1 use std::fmt::{self, Display};
4 use rustc_errors::Diagnostic;
6 use rustc_hir::def::{DefKind, Res};
7 use rustc_middle::ty::print::RegionHighlightMode;
8 use rustc_middle::ty::subst::{GenericArgKind, SubstsRef};
9 use rustc_middle::ty::{self, DefIdTree, RegionVid, Ty};
10 use rustc_span::symbol::{kw, sym, Ident, Symbol};
11 use rustc_span::{Span, DUMMY_SP};
13 use crate::{nll::ToRegionVid, universal_regions::DefiningTy, MirBorrowckCtxt};
15 /// A name for a particular region used in emitting diagnostics. This name could be a generated
16 /// name like `'1`, a name used by the user like `'a`, or a name like `'static`.
17 #[derive(Debug, Clone)]
18 pub(crate) struct RegionName {
19 /// The name of the region (interned).
20 pub(crate) name: Symbol,
21 /// Where the region comes from.
22 pub(crate) source: RegionNameSource,
25 /// Denotes the source of a region that is named by a `RegionName`. For example, a free region that
26 /// was named by the user would get `NamedFreeRegion` and `'static` lifetime would get `Static`.
27 /// This helps to print the right kinds of diagnostics.
28 #[derive(Debug, Clone)]
29 pub(crate) enum RegionNameSource {
30 /// A bound (not free) region that was substituted at the def site (not an HRTB).
31 NamedEarlyBoundRegion(Span),
32 /// A free region that the user has a name (`'a`) for.
33 NamedFreeRegion(Span),
34 /// The `'static` region.
36 /// The free region corresponding to the environment of a closure.
37 SynthesizedFreeEnvRegion(Span, &'static str),
38 /// The region corresponding to an argument.
39 AnonRegionFromArgument(RegionNameHighlight),
40 /// The region corresponding to a closure upvar.
41 AnonRegionFromUpvar(Span, Symbol),
42 /// The region corresponding to the return type of a closure.
43 AnonRegionFromOutput(RegionNameHighlight, &'static str),
44 /// The region from a type yielded by a generator.
45 AnonRegionFromYieldTy(Span, String),
46 /// An anonymous region from an async fn.
47 AnonRegionFromAsyncFn(Span),
48 /// An anonymous region from an impl self type or trait
49 AnonRegionFromImplSignature(Span, &'static str),
52 /// Describes what to highlight to explain to the user that we're giving an anonymous region a
53 /// synthesized name, and how to highlight it.
54 #[derive(Debug, Clone)]
55 pub(crate) enum RegionNameHighlight {
56 /// The anonymous region corresponds to a reference that was found by traversing the type in the HIR.
58 /// The anonymous region corresponds to a `'_` in the generics list of a struct/enum/union.
59 MatchedAdtAndSegment(Span),
60 /// The anonymous region corresponds to a region where the type annotation is completely missing
61 /// from the code, e.g. in a closure arguments `|x| { ... }`, where `x` is a reference.
62 CannotMatchHirTy(Span, String),
63 /// The anonymous region corresponds to a region where the type annotation is completely missing
64 /// from the code, and *even if* we print out the full name of the type, the region name won't
65 /// be included. This currently occurs for opaque types like `impl Future`.
66 Occluded(Span, String),
70 pub(crate) fn was_named(&self) -> bool {
72 RegionNameSource::NamedEarlyBoundRegion(..)
73 | RegionNameSource::NamedFreeRegion(..)
74 | RegionNameSource::Static => true,
75 RegionNameSource::SynthesizedFreeEnvRegion(..)
76 | RegionNameSource::AnonRegionFromArgument(..)
77 | RegionNameSource::AnonRegionFromUpvar(..)
78 | RegionNameSource::AnonRegionFromOutput(..)
79 | RegionNameSource::AnonRegionFromYieldTy(..)
80 | RegionNameSource::AnonRegionFromAsyncFn(..)
