(torchx-fb/penv)(bugfix) handle sys.argv[0] relpaths correctly when finding penv.par, add a CWD/penv.par search fallback to handle unittest @mode/opt

[kiukchung]

Summary:
Fixes the following two scenarios:

#1

~/bin
    - python
    - penv.par

$ cd ~/bin
$ ./python -m mo.du.le

Does not pick up ~/bin/penv.par (as expected) because sys.argv[0] = ./python. Fix is to return (Path(sys.argv[0])/"penv.par").absolute()

#2
Using this interpreter as a unittest resource + torchx local_cwd scheduler does not resolve penv.par from the test source dir since the symlink is resolved by unix and sys.argv[0] is set to the actual interpreter (not the symlinked one)

python_unittest(
   name="foo_test",
   resource={
       "//torchx/fb:python": "python",
       "//torchx/apps:penv": "penv.par",
   }
   ...
)

# buck run mode/opt //foo_test
# outputs in build dir

~/fbcode/buck-out/opt/gen/foo_test#link-tree/
    - python -> buck-out/opt/gen/torchx/fb/python.par
    - penv.par

Hence with the current penv par lookup logic we end up looking for a penv.par in buck-out/opt/gen/torchx/fb/penv.par which does not exist and we just simply fall back to system python.

Reviewed By: aivanou

Differential Revision: D31402466

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D31402466

[codecov]

Codecov Report

Merging #216 (9c0b722) into main (cf95835) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #216   +/-   ##
=======================================
  Coverage   91.10%   91.10%           
=======================================
  Files          57       57           
  Lines        2630     2630           
=======================================
  Hits         2396     2396           
  Misses        234      234           

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