Fix sys.stdout overriding in mypy.api

[AnOctopus]

These are the changes made by @elkhadiy to resolve the problems with stdout not being thread-safe in the api.

Fixes #6125.

[gvanrossum]

Sadly this is not enough. When -v is specified, build.py writes directly to sys.stderr. There are probably also other places where sys.stderr is written to directly. (And possibly even places where sys.stdout is implicitly used via print() calls without file=....)

For example, I have this simple test program:

import mypy.api

stdout, stderr, exitcode = mypy.api.run(['-v', '_.py'])
print('=== stdout ===')
print(stdout)
print('=== stderr ===')
print(stderr)
print('=== exit %d ===' % exitcode)

Note that without your patch, the LOG entries are printed under the === stderr === heading. But with your patch, they precede the === stdout === header.

[gvanrossum]

PS. While a PR is under review, please don't force-push. This makes the life difficult for the reviewer. We always squash commits when we merge them into master.

Is this now ready for another review?

[AnOctopus]

I realized the issue with it when I read through the contributing guidelines a bit more thoroughly and saw it said to not squash them on my end. I believe it's ready for review. It's possible that I missed something in my fixes or that things were messed up when I rebased to the current master, but I think I got all the code reachable from the api, and the simple test program you provided has the expected output.

[gvanrossum]

I think this is much better. Now we just have to figure out a way not to default to the values of sys.stdout/stderr set at module load time...

[gvanrossum]

Thanks. This looks great! I'll merge this now.