CWG 3121 [dcl.fct] Zero-size arrays in function parameters are not allowed

[eisenwave]

Reference (section label): [dcl.fct] paragraph 4

Jens wants a CWG issue for this; see cplusplus/draft#6575 (comment) for previous discussion.

Issue description

Implementations diverge (https://godbolt.org/z/q5bjWEs8o) on whether the following declaration is ill-formed:

void foo(int[0]);

While [dcl.fct] paragraph 4 states that array parameter types are adjusted to pointer types, [dcl.array] paragraph 1 clearly states that a zero-length array is not a valid type in the first place.

It should be clarified that parameter type adjustment does not legitimize zero-length arrays in function parameters.

Proposed resolution

Expand [dcl.fct] example 2 as follows:

 ...
 void h(int (*)(int)) {}         // defines #3
+
+void j(int[0]);                 // error: int[0] is not a valid type

[jensmaurer]

CWG3121