[mypyc] Add back __name__ attribute on nested functions

[ichard26]

Description

Since nested functions are implemented as instances of a special class they don't get a __name__ attribute by default. This commit adds it back by generating a init dunder on callable classes which simply assigns the attribute. This brings mypyc's behaviour more in line with Python's.

Fixes mypyc/mypyc#884

Test Plan

Add asserts to the nestedFunctions run test which checks for the __name__ attribute. Also updated the IR build tests to include the new initializers.

[JukkaL]

Thanks for the PR!

This seems to work fine, but the changes seem to result in about 160 lines of extra C boilerplate per nested C function. This can be bad, since slow compile times due to the volume of generated C is already a problem. Let's figure out a way to do this without such a big code size explosion.

I think that it would be possible to share the extension class we use to represent nested functions, instead of generating one for each nested function. Not sure if this is tricky for some reason, though. This way we'd only have at most 160 lines of boilerplate per module, which is much more reasonable. Do you want to take a stab at sharing the nested function types? I can give some pointers. (This could be a separate PR that we'd merge first.)

@msullivan Do you remember why we generate a class per nested function? Is it just something that nobody has bothered to optimize yet, or is there some fundamental difficulty?

[ichard26]

Do you want to take a stab at sharing the nested function types?

It'd be nice to try although I'm going to be busy for the next two weeks so I won't be able to look into this until then.

[msullivan]

I think the main problem is just that we don't really have any shared classes that we use ever. We could do it, but it'll get duplicated between compilation groups (which is not the end of the world).