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Sema: Expand isolated conformance inference to consider conformances to inherited protocols #82383

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Jun 23, 2025
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Sema: Expand isolated conformance inference to consider conformances to inherited protocols #82383

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22 changes: 17 additions & 5 deletions lib/Sema/TypeCheckConcurrency.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -8155,16 +8155,28 @@ ActorIsolation swift::inferConformanceIsolation(
return nominalIsolation;
}

bool anyIsolatedWitness = false;
auto protocol = conformance->getProtocol();
for (auto requirement : protocol->getMembers()) {
if (isa<TypeDecl>(requirement))

// Also check the value witnesses of each implied conformance to every
// inherited protocol, recursively.
Comment on lines +8160 to +8161
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@DougGregor DougGregor Jun 23, 2025 •
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Comment nit: this isn't checking the value witnesses specifically, it's considering the isolation of the inherited conformances.

for (auto req : protocol->getRequirementSignature().getRequirements()) {
if (req.getKind() != RequirementKind::Conformance ||
!req.getFirstType()->isEqual(ctx.TheSelfType))
continue;

auto valueReq = dyn_cast<ValueDecl>(requirement);
if (!valueReq)
auto *assocConf = conformance->getAssociatedConformance(
req.getFirstType(), req.getProtocolDecl()).getConcrete();
auto isolation = assocConf->getIsolation();
if (isolation.isGlobalActor())
return isolation;
Comment on lines +8170 to +8171
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@DougGregor DougGregor Jun 23, 2025

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When we infer isolation for from multiple sources elsewhere (for example, inferring type isolation from the protocols it conforms to), we refuse to infer isolation when there are conflicting inferences.. for example, @MainActor from one source and @SomeOtherGlobalActor from another source. Should we do the same here, rather than eagerly returning the first global actor isolation we find?

}

bool anyIsolatedWitness = false;
for (auto requirement : protocol->getProtocolRequirements()) {
if (isa<TypeDecl>(requirement))
continue;

auto valueReq = cast<ValueDecl>(requirement);
auto witness = conformance->getWitnessDecl(valueReq);
if (!witness)
continue;
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5 changes: 5 additions & 0 deletions test/Concurrency/Inputs/isolated_conformance_other.swift
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@@ -0,0 +1,5 @@
public protocol P {
func f()
}

public protocol PDerived: P {}
4 changes: 4 additions & 0 deletions test/Concurrency/isolated_conformance_inference.swift
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Expand Up @@ -92,3 +92,7 @@ class InferMeDefaults {
var someGlobalActorState: any P2.Type = DifferingConformances.self // expected-error{{global actor 'SomeGlobalActor'-isolated default value in a main actor-isolated context}}
var bothState: any (P & P2).Type = DifferingConformances.self // expected-error{{default argument cannot be both main actor-isolated and global actor 'SomeGlobalActor'-isolated}}
}

protocol PDerived: P {}

@MainActor struct ImpliedConformanceInference: PDerived { func f() {} }
9 changes: 9 additions & 0 deletions test/Concurrency/isolated_conformance_inference_with_default_actor.swift
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@@ -0,0 +1,9 @@
// RUN: %empty-directory(%t)
// RUN: %target-swift-frontend -emit-module -emit-module-path %t/isolated_conformance_other.swiftmodule %S/Inputs/isolated_conformance_other.swift -swift-version 6
// RUN: %target-typecheck-verify-swift -I %t -swift-version 6 -enable-upcoming-feature InferIsolatedConformances -default-isolation MainActor -swift-version 6
// REQUIRES: swift_feature_InferIsolatedConformances

import isolated_conformance_other

struct S1: P { func f() {} }
struct S2: PDerived { func f() {} }