clang-format does not format `#if 0`'d code

[LebedevRI]

I was really sure this used to work? Apparently even LLVM11's clang-format is affected.

$ cat test.cpp
#if 0
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
#endif

aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
$ clang-format test.cpp 
#if 0
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
#endif

aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
    aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
$ clang-format --version
Debian clang-format version 15.0.0-++20220506111518+37ba1b9d1ac7-1~exp1~20220506111609.477

CC @owenca @mydeveloperday @kwk

[llvmbot]

@llvm/issue-subscribers-clang-format

[mydeveloperday]

clang-format 5 and clang-format 8 produce the same behavior, I don't think this is a regression.

[mkurdej]

I thought that it was behaving always like this. A common workaround I've seen is #if COMMENTED_CODE instead of #if 0.
My 2 cents.

[Hedede]

Yes, it always behaved like this asfar as I can remember. I'm not sure this is a bug, there might be broken code inside #if 0 which can confuse clang-format.
And sometimes I intentionally wrap code inside #if 0 to temporarily prevent formatting when copy-pasting code from git diff (which is a weird use-case but a use-case nonetheless).