Adopt/inherit TerminalWriter from py.io for better width (#41)

This uses an improved version of `shutil.get_terminal_width`, mainly to look at stdin, stderr, and stdout.

Ref: https://bugs.python.org/issue14841
Ref: python/cpython#12697

Rejected/stalled in pylib: pytest-dev/py#219
Suggested to move into pytest in pytest-dev#5056.

src/_pytest/_code/code.py

@@ -895,10 +895,12 @@ def repr_excinfo(self, excinfo):
 
 class TerminalRepr:
     def __str__(self):
+        from _pytest.terminal import TerminalWriter
+
         # FYI this is called from pytest-xdist's serialization of exception
         # information.
         io = StringIO()
-        tw = py.io.TerminalWriter(file=io)
+        tw = TerminalWriter(file=io)
         self.toterminal(tw)
         return io.getvalue().strip()
 

src/_pytest/cacheprovider.py

@@ -404,7 +404,9 @@ def pytest_report_header(config):
 def cacheshow(config, session):
     from pprint import pformat
 
-    tw = py.io.TerminalWriter()
+    from _pytest.terminal import TerminalWriter
+
+    tw = TerminalWriter()
     tw.line("cachedir: " + str(config.cache._cachedir))
     if not config.cache._cachedir.is_dir():
         tw.line("cache is empty")

src/_pytest/config/__init__.py

@@ -66,13 +66,14 @@ def main(args=None, plugins=None) -> "Union[int, _pytest.main.ExitCode]":
                   initialization.
     """
     from _pytest.main import ExitCode
+    from _pytest.terminal import TerminalWriter
 
     try:
         try:
             config = _prepareconfig(args, plugins)
         except ConftestImportFailure as e:
             exc_info = ExceptionInfo(e.excinfo)
-            tw = py.io.TerminalWriter(sys.stderr)
+            tw = TerminalWriter(sys.stderr)
             tw.line(
                 "ImportError while loading conftest '{e.path}'.".format(e=e), red=True
             )
@@ -98,7 +99,7 @@ def main(args=None, plugins=None) -> "Union[int, _pytest.main.ExitCode]":
             finally:
                 config._ensure_unconfigure()
     except UsageError as e:
-        tw = py.io.TerminalWriter(sys.stderr)
+        tw = TerminalWriter(sys.stderr)
         for msg in e.args:
             tw.line("ERROR: {}\n".format(msg), red=True)
         return ExitCode.USAGE_ERROR
@@ -1128,7 +1129,9 @@ def create_terminal_writer(config, *args, **kwargs):
     in the config object. Every code which requires a TerminalWriter object
     and has access to a config object should use this function.
     """
-    tw = py.io.TerminalWriter(*args, **kwargs)
+    from _pytest.terminal import TerminalWriter
+
+    tw = TerminalWriter(*args, **kwargs)
     if config.option.color == "yes":
         tw.hasmarkup = True
     if config.option.color == "no":

src/_pytest/config/argparsing.py

@@ -11,6 +11,7 @@
 import py
 
 from _pytest.config.exceptions import UsageError
+from _pytest.terminal import get_terminal_width
 
 FILE_OR_DIR = "file_or_dir"
 
@@ -417,8 +418,7 @@ class DropShorterLongHelpFormatter(argparse.HelpFormatter):
 
     def __init__(self, *args, **kwargs):
         """Use more accurate terminal width via pylib."""
-        if "width" not in kwargs:
-            kwargs["width"] = py.io.get_terminal_width()
+        kwargs.setdefault("width", get_terminal_width())
         super().__init__(*args, **kwargs)
 
     def _format_action_invocation(self, action):

src/_pytest/terminal.py

@@ -5,6 +5,7 @@
 import argparse
 import collections
 import datetime
+import os
 import platform
 import sys
 import time
@@ -30,6 +31,55 @@
 REPORT_COLLECTING_RESOLUTION = 0.5
 
 
+def _getdimensions():
+    # Improved version of shutil.get_terminal_size that looks at stdin,
+    # stderr, stdout.  Ref: https://bugs.python.org/issue14841.
+    fallback = (80, 24)
+    # columns, lines are the working values
+    try:
+        columns = int(os.environ["COLUMNS"])
+    except (KeyError, ValueError):
+        columns = 0
+    try:
+        lines = int(os.environ["LINES"])
+    except (KeyError, ValueError):
+        lines = 0
+    # only query if necessary
+    if columns <= 0 or lines <= 0:
+        for check in [sys.__stdin__, sys.__stderr__, sys.__stdout__]:
+            try:
+                size = os.get_terminal_size(check.fileno())
+            except (AttributeError, ValueError, OSError):
+                # fd is None, closed, detached, or not a terminal.
+                continue
+            else:
+                break
+        else:
+            size = os.terminal_size(fallback)
+        if columns <= 0:
+            columns = size.columns
+        if lines <= 0:
+            lines = size.lines
+    return columns, lines
+
+
+def get_terminal_width():
+    width, _ = _getdimensions()
+    return width
+
+
+class TerminalWriter(py.io.TerminalWriter):
+    @property
+    def fullwidth(self):
+        if hasattr(self, "_terminal_width"):
+            return self._terminal_width
+        return get_terminal_width()
+
+    @fullwidth.setter
+    def fullwidth(self, value):
+        self._terminal_width = value
+
+
 class MoreQuietAction(argparse.Action):
     """
     a modified copy of the argparse count action which counts down and updates

testing/test_config.py

@@ -1202,7 +1202,7 @@ def test_help_formatter_uses_py_get_terminal_width(testdir, monkeypatch):
     formatter = DropShorterLongHelpFormatter("prog")
     assert formatter._width == 90
 
-    monkeypatch.setattr("py.io.get_terminal_width", lambda: 160)
+    monkeypatch.setattr("_pytest.config.argparsing.get_terminal_width", lambda: 160)
     formatter = DropShorterLongHelpFormatter("prog")
     assert formatter._width == 160
 

testing/test_terminal.py

@@ -1803,3 +1803,38 @@ def test_collecterror(testdir):
             "*= 1 error in *",
         ]
     )
+
+
+def test_getdimensions(monkeypatch):
+    from _pytest.terminal import _getdimensions, get_terminal_width
+
+    monkeypatch.setenv("COLUMNS", "30")
+    monkeypatch.setenv("LINES", "25")
+
+    assert _getdimensions() == (30, 25)
+    assert get_terminal_width() == 30
+
+    calls = []
+
+    def mocked_get_terminal_size(*args):
+        calls.append(args)
+        raise OSError()
+
+    monkeypatch.setattr(os, "get_terminal_size", mocked_get_terminal_size)
+
+    monkeypatch.delenv("COLUMNS")
+    monkeypatch.delenv("LINES")
+    assert _getdimensions() == (80, 24)
+    assert calls == [(0,), (2,), (1,)]
+
+    def mocked_get_terminal_size(fileno):
+        calls.append(fileno)
+        if fileno == 2:
+            return os.terminal_size((12, 34))
+        raise OSError()
+
+    monkeypatch.setattr(os, "get_terminal_size", mocked_get_terminal_size)
+
+    calls = []
+    assert _getdimensions() == (12, 34)
+    assert calls == [0, 2]