Request support for pip format requirements*txt files

[mcandre]

How would this feature be useful?

pipx's spec metadata JSON system for tracking packages does not appear to be very portable. It hardcodes multiple file paths in terms of the particular user who runs pipx install... commands. It doesn't support version constraints. The format is verbose and cumbersome to generate by hand.

Describe the solution you'd like

Native pip already offers a basic format for more modern package tracking with requirements*txt files. Would like to see pipx add support for this format.

When the user runs pipx install without specifying a spec metadata JSON file option, then pipx should automatically look for requirements.txt and apply that configuration when possible.

When the user runs pipx install -r <path>, then pipx should load the given custom pip configuration file path (e.g. requirements-dev.txt).

Describe alternatives you've considered

Moving into a monastery.