Nested virtual environment support in site/venv modules

Feature or enhancement

Proposal:

It's a bit of a niche use case, but it would be helpful if you could have one virtual environment be created that references another as its parent. If you currently attempt to do this, the pyvenv.cfg of the child virtual environment only indirectly references the parent through the command variable (which doesn't appear to be used). The code in site.venv could be enhanced to infer the prefix of the parent environment and add those site packages after the current virtual environment. This would ensure that the order of sys.path entries would be appropriate.

This would allow you to create a group virtual environment with a lot of common packages and still allow users to have their own child environments with additional or newer packages.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

issue で参照されている site.venv の実装がある Lib/site.py から始め、pyvenv.cfg と command 変数が現在どのように扱われているかを確認します。子環境が親のプレフィックスをどのように推測し、親の site packages を子のエントリの後に配置するかを定義します。ネストされた環境で意図した sys.path の順序が公開されれば完了です。