pregenerate the pycodestyle plugin to avoid call overhead

[asottile]

this saves 10-12% off the execution time of flake8 -j1 src/

• best of 10 before: 1.469s
• best of 10 after: 1.301s

the implementation is a tiny bit fragile, though not exceedingly so as we pin pycodestyle.

[andersk]

Would it be even better to generate that code and exec() it at runtime? That could give you a way to remove the overhead for deselected plugins (#751).

[asottile]

Would it be even better to generate that code and exec() it at runtime? That could give you a way to remove the overhead for deselected plugins (#751).

#751 is basically impossible without refactoring how pycodestyle works (checks in pycodestyle do not all fall under unique prefixes and criss cross over)

the codegen is also relatively slow so doing it at runtime would eliminate most of the performance gain

[sigmavirus24]

I'm never really a fan of code generation but the improvement is hard to deny. I suspect most of the speed comes from fewer entry_points given how abysmal that's always been (regardless of how much faster importlib is than setuptools/pkg_resources).

[asottile]

surprisingly, most of the speedup comes from not needing to call keywords_for and building small kwargs dictionaries many many times