[5.0] Test that newer libobjcs let the Swift runtime set up a class's layout #21970
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swiftlang#21942) Specifically, when the class is referenced from Objective-C first, before being referenced from Swift in any way. This is important for resilience, since up until now Objective-C isn't used to the size of a class changing based on anything other than a superclass's size changing. This is basically the test that would have gone with 9024768 had there been a build of libobjc to test it with. rdar://problem/45718008 (cherry picked from commit 7629253)
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@swift-ci Please test |
rdar://problem/47389594 (cherry picked from commit 73fba19)
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@swift-ci Please test |
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AnnaZaks
approved these changes
Jan 19, 2019
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Explanation: When a Swift class is referenced from Objective-C first, new versions of the Objective-C runtime will give the Swift runtime a chance to lay out that class properly. This is important for resilience, since up until now Objective-C isn't used to the size of a class changing based on anything other than a superclass's size changing.
This commit is just a test; the actual implementation went in months ago, but didn't have a libobjc we could test against at the time.
Scope: Most interesting behavior is only tested on unreleased Apple OSs, but it's still testing class layout on released OSs.
Issue: rdar://problem/45718008
Risk: None. Test change only.
Testing: Tested on both old and new 64-bit macOS systems, old and new 64-bit iOS simulators, an old 32-bit iOS simulator, and a new 32-bit watchOS simulator.
Reviewed by: @slavapestov, @mikeash