[Macros] Provide the freestanding macro role for expansion operations. #66509
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…lt type Fixes rdar://108871352.
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.
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.
DougGregor
requested review from
CodaFi,
ahoppen,
bnbarham,
hborla,
rintaro,
slavapestov,
xedin and
zoecarver
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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. Doing this improves diagnostics an eliminates a known compiler crash.
Also, 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://110418969 and rdar://110178899.