Feat: add support for Conda environments

[agoose77]

Pull Request Check List

• A news fragment is added in news/ describing what is new.
• Test cases added for changed code.

Describe what you have changed in this PR.

This PR adds support for CONDA_PREFIX where virtual environments are implemented using Conda.

[codecov-commenter]

Codecov Report

Merging #749 (8d14c40) into main (9ed9e07) will decrease coverage by 0.14%.
The diff coverage is 22.22%.

@@            Coverage Diff             @@
##             main     #749      +/-   ##
==========================================
- Coverage   83.53%   83.39%   -0.15%     
==========================================
  Files          73       73              
  Lines        6154     6167      +13     
  Branches     1101     1103       +2     
==========================================
+ Hits         5141     5143       +2     
- Misses        720      731      +11     
  Partials      293      293              

Flag	Coverage Δ
unittests	83.18% <22.22%> (-0.15%)	⬇️

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Impacted Files	Coverage Δ
pdm/models/candidates.py	87.86% <0.00%> (-0.37%)	⬇️
pdm/utils.py	79.22% <16.66%> (-2.54%)	⬇️
pdm/project/core.py	89.53% <100.00%> (ø)

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[agoose77]

I don't have time to work on this right now, but I'm thinking about the following changes:

• Add is_venv to PythonInfo or Environment, to replace (remove) pdm.utils.is_venv_python
• Replace call to get_env_prefix in

  pdm/pdm/models/candidates.py

  Lines 414 to 416 in 661a4b4

  	virtual_env_prefix = get_env_prefix()
  	if virtual_env_prefix:
  	src_dir = virtual_env_prefix / "src"

  with a check of python/environment.is_venv

This would change the behaviour — right now, as you point out, we don't check if project.python.interpreter is a virtual environment.

[frostming]

I don't have time to work on this right now, but I'm thinking about the following changes:

• Add is_venv to PythonInfo or Environment, to replace (remove) pdm.utils.is_venv_python
• Replace call to get_env_prefix in

  pdm/pdm/models/candidates.py

  Lines 414 to 416 in 661a4b4

  	virtual_env_prefix = get_env_prefix()
  	if virtual_env_prefix:
  	src_dir = virtual_env_prefix / "src"

  
  with a check of python/environment.is_venv

This would change the behaviour — right now, as you point out, we don't check if project.python.interpreter is a virtual environment.

That is a good change, while I prefer to bind it to Environment. Go ahead with it!

[agoose77]

I think we might want to refactor the virtual-environment support here, but I think we should do so in a different PR.

I experimented with adding this information to the PythonInfo class, because I feel that this knowledge belongs with the interpreter. However, it's a bigger change than just adding Conda support, so I'm holding off on it.

For my future benefit:
The Environment class currently distinguishes between using PEP 582 scheme or the sysconfig scheme for installing packages. This distinction is made as follows:

• If the user is inside a venv and passes use_venv=True, then we disable PEP582
• If the user passes -g, then we disable PEP 582

Another name for these classes might be PEP582Environment and GlobalEnvironment