81 | RegionNameSource::AnonRegionFromImplSignature(..) => false,
85 pub(crate) fn span(&self) -> Option<Span> {
87 RegionNameSource::Static => None,
88 RegionNameSource::NamedEarlyBoundRegion(span)
89 | RegionNameSource::NamedFreeRegion(span)
90 | RegionNameSource::SynthesizedFreeEnvRegion(span, _)
91 | RegionNameSource::AnonRegionFromUpvar(span, _)
92 | RegionNameSource::AnonRegionFromYieldTy(span, _)
93 | RegionNameSource::AnonRegionFromAsyncFn(span)
94 | RegionNameSource::AnonRegionFromImplSignature(span, _) => Some(span),
95 RegionNameSource::AnonRegionFromArgument(ref highlight)
96 | RegionNameSource::AnonRegionFromOutput(ref highlight, _) => match *highlight {
97 RegionNameHighlight::MatchedHirTy(span)
98 | RegionNameHighlight::MatchedAdtAndSegment(span)
99 | RegionNameHighlight::CannotMatchHirTy(span, _)
100 | RegionNameHighlight::Occluded(span, _) => Some(span),
105 pub(crate) fn highlight_region_name(&self, diag: &mut Diagnostic) {
107 RegionNameSource::NamedFreeRegion(span)
108 | RegionNameSource::NamedEarlyBoundRegion(span) => {
109 diag.span_label(*span, format!("lifetime `{self}` defined here"));
111 RegionNameSource::SynthesizedFreeEnvRegion(span, note) => {
112 diag.span_label(*span, format!("lifetime `{self}` represents this closure's body"));
115 RegionNameSource::AnonRegionFromArgument(RegionNameHighlight::CannotMatchHirTy(
119 diag.span_label(*span, format!("has type `{type_name}`"));
121 RegionNameSource::AnonRegionFromArgument(RegionNameHighlight::MatchedHirTy(span))
122 | RegionNameSource::AnonRegionFromOutput(RegionNameHighlight::MatchedHirTy(span), _)
123 | RegionNameSource::AnonRegionFromAsyncFn(span) => {
126 format!("let's call the lifetime of this reference `{self}`"),
129 RegionNameSource::AnonRegionFromArgument(
130 RegionNameHighlight::MatchedAdtAndSegment(span),
132 | RegionNameSource::AnonRegionFromOutput(
133 RegionNameHighlight::MatchedAdtAndSegment(span),
136 diag.span_label(*span, format!("let's call this `{self}`"));
138 RegionNameSource::AnonRegionFromArgument(RegionNameHighlight::Occluded(
144 format!("lifetime `{self}` appears in the type {type_name}"),
147 RegionNameSource::AnonRegionFromOutput(
148 RegionNameHighlight::Occluded(span, type_name),
154 "return type{mir_description} `{type_name}` contains a lifetime `{self}`"
158 RegionNameSource::AnonRegionFromUpvar(span, upvar_name) => {
161 format!("lifetime `{self}` appears in the type of `{upvar_name}`"),
164 RegionNameSource::AnonRegionFromOutput(
165 RegionNameHighlight::CannotMatchHirTy(span, type_name),
168 diag.span_label(*span, format!("return type{mir_description} is {type_name}"));
170 RegionNameSource::AnonRegionFromYieldTy(span, type_name) => {
171 diag.span_label(*span, format!("yield type is {type_name}"));
173 RegionNameSource::AnonRegionFromImplSignature(span, location) => {
176 format!("lifetime `{self}` appears in the `impl`'s {location}"),
179 RegionNameSource::Static => {}
184 impl Display for RegionName {
185 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
186 write!(f, "{}", self.name)
190 impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
191 pub(crate) fn mir_def_id(&self) -> hir::def_id::LocalDefId {
192 self.body.source.def_id().expect_local()
195 pub(crate) fn mir_hir_id(&self) -> hir::HirId {
196 self.infcx.tcx.hir().local_def_id_to_hir_id(self.mir_def_id())
199 /// Generate a synthetic region named `'N`, where `N` is the next value of the counter. Then,
200 /// increment the counter.
202 /// This is _not_ idempotent. Call `give_region_a_name` when possible.
203 fn synthesize_region_name(&self) -> Symbol {
204 let c = self.next_region_name.replace_with(|counter| *counter + 1);
205 Symbol::intern(&format!("'{:?}", c))
208 /// Maps from an internal MIR region vid to something that we can
209 /// report to the user. In some cases, the region vids will map
210 /// directly to lifetimes that the user has a name for (e.g.,
211 /// `'static`). But frequently they will not, in which case we
212 /// have to find some way to identify the lifetime to the user. To
213 /// that end, this function takes a "diagnostic" so that it can
214 /// create auxiliary notes as needed.
