Generalize package builds and virtualenv creation

[pytoxbot]

• Bitbucket: https://bitbucket.org/hpk42/tox/issue/338
• Originally reported by: @obestwalter
• Originally created at: 2016-06-24T15:13:14.472

This can serve as a meta issue collecting some outstanding issues that would be fixed by this.

The approach is to write documentation with examples for this and having a discussion around this in this issue.

There also are drafts with discussion notes which can be used to flesh out the documentation for the functionality in a draft and some notes.

related issues:

• Handle mutliple backends for virtual environments (Handle mutliple backends for virtual environments #313)
• Support conda envs when using Miniconda (Support conda envs when using Miniconda #273)
• maybe Support py32 environments (Support for Python 3.2 broken #323)
• use venv or rwt: Unable to run tests against local build of Python #394 (comment)

There is also a project that solved the problem for conda specifically: https://github.com/hayd/ctox

[gaborbernat]

Both package builds and virtual environment creation can be customized via plugins. tox will not enable first-class support for such customization. If plugins require additional changes in core to achieve integration feel free to open respective issues.