Feature request: use caplog with custom formatter

My application uses a quite heavily customized logging formatter. Right now, the logging plugin only allows to specify the formats for the formatter, not completely replacing it. It would be nice if there was a clean way to provide a custom formatter.

This is the workaround I use for now, patching the plugin class on the module:

from _pytest import logging as pytest_logging

def pytest_configure(config):
    config.pluginmanager.get_plugin('logging').LoggingPlugin = MyLoggingPlugin

class MyLoggingPlugin(pytest_logging.LoggingPlugin):
    def __init__(self, config):
        super().__init__(config)
        self.formatter = MyCustomFormatter()

[brechin]

One option (definitely not optimal) would be to instantiate your custom formatter and set it explicitly on the caplog handler.

def test_my_function(caplog)
    formatter = MyCustomFormatter()
    caplog.handler.setFormatter(formatter)

    my_function()
    assert caplog.text == ....

[nicoddemus]

Perhaps this can be implemented as a hook:

@hookimpl(firstresult=True)
def pytest_logging_formatter(config):
    """Return a logging.Formatter instance that will be used by the internal logging capture"""

Then you can do this in your root conftest.py file:

def pytest_logging_formatter(config):
    return MyCustomFormatter()