commit 67e204ff22338d58e653b49715067d8cd2a49ac7
author Parker Timmerman <parker@parkertimmerman.com> Mon Aug 01 11:12:56 2022 -0400
committer GitHub <noreply@github.com> Mon Aug 01 16:12:56 2022 +0100
tree bf7cfdf315f3c1b491a76102ecfbf89f14cd38cb
parent 0fc834bdfa9df75c6ffdcadb5d1bb9fc43cc247b

fix: `rust_doc_test` failure to find params file (#1418)

**Context**
Today `rust_doc_test` fails when Bazel [Args](https://docs.bazel.build/versions/main/skylark/lib/Args.html) "spill" over to a file. To a user this failure is seemingly random because Bazel will auto-magically spill `Args` onto a file when there are too many args for the command line, or when it can improve performance. The generated test script, e.g. `hellolib.rustdoc_test.sh`, is then run from runfiles, which is separate from the Arg file Bazel created.

It's especially tricky because the amount of command line args Windows supports is < macOS < Linux, so there's a "silent" OS dependency here too.

**Solution**
This PR fixes the issue by manually declaring a params file, e.g. `hellolib.rustdoc_opt_params`, that is a sibling file to our test runner, `hellolib.rustdoc_test.sh`. We then pass the path of this optional params file to our test writer. The test writer checks for the presence of the Bazel Args file, and if it finds one, copies the content into our manually declared params file. 

Our manually declared params file then gets moved into runfiles with our test script. The test script can then find the file, and `rustdoc` picks up the args.

Note: Today we detect the params file by matching a prefix of `@` and suffix of `.rustdoc_test.sh-0.params`. I'm not sure if this is accurate for all systems, or all versions of bazel. I tried the [`use_param_file`](https://docs.bazel.build/versions/main/skylark/lib/Args.html#use_param_file) option on `Args` to make it easier to detect a params file, but that seem to overwrite (or just generally effect) the other arguments we'd pass to `rustdoc_test_writer.rs`.

Fixes #1233