example (function arguments):
 141     ///
 142     /// Suppose we are trying to give a name to the lifetime of the
 143     /// reference `x`:
 144     ///
 145     /// ```
 146     /// fn foo(x: &u32) { .. }
 147     /// ```
 148     ///
 149     /// This function would create a label like this:
 150     ///
 151     /// ```text
 152     ///  | fn foo(x: &u32) { .. }
 153     ///           ------- fully elaborated type of `x` is `&'1 u32`
 154     /// ```
 155     ///
 156     /// and then return the name `'1` for us to use.
 157     crate fn give_region_a_name(&self, fr: RegionVid) -> Option<RegionName> {
 158         debug!(
 159             "give_region_a_name(fr={:?}, counter={:?})",
 160             fr,
 161             self.next_region_name.try_borrow().unwrap()
 162         );
 163
 164         assert!(self.regioncx.universal_regions().is_universal_region(fr));
 165
 166         if let Some(value) = self.region_names.try_borrow_mut().unwrap().get(&fr) {
 167             return Some(value.clone());
 168         }
 169
 170         let value = self
 171             .give_name_from_error_region(fr)
 172             .or_else(|| self.give_name_if_anonymous_region_appears_in_arguments(fr))
 173             .or_else(|| self.give_name_if_anonymous_region_appears_in_upvars(fr))
 174             .or_else(|| self.give_name_if_anonymous_region_appears_in_output(fr))
 175             .or_else(|| self.give_name_if_anonymous_region_appears_in_yield_ty(fr));
 176
 177         if let Some(ref value) = value {
 178             self.region_names.try_borrow_mut().unwrap().insert(fr, value.clone());
 179         }
 180
 181         debug!("give_region_a_name: gave name {:?}", value);
 182         value
 183     }
 184
 185     /// Checks for the case where `fr` maps to something that the
 186     /// *user* has a name for. In that case, we'll be able to map
 187     /// `fr` to a `Region<'tcx>`, and that region will be one of
 188     /// named variants.
 189     fn give_name_from_error_region(&self, fr: RegionVid) -> Option<RegionName> {
 190         let error_region = self.to_error_region(fr)?;
 191
 192         let tcx = self.infcx.tcx;
 193
 194         debug!("give_region_a_name: error_region = {:?}", error_region);
 195         match error_region {
 196             ty::ReEarlyBound(ebr) => {
 197                 if ebr.has_name() {
 198                     let span = tcx.hir().span_if_local(ebr.def_id).unwrap_or(DUMMY_SP);
 199                     Some(RegionName {
 200                         name: ebr.name,
 201                         source: RegionNameSource::NamedEarlyBoundRegion(span),
 202                     })
 203                 } else {
 204                     None
 205                 }
 206             }
 207
 208             ty::ReStatic => {
 209                 Some(RegionName { name: kw::StaticLifetime, source: RegionNameSource::Static })
 210             }
 211
 212             ty::ReFree(free_region) => match free_region.bound_region {
 213                 ty::BoundRegion::BrNamed(region_def_id, name) => {
 214                     // Get the span to point to, even if we don't use the name.
 215                     let span = tcx.hir().span_if_local(region_def_id).unwrap_or(DUMMY_SP);
 216                     debug!(
 217                         "bound region named: {:?}, is_named: {:?}",
 218                         name,
 219                         free_region.bound_region.is_named()
 220                     );
 221
 222                     if free_region.bound_region.is_named() {
 223                         // A named region that is actually named.
 224                         Some(RegionName { name, source: RegionNameSource::NamedFreeRegion(span) })
 225                     } else {
 226                         // If we spuriously thought that the region is named, we should let the
 227                         // system generate a true name for error messages. Currently this can
 228                         // happen if we have an elided name in an async fn for example: the
 229                         // compiler will generate a region named `'_`, but reporting such a name is
 230                         // not actually useful, so we synthesize a name for it instead.
