windows: overriding cache dirs with build-exe failing

[jonforums]

On Win10 x64 while trying to host the cache dirs in a ramdisk I'm getting the following:

# purged default global cache dir
PS $ ll C:\Users\Jon\AppData\Local\zig\

## build fails
PS $ C:\Apps\zig\zig.exe build-exe --single-threaded -target native --global-cache-dir R:/global-cache --cache-dir R:/cache -O ReleaseSmall .\lke.zig
error(mingw): unable to turn kernel32.def into kernel32.lib
error(mingw): unable to turn ntdll.def into ntdll.lib
error: unable to build compiler_rt: UnableToWriteArchive
error: unable to build libssp: UnableToWriteArchive
error: unable to build zig's multitarget libc: UnableToWriteArchive
error: unable to generate DLL import .lib file: WritingImportLibFailed

## local and global build caches on R:/ ramdisk
PS $ ll R:\cache\,R:\global-cache\

    Directory: R:\cache

Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
d----           6/23/2021  3:25 PM                h
d----           6/23/2021  3:25 PM                o
d----           6/23/2021  3:25 PM                z

    Directory: R:\global-cache

Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
d----           6/23/2021  3:25 PM                h
d----           6/23/2021  3:25 PM                o
d----           6/23/2021  3:25 PM                z

## my zig env
PS $ C:\Apps\zig\zig.exe env
{
 "zig_exe": "C:\\Apps\\zig\\zig.exe",
 "lib_dir": "C:\\Apps\\zig\\lib\\zig",
 "std_dir": "C:\\Apps\\zig\\lib\\zig\\std",
 "global_cache_dir": "C:\\Users\\Jon\\AppData\\Local\\zig",
 "version": "0.9.0-dev.256+0134cb021"
}

[jonforums]

This appears to be either windows specific, or an issue with the imdisk virtual disk driver I'm using on windows. On Fedora 34, there's no problem hosting the build cache's on a ramdisk:

$ uname -a
Linux dino 5.12.11-300.fc34.x86_64 #1 SMP Wed Jun 16 15:47:58 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

$ sudo mount -t tmpfs -o size=1G,noatime ramdisk /mnt/ramdisk/

$ /opt/zig/zig build-exe -target native --cache-dir /mnt/ramdisk/cache/ --global-cache-dir /mnt/ramdisk/global-cache/ -O ReleaseSmall --single-threaded lke.zig

$ fselect path from /mnt/ramdisk/ maxdepth 3 dfs
/mnt/ramdisk/global-cache
/mnt/ramdisk/global-cache/o
/mnt/ramdisk/global-cache/o/5fc669fb7f0b33eb47e2842430ff9854
/mnt/ramdisk/global-cache/o/8c0ba38cd1edcb53638be37a8852fe90
/mnt/ramdisk/global-cache/h
/mnt/ramdisk/global-cache/h/675ca2ef54cc9233b3305e5aed911c3a.txt
/mnt/ramdisk/global-cache/h/dc243abafdf954894f22f6b1c4fc0af3.txt
/mnt/ramdisk/global-cache/h/96ae433645121b128c0169fcbca97292.txt
/mnt/ramdisk/global-cache/h/cf7c3dcc84a8c8951098f5167ff88115.txt
/mnt/ramdisk/global-cache/z
/mnt/ramdisk/cache
/mnt/ramdisk/cache/z
/mnt/ramdisk/cache/o
/mnt/ramdisk/cache/o/b299a8e6349a8b95593f9ca308f4c744
/mnt/ramdisk/cache/h
/mnt/ramdisk/cache/h/0016f512f0df858a5670903f79a4b952.txt

[jonforums]

This can be closed as it appears to be an artifact of the ImDisk ramdisk driver, not zig:

### from the imdisk page
It emulates disk volumes rather than complete disks, it is not always compatible
with all applications and drivers. You cannot manage things like mount points,
drive letters and similar for ImDisk drives using `mountvol` command line tool or
in Disk Management in Windows.

When using a ramdisk created by Arsenal Image Mounter and 0.11.0-dev.2232+84b89d7cf I get the expected behavior due to AIM emulating full disks not volumes for claimed better compatibility with applications. If I spelunked the zig source it's likely I'd find the WinAPI used to handle cache dir overrides collides with ImDisk's handling of drive letters.

PS $ C:\Apps\zig\zig.exe run -target native --global-cache-dir R:/global-cache --cache-dir R:/cache -O ReleaseSmall .\hello.zig
Hello world!

PS $ ll R:\cache\,R:\global-cache\

    Directory: R:\cache

Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
d----           3/22/2023 11:55 PM                h
d----           3/22/2023 11:55 PM                o
d----           3/22/2023 11:55 PM                z

    Directory: R:\global-cache

Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
d----           3/22/2023 11:55 PM                h
d----           3/22/2023 11:55 PM                o
d----           3/22/2023 11:55 PM                tmp
d----           3/22/2023 11:55 PM                z