Asterisk array size should be supported in typeof and _Atomic type specifiers which are part of a parameter declaration

[Halalaluyafail3]

Clang rejects the following declarations:

void foo(typeof(int(*)[*])(*)[*]);
void bar(_Atomic(int(*)[*])(*)[*]);

If the size is * instead of being an expression, the array type is a variable length array type of unspecified size, which can only be used as part of the nested sequence of declarators or abstract declarators for a parameter declaration, not including anything inside an array size expression in one of those declarators; (footnote) such arrays are nonetheless complete types.

(foonote) They can be used only in function declarations that are not definitions (see 6.7.7.4 and 6.9.2).

These types should be accepted since the array type [*] is part of the nested sequence of declarators and abstract declarators for a parameter declaration.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: None (Halalaluyafail3)

Clang rejects the following declarations: ```c void foo(typeof(int(*)[*])(*)[*]); void bar(_Atomic(int(*)[*])(*)[*]); ``` > If the size is * instead of being an expression, the array type is a variable length array type of unspecified size, which can only be used as part of the nested sequence of declarators or abstract declarators for a parameter declaration, not including anything inside an array size expression in one of those declarators; (footnote) such arrays are nonetheless complete types. > > (foonote) They can be used only in function declarations that are not definitions (see 6.7.7.4 and 6.9.2).

These types should be accepted since the array type [*] is part of the nested sequence of declarators and abstract declarators for a parameter declaration.

[pinskia]

GCC bug report on this: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114873 .
Note EDG (via ICC): gives an error on this too:

<source>(2): error: variable length array with unspecified bound is not allowed
  void foo(typeof(int(*)[*])(*)[*]);
                         ^

<source>(3): error: variable length array with unspecified bound is not allowed
  void bar(_Atomic(int(*)[*])(*)[*]);
                          ^

So 3 all reject it for the same reason. Which makes me suspect this is not valid.

Note MSVC does not support [*] syntax so it is hard to test that.

[shafik]

CC @AaronBallman

[MitalAshok]

This wording changed recently

N3096:

If the size is * instead of being an expression, the array type is a variable length array type of unspecified size, which can only be used in declarations or type names with function prototype scope;

N3149 (maybe?) / N3220

If the size is * instead of being an expression, the array type is a variable length array type of unspecified size, which can only be used as part of the nested sequence of declarators or abstract declarators for a parameter declaration, not including anything inside an array size expression in one of those declarators;

DR#341 seems to ban * to the left of where the omitted identifier would have been (from the definition of "scope"), making these invalid (in the older wording)

N3070 is what prompted the wording change

GB-072
As discussed in N3070, this paragraph leaves it unclear what cases are covered by the function prototype scope restriction on [*] declarators. The intended direction disallowing questionable cases was provided in C99 DR#341.

I don't think it was intentional to allow those two declarations.

[pinskia]

DR#341 seems to ban * to the left of where the omitted identifier would have been (from the definition of "scope"), making these invalid (in the older wording)

That what is mentioned in the GCC bug report too https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114873#c4

[uecker]

I am in favor of allowing it. Conceptually it makes sense to allow it anywhere inside function prototype scope where a size expression is used, because this is what is for: replacing size expressions that could be invalid in a different context with a '*'.