CWG2476 [dcl.spec.auto.general] p2 Is the type of "auto(*)(int)->auto" a generic parameter type placeholder #84

Full name of submitter (unless configured in github; will be published with the issue): Jim X

[dcl.spec.auto.general] p2 says

if it is not the auto type-specifier introducing a trailing-return-type (see below), is a generic parameter type placeholder of the function declaration or lambda-expression.

Consider this example

void fun(auto(*)(int)->auto){

}

The auto type-specifier does introduce a trailing-return-type, so the specified type is not a generic parameter type placeholder?

Divergence: Clang accepts this example but GCC rejects it.

It seems to make sense that Clang accepts the example since [dcl.spec.auto.general] p3 says

If the function declarator includes a trailing-return-type ([dcl.fct]), that trailing-return-type specifies the declared return type of the function.

This declaration behaves as if it were auto(*)(int).

Suggested resolution

if it is either

• not the auto type-specifier introducing a trailing-return-type(see below), or
• the auto type-specifier introducing the trailing-return-type containing a placeholder type

is a generic parameter type placeholder of the function declaration or lambda-expression.