216 /// The names are memoized, so this is both cheap to recompute and idempotent.
218 /// Example (function arguments):
220 /// Suppose we are trying to give a name to the lifetime of the
223 /// ```ignore (pseudo-rust)
224 /// fn foo(x: &u32) { .. }
227 /// This function would create a label like this:
230 /// | fn foo(x: &u32) { .. }
231 /// ------- fully elaborated type of `x` is `&'1 u32`
234 /// and then return the name `'1` for us to use.
235 pub(crate) fn give_region_a_name(&self, fr: RegionVid) -> Option<RegionName> {
237 "give_region_a_name(fr={:?}, counter={:?})",
239 self.next_region_name.try_borrow().unwrap()
242 assert!(self.regioncx.universal_regions().is_universal_region(fr));
244 if let Some(value) = self.region_names.try_borrow_mut().unwrap().get(&fr) {
245 return Some(value.clone());
249 .give_name_from_error_region(fr)
250 .or_else(|| self.give_name_if_anonymous_region_appears_in_arguments(fr))
251 .or_else(|| self.give_name_if_anonymous_region_appears_in_upvars(fr))
252 .or_else(|| self.give_name_if_anonymous_region_appears_in_output(fr))
253 .or_else(|| self.give_name_if_anonymous_region_appears_in_yield_ty(fr))
254 .or_else(|| self.give_name_if_anonymous_region_appears_in_impl_signature(fr))
255 .or_else(|| self.give_name_if_anonymous_region_appears_in_arg_position_impl_trait(fr));
257 if let Some(ref value) = value {
258 self.region_names.try_borrow_mut().unwrap().insert(fr, value.clone());
261 debug!("give_region_a_name: gave name {:?}", value);
265 /// Checks for the case where `fr` maps to something that the
266 /// *user* has a name for. In that case, we'll be able to map
267 /// `fr` to a `Region<'tcx>`, and that region will be one of
269 #[instrument(level = "trace", skip(self))]
270 fn give_name_from_error_region(&self, fr: RegionVid) -> Option<RegionName> {
271 let error_region = self.to_error_region(fr)?;
273 let tcx = self.infcx.tcx;
275 debug!("give_region_a_name: error_region = {:?}", error_region);
276 match *error_region {
277 ty::ReEarlyBound(ebr) => {
279 let span = tcx.hir().span_if_local(ebr.def_id).unwrap_or(DUMMY_SP);
282 source: RegionNameSource::NamedEarlyBoundRegion(span),
290 Some(RegionName { name: kw::StaticLifetime, source: RegionNameSource::Static })
293 ty::ReFree(free_region) => match free_region.bound_region {
294 ty::BoundRegionKind::BrNamed(region_def_id, name) => {
295 // Get the span to point to, even if we don't use the name.
296 let span = tcx.hir().span_if_local(region_def_id).unwrap_or(DUMMY_SP);
298 "bound region named: {:?}, is_named: {:?}",
300 free_region.bound_region.is_named()
303 if free_region.bound_region.is_named() {
304 // A named region that is actually named.
305 Some(RegionName { name, source: RegionNameSource::NamedFreeRegion(span) })
306 } else if let hir::IsAsync::Async = tcx.asyncness(self.mir_hir_id().owner) {
307 // If we spuriously thought that the region is named, we should let the
308 // system generate a true name for error messages. Currently this can
309 // happen if we have an elided name in an async fn for example: the
310 // compiler will generate a region named `'_`, but reporting such a name is
311 // not actually useful, so we synthesize a name for it instead.
312 let name = self.synthesize_region_name();
315 source: RegionNameSource::AnonRegionFromAsyncFn(span),
322 ty::BoundRegionKind::BrEnv => {
323 let def_ty = self.regioncx.universal_regions().defining_ty;
325 let DefiningTy::Closure(_, substs) = def_ty else {
326 // Can't have BrEnv in functions, constants or generators.
