Pass --python-repos-find-links always, and deprecate PANTS_SHA

[huonw]

Currently, the scie-pants launcher sometimes needs to pass an additional argument to the underlying pants invocation, to be able to support PANTS_SHA and its custom wheel location. Effectively turning an invocation like pants goal --arg into pants --pants-repos-find-links=+["..."] goal --arg when appropriate:

scie-pants/package/scie-pants.toml

Lines 57 to 60 in 0a204c5

	exe = "{scie.bindings.install:PANTS_CLIENT_EXE}"
	args = [
	"{scie.bindings.configure:PANTS_SHA_FIND_LINKS}",
	]

However, when not using PANTS_SHA, the pants command becomes pants "" goal --arg, and the spurious empty string results in some commands failing, e.g. pants "" tailor --check thinks --check is a global argument, and this is ambiguous.

To fix this issue, this PR does two things:

1. avoid passing an empty string, via a no-op workaround: always set the PANTS_SHA_FIND_LINKS variable (to a no-op like --python-repos-find-links=-[]), so that scie-pants never passes an empty variable to the pants command, since that makes commands like pants tailor --check :: explode:
2. deprecates PANTS_SHA, so that the hack above doesn't feel so bad: we're on the way to removing the need for PANTS_SHA_FIND_LINKS entirely, thus sidestepping the limitation and the need for the workaround (2)

This could also be fixed via a-scie/jump#130.

Fixes #249

[huonw]

Just noting some manual testing:

I've confirmed the execve syscall in the same way as #249 (comment):

[
  "/root/.cache/nce/0de4b72a5e712632a9421fa33e3c3c0e072a2b7ed9babda918e01bd01164cdbc/bindings/venvs/2.18.0.dev5/bin/pants",
  "--python-repos-find-links=-[]",
  "--no-pantsd",
  "tailor",
  "--check",
  "::"
]

This doesn't seem to interfere with additional manual instances of that arg, e.g. PANTS_PYTHON_REPOS_FIND_LINKS='+["abc"]' ./scie-pants-linux-aarch64 --python-repos-find-links='+["def"]' help-advanced python-repos says:

  --python-repos-find-links="['<str>', '<str>', ...]"
  PANTS_PYTHON_REPOS_FIND_LINKS
  find_links
      default: []
      current value: [
          "abc",
          "def"
      ] (from env var PANTS_PYTHON_REPOS_FIND_LINKS, from command-line flag)

[thejcannon]

Clever, but in the "we need to get unblocked" way 👍

[thejcannon]

Also, does this mean we should bump the version number of scie-pants we check for, and cherry pick to 2.17.x?

😬

[thejcannon]

Also, does this mean we should bump the version number of scie-pants we check for, and cherry pick to 2.17.x?

😬

pantsbuild/pants#19670