1 use std::fmt::{self, Display};
3 use rustc_errors::DiagnosticBuilder;
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};
12 use crate::borrow_check::{nll::ToRegionVid, universal_regions::DefiningTy, MirBorrowckCtxt};
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).
20 /// Where the region comes from.
21 crate source: RegionNameSource,
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.
35 /// The free region corresponding to the environment of a closure.
36 SynthesizedFreeEnvRegion(Span, String),
37 /// The region corresponding to an argument.
38 AnonRegionFromArgument(RegionNameHighlight),
39 /// The region corresponding to a closure upvar.
40 AnonRegionFromUpvar(Span, String),
41 /// The region corresponding to the return type of a closure.
42 AnonRegionFromOutput(Span, String, String),
43 /// The region from a type yielded by a generator.
44 AnonRegionFromYieldTy(Span, String),
45 /// An anonymous region from an async fn.
46 AnonRegionFromAsyncFn(Span),
49 /// Describes what to highlight to explain to the user that we're giving an anonymous region a
50 /// synthesized name, and how to highlight it.
51 #[derive(Debug, Clone)]
52 crate enum RegionNameHighlight {
53 /// The anonymous region corresponds to a reference that was found by traversing the type in the HIR.
55 /// The anonymous region corresponds to a `'_` in the generics list of a struct/enum/union.
56 MatchedAdtAndSegment(Span),
57 /// The anonymous region corresponds to a region where the type annotation is completely missing
58 /// from the code, e.g. in a closure arguments `|x| { ... }`, where `x` is a reference.
59 CannotMatchHirTy(Span, String),
63 crate fn was_named(&self) -> bool {
65 RegionNameSource::NamedEarlyBoundRegion(..)
66 | RegionNameSource::NamedFreeRegion(..)
67 | RegionNameSource::Static => true,
68 RegionNameSource::SynthesizedFreeEnvRegion(..)
69 | RegionNameSource::AnonRegionFromArgument(..)
70 | RegionNameSource::AnonRegionFromUpvar(..)
71 | RegionNameSource::AnonRegionFromOutput(..)
72 | RegionNameSource::AnonRegionFromYieldTy(..)
73 | RegionNameSource::AnonRegionFromAsyncFn(..) => false,
77 crate fn span(&self) -> Option<Span> {
79 RegionNameSource::Static => None,
80 RegionNameSource::NamedEarlyBoundRegion(span)
81 | RegionNameSource::NamedFreeRegion(span)
82 | RegionNameSource::SynthesizedFreeEnvRegion(span, _)
83 | RegionNameSource::AnonRegionFromUpvar(span, _)
84 | RegionNameSource::AnonRegionFromOutput(span, _, _)
85 | RegionNameSource::AnonRegionFromYieldTy(span, _)
86 | RegionNameSource::AnonRegionFromAsyncFn(span) => Some(span),
87 RegionNameSource::AnonRegionFromArgument(ref highlight) => match *highlight {
88 RegionNameHighlight::MatchedHirTy(span)
89 | RegionNameHighlight::MatchedAdtAndSegment(span)
90 | RegionNameHighlight::CannotMatchHirTy(span, _) => Some(span),
95 crate fn highlight_region_name(&self, diag: &mut DiagnosticBuilder<'_>) {
97 RegionNameSource::NamedFreeRegion(span)
98 | RegionNameSource::NamedEarlyBoundRegion(span) => {
99 diag.span_label(*span, format!("lifetime `{}` defined here", self));
101 RegionNameSource::SynthesizedFreeEnvRegion(span, note) => {
104 format!("lifetime `{}` represents this closure's body", self),
108 RegionNameSource::AnonRegionFromArgument(RegionNameHighlight::CannotMatchHirTy(
112 diag.span_label(*span, format!("has type `{}`", type_name));
114 RegionNameSource::AnonRegionFromArgument(RegionNameHighlight::MatchedHirTy(span))
115 | RegionNameSource::AnonRegionFromAsyncFn(span) => {
118 format!("let's call the lifetime of this reference `{}`", self),
121 RegionNameSource::AnonRegionFromArgument(
122 RegionNameHighlight::MatchedAdtAndSegment(span),
124 diag.span_label(*span, format!("let's call this `{}`", self));
126 RegionNameSource::AnonRegionFromUpvar(span, upvar_name) => {
129 format!("lifetime `{}` appears in the type of `{}`", self, upvar_name),
132 RegionNameSource::AnonRegionFromOutput(span, mir_description, type_name) => {
133 diag.span_label(*span, format!("return type{} is {}", mir_description, type_name));
135 RegionNameSource::AnonRegionFromYieldTy(span, type_name) => {
136 diag.span_label(*span, format!("yield type is {}", type_name));
138 RegionNameSource::Static => {}
143 impl Display for RegionName {
144 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
145 write!(f, "{}", self.name)
149 impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
150 crate fn mir_def_id(&self) -> hir::def_id::LocalDefId {
151 self.body.source.def_id().as_local().unwrap()
154 crate fn mir_hir_id(&self) -> hir::HirId {
155 self.infcx.tcx.hir().local_def_id_to_hir_id(self.mir_def_id())
158 /// Generate a synthetic region named `'N`, where `N` is the next value of the counter. Then,
159 /// increment the counter.
