Clean up terminal width handling

[The-Compiler]

This PR does three related cleanups (cc'ing @ilevkivskyi who seems to have implemented most of the underlying code):

---

Use shutil.get_terminal_size()

The documentation for Python's os.get_terminal_size() says:

shutil.get_terminal_size() is the high-level function which should normally be used, os.get_terminal_size is the low-level implementation.

shutil.get_terminal_size() already takes care of various corner cases such as:

• Providing a fallback (to 80 columns, like the current DEFAULT_COLUMNS)
• Returning that fallback if os.get_terminal_size() raises OSError
• Doing the same if it returns a size of 0

In addition to that:

• It takes care of some more corner cases ("stdout is None, closed, detached, or not a terminal, or os.get_terminal_size() is unsupported")
• It adds support for the COLUMNS environment variable (rather than the non-standard MYPY_FORCE_TERMINAL_WIDTH)

---

Move MYPY_FORCE_TERMINAL_WIDTH handling into get_terminal_width()

Those two callers are the only two, and both check MYPY_FORCE_TERMINAL_WIDTH before calling get_terminal_width().

---

Remove fixed_terminal_width from utils.colorize docstring

This was added by 91adf61, yet colorize() doesn't actually have a fixed_terminal_width argument.

[ilevkivskyi]

LGTM

[asottile]

this regressed 9dcccca

[The-Compiler]

@asottile Can you elaborate? shutil.get_terminal_size handles this case and the test you added there seems to pass as well.

[asottile]

handles this case

look carefully, it handles when os.get_terminal_size raises but not when it returns (0, 0)

and the test you added there seems to pass as well

nope

=================================== FAILURES ===================================
_______ TestGetTerminalSize.test_get_terminal_size_in_pty_defaults_to_80 _______
[gw0] linux -- Python 3.8.5 /tmp/mypy/venv/bin/python

self = <t.TestGetTerminalSize testMethod=test_get_terminal_size_in_pty_defaults_to_80>

    def test_get_terminal_size_in_pty_defaults_to_80(self) -> None:
        # when run using a pty, `os.get_terminal_size()` returns `0, 0`
        ret = os.terminal_size((0, 0))
        with mock.patch.object(os, 'get_terminal_size', return_value=ret):
>           assert get_terminal_width() == 80
E           AssertionError: assert 0 == 80
E            +  where 0 = get_terminal_width()

t.py:12: AssertionError
=========================== short test summary info ============================
FAILED t.py::TestGetTerminalSize::test_get_terminal_size_in_pty_defaults_to_80
============================== 1 failed in 0.50s ===============================

[asottile]

note that the test never made it into master because it was "not useful" #8145

[The-Compiler]

Well, I agree the test would've been useful 😉 I didn't catch that it indeed didn't end up being committed...

Seems to me like this should really be handled correctly in the stdlib by shutil.get_terminal_size. I can re-add the workaround to mypy, unless you're already on it.

[asottile]

feel free

[The-Compiler]

Sorry for the trouble - here's a fix: #9651