[PATCH] D133574: [C2x] reject type definitions in offsetof

[YingChi Long via Phabricator via cfe-commits]

inclyc added a comment.

Emm, is it necessary to add a `LangOpts` check so that this change only applies to c2x? If clang was invoked without `-std=c2x`, should we just accept `offsetof` with definitions?



================
Comment at: clang/include/clang/Basic/DiagnosticSemaKinds.td:1650
+def err_type_defined_in_offsetof : Error<
+  "%0 cannot be defined in '__builtin_offsetof'">;
 
----------------
aaron.ballman wrote:
> We might want this change, we might not -- can you test the diagnostic behavior when using `#include <stddef.h>`? Does it print `__builtin_offsetof` in the following example?
> ```
> #include <stddef.h>
> 
> int main() {
>   return offsetof(struct S { int a; }, a);
> }
> ```
> when executed with `clang -fsyntax-only -ffreestanding -std=c2x test.c`
> 
> If it prints the builtin name, I think we'll want to look at the builtin token to see if it was expanded from a macro named `offsetof` to improve the diagnostic quality.
```
local/offsetofcc.c:4:26: error: 'struct S' cannot be defined in '__builtin_offsetof'
  return offsetof(struct S { int a; }, a);
                         ^
1 error generated.
```
> If it prints the builtin name, I think we'll want to look at the builtin token to see if it was expanded from a macro named offsetof to improve the diagnostic quality.

OK


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https://reviews.llvm.org/D133574