161 /// This is _not_ idempotent. Call `give_region_a_name` when possible.
162 fn synthesize_region_name(&self) -> Symbol {
163 let c = self.next_region_name.replace_with(|counter| *counter + 1);
164 Symbol::intern(&format!("'{:?}", c))
167 /// Maps from an internal MIR region vid to something that we can
168 /// report to the user. In some cases, the region vids will map
169 /// directly to lifetimes that the user has a name for (e.g.,
170 /// `'static`). But frequently they will not, in which case we
171 /// have to find some way to identify the lifetime to the user. To
172 /// that end, this function takes a "diagnostic" so that it can
173 /// create auxiliary notes as needed.
175 /// The names are memoized, so this is both cheap to recompute and idempotent.
177 /// Example (function arguments):
179 /// Suppose we are trying to give a name to the lifetime of the
183 /// fn foo(x: &u32) { .. }
186 /// This function would create a label like this:
189 /// | fn foo(x: &u32) { .. }
190 /// ------- fully elaborated type of `x` is `&'1 u32`
193 /// and then return the name `'1` for us to use.
194 crate fn give_region_a_name(&self, fr: RegionVid) -> Option<RegionName> {
196 "give_region_a_name(fr={:?}, counter={:?})",
198 self.next_region_name.try_borrow().unwrap()
201 assert!(self.regioncx.universal_regions().is_universal_region(fr));
203 if let Some(value) = self.region_names.try_borrow_mut().unwrap().get(&fr) {
204 return Some(value.clone());
208 .give_name_from_error_region(fr)
209 .or_else(|| self.give_name_if_anonymous_region_appears_in_arguments(fr))
210 .or_else(|| self.give_name_if_anonymous_region_appears_in_upvars(fr))
211 .or_else(|| self.give_name_if_anonymous_region_appears_in_output(fr))
212 .or_else(|| self.give_name_if_anonymous_region_appears_in_yield_ty(fr));
214 if let Some(ref value) = value {
215 self.region_names.try_borrow_mut().unwrap().insert(fr, value.clone());
218 debug!("give_region_a_name: gave name {:?}", value);
222 /// Checks for the case where `fr` maps to something that the
223 /// *user* has a name for. In that case, we'll be able to map
224 /// `fr` to a `Region<'tcx>`, and that region will be one of
226 fn give_name_from_error_region(&self, fr: RegionVid) -> Option<RegionName> {
227 let error_region = self.to_error_region(fr)?;
229 let tcx = self.infcx.tcx;
231 debug!("give_region_a_name: error_region = {:?}", error_region);
233 ty::ReEarlyBound(ebr) => {
235 let span = tcx.hir().span_if_local(ebr.def_id).unwrap_or(DUMMY_SP);
238 source: RegionNameSource::NamedEarlyBoundRegion(span),
246 Some(RegionName { name: kw::StaticLifetime, source: RegionNameSource::Static })
249 ty::ReFree(free_region) => match free_region.bound_region {
250 ty::BoundRegion::BrNamed(region_def_id, name) => {
251 // Get the span to point to, even if we don't use the name.
