[6.3] CustomAvailability: synthesized dynamic availability checking function should be private #85565
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…n should be private When compiling a Swift module in incremental mode, each Swift source file is compiled into an object file and we use linker to link them together. Because the predicate function for checking dynamic feature availability is eagerly synthesized per compilation unit, the linker will complain about duplicated symbols for them. Setting their visibility as private ensures that linker doesn't see them, thus addressing the linker errors. One workaround for this problem is to enable WMO. rdar://164971313
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@swift-ci please test |
bnbarham
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Nov 18, 2025
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@swift-ci please smoke test Windows |
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Explanation: When compiling a Swift module in incremental mode, each Swift source file is compiled into an object file and we use linker to link them together. Because the predicate function for checking dynamic feature availability is eagerly synthesized per compilation unit, the linker will complain about duplicated symbols for them. Setting their visibility as private ensures that linker doesn't see them, thus addressing the linker errors. One workaround for this problem is to enable WMO.
Scope: This affects Clang custom availability users who build their codebase incrementally
Reviewer: @slavapestov
Risk: Low
Radar: rdar://164971313
Testing: Unit test added
Original PR: CustomAvailability: synthesized dynamic availability checking function should be private #85549