Keyword arguments brain dump

[christopher-dG]

Here is all my thoughts about trying to support keyword arguments so that I don't go down the same rabbit hole more than once.

Cassette doesn't really support overdubbing functions with keyword arguments right now but you can sort of do it with JuliaLabs/Cassette.jl#48 (comment).

Idea 1: Implement that overdub method with the kwftype along with each normal overdub implementation
Problem: How to recurse with keywords? That seems completely unsupported right now. Trying recurse(ctx, () -> f(args...; kwargs...) just loops back around forever.

Solution?: Get the body method that contains all the keywords as positional arguments with LoweredCodeUtils, then call that method with the keywords
Problem: There are no longer any default values so this dies if the user didn't supply all keywords.
Solution?: Find the default values by reading the source code (functionloc, Meta.parse, etc.)
Problem: This gets us into eval hell, and we can't possibly cover all the ways that the functions are defined (via macros, generated functions, etc.)

Solution?: Add one method to each mocked function that takes a new Keywords struct (owned by SimpleMock to avoid piracy), then recurse into that instead

Problem: I haven't tried to implement this but I think this gets us into the same loop as () -> f(args...; kwargs...) (where the recurse just ends up calling the function with keywords again, hitting the overdub and recursing again)

Solution?: Go back to multiple dynamically-generated Context types, and only support keywords when there are no filter functions (should_mock always returns true, so omit it). This is the only one that might actually work, which kind of sucks. But i probably shouldn't work too hard for this when Cassette should in theory eventually support kwargs by itself.
Problem: Goodbye speed

Actual solution: Learn how Cassette and/or Julia work and help get kwargs supported in Cassette

One more thing to note: Choosing whether or not to implement overdub for keywords per-function is not helpful, because we want to be able to mock calls to non-kwfuncs even if they have keywords.

[christopher-dG]

The last solution (multiple context types, keywords are dropped on recurse) is implemented and I'll probably release that. Keeping this open until Cassette supports kwargs for real though.