 231                         let name = self.synthesize_region_name();
 232                         Some(RegionName {
 233                             name,
 234                             source: RegionNameSource::AnonRegionFromAsyncFn(span),
 235                         })
 236                     }
 237                 }
 238
 239                 ty::BoundRegion::BrEnv => {
 240                     let mir_hir_id = self
 241                         .infcx
 242                         .tcx
 243                         .hir()
 244                         .as_local_hir_id(self.mir_def_id)
 245                         .expect("non-local mir");
 246                     let def_ty = self.regioncx.universal_regions().defining_ty;
 247
 248                     if let DefiningTy::Closure(_, substs) = def_ty {
 249                         let args_span = if let hir::ExprKind::Closure(_, _, _, span, _) =
 250                             tcx.hir().expect_expr(mir_hir_id).kind
 251                         {
 252                             span
 253                         } else {
 254                             bug!("Closure is not defined by a closure expr");
 255                         };
 256                         let region_name = self.synthesize_region_name();
 257
 258                         let closure_kind_ty = substs.as_closure().kind_ty();
 259                         let note = match closure_kind_ty.to_opt_closure_kind() {
 260                             Some(ty::ClosureKind::Fn) => {
 261                                 "closure implements `Fn`, so references to captured variables \
 262                                  can't escape the closure"
 263                             }
 264                             Some(ty::ClosureKind::FnMut) => {
 265                                 "closure implements `FnMut`, so references to captured variables \
 266                                  can't escape the closure"
 267                             }
 268                             Some(ty::ClosureKind::FnOnce) => {
 269                                 bug!("BrEnv in a `FnOnce` closure");
 270                             }
 271                             None => bug!("Closure kind not inferred in borrow check"),
 272                         };
 273
 274                         Some(RegionName {
 275                             name: region_name,
 276                             source: RegionNameSource::SynthesizedFreeEnvRegion(
 277                                 args_span,
 278                                 note.to_string(),
 279                             ),
 280                         })
 281                     } else {
 282                         // Can't have BrEnv in functions, constants or generators.
 283                         bug!("BrEnv outside of closure.");
 284                     }
 285                 }
 286
 287                 ty::BoundRegion::BrAnon(_) => None,
 288             },
 289
 290             ty::ReLateBound(..)
 291             | ty::ReScope(..)
 292             | ty::ReVar(..)
 293             | ty::RePlaceholder(..)
 294             | ty::ReEmpty(_)
 295             | ty::ReErased => None,
 296         }
 297     }
 298
 299     /// Finds an argument that contains `fr` and label it with a fully
 300     /// elaborated type, returning something like `'1`. Result looks
 301     /// like:
 302     ///
 303     /// ```text
 304     ///  | fn foo(x: &u32) { .. }
 305     ///           ------- fully elaborated type of `x` is `&'1 u32`
 306     /// ```
 307     fn give_name_if_anonymous_region_appears_in_arguments(
 308         &self,
 309         fr: RegionVid,
 310     ) -> Option<RegionName> {
 311         let implicit_inputs = self.regioncx.universal_regions().defining_ty.implicit_inputs();
 312         let argument_index = self.regioncx.get_argument_index_for_region(self.infcx.tcx, fr)?;
 313
 314         let arg_ty = self.regioncx.universal_regions().unnormalized_input_tys
 315             [implicit_inputs + argument_index];
 316         if let Some(region_name) =
 317             self.give_name_if_we_can_match_hir_ty_from_argument(fr, arg_ty, argument_index)
 318         {
 319             return Some(region_name);
 320         }
 321
 322         self.give_name_if_we_cannot_match_hir_ty(fr, arg_ty)
 323     }
 324
 325     fn give_name_if_we_can_match_hir_ty_from_argument(
 326         &self,
 327         needle_fr: RegionVid,
 328         argument_ty: Ty<'tcx>,
 329         argument_index: usize,
 330     ) -> Option<RegionName> {
 331         let mir_hir_id = self.infcx.tcx.hir().as_local_hir_id(self.mir_def_id)?;
 332         let fn_decl = self.infcx.tcx.hir().fn_decl_by_hir_id(mir_hir_id)?;
 333         let argument_hir_ty: &hir::Ty<'_> = fn_decl.inputs.get(argument_index)?;
 334         match argument_hir_ty.kind {
 335             // This indicates a variable with no type annotation, like
 336             // `|x|`... in that case, we can't highlight the type but
 337             // must highlight the variable.
