PackageFinder.find_requirement always fallback to sdist because being given the wrong ABI tag

[linw1995]

• I have searched the issue tracker and believe that this is not a duplicate.

Steps to reproduce

1. For example, use the Py3.9 to install PDM
2. use PDM to set up a project with Py3.9
3. execute pdm add lxml to install lxml via wheel installation.
4. use PDM to switch Python executable to Py3.8. pdm use -f 3.8
5. execute pdm sync -v to install lxml

Actual behavior

It installs lxml via compiling from source unlike the previous case although lxml has prebuilt wheels with Py3.8.

Expected behavior

It installs lxml via wheel installation.

Environment Information

# Paste the output of `pdm info && pdm info --env` below:
PDM version:        1.5.0b1.dev12+gd48c6d3
Python Interpreter: /usr/bin/python3 (3.8.2)
Project Root:       /private/tmp/lxml
Project Packages:   /private/tmp/lxml/__pypackages__/3.8
{
  "implementation_name": "cpython",
  "implementation_version": "3.8.2",
  "os_name": "posix",
  "platform_machine": "x86_64",
  "platform_release": "20.3.0",
  "platform_system": "Darwin",
  "platform_version": "Darwin Kernel Version 20.3.0: Thu Jan 21 00:07:06 PST 2021; root:xnu-7195.81.3~1/RELEASE_X86_64",
  "python_full_version": "3.8.2",
  "platform_python_implementation": "CPython",
  "python_version": "3.8",
  "sys_platform": "darwin"
}

Hotfix

I find out what causes this problem. The get_abi_tag function from pdm.models.pip_shims is executed by the Python interpreter of PDM instead of the interpreter which we have chosen.

linw1995@f4fb1ea

This commit works well with most kinds of Python interpreters. But the better way is executing the whole get_abi_tag function by the interpreter we want. To do this, we may need to endure installing extras dependencies like the wheel package. But it is possible we are able to move the codes which we need from the wheel package into the PDM package.

[frostming]

Let me clarify the root cause, what exact part makes the wheel doesn't match for Py 3.8? soabi, impl, python_version, or the d, m, u flags?

[linw1995]

PDM with Py3.9 gets soabi = 'cp39' and it uses this to find packages for the Py3.8 environment.

[frostming]

Oh, I wasn't aware of that, I never print that value on macos and it is empty on Windows. :(