Dynamically generate VIRTUAL_ENV environment variable

[hsiaoyi0504]

Currently, the VIRTUAL_ENV environment variable in activate script will be generated when virtual environment is created.
However, if we change the name of the folder. It would not work.

Isn't it better to generate VIRTUAL_ENV variable dynamically using the path of the activate script ?
Maybe I am wrong, but based on my understanding, the activate script is a bash script and we can get the path of this script using mechanism similar to DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )".

[asottile]

moving a virtualenv is generally not a supported operation as the shebangs (#!...) of installed console_scripts contain full absolute paths. (though you can use something like virtualenv-tools3 to relocate a venv ~safely)

that said, I had a usecase for almost exactly what's desired here as I'm managing virtualenvs inside ~/.cache/... and then symlinking them to ./venv (sorry, closed source tool) and wanted which python to resolve as ./venv/bin/python instead of ~/.cache/ugly long path/bin/python

I used this chunk of code to accomplish what I wanted:

        def _fixup_activate_file(filename: str, replacement: str) -> None:
            dest = os.path.join(target, 'bin', filename)
            backup = f'{dest}.old'
            os.rename(dest, backup)

            with open(backup) as f:
                contents = f.read()
            with open(dest, 'w') as f:
                f.write(contents.replace(f'"{target}"', replacement))

        # make relocatable activate files
        _fixup_activate_file(
            'activate',
            # bash / zsh (sh not supported, is this ok?)
            '"$(cd "$(dirname "$(dirname "${BASH_SOURCE:0}")")"; pwd)"',
        )
        _fixup_activate_file(
            'activate.fish',
            "(bash -c 'cd '(dirname (dirname (status --current-filename)))'; pwd')",  # noqa: E501
        )

note that this doesn't work for sh, but I only needed to support bash / zsh / fish

[stale]

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[gaborbernat]

We no longer support the relocate-able flag, so this is now out of scope too.