fix: patch also stdout.flush() from colorama for pypa#4170

bc on Windows it breaks with OSError(errno.EINVAL) after pip has broken.
+ Fix a bit the TC according to PY2 behavior.

src/pip/_vendor/colorama/ansitowin32.py

@@ -1,4 +1,5 @@
 # Copyright Jonathan Hartley 2013. BSD 3-Clause license, see LICENSE file.
+import errno
 import re
 import sys
 import os
@@ -136,12 +137,25 @@ def get_win32_calls(self):
             }
         return dict()
 
+    def _flush(self):
+        """Ignore `BrokenPipeErrors` eg. when piped in `head` UNIX cmd."""
+        try:
+            self.wrapped.flush()
+        except (IOError, OSError) as ex:  # Python-2 has no `BrokenPipeError`
+            # Windows also fails with:
+            #   File "pip\_vendor\colorama\ansitowin32.py", line 143, in _flush
+            #   self.wrapped.flush()
+            #    OSError: [Errno 22] Invalid argument
+            #
+            if ex.errno not in (errno.EPIPE, errno.EINVAL):
+                raise
+
     def write(self, text):
         if self.strip or self.convert:
             self.write_and_convert(text)
         else:
             self.wrapped.write(text)
-            self.wrapped.flush()
+            self._flush()
         if self.autoreset:
             self.reset_all()
 
@@ -172,7 +186,7 @@ def write_and_convert(self, text):
     def write_plain_text(self, text, start, end):
         if start < end:
             self.wrapped.write(text[start:end])
-            self.wrapped.flush()
+            self._flush()
 
 
     def convert_ansi(self, paramstring, command):

tests/functional/test_logging.py

@@ -6,6 +6,7 @@
 import subprocess
 
 import pytest
+from pip._vendor.six import PY2
 
 
 @pytest.mark.usefixtures('script')
@@ -121,15 +122,16 @@ def test_broken_pipe_logger():
     # `download` cmd has a lot of log-statements.
     cmd = 'pip download -v pip'
 
-    # When the stream where logging is writting is broken,
-    # at least these 2 lines are emitted in stderr:
+    stderr = _run_and_brake_stdout(cmd, shell=True, check=True)
+    # When breaks the stream that the logging is writing into,
+    # in PY3 these 2 lines are emitted in stderr:
     #    Exception ignored in: <_io.TextIOWrapper name='<stdout>' mode='w' ...
     #    BrokenPipeError: [Errno 32] Broken pipe\n"
-    exp_stder_nlines = 2
-    exp_stderr_msg = b'Exception ignored in'
-
-    stderr = _run_and_brake_stdout(cmd, shell=True, check=True)
-    # Before #5721, it command does not stop, but it continued
-    # printing ~4 lines per each broken-pipe error!
-    assert stderr.count(b'\n') == exp_stder_nlines, stderr
-    assert exp_stderr_msg in stderr, stderr
+    #
+    # Before #5721, pip did not stop the 1st time, but it continued
+    # printing them lines on each `stream.flush()`!
+    if PY2:
+        assert not stderr, stderr
+    else:
+        assert stderr.count(b'\n') == 2
+        assert b'Exception ignored in' in stderr, stderr