327 bug!("BrEnv outside of closure.");
329 let hir::ExprKind::Closure(&hir::Closure { fn_decl_span, .. })
330 = tcx.hir().expect_expr(self.mir_hir_id()).kind
332 bug!("Closure is not defined by a closure expr");
334 let region_name = self.synthesize_region_name();
336 let closure_kind_ty = substs.as_closure().kind_ty();
337 let note = match closure_kind_ty.to_opt_closure_kind() {
338 Some(ty::ClosureKind::Fn) => {
339 "closure implements `Fn`, so references to captured variables \
340 can't escape the closure"
342 Some(ty::ClosureKind::FnMut) => {
343 "closure implements `FnMut`, so references to captured variables \
344 can't escape the closure"
346 Some(ty::ClosureKind::FnOnce) => {
347 bug!("BrEnv in a `FnOnce` closure");
349 None => bug!("Closure kind not inferred in borrow check"),
354 source: RegionNameSource::SynthesizedFreeEnvRegion(fn_decl_span, note),
358 ty::BoundRegionKind::BrAnon(..) => None,
361 ty::ReLateBound(..) | ty::ReVar(..) | ty::RePlaceholder(..) | ty::ReErased => None,
365 /// Finds an argument that contains `fr` and label it with a fully
366 /// elaborated type, returning something like `'1`. Result looks
370 /// | fn foo(x: &u32) { .. }
371 /// ------- fully elaborated type of `x` is `&'1 u32`
373 #[instrument(level = "trace", skip(self))]
374 fn give_name_if_anonymous_region_appears_in_arguments(
377 ) -> Option<RegionName> {
378 let implicit_inputs = self.regioncx.universal_regions().defining_ty.implicit_inputs();
379 let argument_index = self.regioncx.get_argument_index_for_region(self.infcx.tcx, fr)?;
381 let arg_ty = self.regioncx.universal_regions().unnormalized_input_tys
382 [implicit_inputs + argument_index];
383 let (_, span) = self.regioncx.get_argument_name_and_span_for_region(
390 .get_argument_hir_ty_for_highlighting(argument_index)
391 .and_then(|arg_hir_ty| self.highlight_if_we_can_match_hir_ty(fr, arg_ty, arg_hir_ty))
393 // `highlight_if_we_cannot_match_hir_ty` needs to know the number we will give to
394 // the anonymous region. If it succeeds, the `synthesize_region_name` call below
395 // will increment the counter, "reserving" the number we just used.
396 let counter = *self.next_region_name.try_borrow().unwrap();
397 self.highlight_if_we_cannot_match_hir_ty(fr, arg_ty, span, counter)
401 name: self.synthesize_region_name(),
402 source: RegionNameSource::AnonRegionFromArgument(highlight),
406 fn get_argument_hir_ty_for_highlighting(
408 argument_index: usize,
409 ) -> Option<&hir::Ty<'tcx>> {
410 let fn_decl = self.infcx.tcx.hir().fn_decl_by_hir_id(self.mir_hir_id())?;
411 let argument_hir_ty: &hir::Ty<'_> = fn_decl.inputs.get(argument_index)?;
412 match argument_hir_ty.kind {
413 // This indicates a variable with no type annotation, like
414 // `|x|`... in that case, we can't highlight the type but
415 // must highlight the variable.
416 // NOTE(eddyb) this is handled in/by the sole caller
417 // (`give_name_if_anonymous_region_appears_in_arguments`).
418 hir::TyKind::Infer => None,
420 _ => Some(argument_hir_ty),
424 /// Attempts to highlight the specific part of a type in an argument
425 /// that has no type annotation.
426 /// For example, we might produce an annotation like this:
432 /// | | has type `&'1 u32`
433 /// | has type `&'2 u32`
435 fn highlight_if_we_cannot_match_hir_ty(
437 needle_fr: RegionVid,
441 ) -> RegionNameHighlight {
442 let mut highlight = RegionHighlightMode::new(self.infcx.tcx);
443 highlight.highlighting_region_vid(needle_fr, counter);
445 self.infcx.extract_inference_diagnostics_data(ty.into(), Some(highlight)).name;
448 "highlight_if_we_cannot_match_hir_ty: type_name={:?} needle_fr={:?}",
451 if type_name.contains(&format!("'{counter}")) {
452 // Only add a label if we can confirm that a region was labelled.
