Add 'dist' build

[rpkilby]

Description

This is a continuation of #5624, proposing that the package be moved under a src dir. To recap:

tox does create and install the package distribution into the test environment, however this conflicts with the rest_framework package that's located on the current path. Because the distribution and local files conflict, you cannot effectively test the distribution's packaged files. eg, the distribution may not be correctly configured (missing templates/static files), but the files on the local path do have them, so the tests pass erroneously.

The solution is to move the package off of the path (usually into a src directory), so that the local files are not importable.

This iteration fixes issues with coverage data. Most of the builds do use the local files via an editable install. As such, all coverage data is under /src/rest_framework instead of spread across multiple venvs. Testing the distribution is done wit a single build that doesn't collect coverage data.

As far as I can tell, the only potential downside is that git blame will be hampered a bit, given the file moves.

Changes

• Moved package under src dir
• Added dist build.
• Updated support builds (lint, docs) to use python 3.6

[tomchristie]

proposing that the package be moved under a src dir

On first sight I'm not in favour of us having to change a several year-long layout, in order to address tooling issues.

[tomchristie]

Could we do something like ensure that the script cd's into a different directory when testing the distribution? Any other options?

[xordoquy]

TBH, I'm fine with this. Other options are possibly worst in my opinion.
Some reasons are explained here but there are a lot of other links that would tell more about.

[rpkilby]

Could we do something like ensure that the script cd's into a different directory when testing the distribution?

Changing directories won't have an effect, but we could add a flag to runtests that enables removing the script's directory from sys.path.

[tomchristie]

Changing directories won't have an effect, but we could add a flag to runtests that enables removing the script's directory from sys.path.

I'd far prefer that, yup. If we can make a more minimal change, then we should.

[rpkilby]

Sounds good. I'll update the PR later.

[tomchristie]

I'll update the PR later.

Okey doke. I suppose either rebase, or issue a new PR and close this.

[rpkilby]

Okay, this should be good to go now. There was an issue in that pytest would re-add the package's root directory after it had been removed. The solution is to just import rest_framework, caching the installed version in sys.modules before the root directory is added back in.

Also, I temporarily committed 909ba98 to demonstrate the packaging failures (see: failing build).

[carltongibson]

OK. Nice. Very neatly done. 👏