Deprecate TerminalReporter.writer

Fix pytest-dev#6779

changelog/6779.deprecation.rst

@@ -0,0 +1,3 @@
+The ``TerminalReporter.writer`` attribute has been deprecated and should no longer be used. This
+was inadvertently exposed as part of the public API of that plugin and ties it too much
+with ``py.io.TerminalWriter``.

doc/en/deprecations.rst

@@ -37,7 +37,7 @@ display captured output when tests fail: ``no``, ``stdout``, ``stderr``, ``log``
 Node Construction changed to ``Node.from_parent``
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-.. deprecated:: 5.3
+.. deprecated:: 5.4
 
 The construction of nodes new should use the named constructor ``from_parent``.
 This limitation in api surface intends to enable better/simpler refactoring of the collection tree.
@@ -95,6 +95,18 @@ The plan is remove the ``--result-log`` option in pytest 6.0 if ``pytest-reportl
 to all users and is deemed stable. The ``pytest-reportlog`` plugin might even be merged into the core
 at some point, depending on the plans for the plugins and number of users using it.
 
+TerminalReporter.writer
+~~~~~~~~~~~~~~~~~~~~~~~
+
+.. deprecated:: 5.4
+
+The ``TerminalReporter.writer`` attribute has been deprecated and should no longer be used. This
+was inadvertently exposed as part of the public API of that plugin and ties it too much
+with ``py.io.TerminalWriter``.
+
+Plugins that used ``TerminalReporter.writer`` directly should instead use ``TerminalReporter``
+methods that provide the same functionality.
+
 
 Removed Features
 ----------------

src/_pytest/terminal.py

@@ -8,6 +8,7 @@
 import platform
 import sys
 import time
+import warnings
 from functools import partial
 from typing import Any
 from typing import Callable
@@ -25,6 +26,7 @@
 
 import pytest
 from _pytest import nodes
+from _pytest._io import TerminalWriter
 from _pytest.config import Config
 from _pytest.config import ExitCode
 from _pytest.main import Session
@@ -270,7 +272,7 @@ def __init__(self, config: Config, file=None) -> None:
         self.startdir = config.invocation_dir
         if file is None:
             file = sys.stdout
-        self.writer = self._tw = _pytest.config.create_terminal_writer(config, file)
+        self._tw = _pytest.config.create_terminal_writer(config, file)
         self._screen_width = self._tw.fullwidth
         self.currentfspath = None  # type: Any
         self.reportchars = getreportopt(config)
@@ -280,6 +282,16 @@ def __init__(self, config: Config, file=None) -> None:
         self._show_progress_info = self._determine_show_progress_info()
         self._collect_report_last_write = None  # type: Optional[float]
 
+    @property
+    def writer(self) -> TerminalWriter:
+        warnings.warn(
+            pytest.PytestDeprecationWarning(
+                "TerminalReporter.writer attribute is deprecated, use TerminalReporter._tw instead at your own risk.\n"
+                "See https://docs.pytest.org/en/latest/deprecations.html#terminalreporter-writer for more information."
+            )
+        )
+        return self._tw
+
     def _determine_show_progress_info(self):
         """Return True if we should display progress information based on the current config"""
         # do not show progress if we are not capturing output (#3038)
@@ -972,7 +984,7 @@ def show_simple(stat, lines: List[str]) -> None:
             failed = self.stats.get(stat, [])
             if not failed:
                 return
-            termwidth = self.writer.fullwidth
+            termwidth = self._tw.fullwidth
             config = self.config
             for rep in failed:
                 line = _get_line_with_reprcrash_message(config, rep, termwidth)

testing/deprecated_test.py

@@ -27,7 +27,7 @@ def test():
 
 def test_terminal_reporter_writer_attr(pytestconfig):
     """Check that TerminalReporter._tw is also available as 'writer' (#2984)
-    This attribute is planned to be deprecated in 3.4.
+    This attribute has been deprecated in 5.4.
     """
     try:
         import xdist  # noqa
@@ -36,7 +36,8 @@ def test_terminal_reporter_writer_attr(pytestconfig):
     except ImportError:
         pass
     terminal_reporter = pytestconfig.pluginmanager.get_plugin("terminalreporter")
-    assert terminal_reporter.writer is terminal_reporter._tw
+    with pytest.warns(pytest.PytestDeprecationWarning):
+        assert terminal_reporter.writer is terminal_reporter._tw
 
 
 @pytest.mark.parametrize("plugin", sorted(deprecated.DEPRECATED_EXTERNAL_PLUGINS))