fix: correctly obtain relative path required for the venv created by --bootstrap_impl=script

[chowder]

Computing the relative path from the venv interpreter to the underlying interpreter was
incorrectly using the actual interpreter's directory depth, not the venv interpreter's
directory depth, when computing the distance from the venv interpreter to the runfiles root.
The net effect is the correct relative path would only be computed for binaries with
the same directory depth as the actual interpreter (e.g. 2).

This went undetected in CI because the tests for this logic just happen to have the
same directory depth as the actual interpreter used.

To fix, compute the relative path to the runfiles root using the venv interpreter
directory. Also added a test in a more nested directory to test this case.

Along the way:

• Change relative path computation to compute a minimum relative path.
• Fix the internals to pass a runfiles-root relative path, not main-repo relative path,
  for the actual interpreter, as intended.

Fixes #2169

[ewianda]

The following rules were tested and validated:

• py_binary
• py_test
• py_console_script
• rules_oci Python image

---

[rickeylev]

Ah, hah. I'm guessing the reason this worked in CI is the path depth of the test programs was the same as the path depth of the underlying interpreter? 😂

Thanks for the PR!

The relative path logic looks overly complicated, though? All it has to do is calculate how many up-escapes are needed to get from the {prefix}.venv/bin/python3 location to the runfiles root, then append the ../-stripped value of the actual interpreter to that.

I think the ../ prefixed part of e.g. runtime.interpreter.short_path (or any .short_path) is there in lieu of external/, and represents "go up one dir from the main repo" (because its referring to some external repo).

[chowder]

Yeah it's kinda complicated (don't like it) - I wasn't sure what were all the edge cases here, so writing it generically was the only way I knew how to do it.

Would something like this suffice?

        venv_bin_dir = paths.dirname(interpreter.short_path)

        if venv_bin_dir.startswith("../"):
            escapes = venv_bin_dir.count("/") - 1
        else:
            escapes = venv_bin_dir.count("/") + 1

        parent = "/".join([".."] * escapes)
        rel_path = parent + "/" + interpreter_actual_path
        ctx.actions.symlink(output = interpreter, target_path = rel_path)

(Wouldn't support a py_binary using a python binary checked into the main repo as a toolchain, unless we prepend the workspace name to interpreter_actual_path where it doesn't lead with ../)

Happy for you to replace this with whatever you see fit too. :)

[rickeylev]

would something like this suffice

Yes, it should. I pushed a change that basically did that -- compute the relative path between two runfiles-root-relative paths instead of main-repo-relative paths. I kept the relative_path function since I like that it will compute a minimum relative-path.

I also pushed a test to reproduce the problem. It creates a test in a much more deeply nested directory than where the actual interpreter is. As well as some other cleanup.

[rickeylev]

I wasn't sure what were all the edge cases here

I think you got them all, so good job 🙂 . That short_path is a main-repo relative path, and gets ../ prepended for external things is the main edge case. The code was a bit confusing because it said it was passing runfiles-root-relative paths around, but it actually wasn't (interpreter_actual_path was the plain short_path value, which then got fixed up later), and the some later code was papering over that. I went and fixed that.

[rickeylev]

The CI failure is due to bazel-contrib/bazel_features#82, so I'll force-merge past it.

[rickeylev]

Ah, actually, I don't think I can force-merge because I'm not an admin. I'll ask about getting admin back. Otherwise, we can just switch the "upcoming bazel" CI to 8rc2 instead of 8rc3

[chowder]

@rickeylev Thanks for the changes. :)

[ewianda]

Apologies. Just noticed that rules_pkg is failing

  File "/home/ewianda/.cache/bazel/_bazel_ewianda/00aeeab5df0e41ab9e87aa07d33c6a73/sandbox/linux-sandbox/43/execroot/_main/bazel-out/k8-opt-exec-ST-d57f47055a04/bin/external/rules_pkg~/pkg/private/tar/build_tar.runfiles/_main/../rules_pkg~/pkg/private/tar/build_tar.py", line 486, in <module>
    main()
  File "/home/ewianda/.cache/bazel/_bazel_ewianda/00aeeab5df0e41ab9e87aa07d33c6a73/sandbox/linux-sandbox/43/execroot/_main/bazel-out/k8-opt-exec-ST-d57f47055a04/bin/external/rules_pkg~/pkg/private/tar/build_tar.runfiles/_main/../rules_pkg~/pkg/private/tar/build_tar.py", line 477, in main
    output.add_manifest_entry(entry, file_attributes)
  File "/home/ewianda/.cache/bazel/_bazel_ewianda/00aeeab5df0e41ab9e87aa07d33c6a73/sandbox/linux-sandbox/43/execroot/_main/bazel-out/k8-opt-exec-ST-d57f47055a04/bin/external/rules_pkg~/pkg/private/tar/build_tar.runfiles/_main/../rules_pkg~/pkg/private/tar/build_tar.py", line 342, in add_manifest_entry
    self.add_file(entry.src, entry.dest, **attrs)
  File "/home/ewianda/.cache/bazel/_bazel_ewianda/00aeeab5df0e41ab9e87aa07d33c6a73/sandbox/linux-sandbox/43/execroot/_main/bazel-out/k8-opt-exec-ST-d57f47055a04/bin/external/rules_pkg~/pkg/private/tar/build_tar.runfiles/_main/../rules_pkg~/pkg/private/tar/build_tar.py", line 111, in add_file
    self.tarfile.add_file(
  File "/home/ewianda/.cache/bazel/_bazel_ewianda/00aeeab5df0e41ab9e87aa07d33c6a73/sandbox/linux-sandbox/43/execroot/_main/bazel-out/k8-opt-exec-ST-d57f47055a04/bin/external/rules_pkg~/pkg/private/tar/build_tar.runfiles/rules_pkg~/pkg/private/tar/tar_writer.py", line 251, in add_file
    with open(file_content, 'rb') as f:
         ^^^^^^^^^^^^^^^^^^^^^^^^
FileNotFoundError: [Errno 2] No such file or directory: 'bazel-out/k8-fastbuild/bin/external/rules_pkg~/pkg/private/tar/_build_tar.venv/bin/python3'