add cwd to cache prefix

[chrisirhc]

Caveat: I don't know what I'm doing with zig. The zig code was mostly code assistant-generated.

I don't think this is a breaking change, but if somebody does rely on the cache location, they can set the HERMETIC_CC_TOOLCHAIN_CACHE_PREFIX to one of the prior values (/tmp, /var/tmp, C:\Temp) to maintain same behavior.

Test Plan

I added a debug print statement for the zig_cache_dir variable to see its value.
I tried the following test cases:

Input:HERMETIC_CC_TOOLCHAIN_CACHE_PREFIX	Output: zig_cache_dir (Printed value)
unset	<workspace root>/zig-cache
/tmp/my-test-cache	/tmp/my-test-cache
my-test-cache	<workspace root>/my-test-cache

Where <workspace root> for me looked like /private/var/tmp/_bazel_…/…/sandbox/darwin-sandbox/…/execroot/_main.

Closes #83
Closes #183
Closes #187

[chrisirhc]

Ready for review

[chrisirhc]

Not sure why https://github.com/uber/hermetic_cc_toolchain/actions/runs/11867448986/job/33075522540 passed yet https://github.com/uber/hermetic_cc_toolchain/actions/runs/11914055410/job/33201139834?pr=200 fails.

The error is:
error: unable to create compilation: Unexpected

Maybe related to: ziglang/zig#19973 , but I don't have a windows machine to test on.

Next things to try:

• to run using a dev/debug build of Zig to see a full trace
• to fiddle around on a windows machine
• try upgrading to zig 0.13 (Dead end, more issues, see upgrade to zig 0.13.0 #203 (comment) )

[chrisirhc]

Not sure why https://github.com/uber/hermetic_cc_toolchain/actions/runs/11867448986/job/33075522540 passed yet https://github.com/uber/hermetic_cc_toolchain/actions/runs/11914055410/job/33201139834?pr=200 fails.

The error is: error: unable to create compilation: Unexpected

Rerunning the CI seems to have passed (after I rebased back to a non-upgraded zig 0.13/14 attempt).
I'm guessing this is an intermittent error. 🤷 🫤

Moving this back to "Ready for review"

[linzhp]

@sluongng @laurentlb can you verify if this works for you?

[linzhp]

Can we put it in either bazel-zig-cache or bazel-out/zig-cache? Most bazel project have either /bazel-* or /bazel-out in their .gitignore. They don't need to ignore additional directory if we reuse the existing directories.

[cerisier]

Unless mistaken, wouldn't this store the cache inside the action sandbox root, unique to each cc target?
Also, wouldn't it be destroyed between each build invocation ?