sccache breaks -Wimplicit-fallthrough

[anholt]

I've been looking at using sccache to improve Mesa build times, and I noticed that after getting sccache working locally, my build was spewing -Wimplcit-fallthrough errors. Sample code:

#include <stdio.h>

int main(int argc, char **argv)
{
    switch (argc) {
    case 0:
        printf("0\n");
        /* fallthrough */
    case 1:
        printf("1\n");
        break;
    }
    return 0;
}

Output:

% /usr/bin/gcc-10 -Wimplicit-fallthrough -c -o fallthrough-test fallthrough-test.c        
% sccache /usr/bin/gcc-10 -Wimplicit-fallthrough -c -o fallthrough-test fallthrough-test.c
fallthrough-test.c: In function 'main':
fallthrough-test.c:7:3: warning: this statement may fall through [-Wimplicit-fallthrough=]
    7 | # 1 "fallthrough-test.c"
      |   ^~~~~~~~~~~~~
fallthrough-test.c:9:2: note: here
    9 | # 27 "/usr/include/stdio.h" 3 4
      |  ^~~~

[mstange]

Hmm, maybe preprocessing was removing the /* fallthrough */ comment? I'm not sure if the preprocessor touches regular comments, I thought it didn't. Could you retest with rewrite_includes_only = true in your config's [dist] section?

[anholt]

It does seem like that option would be required. However I'm failing to reproduce now (possibly due to a new compiler, possibly that I changed something else in sccache configuration since then before I dropped using it)