252 let span = tcx.hir().span_if_local(region_def_id).unwrap_or(DUMMY_SP);
254 "bound region named: {:?}, is_named: {:?}",
256 free_region.bound_region.is_named()
259 if free_region.bound_region.is_named() {
260 // A named region that is actually named.
261 Some(RegionName { name, source: RegionNameSource::NamedFreeRegion(span) })
263 // If we spuriously thought that the region is named, we should let the
264 // system generate a true name for error messages. Currently this can
265 // happen if we have an elided name in an async fn for example: the
266 // compiler will generate a region named `'_`, but reporting such a name is
267 // not actually useful, so we synthesize a name for it instead.
268 let name = self.synthesize_region_name();
271 source: RegionNameSource::AnonRegionFromAsyncFn(span),
276 ty::BoundRegion::BrEnv => {
277 let def_ty = self.regioncx.universal_regions().defining_ty;
279 if let DefiningTy::Closure(_, substs) = def_ty {
280 let args_span = if let hir::ExprKind::Closure(_, _, _, span, _) =
281 tcx.hir().expect_expr(self.mir_hir_id()).kind
285 bug!("Closure is not defined by a closure expr");
287 let region_name = self.synthesize_region_name();
289 let closure_kind_ty = substs.as_closure().kind_ty();
290 let note = match closure_kind_ty.to_opt_closure_kind() {
291 Some(ty::ClosureKind::Fn) => {
292 "closure implements `Fn`, so references to captured variables \
293 can't escape the closure"
295 Some(ty::ClosureKind::FnMut) => {
296 "closure implements `FnMut`, so references to captured variables \
297 can't escape the closure"
299 Some(ty::ClosureKind::FnOnce) => {
300 bug!("BrEnv in a `FnOnce` closure");
302 None => bug!("Closure kind not inferred in borrow check"),
307 source: RegionNameSource::SynthesizedFreeEnvRegion(
313 // Can't have BrEnv in functions, constants or generators.
314 bug!("BrEnv outside of closure.");
318 ty::BoundRegion::BrAnon(_) => None,
323 | ty::RePlaceholder(..)
325 | ty::ReErased => None,
329 /// Finds an argument that contains `fr` and label it with a fully
330 /// elaborated type, returning something like `'1`. Result looks
334 /// | fn foo(x: &u32) { .. }
335 /// ------- fully elaborated type of `x` is `&'1 u32`
337 fn give_name_if_anonymous_region_appears_in_arguments(
340 ) -> Option<RegionName> {
341 let implicit_inputs = self.regioncx.universal_regions().defining_ty.implicit_inputs();
342 let argument_index = self.regioncx.get_argument_index_for_region(self.infcx.tcx, fr)?;
344 let arg_ty = self.regioncx.universal_regions().unnormalized_input_tys
345 [implicit_inputs + argument_index];
346 let (_, span) = self.regioncx.get_argument_name_and_span_for_region(
352 self.get_argument_hir_ty_for_highlighting(argument_index)
353 .and_then(|arg_hir_ty| self.highlight_if_we_can_match_hir_ty(fr, arg_ty, arg_hir_ty))
355 // `highlight_if_we_cannot_match_hir_ty` needs to know the number we will give to
356 // the anonymous region. If it succeeds, the `synthesize_region_name` call below
357 // will increment the counter, "reserving" the number we just used.
358 let counter = *self.next_region_name.try_borrow().unwrap();
359 self.highlight_if_we_cannot_match_hir_ty(fr, arg_ty, span, counter)
361 .map(|highlight| RegionName {
362 name: self.synthesize_region_name(),
363 source: RegionNameSource::AnonRegionFromArgument(highlight),
367 fn get_argument_hir_ty_for_highlighting(
369 argument_index: usize,
370 ) -> Option<&hir::Ty<'tcx>> {
371 let fn_decl = self.infcx.tcx.hir().fn_decl_by_hir_id(self.mir_hir_id())?;
372 let argument_hir_ty: &hir::Ty<'_> = fn_decl.inputs.get(argument_index)?;
373 match argument_hir_ty.kind {
374 // This indicates a variable with no type annotation, like
375 // `|x|`... in that case, we can't highlight the type but
376 // must highlight the variable.