453 RegionNameHighlight::CannotMatchHirTy(span, type_name)
455 RegionNameHighlight::Occluded(span, type_name)
459 /// Attempts to highlight the specific part of a type annotation
460 /// that contains the anonymous reference we want to give a name
461 /// to. For example, we might produce an annotation like this:
464 /// | fn a<T>(items: &[T]) -> Box<dyn Iterator<Item = &T>> {
465 /// | - let's call the lifetime of this reference `'1`
468 /// the way this works is that we match up `ty`, which is
469 /// a `Ty<'tcx>` (the internal form of the type) with
470 /// `hir_ty`, a `hir::Ty` (the syntax of the type
471 /// annotation). We are descending through the types stepwise,
472 /// looking in to find the region `needle_fr` in the internal
473 /// type. Once we find that, we can use the span of the `hir::Ty`
474 /// to add the highlight.
476 /// This is a somewhat imperfect process, so along the way we also
477 /// keep track of the **closest** type we've found. If we fail to
478 /// find the exact `&` or `'_` to highlight, then we may fall back
479 /// to highlighting that closest type instead.
480 fn highlight_if_we_can_match_hir_ty(
482 needle_fr: RegionVid,
484 hir_ty: &hir::Ty<'_>,
485 ) -> Option<RegionNameHighlight> {
486 let search_stack: &mut Vec<(Ty<'tcx>, &hir::Ty<'_>)> = &mut vec![(ty, hir_ty)];
488 while let Some((ty, hir_ty)) = search_stack.pop() {
489 match (ty.kind(), &hir_ty.kind) {
490 // Check if the `ty` is `&'X ..` where `'X`
491 // is the region we are looking for -- if so, and we have a `&T`
492 // on the RHS, then we want to highlight the `&` like so:
495 // - let's call the lifetime of this reference `'1`
497 ty::Ref(region, referent_ty, _),
498 hir::TyKind::Rptr(_lifetime, referent_hir_ty),
500 if region.to_region_vid() == needle_fr {
501 // Just grab the first character, the `&`.
502 let source_map = self.infcx.tcx.sess.source_map();
503 let ampersand_span = source_map.start_point(hir_ty.span);
505 return Some(RegionNameHighlight::MatchedHirTy(ampersand_span));
508 // Otherwise, let's descend into the referent types.
509 search_stack.push((*referent_ty, &referent_hir_ty.ty));
512 // Match up something like `Foo<'1>`
514 ty::Adt(_adt_def, substs),
515 hir::TyKind::Path(hir::QPath::Resolved(None, path)),
518 // Type parameters of the type alias have no reason to
519 // be the same as those of the ADT.
520 // FIXME: We should be able to do something similar to
521 // match_adt_and_segment in this case.
522 Res::Def(DefKind::TyAlias, _) => (),
524 if let Some(last_segment) = path.segments.last() {
525 if let Some(highlight) = self.match_adt_and_segment(
531 return Some(highlight);
538 // The following cases don't have lifetimes, so we
539 // just worry about trying to match up the rustc type
540 // with the HIR types:
541 (&ty::Tuple(elem_tys), hir::TyKind::Tup(elem_hir_tys)) => {
542 search_stack.extend(iter::zip(elem_tys, *elem_hir_tys));
545 (ty::Slice(elem_ty), hir::TyKind::Slice(elem_hir_ty))
546 | (ty::Array(elem_ty, _), hir::TyKind::Array(elem_hir_ty, _)) => {
547 search_stack.push((*elem_ty, elem_hir_ty));
550 (ty::RawPtr(mut_ty), hir::TyKind::Ptr(mut_hir_ty)) => {
551 search_stack.push((mut_ty.ty, &mut_hir_ty.ty));
555 // FIXME there are other cases that we could trace
563 /// We've found an enum/struct/union type with the substitutions
564 /// `substs` and -- in the HIR -- a path type with the final
565 /// segment `last_segment`. Try to find a `'_` to highlight in
566 /// the generic args (or, if not, to produce new zipped pairs of
567 /// types+hir to search through).