 338             // NOTE(eddyb) this is handled in/by the sole caller
 339             // (`give_name_if_anonymous_region_appears_in_arguments`).
 340             hir::TyKind::Infer => None,
 341
 342             _ => self.give_name_if_we_can_match_hir_ty(needle_fr, argument_ty, argument_hir_ty),
 343         }
 344     }
 345
 346     /// Attempts to highlight the specific part of a type in an argument
 347     /// that has no type annotation.
 348     /// For example, we might produce an annotation like this:
 349     ///
 350     /// ```text
 351     ///  |     foo(|a, b| b)
 352     ///  |          -  -
 353     ///  |          |  |
 354     ///  |          |  has type `&'1 u32`
 355     ///  |          has type `&'2 u32`
 356     /// ```
 357     fn give_name_if_we_cannot_match_hir_ty(
 358         &self,
 359         needle_fr: RegionVid,
 360         argument_ty: Ty<'tcx>,
 361     ) -> Option<RegionName> {
 362         let counter = *self.next_region_name.try_borrow().unwrap();
 363         let mut highlight = RegionHighlightMode::default();
 364         highlight.highlighting_region_vid(needle_fr, counter);
 365         let type_name = self.infcx.extract_type_name(&argument_ty, Some(highlight)).0;
 366
 367         debug!(
 368             "give_name_if_we_cannot_match_hir_ty: type_name={:?} needle_fr={:?}",
 369             type_name, needle_fr
 370         );
 371         let assigned_region_name = if type_name.find(&format!("'{}", counter)).is_some() {
 372             // Only add a label if we can confirm that a region was labelled.
 373             let argument_index =
 374                 self.regioncx.get_argument_index_for_region(self.infcx.tcx, needle_fr)?;
 375             let (_, span) = self.regioncx.get_argument_name_and_span_for_region(
 376                 &self.body,
 377                 &self.local_names,
 378                 argument_index,
 379             );
 380
 381             Some(RegionName {
 382                 // This counter value will already have been used, so this function will increment
 383                 // it so the next value will be used next and return the region name that would
 384                 // have been used.
 385                 name: self.synthesize_region_name(),
 386                 source: RegionNameSource::CannotMatchHirTy(span, type_name),
 387             })
 388         } else {
 389             None
 390         };
 391
 392         assigned_region_name
 393     }
 394
 395     /// Attempts to highlight the specific part of a type annotation
 396     /// that contains the anonymous reference we want to give a name
 397     /// to. For example, we might produce an annotation like this:
 398     ///
 399     /// ```text
 400     ///  | fn a<T>(items: &[T]) -> Box<dyn Iterator<Item = &T>> {
 401     ///  |                - let's call the lifetime of this reference `'1`
 402     /// ```
 403     ///
 404     /// the way this works is that we match up `argument_ty`, which is
 405     /// a `Ty<'tcx>` (the internal form of the type) with
 406     /// `argument_hir_ty`, a `hir::Ty` (the syntax of the type
 407     /// annotation). We are descending through the types stepwise,
 408     /// looking in to find the region `needle_fr` in the internal
 409     /// type. Once we find that, we can use the span of the `hir::Ty`
 410     /// to add the highlight.
 411     ///
 412     /// This is a somewhat imperfect process, so along the way we also
 413     /// keep track of the **closest** type we've found. If we fail to
 414     /// find the exact `&` or `'_` to highlight, then we may fall back
 415     /// to highlighting that closest type instead.
 416     fn give_name_if_we_can_match_hir_ty(
 417         &self,
 418         needle_fr: RegionVid,
 419         argument_ty: Ty<'tcx>,
 420         argument_hir_ty: &hir::Ty<'_>,
 421     ) -> Option<RegionName> {
 422         let search_stack: &mut Vec<(Ty<'tcx>, &hir::Ty<'_>)> =
 423             &mut vec![(argument_ty, argument_hir_ty)];
 424
 425         while let Some((ty, hir_ty)) = search_stack.pop() {
 426             match (&ty.kind, &hir_ty.kind) {
 427                 // Check if the `argument_ty` is `&'X ..` where `'X`
 428                 // is the region we are looking for -- if so, and we have a `&T`
 429                 // on the RHS, then we want to highlight the `&` like so:
 430                 //
 431                 //     &
 432                 //     - let's call the lifetime of this reference `'1`
 433                 (
 434                     ty::Ref(region, referent_ty, _),
 435                     hir::TyKind::Rptr(_lifetime, referent_hir_ty),
 436                 ) => {
 437                     if region.to_region_vid() == needle_fr {
 438                         let region_name = self.synthesize_region_name();
 439
 440                         // Just grab the first character, the `&`.
