Log filenames when running pytest-mypy

conftest.py

@@ -1,6 +1,10 @@
+from __future__ import annotations
+
+import os
 import sys
 
 import pytest
+from pytest_mypy import MypyFileItem, MypyResults
 
 pytest_plugins = 'setuptools.tests.fixtures'
 
@@ -20,7 +24,18 @@ def pytest_addoption(parser):
     )
 
 
+def mypy_error_formatter_show_filename(
+    item: MypyFileItem, results: MypyResults, errors: list[str]
+) -> str:  # pragma: nocover # This shouldn't run on success
+    """Include the relative file path before each reported error."""
+    return '\n'.join(
+        f'{item.path.relative_to(os.getcwd())}:{error}' for error in errors
+    )
+
+
 def pytest_configure(config):
+    mypy_plugin = config.pluginmanager.getplugin('mypy')
+    mypy_plugin.file_error_formatter = mypy_error_formatter_show_filename
     config.addinivalue_line("markers", "integration: integration tests")
     config.addinivalue_line("markers", "uses_network: tests may try to download files")
     _IntegrationTestSpeedups.disable_plugins_already_run(config)