568 fn match_adt_and_segment<'hir>(
570 substs: SubstsRef<'tcx>,
571 needle_fr: RegionVid,
572 last_segment: &'hir hir::PathSegment<'hir>,
573 search_stack: &mut Vec<(Ty<'tcx>, &'hir hir::Ty<'hir>)>,
574 ) -> Option<RegionNameHighlight> {
575 // Did the user give explicit arguments? (e.g., `Foo<..>`)
576 let args = last_segment.args.as_ref()?;
578 self.try_match_adt_and_generic_args(substs, needle_fr, args, search_stack)?;
579 match lifetime.name {
580 hir::LifetimeName::Param(_, hir::ParamName::Plain(_) | hir::ParamName::Error)
581 | hir::LifetimeName::Error
582 | hir::LifetimeName::Static => {
583 let lifetime_span = lifetime.span;
584 Some(RegionNameHighlight::MatchedAdtAndSegment(lifetime_span))
587 hir::LifetimeName::Param(_, hir::ParamName::Fresh)
588 | hir::LifetimeName::ImplicitObjectLifetimeDefault
589 | hir::LifetimeName::Infer => {
590 // In this case, the user left off the lifetime; so
591 // they wrote something like:
597 // where the fully elaborated form is `Foo<'_, '1,
598 // T>`. We don't consider this a match; instead we let
599 // the "fully elaborated" type fallback above handle
606 /// We've found an enum/struct/union type with the substitutions
607 /// `substs` and -- in the HIR -- a path with the generic
608 /// arguments `args`. If `needle_fr` appears in the args, return
609 /// the `hir::Lifetime` that corresponds to it. If not, push onto
610 /// `search_stack` the types+hir to search through.
611 fn try_match_adt_and_generic_args<'hir>(
613 substs: SubstsRef<'tcx>,
614 needle_fr: RegionVid,
615 args: &'hir hir::GenericArgs<'hir>,
616 search_stack: &mut Vec<(Ty<'tcx>, &'hir hir::Ty<'hir>)>,
617 ) -> Option<&'hir hir::Lifetime> {
618 for (kind, hir_arg) in iter::zip(substs, args.args) {
619 match (kind.unpack(), hir_arg) {
620 (GenericArgKind::Lifetime(r), hir::GenericArg::Lifetime(lt)) => {
621 if r.to_region_vid() == needle_fr {
626 (GenericArgKind::Type(ty), hir::GenericArg::Type(hir_ty)) => {
627 search_stack.push((ty, hir_ty));
630 (GenericArgKind::Const(_ct), hir::GenericArg::Const(_hir_ct)) => {
631 // Lifetimes cannot be found in consts, so we don't need
632 // to search anything here.
636 GenericArgKind::Lifetime(_)
637 | GenericArgKind::Type(_)
638 | GenericArgKind::Const(_),
641 // HIR lowering sometimes doesn't catch this in erroneous
642 // programs, so we need to use delay_span_bug here. See #82126.
643 self.infcx.tcx.sess.delay_span_bug(
645 &format!("unmatched subst and hir arg: found {:?} vs {:?}", kind, hir_arg),
654 /// Finds a closure upvar that contains `fr` and label it with a
655 /// fully elaborated type, returning something like `'1`. Result
659 /// | let x = Some(&22);
660 /// - fully elaborated type of `x` is `Option<&'1 u32>`
662 #[instrument(level = "trace", skip(self))]
663 fn give_name_if_anonymous_region_appears_in_upvars(&self, fr: RegionVid) -> Option<RegionName> {
664 let upvar_index = self.regioncx.get_upvar_index_for_region(self.infcx.tcx, fr)?;
665 let (upvar_name, upvar_span) = self.regioncx.get_upvar_name_and_span_for_region(
670 let region_name = self.synthesize_region_name();
674 source: RegionNameSource::AnonRegionFromUpvar(upvar_span, upvar_name),
678 /// Checks for arguments appearing in the (closure) return type. It
679 /// must be a closure since, in a free fn, such an argument would
680 /// have to either also appear in an argument (if using elision)
681 /// or be early bound (named, not in argument).
