[Bug c/87183] New: -Wformat: format-extra-args fails to catch ex: printf(PRIu32, 1)

[noah.pendleton at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87183

Bug ID: 87183
   Summary: -Wformat: format-extra-args fails to catch ex:
printf(PRIu32, 1)
   Product: gcc
   Version: 9.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c
  Assignee: unassigned at gcc dot gnu.org
  Reporter: noah.pendleton at gmail dot com
  Target Milestone: ---

Created attachment 44644
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=44644&action=edit
preprocessed file

>>Description:
Using  format specifiers but omitting the `%` prefix causes the
`-Werror=format-extra-args` error to not be omitted:

```c
#include 

printf(PRIu32, 2); // doesn't warn
printf(PRIu32 "", 2);  // doesn't warn
printf("u", 2);// warns
printf("" PRIu32, 2);  // warns
```

Interestingly, defining PRIu32 in the test file and not using 
yields the expected behavior, eg:

```c
#define PRIu32 "u"

printf(PRIu32, 2); // warns
printf(PRIu32 "", 2);  // warns
printf("u", 2);// warns
printf("" PRIu32, 2);  // warns
```

>>Info:
gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc/x86_64-linux-gnu/9.0.0/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../configure --enable-languages=c,c++,fortran
--disable-multilib --disable-bootstrap --build=x86_64-linux-gnu
Thread model: posix
gcc version 9.0.0 20180831 (experimental) (GCC)

>>Complete Command Line:
gcc -Wall -Werror test.c

>>Complete Compiler Output:
test.c: In function 'main':
test.c:7:12: error: too many arguments for format [-Werror=format-extra-args]
7 | printf("u", 2);// fails
  |^~~
test.c:8:12: error: too many arguments for format [-Werror=format-extra-args]
8 | printf("" PRIu32, 2);  // fails
  |^~
cc1: all warnings being treated as errors

>>Preprocessed file attached.

[Bug c/87183] -Wformat: format-extra-args fails to catch ex: printf(PRIu32, 1)

[noah.pendleton at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87183

--- Comment #1 from Noah Pendleton  ---
Typo, the description should read-
"Using  format specifiers but omitting the `%` prefix causes
the `-Werror=format-extra-args` error to not be **emitted**:" 😬

[Bug c/87183] -Wformat: format-extra-args fails to catch ex: printf(PRIu32, 1)

[noah.pendleton at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87183

--- Comment #3 from Noah Pendleton  ---
Yep, looks like it, enabling `-Wsystem-headers` yields the expected result:
```bash
gcc -Wall -Werror -Wsystem-headers test.c
In file included from test.c:1:
test.c: In function 'main':
test.c:5:12: error: too many arguments for format [-Werror=format-extra-args]
5 | printf(PRIu32, 2); // doesn't warn
  |^~
test.c:6:12: error: too many arguments for format [-Werror=format-extra-args]
6 | printf(PRIu32 "", 2);  // doesn't warn
  |^~
test.c:7:12: error: too many arguments for format [-Werror=format-extra-args]
7 | printf("u", 2);// warns
  |^~~
test.c:8:12: error: too many arguments for format [-Werror=format-extra-args]
8 | printf("" PRIu32, 2);  // warns
  |^~
cc1: all warnings being treated as errors
```