`target-dir` is incorrect choice for storing test data

[epage]

build-dir was split out of target-dir for non-final artifacts. We plan to eventually add an artifact-dir and deprecate the target-dir.

Instead of using cargo metadata, CARGO_TARGET_TEMPDIR should be used.

[flub]

Could you point to any docs on CARGO_TARGET_TEMPDIR? I tried looking for this but can't seem to find anything.

[epage]

At https://doc.rust-lang.org/cargo/reference/environment-variables.html#environment-variables-cargo-sets-for-crates

CARGO_TARGET_TMPDIR — Only set when building integration test or benchmark code. This is a path to a directory inside the target directory where integration tests or benchmarks are free to put any data needed by the tests/benches. Cargo initially creates this directory but doesn’t manage its content in any way, this is the responsibility of the test code.

By this only being set at compile time, you would only be able to access it via a macro that is expanded in the caller's code. We just made CARGO_BIN_EXE_* available at runtime and it could make sense to expose this as well.

[flub]

Thanks for the reference! Not sure why I didn't find that before.

This was also already raised in #2 once, btw. But happy to re-visit.

I think CARGO_TARGET_TEMPDIR only being set for integration tests is rather unfortunate, as that would mean the location would be different depending on what kind of tests you are running. I would prefer to have an easily reachable place that's always the same.

FWIW, at the very beginning tempdir used the system-wide temporary directory, e.g. /tmp on unix-like systems. But users convinced me that using the target dir was more convenient, even though it is a strict violation of something cargo owned. And in practice this turned out to be true.

Would using the build-dir be an acceptable option? I guess not really from a cargo perspective as that's also entirely owned by cargo. But it is kind of convenient to have everything together in ./target/.

[epage]

As this isn't about final artifacts, build-dir is more appropriate and CARGO_TARGET_TEMPDIR now points within build-dir despite the name.

if there are limitations that are getting in the way, feel free to open an issue!