682 #[instrument(level = "trace", skip(self))]
683 fn give_name_if_anonymous_region_appears_in_output(&self, fr: RegionVid) -> Option<RegionName> {
684 let tcx = self.infcx.tcx;
687 let return_ty = self.regioncx.universal_regions().unnormalized_output_ty;
688 debug!("give_name_if_anonymous_region_appears_in_output: return_ty = {:?}", return_ty);
689 if !tcx.any_free_region_meets(&return_ty, |r| r.to_region_vid() == fr) {
693 let mir_hir_id = self.mir_hir_id();
695 let (return_span, mir_description, hir_ty) = match hir.get(mir_hir_id) {
696 hir::Node::Expr(hir::Expr {
697 kind: hir::ExprKind::Closure(&hir::Closure { fn_decl, body, fn_decl_span, .. }),
700 let (mut span, mut hir_ty) = match fn_decl.output {
701 hir::FnRetTy::DefaultReturn(_) => {
702 (tcx.sess.source_map().end_point(fn_decl_span), None)
704 hir::FnRetTy::Return(hir_ty) => (fn_decl.output.span(), Some(hir_ty)),
706 let mir_description = match hir.body(body).generator_kind {
707 Some(hir::GeneratorKind::Async(gen)) => match gen {
708 hir::AsyncGeneratorKind::Block => " of async block",
709 hir::AsyncGeneratorKind::Closure => " of async closure",
710 hir::AsyncGeneratorKind::Fn => {
712 hir.get_by_def_id(hir.get_parent_item(mir_hir_id).def_id);
713 let output = &parent_item
715 .expect("generator lowered from async fn should be in fn")
717 span = output.span();
718 if let hir::FnRetTy::Return(ret) = output {
719 hir_ty = Some(self.get_future_inner_return_ty(*ret));
724 Some(hir::GeneratorKind::Gen) => " of generator",
725 None => " of closure",
727 (span, mir_description, hir_ty)
729 node => match node.fn_decl() {
731 let hir_ty = match fn_decl.output {
732 hir::FnRetTy::DefaultReturn(_) => None,
733 hir::FnRetTy::Return(ty) => Some(ty),
735 (fn_decl.output.span(), "", hir_ty)
737 None => (self.body.span, "", None),
741 let highlight = hir_ty
742 .and_then(|hir_ty| self.highlight_if_we_can_match_hir_ty(fr, return_ty, hir_ty))
744 // `highlight_if_we_cannot_match_hir_ty` needs to know the number we will give to
745 // the anonymous region. If it succeeds, the `synthesize_region_name` call below
746 // will increment the counter, "reserving" the number we just used.
747 let counter = *self.next_region_name.try_borrow().unwrap();
748 self.highlight_if_we_cannot_match_hir_ty(fr, return_ty, return_span, counter)
752 name: self.synthesize_region_name(),
753 source: RegionNameSource::AnonRegionFromOutput(highlight, mir_description),
757 /// From the [`hir::Ty`] of an async function's lowered return type,
758 /// retrieve the `hir::Ty` representing the type the user originally wrote.
760 /// e.g. given the function:
763 /// async fn foo() -> i32 { 2 }
766 /// this function, given the lowered return type of `foo`, an [`OpaqueDef`] that implements `Future<Output=i32>`,
767 /// returns the `i32`.
769 /// [`OpaqueDef`]: hir::TyKind::OpaqueDef
770 fn get_future_inner_return_ty(&self, hir_ty: &'tcx hir::Ty<'tcx>) -> &'tcx hir::Ty<'tcx> {
771 let hir = self.infcx.tcx.hir();
773 let hir::TyKind::OpaqueDef(id, _, _) = hir_ty.kind else {
776 "lowered return type of async fn is not OpaqueDef: {:?}",
780 let opaque_ty = hir.item(id);
781 if let hir::ItemKind::OpaqueTy(hir::OpaqueTy {
784 hir::GenericBound::LangItemTrait(
785 hir::LangItem::Future,
792 ident: Ident { name: sym::Output, .. },
794 hir::TypeBindingKind::Equality { term: hir::Term::Ty(ty) },
809 "bounds from lowered return type of async fn did not match expected format: {:?}",
815 #[instrument(level = "trace", skip(self))]
816 fn give_name_if_anonymous_region_appears_in_yield_ty(
819 ) -> Option<RegionName> {
820 // Note: generators from `async fn` yield `()`, so we don't have to
821 // worry about them here.
