https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119893
Bug ID: 119893
Summary: '-Wnonnull' should not warn null pointer use in
'typeof' expression
Product: gcc
Version: 14.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: Explorer09 at gmail dot com
Target Milestone: ---
Test code:
```c
__attribute__((nonnull)) \
int func(void *p);
__typeof__(func((void *)0)) func2(void *p);
typeof(func((void *)0)) main(void)
{
return 0;
}
```
Compiling with `gcc -std=gnu23 -Wnonnull` produces warnings like these:
```text
<source>:4:12: warning: argument 1 null where non-null expected [-Wnonnull]
4 | __typeof__(func((void *)0)) func2(void *p);
| ^~~~
<source>:2:30: note: in a call to function 'func' declared 'nonnull'
2 | __attribute__((nonnull)) int func(void *p);
| ^~~~
<source>:6:8: warning: argument 1 null where non-null expected [-Wnonnull]
6 | typeof(func((void *)0)) main(void) {
| ^~~~
<source>:2:30: note: in a call to function 'func' declared 'nonnull'
2 | __attribute__((nonnull)) int func(void *p);
| ^~~~
```
Clang 20 produces no warnings, and I expect GCC produce no warnings either. In
this 'typeof' expression, the function should be never called and the fact I
passed a `(void *)0` there shouldn't matter.
A workaround is to add an offset to null pointer so the address becomes
technically non-zero:
```c
/* Workaround */
__typeof__(func(1 + (void *)0)) func2(void *p);
```
