diff options
| -rw-r--r-- | compiler/rustc_ast_lowering/src/lib.rs | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs index 69398918f89..e7a20651107 100644 --- a/compiler/rustc_ast_lowering/src/lib.rs +++ b/compiler/rustc_ast_lowering/src/lib.rs @@ -1345,10 +1345,16 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> { self.with_hir_id_owner(opaque_ty_node_id, |lctx| { if origin != hir::OpaqueTyOrigin::TyAlias { + // When lowering `fn foo<'a>() -> impl Debug + 'a`, the `lifetime_collector` finds + // the set of lifetimes that appear in the bounds (in this case, 'a) and returns + // that set in the variable lifetimes_in_bounds. let lifetimes_in_bounds = lifetime_collector::lifetimes_in_bounds(&lctx.resolver, bounds); debug!(?lifetimes_in_bounds); + // For each captured lifetime (e.g., 'a), we create a new lifetime parameter that + // is a generic defined on the TAIT, so we have type Foo<'a1> = ... and we + // establish a mapping from the original parameter 'a to the new parameter 'a1. collected_lifetimes = lctx.create_lifetime_defs( opaque_ty_def_id, &lifetimes_in_bounds, @@ -1359,6 +1365,8 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> { debug!(?collected_lifetimes); lctx.with_remapping(new_remapping, |lctx| { + // Then when we lower the param bounds, references to 'a are remapped to 'a1, so we + // get back Debug + 'a1, which is suitable for use on the TAIT. let hir_bounds = lctx.lower_param_bounds(bounds, itctx); let lifetime_defs = lctx.arena.alloc_from_iter(collected_lifetimes.iter().map( |