 441                         let source_map = self.infcx.tcx.sess.source_map();
 442                         let ampersand_span = source_map.start_point(hir_ty.span);
 443
 444                         return Some(RegionName {
 445                             name: region_name,
 446                             source: RegionNameSource::MatchedHirTy(ampersand_span),
 447                         });
 448                     }
 449
 450                     // Otherwise, let's descend into the referent types.
 451                     search_stack.push((referent_ty, &referent_hir_ty.ty));
 452                 }
 453
 454                 // Match up something like `Foo<'1>`
 455                 (
 456                     ty::Adt(_adt_def, substs),
 457                     hir::TyKind::Path(hir::QPath::Resolved(None, path)),
 458                 ) => {
 459                     match path.res {
 460                         // Type parameters of the type alias have no reason to
 461                         // be the same as those of the ADT.
 462                         // FIXME: We should be able to do something similar to
 463                         // match_adt_and_segment in this case.
 464                         Res::Def(DefKind::TyAlias, _) => (),
 465                         _ => {
 466                             if let Some(last_segment) = path.segments.last() {
 467                                 if let Some(name) = self.match_adt_and_segment(
 468                                     substs,
 469                                     needle_fr,
 470                                     last_segment,
 471                                     search_stack,
 472                                 ) {
 473                                     return Some(name);
 474                                 }
 475                             }
 476                         }
 477                     }
 478                 }
 479
 480                 // The following cases don't have lifetimes, so we
 481                 // just worry about trying to match up the rustc type
 482                 // with the HIR types:
 483                 (ty::Tuple(elem_tys), hir::TyKind::Tup(elem_hir_tys)) => {
 484                     search_stack.extend(elem_tys.iter().map(|k| k.expect_ty()).zip(*elem_hir_tys));
 485                 }
 486
 487                 (ty::Slice(elem_ty), hir::TyKind::Slice(elem_hir_ty))
 488                 | (ty::Array(elem_ty, _), hir::TyKind::Array(elem_hir_ty, _)) => {
 489                     search_stack.push((elem_ty, elem_hir_ty));
 490                 }
 491
 492                 (ty::RawPtr(mut_ty), hir::TyKind::Ptr(mut_hir_ty)) => {
 493                     search_stack.push((mut_ty.ty, &mut_hir_ty.ty));
 494                 }
 495
 496                 _ => {
 497                     // FIXME there are other cases that we could trace
 498                 }
 499             }
 500         }
 501
 502         None
 503     }
 504
 505     /// We've found an enum/struct/union type with the substitutions
 506     /// `substs` and -- in the HIR -- a path type with the final
 507     /// segment `last_segment`. Try to find a `'_` to highlight in
 508     /// the generic args (or, if not, to produce new zipped pairs of
 509     /// types+hir to search through).
