terminalwriter: remove TerminalWriter's stringio argument

Had a mark indicating it should be removed, and I agree, it's better to
just use the `file` argument.

src/_pytest/_io/terminalwriter.py

@@ -4,7 +4,6 @@ import shutil
 import sys
 import unicodedata
 from functools import lru_cache
-from io import StringIO
 from typing import Sequence
 
 
@@ -83,13 +82,9 @@ class TerminalWriter:
         invert=7,
     )
 
-    # XXX deprecate stringio argument
-    def __init__(self, file=None, stringio=False):
+    def __init__(self, file=None):
         if file is None:
-            if stringio:
-                self.stringio = file = StringIO()
-            else:
-                from sys import stdout as file
+            file = sys.stdout
         if hasattr(file, "isatty") and file.isatty() and colorama:
             file = colorama.AnsiToWin32(file).stream
         self._file = file

src/_pytest/pastebin.py

@@ -1,5 +1,6 @@
 """ submit failure or test session information to a pastebin service. """
 import tempfile
+from io import StringIO
 from typing import IO
 
 import pytest
@@ -99,11 +100,10 @@ def pytest_terminal_summary(terminalreporter):
                 msg = rep.longrepr.reprtraceback.reprentries[-1].reprfileloc
             except AttributeError:
                 msg = tr._getfailureheadline(rep)
-            tw = _pytest.config.create_terminal_writer(
-                terminalreporter.config, stringio=True
-            )
+            file = StringIO()
+            tw = _pytest.config.create_terminal_writer(terminalreporter.config, file)
             rep.toterminal(tw)
-            s = tw.stringio.getvalue()
+            s = file.getvalue()
             assert len(s)
             pastebinurl = create_new_paste(s)
             tr.write_line("{} --> {}".format(msg, pastebinurl))

src/_pytest/reports.py

@@ -82,10 +82,11 @@ class BaseReport:
 
         .. versionadded:: 3.0
         """
-        tw = TerminalWriter(stringio=True)
+        file = StringIO()
+        tw = TerminalWriter(file)
         tw.hasmarkup = False
         self.toterminal(tw)
-        exc = tw.stringio.getvalue()
+        exc = file.getvalue()
         return exc.strip()
 
     @property

testing/code/test_excinfo.py

@@ -1,3 +1,4 @@
+import io
 import operator
 import os
 import queue
@@ -1037,10 +1038,11 @@ raise ValueError()
         """
         )
         excinfo = pytest.raises(ValueError, mod.f)
-        tw = TerminalWriter(stringio=True)
+        file = io.StringIO()
+        tw = TerminalWriter(file=file)
         repr = excinfo.getrepr(**reproptions)
         repr.toterminal(tw)
-        assert tw.stringio.getvalue()
+        assert file.getvalue()
 
     def test_traceback_repr_style(self, importasmod, tw_mock):
         mod = importasmod(
@@ -1255,11 +1257,12 @@ raise ValueError()
         getattr(excinfo.value, attr).__traceback__ = None
 
         r = excinfo.getrepr()
-        tw = TerminalWriter(stringio=True)
+        file = io.StringIO()
+        tw = TerminalWriter(file=file)
         tw.hasmarkup = False
         r.toterminal(tw)
 
-        matcher = LineMatcher(tw.stringio.getvalue().splitlines())
+        matcher = LineMatcher(file.getvalue().splitlines())
         matcher.fnmatch_lines(
             [
                 "ValueError: invalid value",