logging: Make it possible to add cli colors to custom log levels

Closes #8803
PR #8804

Co-authored-by: Bruno Oliveira <nicoddemus@gmail.com>
Co-authored-by: Terje Runde <terje.runde@flir.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

AUTHORS

@@ -309,6 +309,7 @@ Tanvi Mehta
 Tarcisio Fischer
 Tareq Alayan
 Ted Xiao
+Terje Runde
 Thomas Grainger
 Thomas Hisch
 Tim Hoffmann

changelog/8803.improvement.rst

@@ -0,0 +1,9 @@
+It is now possible to add colors to custom log levels on cli log.
+
+By using :func:`add_color_level <_pytest.logging.add_color_level` from a ``pytest_configure`` hook, colors can be added::
+
+    logging_plugin = config.pluginmanager.get_plugin('logging-plugin')
+    logging_plugin.log_cli_handler.formatter.add_color_level(logging.INFO, 'cyan')
+    logging_plugin.log_cli_handler.formatter.add_color_level(logging.SPAM, 'blue')
+
+    See :ref:`log_colors` for more information.

doc/en/how-to/logging.rst

@@ -219,6 +219,30 @@ option names are:
 You can call ``set_log_path()`` to customize the log_file path dynamically. This functionality
 is considered **experimental**.
 
+.. _log_colors:
+
+Customizing Colors
+^^^^^^^^^^^^^^^^^^
+
+Log levels are colored if colored terminal output is enabled. Changing
+from default colors or putting color on custom log levels is supported
+through ``add_color_level()``. Example:
+
+.. code-block:: python
+
+    @pytest.hookimpl
+    def pytest_configure(config):
+        logging_plugin = config.pluginmanager.get_plugin("logging-plugin")
+
+        # Change color on existing log level
+        logging_plugin.log_cli_handler.formatter.add_color_level(logging.INFO, "cyan")
+
+        # Add color to a custom log level (a custom log level `SPAM` is already set up)
+        logging_plugin.log_cli_handler.formatter.add_color_level(logging.SPAM, "blue")
+.. warning::
+
+    This feature and its API are considered **experimental** and might change
+    between releases without a deprecation notice.
 .. _log_release_notes:
 
 Release notes

src/_pytest/logging.py

@@ -63,28 +63,43 @@ class ColoredLevelFormatter(logging.Formatter):
 
     def __init__(self, terminalwriter: TerminalWriter, *args, **kwargs) -> None:
         super().__init__(*args, **kwargs)
+        self._terminalwriter = terminalwriter
         self._original_fmt = self._style._fmt
         self._level_to_fmt_mapping: Dict[int, str] = {}
 
+        for level, color_opts in self.LOGLEVEL_COLOROPTS.items():
+            self.add_color_level(level, *color_opts)
+
+    def add_color_level(self, level: int, *color_opts: str) -> None:
+        """Add or update color opts for a log level.
+
+        :param level:
+            Log level to apply a style to, e.g. ``logging.INFO``.
+        :param color_opts:
+            ANSI escape sequence color options. Capitalized colors indicates
+            background color, i.e. ``'green', 'Yellow', 'bold'`` will give bold
+            green text on yellow background.
+
+        .. warning::
+            This is an experimental API.
+        """
+
         assert self._fmt is not None
         levelname_fmt_match = self.LEVELNAME_FMT_REGEX.search(self._fmt)
         if not levelname_fmt_match:
             return
         levelname_fmt = levelname_fmt_match.group()
 
-        for level, color_opts in self.LOGLEVEL_COLOROPTS.items():
-            formatted_levelname = levelname_fmt % {
-                "levelname": logging.getLevelName(level)
-            }
+        formatted_levelname = levelname_fmt % {"levelname": logging.getLevelName(level)}
 
-            # add ANSI escape sequences around the formatted levelname
-            color_kwargs = {name: True for name in color_opts}
-            colorized_formatted_levelname = terminalwriter.markup(
-                formatted_levelname, **color_kwargs
-            )
-            self._level_to_fmt_mapping[level] = self.LEVELNAME_FMT_REGEX.sub(
-                colorized_formatted_levelname, self._fmt
-            )
+        # add ANSI escape sequences around the formatted levelname
+        color_kwargs = {name: True for name in color_opts}
+        colorized_formatted_levelname = self._terminalwriter.markup(
+            formatted_levelname, **color_kwargs
+        )
+        self._level_to_fmt_mapping[level] = self.LEVELNAME_FMT_REGEX.sub(
+            colorized_formatted_levelname, self._fmt
+        )
 
     def format(self, record: logging.LogRecord) -> str:
         fmt = self._level_to_fmt_mapping.get(record.levelno, self._original_fmt)