pregenerate the pycodestyle plugin to avoid call overhead

tests/unit/plugins/pycodestyle_test.py

@@ -0,0 +1,33 @@
+import importlib.machinery
+import importlib.util
+import os.path
+
+import flake8.plugins.pycodestyle
+
+HERE = os.path.dirname(os.path.abspath(__file__))
+
+
+def test_up_to_date():
+    """Validate that the generated pycodestyle plugin is up to date.
+
+    We generate two "meta" plugins for pycodestyle to avoid calling overhead.
+
+    To regenerate run:
+
+        ./bin/gen-pycodestyle-plugin > src/flake8/plugins/pycodestyle.py
+    """
+
+    path = os.path.join(HERE, "../../../bin/gen-pycodestyle-plugin")
+    name = os.path.basename(path)
+    loader = importlib.machinery.SourceFileLoader(name, path)
+    spec = importlib.util.spec_from_loader(loader.name, loader)
+    assert spec is not None
+    mod = importlib.util.module_from_spec(spec)
+    loader.exec_module(mod)
+
+    expected = "".join(f"{line}\n" for line in mod.lines())
+
+    with open(flake8.plugins.pycodestyle.__file__) as f:
+        contents = f.read()
+
+    assert contents == expected