 510     fn match_adt_and_segment<'hir>(
 511         &self,
 512         substs: SubstsRef<'tcx>,
 513         needle_fr: RegionVid,
 514         last_segment: &'hir hir::PathSegment<'hir>,
 515         search_stack: &mut Vec<(Ty<'tcx>, &'hir hir::Ty<'hir>)>,
 516     ) -> Option<RegionName> {
 517         // Did the user give explicit arguments? (e.g., `Foo<..>`)
 518         let args = last_segment.args.as_ref()?;
 519         let lifetime =
 520             self.try_match_adt_and_generic_args(substs, needle_fr, args, search_stack)?;
 521         match lifetime.name {
 522             hir::LifetimeName::Param(_)
 523             | hir::LifetimeName::Error
 524             | hir::LifetimeName::Static
 525             | hir::LifetimeName::Underscore => {
 526                 let region_name = self.synthesize_region_name();
 527                 let ampersand_span = lifetime.span;
 528                 Some(RegionName {
 529                     name: region_name,
 530                     source: RegionNameSource::MatchedAdtAndSegment(ampersand_span),
 531                 })
 532             }
 533
 534             hir::LifetimeName::ImplicitObjectLifetimeDefault | hir::LifetimeName::Implicit => {
 535                 // In this case, the user left off the lifetime; so
 536                 // they wrote something like:
 537                 //
 538                 // ```
 539                 // x: Foo<T>
 540                 // ```
 541                 //
 542                 // where the fully elaborated form is `Foo<'_, '1,
 543                 // T>`. We don't consider this a match; instead we let
 544                 // the "fully elaborated" type fallback above handle
 545                 // it.
 546                 None
 547             }
 548         }
 549     }
 550
 551     /// We've found an enum/struct/union type with the substitutions
 552     /// `substs` and -- in the HIR -- a path with the generic
 553     /// arguments `args`. If `needle_fr` appears in the args, return
 554     /// the `hir::Lifetime` that corresponds to it. If not, push onto
 555     /// `search_stack` the types+hir to search through.
 556     fn try_match_adt_and_generic_args<'hir>(
 557         &self,
 558         substs: SubstsRef<'tcx>,
 559         needle_fr: RegionVid,
 560         args: &'hir hir::GenericArgs<'hir>,
 561         search_stack: &mut Vec<(Ty<'tcx>, &'hir hir::Ty<'hir>)>,
 562     ) -> Option<&'hir hir::Lifetime> {
 563         for (kind, hir_arg) in substs.iter().zip(args.args) {
 564             match (kind.unpack(), hir_arg) {
 565                 (GenericArgKind::Lifetime(r), hir::GenericArg::Lifetime(lt)) => {
 566                     if r.to_region_vid() == needle_fr {
 567                         return Some(lt);
 568                     }
 569                 }
 570
 571                 (GenericArgKind::Type(ty), hir::GenericArg::Type(hir_ty)) => {
 572                     search_stack.push((ty, hir_ty));
 573                 }
 574
 575                 (GenericArgKind::Const(_ct), hir::GenericArg::Const(_hir_ct)) => {
 576                     // Lifetimes cannot be found in consts, so we don't need
 577                     // to search anything here.
 578                 }
 579
 580                 (
 581                     GenericArgKind::Lifetime(_)
 582                     | GenericArgKind::Type(_)
 583                     | GenericArgKind::Const(_),
 584                     _,
 585                 ) => {
 586                     // I *think* that HIR lowering should ensure this
 587                     // doesn't happen, even in erroneous
 588                     // programs. Else we should use delay-span-bug.
 589                     span_bug!(
 590                         hir_arg.span(),
 591                         "unmatched subst and hir arg: found {:?} vs {:?}",
 592                         kind,
 593                         hir_arg,
 594                     );
 595                 }
 596             }
 597         }
 598
 599         None
 600     }
 601
 602     /// Finds a closure upvar that contains `fr` and label it with a
 603     /// fully elaborated type, returning something like `'1`. Result
 604     /// looks like:
 605     ///
 606     /// ```text
 607     ///  | let x = Some(&22);
 608     ///        - fully elaborated type of `x` is `Option<&'1 u32>`
 609     /// ```
 610     fn give_name_if_anonymous_region_appears_in_upvars(&self, fr: RegionVid) -> Option<RegionName> {
 611         let upvar_index = self.regioncx.get_upvar_index_for_region(self.infcx.tcx, fr)?;
 612         let (upvar_name, upvar_span) = self.regioncx.get_upvar_name_and_span_for_region(
 613             self.infcx.tcx,
 614             &self.upvars,
 615             upvar_index,
 616         );
 617         let region_name = self.synthesize_region_name();
 618
 619         Some(RegionName {
 620             name: region_name,
 621             source: RegionNameSource::AnonRegionFromUpvar(upvar_span, upvar_name.to_string()),
 622         })
 623     }
 624
 625     /// Checks for arguments appearing in the (closure) return type. It
 626     /// must be a closure since, in a free fn, such an argument would
 627     /// have to either also appear in an argument (if using elision)
 628     /// or be early bound (named, not in argument).
