Using the same environment for every build seems to break autodoc?

[njsmith]

I was looking at migrating from RTD to sphinxcontrib-versioning, but my project makes extensive use of autodoc, and I was running into problems due to this. RTD always sets up a fresh virtualenv, installs the project into it, and then uses that virtualenv to do the build, so the version of the project that autodoc sees always matches the version of the docs being built.

It looks like sphinxcontrib-versioning doesn't have any way to do this currently – it always builds all the docs in the same environment. Is that correct? Would it be possible to do a fresh-virtualenv-per-build approach instead?