[cfe-dev] Clang ignores nonnull attributes on pointer-to-member-function declarations

[Richard Smith]

On Mon, Jul 13, 2015 at 2:00 PM, Tom Honermann <thonermann at coverity.com>
wrote:

> On 07/13/2015 03:33 PM, Richard Smith wrote:
>
>> On Mon, Jul 13, 2015 at 10:41 AM, Joerg Sonnenberger
>> <joerg at britannica.bec.de <mailto:joerg at britannica.bec.de>> wrote:
>>
>>     On Mon, Jul 13, 2015 at 11:31:54AM -0400, Tom Honermann wrote:
>>     > Clang (3.4-trunk) ignores nonnull attributes on
>> pointer-to-member-function
>>     > declarations.
>>
>>     You are aware that 3.4-trunk is quite old and we are about to start
>> the
>>     3.7 release cycle?
>>
>>
>> I read that as "from version 3.4 to trunk"
>>
>
> And that is how I intended it.
>
>  And it's true: clang trunk
>> still behaves as described. But I'm a bit confused, because the
>> referenced GCC bug report says they made this work:
>>
>> struct Foo;
>> void foo (void (Foo::*) () __attribute__ ((nonnull)));
>>
>> ... where the attribute would presumably apply to the pointer-to-member,
>> and the request is to support this:
>>
>> void (S::*pmf)(int *p1)
>>      __attribute__((nonnull));
>>
>> ... where the attribute (again, presumably) jumps over the
>> pointer-to-member and applies to the pointer parameter? This does not
>> seem consistent. What is the actual GCC behavior?
>>
>
> Interesting.  It didn't occur to me that the case in the gcc bug report is
> ambiguous with respect to Clang's support for infix nonnull attributes.
>
> As specified, the attribute is either an infix attribute specifying that
> the pointer-to-member-function parameter value must not be null, or it is a
> non-infix attribute specifying that all of the parameters of the target of
> the pointer-to-member-function must not be null.
>
> I don't think gcc supports infix nonnull attributes, so I believe the
> latter behavior is what is intended.  gcc compiler warnings appear to bear
> this out:
>
> $ cat t.cpp
> struct S;
> void f1(S *s, void (S::*pmf)(void*) __attribute__ ((nonnull))) {
>     (s->*pmf)(0);
> }
> void f2(S *s) {
>     f1(s, 0);
> }
>
> $ gcc -c -Wall t.cpp
> t.cpp: In function ‘void f1(S*, void (S::*)(void*))’:
> t.cpp:3:16: warning: null argument where non-null required (argument 2)
> [-Wnonnull]
>      (s->*pmf)(0);
>                 ^
>
> Note that there is a warning when passing a null argument with the
> pointer-to-member-function invocation, but not when passing a null argument
> as the pointer-to-member-function value.


OK, we'll need to figure out how to integrate this into our
__attribute__((nonnull)) semantics. Please do file that PR so we don't
forget!
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