822 let yield_ty = self.regioncx.universal_regions().yield_ty?;
823 debug!("give_name_if_anonymous_region_appears_in_yield_ty: yield_ty = {:?}", yield_ty);
825 let tcx = self.infcx.tcx;
827 if !tcx.any_free_region_meets(&yield_ty, |r| r.to_region_vid() == fr) {
831 let mut highlight = RegionHighlightMode::new(tcx);
832 highlight.highlighting_region_vid(fr, *self.next_region_name.try_borrow().unwrap());
834 self.infcx.extract_inference_diagnostics_data(yield_ty.into(), Some(highlight)).name;
836 let yield_span = match tcx.hir().get(self.mir_hir_id()) {
837 hir::Node::Expr(hir::Expr {
838 kind: hir::ExprKind::Closure(&hir::Closure { fn_decl_span, .. }),
840 }) => tcx.sess.source_map().end_point(fn_decl_span),
845 "give_name_if_anonymous_region_appears_in_yield_ty: \
846 type_name = {:?}, yield_span = {:?}",
847 yield_span, type_name,
851 name: self.synthesize_region_name(),
852 source: RegionNameSource::AnonRegionFromYieldTy(yield_span, type_name),
856 fn give_name_if_anonymous_region_appears_in_impl_signature(
859 ) -> Option<RegionName> {
860 let ty::ReEarlyBound(region) = *self.to_error_region(fr)? else {
863 if region.has_name() {
867 let tcx = self.infcx.tcx;
868 let region_parent = tcx.parent(region.def_id);
869 if tcx.def_kind(region_parent) != DefKind::Impl {
874 .any_free_region_meets(&tcx.type_of(region_parent), |r| *r == ty::ReEarlyBound(region));
877 name: self.synthesize_region_name(),
878 source: RegionNameSource::AnonRegionFromImplSignature(
879 tcx.def_span(region.def_id),
880 // FIXME(compiler-errors): Does this ever actually show up
881 // anywhere other than the self type? I couldn't create an
882 // example of a `'_` in the impl's trait being referenceable.
883 if found { "self type" } else { "header" },
888 fn give_name_if_anonymous_region_appears_in_arg_position_impl_trait(
891 ) -> Option<RegionName> {
892 let ty::ReEarlyBound(region) = *self.to_error_region(fr)? else {
895 if region.has_name() {
899 let predicates = self
902 .predicates_of(self.body.source.def_id())
903 .instantiate_identity(self.infcx.tcx)
906 if let Some(upvar_index) = self
911 .position(|ty| self.any_param_predicate_mentions(&predicates, ty, region))
913 let (upvar_name, upvar_span) = self.regioncx.get_upvar_name_and_span_for_region(
918 let region_name = self.synthesize_region_name();
922 source: RegionNameSource::AnonRegionFromUpvar(upvar_span, upvar_name),
924 } else if let Some(arg_index) = self
927 .unnormalized_input_tys
929 .position(|ty| self.any_param_predicate_mentions(&predicates, *ty, region))
931 let (arg_name, arg_span) = self.regioncx.get_argument_name_and_span_for_region(
936 let region_name = self.synthesize_region_name();
940 source: RegionNameSource::AnonRegionFromArgument(
941 RegionNameHighlight::CannotMatchHirTy(arg_span, arg_name?.to_string()),
949 fn any_param_predicate_mentions(
951 predicates: &[ty::Predicate<'tcx>],
953 region: ty::EarlyBoundRegion,
955 let tcx = self.infcx.tcx;
956 ty.walk().any(|arg| {
957 if let ty::GenericArgKind::Type(ty) = arg.unpack()
958 && let ty::Param(_) = ty.kind()
960 predicates.iter().any(|pred| {
961 match pred.kind().skip_binder() {
962 ty::PredicateKind::Clause(ty::Clause::Trait(data)) if data.self_ty() == ty => {}
963 ty::PredicateKind::Clause(ty::Clause::Projection(data)) if data.projection_ty.self_ty() == ty => {}
966 tcx.any_free_region_meets(pred, |r| {
967 *r == ty::ReEarlyBound(region)