@cstrahan, thanks for your PR! By analyzing the history of the files in this pull request, we identified @FRidh, @rasendubi and @dezgeg to be potential reviewers.

With the code as it is right now, I inject the following into __main__.py:

import os; os.environ['PATH'] = ('{0}:{1}' if os.getenv('PATH', '') != '' else '{1}').format('$program_PATH', os.getenv('PATH', ''))

... where $program_PATH is substituted with the environment variable that the wrapPython hook sets up.

That preserves the behavior of the wrapper script, but I don't know if it's really necessary. In fact, that puts the build-time python on PATH (as should be expected), which could can then cause problems for some people's use of ycmd -- ycmd will by default attempt to start the JediHTTP with the pthon on PATH which will end up being python 2, but that'll cause problems if someone want's to, say in a shell.nix, put python 3 on their PATH so they can have JediHTTP parse their python 3 project. They can always specify a specific python in their config... but IMO the PATH based approach should continue to work.

So, I think I'm not going to try to preserve the PATH manipulation -- I don't think it'll cause any problems to do so in this package.

Also TODO in a separate PR: have the vim plugin use this package, instead of it also compiling ycmd.

In the latest commit I've switched to using the vendored python libs - YouCompleteMe expects that it can source those libs, and things get very tricky when trying to use our packaged libraries while trying not to break YCM's assumptions. We could probably patch YCM's source, but by using the vendored python libs, we make our packaged YouCompleteMe and ycmd work seamlessly together (see #22614 for the changes to the vim plugin).

This does seem to break darwin build: https://hydra.nixos.org/build/48027016