[clang-format] Formatting a C file only works with Cpp formatting settings

[hueychen27]

Let this be the file, unformatted.c, to be formatted in the examples:

 int      main(int  argc , char  * argv [] ) {
     int * thing;
    int *eee;
}

This will not format the C code at all as clang-format returns Configuration file(s) do(es) not support C++:

---
Language: C

IndentWidth: 9
PointerAlignment: Left

Adding BaseOnStyle: LLVM to the top of the file will run without an error, but the custom settings defined are ignored:

BasedOnStyle: LLVM
---
Language: C

IndentWidth: 9
PointerAlignment: Left

Formatted file:

int main(int argc, char *argv[]) {
  int *thing;
  int *eee;
}

For some reason, changing Language: C to use Cpp works.

BasedOnStyle: LLVM
---
Language: Cpp

IndentWidth: 9
PointerAlignment: Left

Formatted file:

int main(int argc, char* argv[]) {
         int* thing;
         int* eee;
}

Why is Language: C ignored?

clang-format version:

$ clang-format-21 --version
Debian clang-format version 21.0.0 (++20250612091244+3f0cf742ac4e-1~exp1)

[llvmbot]

@llvm/issue-subscribers-clang-format

Author: None (hueychen27)

Let this be the file, `unformatted.c`, to be formatted in the examples: ```c int main(int argc , char * argv [] ) { int * thing; int *eee; } ```

This will not format the C code at all as clang-format returns Configuration file(s) do(es) not support C++:

---
Language: C

IndentWidth: 9
PointerAlignment: Left

Adding BaseOnStyle: LLVM to the top of the file will run without an error, but the custom settings defined are ignored:

BasedOnStyle: LLVM
---
Language: C

IndentWidth: 9
PointerAlignment: Left

Formatted file:

int main(int argc, char *argv[]) {
  int *thing;
  int *eee;
}

For some reason, changing Language: C to use Cpp works.

BasedOnStyle: LLVM
---
Language: Cpp

IndentWidth: 9
PointerAlignment: Left

Formatted file:

int main(int argc, char* argv[]) {
         int* thing;
         int* eee;
}

Why is Language: C ignored?

clang-format version:

$ clang-format-21 --version
Debian clang-format version 21.0.0 (++20250612091244+3f0cf742ac4e-1~exp1)

[owenca]

Works correctly in 20.1.7 and main.

[hueychen27]

@owenca Is my version old?

[owenca]

It must be. Please try the latest release 20.1.7 or current main (e.g. 1506ba9).

[hueychen27]

@owenca Huh, the current main still has the same bug. How did you reproduce?

[owenca]

$ cat a.c
 int      main(int  argc , char  * argv [] ) {
     int * thing;
    int *eee;
}
$ cat .clang-format
---
Language: C

IndentWidth: 9
PointerAlignment: Left
$ clang-format -version
clang-format version 20.1.7
$ clang-format a.c
int main(int argc, char* argv[]) {
         int* thing;
         int* eee;
}
$ 

And so on. Same for version 21.0.0git 1506ba9.

[hueychen27]

I used vscodium, is that the issue?