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[Sema] Fix #84644: Implicit initializers now inherit default actor isolation. #84815

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[Sema] Fix #84644: Implicit initializers now inherit default actor isolation. #84815

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[Sema] Propagate default actor isolation to synthesized default initi…
Harshit7m Oct 10, 2025
9336d0e
Create default_actor_isolation_initializer.swift
Harshit7m Oct 10, 2025
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7 changes: 6 additions & 1 deletion lib/Sema/CodeSynthesis.cpp
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Expand Up @@ -1703,9 +1703,14 @@ SynthesizeDefaultInitRequest::evaluate(Evaluator &evaluator,
ImplicitConstructorKind::DefaultDistributedActor :
ImplicitConstructorKind::Default;
if (auto ctor = createImplicitConstructor(decl, ctorKind, ctx)) {
if (auto isolation = decl->getDefaultActorIsolation()) {
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I don't think there is a getDefaultActorIsolation method also I don't think we want a "default" here we want to match isolation of the type, that's the isolation we need to get.

/// Ensure the synthesized default initializer inherits the class's
/// default actor isolation (e.g., @MainActor) to avoid
/// override-isolation mismatches in subclasses.
ctor->setActorIsolation(isolation);
}
// Add the constructor.
decl->addMember(ctor);

// Lazily synthesize an empty body for the default constructor.
ctor->setBodySynthesizer(synthesizeSingleReturnFunctionBody);
return ctor;
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7 changes: 7 additions & 0 deletions test/Concurrency/default_actor_isolation_initializer.swift
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@@ -0,0 +1,7 @@
// RUN: %target-typecheck-verify-swift -enable-upcoming-feature GlobalActorIsMainActor -enable-upcoming-feature RegionBasedIsolation
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We don't have GlobalActorIsMainActor, it's actually spelled as -default-isolation MainActor, also I don't think you need RegionBasedIsolation here either.

// expected-no-diagnostics

@MainActor
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Since the main-actor mode is on by default, this annotation is not needed.

class Thing {}

class SubThing: Thing {}
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We need to check SILGen output to make sure that initializers are isolated correctly, both initializers should be marked as MainActor in the output. I think you can move this to test/Concurrency/assume_mainactor.swift and add the checks there (it already checks for deinit).