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Auto merge of #105094 - Swatinem:generator-not-future, r=compiler-errors

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Make sure async constructs do not `impl Generator`

Async lowering turns async functions and blocks into generators internally.
Though these special kinds of generators should not `impl Generator` themselves.
The other way around, normal generators should not `impl Future`.

This was discovered in https://github.com/rust-lang/rust/pull/105082#issuecomment-1332210907 and is a regression from https://github.com/rust-lang/rust/pull/104321.

r? `@compiler-errors`
This commit is contained in:
bors 2022-12-04 22:46:11 +00:00
commit d1449560e3
3 changed files with 131 additions and 1 deletions
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6
compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
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@ -203,7 +203,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
// type/region parameters.
let self_ty = obligation.self_ty().skip_binder();
match self_ty.kind() {
ty::Generator(..) => {
// async constructs get lowered to a special kind of generator that
// should *not* `impl Generator`.
ty::Generator(did, ..) if !self.tcx().generator_is_async(*did) => {
debug!(?self_ty, ?obligation, "assemble_generator_candidates",);
candidates.vec.push(GeneratorCandidate);
@ -223,6 +225,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
) {
let self_ty = obligation.self_ty().skip_binder();
if let ty::Generator(did, ..) = self_ty.kind() {
// async constructs get lowered to a special kind of generator that
// should directly `impl Future`.
if self.tcx().generator_is_async(*did) {
debug!(?self_ty, ?obligation, "assemble_future_candidates",);