Backport compatibility macro fixes to 5.8 #63995
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#59072 accidentally changed the SWIFT_CLASS_NAMED macro to use `__attribute` when it previously used `__attribute__` (note the trailing underscores). While both keywords have the same semantics in clang, they are technically different tokens, so clang refuses to merge macro definitions that use one instead of the other; instead it would diagnose an ambiguity when a generated header from a new compiler imported a generated header from an old compiler. Change back to the old token to avoid this problem. Fixes rdar://104252758.
fixes 63837
rdar://106046585
rdar://106086816
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@swift-ci Please test |
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@swift-ci Please build toolchain macOS Platform |
beccadax
approved these changes
Mar 1, 2023
airspeedswift
approved these changes
Mar 2, 2023
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This PR backports the following changes onto
release/5.8:Explanation: #59072 introduced an implementation change to the Objective-C compatibility header, but it also created a regression for projects that link against headers generated by different Swift versions, where their projects would encounter "macro redefined" errors.
Scope: Regression affecting projects with prebuilt dependencies built by older versions of Swift
Issue: rdar://106086816
Risk: Low. Projects that build all their code with the same compiler are unaffected. The change is isolated to the Objective-C compatibility header generation, and does not affect normal compilation.
Testing: Locally building a project that included a generated header from Swift 5.7 against a header generated with Swift 5.8. A future PR will implement an automated test to ensure that these "macro redefinition" errors are all handled.
Reviewer: @airspeedswift @beccadax