Merge pull request #41130 from kavon/changelog-se327-default-value

Author: swift-ci

CHANGELOG.md

@@ -42,6 +42,27 @@ _**Note:** This is in reverse chronological order, so newer entries are added to
 Swift 5.6
 ---------
 
+* [SE-0327][]:
+
+In Swift 5 mode, a warning is now emitted if the default-value expression of an
+instance-member property requires global-actor isolation. For example:
+
+```swift
+@MainActor
+func partyGenerator() -> [PartyMember] { fatalError("todo") }
+
+class Party {
+  @MainActor var members: [PartyMember] = partyGenerator()
+  //                                      ^~~~~~~~~~~~~~~~
+  // warning: expression requiring global actor 'MainActor' cannot
+  //          appear in default-value expression of property 'members'
+}
+```
+
+Previously, the isolation granted by the type checker matched the isolation of
+the property itself, but at runtime that is not guaranteed. In Swift 6, 
+such default-value expressions will become an error if they require isolation.
+
 * Actor isolation checking now understands that `defer` bodies share the isolation of their enclosing function.
 
   ```swift
@@ -8936,6 +8957,7 @@ Swift 1.0
 [SE-0322]: <https://github.com/apple/swift-evolution/blob/main/proposals/0322-temporary-buffers.md>
 [SE-0324]: <https://github.com/apple/swift-evolution/blob/main/proposals/0324-c-lang-pointer-arg-conversion.md>
 [SE-0323]: <https://github.com/apple/swift-evolution/blob/main/proposals/0323-async-main-semantics.md>
+[SE-0327]: <https://github.com/apple/swift-evolution/blob/main/proposals/0327-actor-initializers.md>
 [SE-0328]: <https://github.com/apple/swift-evolution/blob/main/proposals/0328-structural-opaque-result-types.md>
 [SE-0331]: <https://github.com/apple/swift-evolution/blob/main/proposals/0331-remove-sendable-from-unsafepointer.md>
 [SE-0337]: <https://github.com/apple/swift-evolution/blob/main/proposals/0337-support-incremental-migration-to-concurrency-checking.md>