Feature request: "pip find" to replace internal PackageFinder usage

[di]

What's the problem this feature will solve?
Currently there is no way for third-party projects to use PackageFinder's logic via the command line. Instead, projects like pip-compile and pipenv need to import from the _internal API.

Describe the solution you'd like
Ideally this would mimic PackageFinder.find_all_candidates() as much as possible, and would have a human-friendly and machine-friendly format. Something like:

$ pip find bar
bar    0.1.0    https://files.pythonhosted.org/packages/2c/85/d6397edeceb1c81b5b99b1046033c8854abac3e50971c8d2915e63ce54c0/bar-0.1.0.tar.gz#sha256=6a711b5b06a662fe3f8e897310456b02127fb15d89310161fc8af7f415e270a1 (from https://pypi.org/simple/bar/)
bar    0.2.0    https://files.pythonhosted.org/packages/ba/bf/81ef8a2c80f4f86e9e6570605b7b5a277950cbd0ff9be901633159f4110e/bar-0.2.0.tar.gz#sha256=4a97e8664a22eec73f65d522cc36b4c693b61f0557760a856bb18a8fb67a8881 (from https://pypi.org/simple/bar/)
bar    0.2.1    https://files.pythonhosted.org/packages/77/d6/760c7a0ee7385ba4b0abb1d38af97e8c2f34cb47fe301315e48204088047/bar-0.2.1.tar.gz#sha256=b0a71c865729f9e8ac0f74e666b46c5ed1f5addac3425be7e06ca4828cec90ef (from https://pypi.org/simple/bar/)

$ pip find bar --format json
[
  {
    "name": "bar",
    "version": "0.1.0",
    "link": "https://files.pythonhosted.org/packages/2c/85/d6397edeceb1c81b5b99b1046033c8854abac3e50971c8d2915e63ce54c0/bar-0.1.0.tar.gz#sha256=6a711b5b06a662fe3f8e897310456b02127fb15d89310161fc8af7f415e270a1",
    "index": "https://pypi.org/simple/bar/"
  }, {
    "name": "bar",
    "version": "0.2.0",
    "link": "https://files.pythonhosted.org/packages/ba/bf/81ef8a2c80f4f86e9e6570605b7b5a277950cbd0ff9be901633159f4110e/bar-0.2.0.tar.gz#sha256=4a97e8664a22eec73f65d522cc36b4c693b61f0557760a856bb18a8fb67a8881",
    "index": "https://pypi.org/simple/bar/"
  }, {
    "name": "bar",
    "version": "0.2.1",
    "link": "https://files.pythonhosted.org/packages/77/d6/760c7a0ee7385ba4b0abb1d38af97e8c2f34cb47fe301315e48204088047/bar-0.2.1.tar.gz#sha256=b0a71c865729f9e8ac0f74e666b46c5ed1f5addac3425be7e06ca4828cec90ef",
    "index": "https://pypi.org/simple/bar/"
  }
]

Alternative Solutions

• Splitting out the PackageFinder logic into a separate package (Splitting out PackageFinder logic #5800) and having third-parties use this instead
• Refactor pip search to use PackageFinder ("pip search" should use PackageFinder, not XML-RPC API #395) and add extra options there to overload the current behavior/API of pip search

Additional context
Recent internal API changes in 19.2 will break pip-compile: jazzband/pip-tools#853

[cjerdonek]

This is similar to or the same as #6430 .

[di]

@cjerdonek Thanks, I took a look but didn't find that issue. I agree this is similar with two slight differences, which I think could probably be absorbed into that issue:

• optional JSON output
• showing all results, not just the one which will be installed

EDIT: I see later comments on that issue mention "outputting all possible links for this specification" which sounds like my second difference here.

[di]

Closing as a duplicate of #6430.