https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118375
Bug ID: 118375
Summary: Fixits for feature test macros (FTMs)
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Keywords: diagnostic
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: sjames at gcc dot gnu.org
CC: dmalcolm at gcc dot gnu.org
Target Milestone: ---
We don't currently include any hints for feature test macros (FTMs) but this
came up quite a lot with the C99/GCC 14 porting work especially.
For example, with this in C:
```
// no _GNU_SOURCE defined
#include <errno.h>
int main() {
char* x = program_invocation_name;
}
```
We get:
```
<source>:1:1: error: expected identifier or '(' before '/' token
1 | /#include <errno.h>
| ^
<source>:1:2: error: stray '#' in program
1 | /#include <errno.h>
| ^
Compiler returned: 1
```
We could emit fixits for these. Note that this is rarely an issue for C++ (see
PR11196 and so on).
(See also PR115735 where we've discussed scraping some information out of glibc
docs.)
(dave, I've cc'd you on this for completeness but it hasn't come up in this
cycle and it *tends* to be more of an issue with either older glibc or musl, as
we've moved towards including more in _DEFAULT_SOURCE for glibc in recent years
to avoid people getting this wrong.)
