[clang-tidy] bugprone-tagged-union-member-count false warning when using enum & pthread_mutex_t

[abdelmaged]

Source C file:

#include <pthread.h>

typedef enum {
  MYENUM_ONE,
  MYENUM_TWO,
} myEnumT;

typedef struct {
  pthread_mutex_t mtx;       
  myEnumT         my_enum;
} myTypeT;

Using clang-tidy bugprone-tagged-union-member-count:

<source>:8:9: warning: tagged union has more data members (3) than tags (2)! [bugprone-tagged-union-member-count]
    8 | typedef struct {
      |         ^
1 warning generated.

This is incorrect warning.

clang-tidy vesion: 20.1.1

Issue also reproducible in this link:
https://godbolt.org/z/o3fb9bbrb

[llvmbot]

@llvm/issue-subscribers-clang-tidy

Author: None (abdelmaged)

Source C file: ``` #include <pthread.h>

typedef enum {
MYENUM_ONE,
MYENUM_TWO,
} myEnumT;

typedef struct {
pthread_mutex_t mtx;
myEnumT my_enum;
} myTypeT;

Using clang-tidy bugprone-tagged-union-member-count:

<source>:8:9: warning: tagged union has more data members (3) than tags (2)! [bugprone-tagged-union-member-count]
8 | typedef struct {
| ^
1 warning generated.

This is incorrect warning.

clang-tidy vesion: 20.1.1

Issue also reproducible in this link:
https://godbolt.org/z/o3fb9bbrb

</details>

[vbvictor]

What a coincidence that pthread_mutex_t is actually a union with 3 fields

typedef union
{
  struct __pthread_mutex_s __data;
  char __size[__SIZEOF_PTHREAD_MUTEX_T];
  long int __align;
} pthread_mutex_t;

I think to avoid such problem, we should exclude unions/structs that come from system headers.

[vbvictor]

CC @tigbr, you may be interested in this issue

[tigbr]

Hi @abdelmaged!

Thank you for reporting this issue. Fixing it would be a good improvement to the check. The solution suggested by @vbvictor seems reasonable.

Due to a lack of permissions I cannot assign myself to this issue. Perhaps @Szelethus can help with that?

[vbvictor]

You can still take this issue right-away and work on it.

[tigbr]

I have opened a pull request that implements the filtering of system defined types as mentioned.