[cfe-dev] Clang ignores nonnull attributes on declarations following definitions when compiling as C++

[Tom Honermann]

Clang (3.4-trunk) ignores nonnull attributes on declarations following 
definitions when compiling as C++, but not as C.  I presume the 
difference has to do with tentative definitions in C.

A test case is below.  Recent versions of gcc and EDG both allow nonnull 
attributes on declarations following a definition, at least for this 
test case.  Is it desirable for Clang to act differently in this respect?

Tom.

$ cat t.c
void (*pf)(int *p1);
extern void (*pf)(int *p1)
     __attribute__((nonnull));
void f() {
     pf(0);
}


# Compiling as C, no warning is emitted, the nonnull attribute
# is present in the resulting AST:
$ clang -c -Xclang -ast-dump t.c
t.c:5:9: warning: null passed to a callee that requires a non-null 
argument [-Wnonnull]
     pf(0);
        ~^
...
`-VarDecl 0x822dda0 prev 0x822dc50 <line:2:1, col:26> col:15 pf 'void 
(*)(int *)' extern
   `-NonNullAttr 0x822de00 <line:3:20>
...


# Compiling as C++, a warning is emitted and the nonnull attribute
# is not present in the resulting AST:
$ clang -c -Xclang -ast-dump -x c++ t.c
t.c:3:20: warning: attribute declaration must precede definition 
[-Wignored-attributes]
     __attribute__((nonnull));
                    ^
t.c:1:8: note: previous definition is here
void (*pf)(int *p1);
        ^
...
`-VarDecl 0x82e41e0 prev 0x82e4090 <line:2:1, col:26> col:15 pf 'void 
(*)(int *)' extern
...
1 warning generated.


# gcc (4.6.3) emits a warning when invoking *pf with a null argument 
regardless of whether the code is compiled as C or C++:
$ gcc -Wall -c t.c
t.c: In function 'f':
t.c:5:5: warning: null argument where non-null required (argument 1) 
[-Wnonnull]
$ gcc -Wall -c -x c++ t.c
t.c: In function 'void f()':
t.c:5:9: warning: null argument where non-null required (argument 1) 
[-Wnonnull]