[Parse] Warn if the same argument is specified more than once in @available #20997
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Previously, if the `message` or `available` argument to an `@available` attribute was specified two or more times, the last value would be used and the earlier ones would be silently discarded. This change emits a warning instead; we can strengthen this into an error in a future version of Swift. Fixes rdar://problem/46348825.
Add the warning for introduced, deprecated, and obsoleted; also ensures behavior is *completely* backwards-compatible by continuing to use the last argument’s value, rather than the first one.
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@swift-ci please smoke test |
jrose-apple
approved these changes
Dec 4, 2018
beccadax
changed the title
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Previously, if an argument to an
@availableattribute was duplicated, the first value would be silently dropped. With this change, the compiler produces a warning instead. (We emit a warning instead of an error to preserve source compatibility.)Resolves rdar://problem/46348825.