377 // NOTE(eddyb) this is handled in/by the sole caller
378 // (`give_name_if_anonymous_region_appears_in_arguments`).
379 hir::TyKind::Infer => None,
381 _ => Some(argument_hir_ty),
385 /// Attempts to highlight the specific part of a type in an argument
386 /// that has no type annotation.
387 /// For example, we might produce an annotation like this:
393 /// | | has type `&'1 u32`
394 /// | has type `&'2 u32`
396 fn highlight_if_we_cannot_match_hir_ty(
398 needle_fr: RegionVid,
402 ) -> Option<RegionNameHighlight> {
403 let mut highlight = RegionHighlightMode::default();
404 highlight.highlighting_region_vid(needle_fr, counter);
406 self.infcx.extract_inference_diagnostics_data(ty.into(), Some(highlight)).name;
409 "highlight_if_we_cannot_match_hir_ty: type_name={:?} needle_fr={:?}",
412 if type_name.find(&format!("'{}", counter)).is_some() {
413 // Only add a label if we can confirm that a region was labelled.
414 Some(RegionNameHighlight::CannotMatchHirTy(span, type_name))
420 /// Attempts to highlight the specific part of a type annotation
421 /// that contains the anonymous reference we want to give a name
422 /// to. For example, we might produce an annotation like this:
425 /// | fn a<T>(items: &[T]) -> Box<dyn Iterator<Item = &T>> {
426 /// | - let's call the lifetime of this reference `'1`
429 /// the way this works is that we match up `ty`, which is
430 /// a `Ty<'tcx>` (the internal form of the type) with
431 /// `hir_ty`, a `hir::Ty` (the syntax of the type
432 /// annotation). We are descending through the types stepwise,
433 /// looking in to find the region `needle_fr` in the internal
434 /// type. Once we find that, we can use the span of the `hir::Ty`
435 /// to add the highlight.
437 /// This is a somewhat imperfect process, so along the way we also
438 /// keep track of the **closest** type we've found. If we fail to
439 /// find the exact `&` or `'_` to highlight, then we may fall back
440 /// to highlighting that closest type instead.
441 fn highlight_if_we_can_match_hir_ty(
443 needle_fr: RegionVid,
445 hir_ty: &hir::Ty<'_>,
446 ) -> Option<RegionNameHighlight> {
447 let search_stack: &mut Vec<(Ty<'tcx>, &hir::Ty<'_>)> = &mut vec![(ty, hir_ty)];
449 while let Some((ty, hir_ty)) = search_stack.pop() {
450 match (&ty.kind(), &hir_ty.kind) {
451 // Check if the `ty` is `&'X ..` where `'X`
452 // is the region we are looking for -- if so, and we have a `&T`
453 // on the RHS, then we want to highlight the `&` like so:
456 // - let's call the lifetime of this reference `'1`
458 ty::Ref(region, referent_ty, _),
459 hir::TyKind::Rptr(_lifetime, referent_hir_ty),
461 if region.to_region_vid() == needle_fr {
462 // Just grab the first character, the `&`.
463 let source_map = self.infcx.tcx.sess.source_map();
464 let ampersand_span = source_map.start_point(hir_ty.span);
466 return Some(RegionNameHighlight::MatchedHirTy(ampersand_span));
469 // Otherwise, let's descend into the referent types.
470 search_stack.push((referent_ty, &referent_hir_ty.ty));
473 // Match up something like `Foo<'1>`
475 ty::Adt(_adt_def, substs),
476 hir::TyKind::Path(hir::QPath::Resolved(None, path)),
479 // Type parameters of the type alias have no reason to
480 // be the same as those of the ADT.
481 // FIXME: We should be able to do something similar to
482 // match_adt_and_segment in this case.
