[Bug c++/54161] New: sizeof(void) expressions are accepted

["daniel.kruegler at googlemail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54161

             Bug #: 54161
           Summary: sizeof(void) expressions are accepted
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: daniel.kruegler@googlemail.com


gcc 4.8.0 20120729 (experimental) accepts the following code even using the
following options:

-Wall -pedantic -ansi

with either of -std=c++98 or -std=c++0x

//----
void f();
void (&g())();

const int a = sizeof(void);
const int b = sizeof(void());
const int c = sizeof(f());
const int d = sizeof(g());

typedef char test[a + b + c + d > 0 ? 1 : -1];
//----

albeit issuing warnings:

"4|warning: invalid application of 'sizeof' to a void type [-Wpedantic]|
5|warning: invalid application of 'sizeof' to a function type [-Wpedantic]|
6|warning: invalid application of 'sizeof' to a void type [-Wpedantic]|
7|warning: invalid application of 'sizeof' to a function type [-Wpedantic]|
"

This code is ill-formed according to [expr.sizeof] p1:

"The sizeof operator shall not be applied to an expression that has function or
incomplete type, [..], to the parenthesized name of such types, or to an lvalue
that designates a bit-field."

and thus should be rejected.

The current behaviour is especially annoying, because such expression can occur
in SFINAE expression where corresponding template specializations are not
excluded from the set.