Fix @available(macCatalyst N, iOS N+M) bug #31025
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Previously, availability checking computed a declaration’s availability as the intersection of all @available attributes with active platforms. This meant that Swift would not allow you to use an API that was available earlier in a child platform than in its parent until it was also available in the parent platform. That was incorrect. This PR corrects availability checking to find the most specific @available attribute with an introduced version and use that instead. Fixes rdar://60892534.
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This was reviewed internally to Apple by @devincoughlin. It has also been tested there, since Swift CI's ability to test Mac Catalyst changes is currently limited, so I'll stick to a smoke test here. |
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@swift-ci please smoke test and merge |
The previous commit broke a promise made by the implementation it replaced: if there were two or more @available(introduced:) attributes for the same platform, the greatest version wins. This commit restores that property while still completely overriding the parent platform’s availability with a child platform’s.
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@swift-ci please test |
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@devincoughlin Requesting a re-review because I discovered a bug in the original implementation. |
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DougGregor
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Apr 20, 2020
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DougGregor
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This looks like the right semantics, thanks!
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Previously, availability checking computed a declaration’s availability as the intersection of all
@availableattributes with active platforms. This meant that Swift would not allow you to use an API that was available earlier in a child platform than in its parent until it was also available in the parent platform. That was incorrect.This PR corrects availability checking to find the most specific
@availableattribute with anintroduced:version and use that instead.Fixes rdar://60892534, rdar://61813677.