utils: guard mkdir call with std.file.exists

[pabloyoyoista]

Fixes the following stack trace:

2023-04-23 21:02:16 - INFO: Exporting data for v3.15 (main/aarch64) 2023-04-23 21:02:16std.file.FileException@/usr/include/d/std/file.d(2972): /home/abuild/cache/export/media/v3.15/g/gv/gvim.desktop/4016a69fc2135fa29a3414b2c8bd20d9//icons: File exists ---------------- ??:? @trusted bool std.file.cenforce!(bool).cenforce(bool, scope const(char)[], scope const(char)*, immutable(char)[], ulong) [0x563624998170] ??:? @safe void std.file.mkdir!(immutable(char)[]).mkdir(immutable(char)[]) [0x563624a439d0] ??:? @trusted void asgen.utils.copyDir(in immutable(char)[], in immutable(char)[], bool) [0x563624a43500] ??:? /usr/bin/appstream-generator [0x5636249e2190] ??:? void std.parallelism.ParallelForeach!(asgen.backends.interfaces.Package[]).ParallelForeach.opApply(scope int delegate(ref asgen.backends.interfaces.Package)).doIt() [0x5636249e8f30] ??:? void std.parallelism.TaskPool.executeWorkLoop() [0x7fd515e4efe0] ??:? thread_entryPoint [0x7fd515b9d5b0]

• DEBUG: Building final metadata and hints files.

This occurred once during debugging, but haven't tested this in-depth. Anyway, looking at the code seems sort of obvious fix.

[nekopsykose]

isn't this still liable to TOCTOU in the exact same way? it's better to catch the FileException or something instead and check what it is (though i'm not sure it disambiguates 'what exception')

[nekopsykose]

or maybe there's an api better than that 'mkdir' that can just pass if it already exists

[nekopsykose]

(the toctou here is something can make the dir between when you check it and when you mkdir it, which would crash the same way, just much more rare)

[pabloyoyoista]

Sure, thank you both! I am pretty lost with D. It's changed now!

[nekopsykose]

you should update the commit message too

[pabloyoyoista]

Done!