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[Associated type inference] Resolve @_implements on AsyncSequence.Failure #72552

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Merged
merged 2 commits into from
Mar 25, 2024
Merged

[Associated type inference] Resolve @_implements on AsyncSequence.Failure #72552

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78430e0
[Associated type inference] Resolve `@_implements` on AsyncSequence.F…
DougGregor Mar 24, 2024
99742fb
Add test for multiple `@_implements` on associated types
DougGregor Mar 25, 2024
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17 changes: 9 additions & 8 deletions lib/Sema/AssociatedTypeInference.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -430,13 +430,6 @@ static ResolveWitnessResult resolveTypeWitnessViaLookup(
auto *dc = conformance->getDeclContext();
auto &ctx = dc->getASTContext();

// Prior to Swift 6, don't look for a named type witness for
// AsyncSequence.Failure. We'll always infer it from
// AsyncIteratorProtocol.Failure.
if (isAsyncSequenceFailure(assocType) &&
!ctx.LangOpts.isSwiftVersionAtLeast(6))
return ResolveWitnessResult::Missing;

// Conformances constructed by the ClangImporter should have explicit type
// witnesses already.
if (isa<ClangModuleUnit>(dc->getModuleScopeContext())) {
Expand Down Expand Up @@ -479,10 +472,18 @@ static ResolveWitnessResult resolveTypeWitnessViaLookup(
// Also skip candidates in protocol extensions, because they tend to cause
// request cycles. We'll look at those during associated type inference.
if (assocType->getName() != typeDecl->getName() &&
!(witnessHasImplementsAttrForRequiredName(typeDecl, assocType) &&
!(witnessHasImplementsAttrForExactRequirement(typeDecl, assocType) &&
!typeDecl->getDeclContext()->getSelfProtocolDecl()))
continue;

// Prior to Swift 6, ignore a member named Failure when matching
// AsyncSequence.Failure. We'll infer it from the AsyncIterator.Failure
// instead.
if (isAsyncSequenceFailure(assocType) &&
!ctx.LangOpts.isSwiftVersionAtLeast(6) &&
assocType->getName() == typeDecl->getName())
continue;;

auto *genericDecl = cast<GenericTypeDecl>(typeDecl);

// If the declaration has generic parameters, it cannot witness an
Expand Down
12 changes: 12 additions & 0 deletions test/Concurrency/async_sequence_syntax.swift
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Expand Up @@ -119,3 +119,15 @@ public struct ReaderSeq: AsyncSequence, Sendable {
func test1() -> Error {
return ReaderSeq.Failure.x
}

@available(SwiftStdlib 5.1, *)
public struct MineOwnIterator<Element>: AsyncSequence, AsyncIteratorProtocol {
public mutating func next() async -> Element? { nil }
public func makeAsyncIterator() -> Self { self }

@_implements(AsyncIteratorProtocol, Failure)
public typealias __AsyncIteratorProtocol_Failure = Never

@_implements(AsyncSequence, Failure)
public typealias __AsyncSequence_Failure = Never
}