483 Res::Def(DefKind::TyAlias, _) => (),
485 if let Some(last_segment) = path.segments.last() {
486 if let Some(highlight) = self.match_adt_and_segment(
492 return Some(highlight);
499 // The following cases don't have lifetimes, so we
500 // just worry about trying to match up the rustc type
501 // with the HIR types:
502 (ty::Tuple(elem_tys), hir::TyKind::Tup(elem_hir_tys)) => {
503 search_stack.extend(elem_tys.iter().map(|k| k.expect_ty()).zip(*elem_hir_tys));
506 (ty::Slice(elem_ty), hir::TyKind::Slice(elem_hir_ty))
507 | (ty::Array(elem_ty, _), hir::TyKind::Array(elem_hir_ty, _)) => {
508 search_stack.push((elem_ty, elem_hir_ty));
511 (ty::RawPtr(mut_ty), hir::TyKind::Ptr(mut_hir_ty)) => {
512 search_stack.push((mut_ty.ty, &mut_hir_ty.ty));
516 // FIXME there are other cases that we could trace
524 /// We've found an enum/struct/union type with the substitutions
525 /// `substs` and -- in the HIR -- a path type with the final
526 /// segment `last_segment`. Try to find a `'_` to highlight in
527 /// the generic args (or, if not, to produce new zipped pairs of
528 /// types+hir to search through).
529 fn match_adt_and_segment<'hir>(
531 substs: SubstsRef<'tcx>,
532 needle_fr: RegionVid,
533 last_segment: &'hir hir::PathSegment<'hir>,
534 search_stack: &mut Vec<(Ty<'tcx>, &'hir hir::Ty<'hir>)>,
535 ) -> Option<RegionNameHighlight> {
536 // Did the user give explicit arguments? (e.g., `Foo<..>`)
537 let args = last_segment.args.as_ref()?;
539 self.try_match_adt_and_generic_args(substs, needle_fr, args, search_stack)?;
540 match lifetime.name {
541 hir::LifetimeName::Param(_)
542 | hir::LifetimeName::Error
543 | hir::LifetimeName::Static
544 | hir::LifetimeName::Underscore => {
545 let lifetime_span = lifetime.span;
546 Some(RegionNameHighlight::MatchedAdtAndSegment(lifetime_span))
549 hir::LifetimeName::ImplicitObjectLifetimeDefault | hir::LifetimeName::Implicit => {
550 // In this case, the user left off the lifetime; so
551 // they wrote something like:
557 // where the fully elaborated form is `Foo<'_, '1,
558 // T>`. We don't consider this a match; instead we let
559 // the "fully elaborated" type fallback above handle
566 /// We've found an enum/struct/union type with the substitutions
567 /// `substs` and -- in the HIR -- a path with the generic
568 /// arguments `args`. If `needle_fr` appears in the args, return
569 /// the `hir::Lifetime` that corresponds to it. If not, push onto
570 /// `search_stack` the types+hir to search through.
571 fn try_match_adt_and_generic_args<'hir>(
573 substs: SubstsRef<'tcx>,
574 needle_fr: RegionVid,
575 args: &'hir hir::GenericArgs<'hir>,
576 search_stack: &mut Vec<(Ty<'tcx>, &'hir hir::Ty<'hir>)>,
577 ) -> Option<&'hir hir::Lifetime> {
578 for (kind, hir_arg) in substs.iter().zip(args.args) {
579 match (kind.unpack(), hir_arg) {
580 (GenericArgKind::Lifetime(r), hir::GenericArg::Lifetime(lt)) => {
581 if r.to_region_vid() == needle_fr {
586 (GenericArgKind::Type(ty), hir::GenericArg::Type(hir_ty)) => {
587 search_stack.push((ty, hir_ty));
590 (GenericArgKind::Const(_ct), hir::GenericArg::Const(_hir_ct)) => {
591 // Lifetimes cannot be found in consts, so we don't need
592 // to search anything here.
596 GenericArgKind::Lifetime(_)
597 | GenericArgKind::Type(_)
598 | GenericArgKind::Const(_),
601 // I *think* that HIR lowering should ensure this
602 // doesn't happen, even in erroneous
603 // programs. Else we should use delay-span-bug.
