Simplify Travis-CI configuration

[srittau]

This removes the indirection of setting environment variables to
install and run tests. Also, use an explicit version for running
mypy with typed-ast.

[bluetech]

TEST_CMD does seem like an unhelpful indirection.

However, the INSTALL does avoid some repetition, so seems helpful to keep?

Also, use an explicit version for running mypy with typed-ast.

This sounds good for future proofing.

[bluetech]

Does this have any significance or are they the same?

[srittau]

As far as I understand it, they are different indeed: In a matrix build, every possible combination of configurations is run, jobs are more straight-forward. Since in our case each jobs is quite different from the others, a matrix build does not make much sense.

[bluetech]

Got it, jobs does sound more appropriate.

[bluetech]

Are you sure typed_ast should be removed here? As I understand it, mypy still depends on it even on 3.8.

[srittau]

That doesn't seem to be the case, since the build succeeds. At least at runtime it should not need it.

[bluetech]

Didn't check but it probably installs typed_ast from PyPI because it is a dependency of mypy. But the intention was to check with the git typed_ast.

[srittau]

I just looked at the travis log. It is indeed installing typed-ast from pypi, but I assume that it will not get used by mypy.

[bluetech]

I asked about it here -- according to the replies, it it still needed in Python 3.8 to parse Python 2 code.

[srittau]

Ah, good point. But this shouldn't be a problem for us, since we are only parsing stubs and are not running mypy in Python 2 mode. I think using typed-ast from pypi is fine, but in the end it doesn't matter much, especially considering that typed-ast will probably not be developed any further.

I actually think it might be beneficial to use typed-ast from pypi in the < 3.8 test, but that's a discussion for another PR.

[srittau]

Concerning INSTALL: I don't find the indirection particularly appealing, especially since the only duplication is between the flake8 and pytest steps. And in a next step it would possible make sense to split the packages installed for CI, since installing pytest takes quite some time and is just unnecessary for the flake8 step.

[bluetech]

the only duplication is between the flake8 and pytest steps

It also deduplicates the pip install -U git+git://github.com/python/mypy git+git://github.com/python/typed_ast part which is what I was thinking about.