Description

Compiler error if both a class and its subclass have no explicit initializers.

Reproduction

Make a new Xcode project, turn on Swift 6 along with all the trimmings (approachable concurrency, default actor isolation to MainActor).

class Thing {} class SubThing: Thing {} 

Compiler: "Main actor-isolated initializer 'init()' has different actor isolation from nonisolated overridden declaration"

Expected behavior

It should just compile. There is no there there, so what's the problem?

Environment

Xcode Version 26.0 (17A324)

% swiftc -version swift-driver version: 1.127.14.1 Apple Swift version 6.2 (swiftlang-6.2.0.19.9 clang-1700.3.19.1) Target: arm64-apple-macosx26.0 

Additional information

The fact that there is no init seems to be the problem. If you add init() {} to Thing, the error goes away. It is as if a class has an implicit init which has not gotten the memo about everything being main actor isolated by default.