606 "unmatched subst and hir arg: found {:?} vs {:?}",
617 /// Finds a closure upvar that contains `fr` and label it with a
618 /// fully elaborated type, returning something like `'1`. Result
622 /// | let x = Some(&22);
623 /// - fully elaborated type of `x` is `Option<&'1 u32>`
625 fn give_name_if_anonymous_region_appears_in_upvars(&self, fr: RegionVid) -> Option<RegionName> {
626 let upvar_index = self.regioncx.get_upvar_index_for_region(self.infcx.tcx, fr)?;
627 let (upvar_name, upvar_span) = self.regioncx.get_upvar_name_and_span_for_region(
632 let region_name = self.synthesize_region_name();
636 source: RegionNameSource::AnonRegionFromUpvar(upvar_span, upvar_name.to_string()),
640 /// Checks for arguments appearing in the (closure) return type. It
641 /// must be a closure since, in a free fn, such an argument would
642 /// have to either also appear in an argument (if using elision)
643 /// or be early bound (named, not in argument).
644 fn give_name_if_anonymous_region_appears_in_output(&self, fr: RegionVid) -> Option<RegionName> {
645 let tcx = self.infcx.tcx;
647 let return_ty = self.regioncx.universal_regions().unnormalized_output_ty;
648 debug!("give_name_if_anonymous_region_appears_in_output: return_ty = {:?}", return_ty);
649 if !tcx.any_free_region_meets(&return_ty, |r| r.to_region_vid() == fr) {
653 let mut highlight = RegionHighlightMode::default();
654 highlight.highlighting_region_vid(fr, *self.next_region_name.try_borrow().unwrap());
656 self.infcx.extract_inference_diagnostics_data(return_ty.into(), Some(highlight)).name;
658 let (return_span, mir_description) = match tcx.hir().get(self.mir_hir_id()) {
659 hir::Node::Expr(hir::Expr {
660 kind: hir::ExprKind::Closure(_, return_ty, _, span, gen_move),
663 match return_ty.output {
664 hir::FnRetTy::DefaultReturn(_) => tcx.sess.source_map().end_point(*span),
665 hir::FnRetTy::Return(_) => return_ty.output.span(),
667 if gen_move.is_some() { " of generator" } else { " of closure" },
669 hir::Node::ImplItem(hir::ImplItem {
670 kind: hir::ImplItemKind::Fn(method_sig, _),
672 }) => (method_sig.decl.output.span(), ""),
673 _ => (self.body.span, ""),
677 // This counter value will already have been used, so this function will increment it
678 // so the next value will be used next and return the region name that would have been
680 name: self.synthesize_region_name(),
681 source: RegionNameSource::AnonRegionFromOutput(
683 mir_description.to_string(),
689 fn give_name_if_anonymous_region_appears_in_yield_ty(
692 ) -> Option<RegionName> {
693 // Note: generators from `async fn` yield `()`, so we don't have to
694 // worry about them here.
695 let yield_ty = self.regioncx.universal_regions().yield_ty?;
696 debug!("give_name_if_anonymous_region_appears_in_yield_ty: yield_ty = {:?}", yield_ty,);
698 let tcx = self.infcx.tcx;
700 if !tcx.any_free_region_meets(&yield_ty, |r| r.to_region_vid() == fr) {
704 let mut highlight = RegionHighlightMode::default();
705 highlight.highlighting_region_vid(fr, *self.next_region_name.try_borrow().unwrap());
707 self.infcx.extract_inference_diagnostics_data(yield_ty.into(), Some(highlight)).name;
709 let yield_span = match tcx.hir().get(self.mir_hir_id()) {
710 hir::Node::Expr(hir::Expr {
711 kind: hir::ExprKind::Closure(_, _, _, span, _), ..
712 }) => (tcx.sess.source_map().end_point(*span)),
717 "give_name_if_anonymous_region_appears_in_yield_ty: \
718 type_name = {:?}, yield_span = {:?}",
719 yield_span, type_name,
723 name: self.synthesize_region_name(),
724 source: RegionNameSource::AnonRegionFromYieldTy(yield_span, type_name),