 629     fn give_name_if_anonymous_region_appears_in_output(&self, fr: RegionVid) -> Option<RegionName> {
 630         let tcx = self.infcx.tcx;
 631
 632         let return_ty = self.regioncx.universal_regions().unnormalized_output_ty;
 633         debug!("give_name_if_anonymous_region_appears_in_output: return_ty = {:?}", return_ty);
 634         if !tcx.any_free_region_meets(&return_ty, |r| r.to_region_vid() == fr) {
 635             return None;
 636         }
 637
 638         let mut highlight = RegionHighlightMode::default();
 639         highlight.highlighting_region_vid(fr, *self.next_region_name.try_borrow().unwrap());
 640         let type_name = self.infcx.extract_type_name(&return_ty, Some(highlight)).0;
 641
 642         let mir_hir_id = tcx.hir().as_local_hir_id(self.mir_def_id).expect("non-local mir");
 643
 644         let (return_span, mir_description) = match tcx.hir().get(mir_hir_id) {
 645             hir::Node::Expr(hir::Expr {
 646                 kind: hir::ExprKind::Closure(_, return_ty, _, span, gen_move),
 647                 ..
 648             }) => (
 649                 match return_ty.output {
 650                     hir::FnRetTy::DefaultReturn(_) => tcx.sess.source_map().end_point(*span),
 651                     hir::FnRetTy::Return(_) => return_ty.output.span(),
 652                 },
 653                 if gen_move.is_some() { " of generator" } else { " of closure" },
 654             ),
 655             hir::Node::ImplItem(hir::ImplItem {
 656                 kind: hir::ImplItemKind::Fn(method_sig, _),
 657                 ..
 658             }) => (method_sig.decl.output.span(), ""),
 659             _ => (self.body.span, ""),
 660         };
 661
 662         Some(RegionName {
 663             // This counter value will already have been used, so this function will increment it
 664             // so the next value will be used next and return the region name that would have been
 665             // used.
 666             name: self.synthesize_region_name(),
 667             source: RegionNameSource::AnonRegionFromOutput(
 668                 return_span,
 669                 mir_description.to_string(),
 670                 type_name,
 671             ),
 672         })
 673     }
 674
 675     fn give_name_if_anonymous_region_appears_in_yield_ty(
 676         &self,
 677         fr: RegionVid,
 678     ) -> Option<RegionName> {
 679         // Note: generators from `async fn` yield `()`, so we don't have to
 680         // worry about them here.
 681         let yield_ty = self.regioncx.universal_regions().yield_ty?;
 682         debug!("give_name_if_anonymous_region_appears_in_yield_ty: yield_ty = {:?}", yield_ty,);
 683
 684         let tcx = self.infcx.tcx;
 685
 686         if !tcx.any_free_region_meets(&yield_ty, |r| r.to_region_vid() == fr) {
 687             return None;
 688         }
 689
 690         let mut highlight = RegionHighlightMode::default();
 691         highlight.highlighting_region_vid(fr, *self.next_region_name.try_borrow().unwrap());
 692         let type_name = self.infcx.extract_type_name(&yield_ty, Some(highlight)).0;
 693
 694         let mir_hir_id = tcx.hir().as_local_hir_id(self.mir_def_id).expect("non-local mir");
 695
 696         let yield_span = match tcx.hir().get(mir_hir_id) {
 697             hir::Node::Expr(hir::Expr {
 698                 kind: hir::ExprKind::Closure(_, _, _, span, _), ..
 699             }) => (tcx.sess.source_map().end_point(*span)),
 700             _ => self.body.span,
 701         };
 702
 703         debug!(
 704             "give_name_if_anonymous_region_appears_in_yield_ty: \
 705              type_name = {:?}, yield_span = {:?}",
 706             yield_span, type_name,
 707         );
 708
 709         Some(RegionName {
 710             name: self.synthesize_region_name(),
 711             source: RegionNameSource::AnonRegionFromYieldTy(yield_span, type_name),
 712         })
 713     }
 714 }