[5.9] [Macros] Tighten declaration semantics and improve expansion of freestanding macros #66527
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DougGregor
commented
Jun 10, 2023
DougGregor
commented
- Explanation: Implement missing-but-required declaration semantics for macro declarations, including diagnosing the presence of a result type on a macro that isn't a freestanding expression macro (it can't be used) and diagnosing multiple freestanding roles on a given macro declaration (SE-0397 requires this). While here, thread the intended freestanding macro role through to the macro expansion code, providing better diagnostics when there is a mismatch between the macro declaration and its implementations (previously, we would crash).
- Scope: Narrow; only affects validation of freestanding macro declarations and expansions.
- Risk: Low; narrow change to perform better validation when declaring and expanding freestanding macros.
- Reviewed by: @rintaro , @ahoppen
- Issue: rdar://108871352, rdar://110418969, rdar://110178899
- Original pull request: [Macros] Only freestanding expression macros can have a non-Void result type #66504, [Macros] Provide the freestanding macro role for expansion operations. #66509, [Macros] Tighten restriction on non-expression macros not having return types #66526
…lt type Fixes rdar://108871352. (cherry picked from commit 759f520)
The compiler knows (from a macro declaration) what freestanding macro role a macro implementation is expected to implement. Pass that through to the macro expansion code itself, rather than guessing based on the protocol conformances of the implementation type. We already use this approach with attached macros, so this is more of the same. Eliminates a crash and improves diagnostics when the freestanding macro role and its implementation are out of sync, fixing rdar://110418969. (cherry picked from commit 3c04cff)
Per SE-0397, a macro may only have a single freestanding macro role, otherwise we would have an ambiguity in how a particular freestanding macro would be expanded. Produce an error on such macro declarations. Fixes rdar://110178899. (cherry picked from commit c5ec389)
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hborla
approved these changes
Jun 10, 2023
…rn types There is no reason to special-case `Void` to permit it. Rather, make this a syntactic rule. Thanks to Alex Hoppen for the suggestion.
…terfaces This allows us to continue to accept Swift interface files created with older versions of the Swift 5.9 compiler that emitted a spurious `-> ()` on non-expression macro declarations.
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