Using recurse with keywords

[christopher-dG]

Related to #48, mentioned on Slack and @vchuravy encouraged me to open an issue.

using Cassette: Cassette

Cassette.@context Ctx

# Here's the "normal" case where we don't accept keyword arguments

f(_args...) = println("f")

function Cassette.overdub(ctx::Ctx, ::typeof(f), args...)
    if false  # But really, sometimes true.
        :hi
    else
        # When there are no keywords, everything is fine.
        Cassette.recurse(ctx, f, args...)
    end
end

# Cassette.overdub(Ctx(), () -> f(1))

# And here's the weird one with kwargs

g(_args...; _kwargs...) = println("g")

Cassette.overdub(ctx::Ctx, ::Core.kwftype(typeof(g)), kwargs, ::typeof(g), args...) =
    Cassette.overdub(ctx, g, args...; kwargs...)

function Cassette.overdub(ctx::Ctx, ::typeof(g), args...; kwargs...)
    if false  # But really, sometimes true.
        :hi
    else
        # How can I recurse into f with keywords?
        # 1. This throws an exception:
        #   Cassette.recurse(ctx, g, args...; kwargs...)
        # 2. This just loops back to this point, causing a stack overflow:
        #   Cassette.recurse(ctx, () -> g(args...; kwargs...))
        "????????????"
    end
end

# Cassette.overdub(Ctx(), () -> g(; x=1))

To me, this is expected behaviour:

Option 1 shouldn't work because recurse is not defined with keyword arguments.

Option 2 recurses into a new anon function, which then calls g(args...; kwargs...), which reaches overdub(ctx::Ctx, ::Core.kwftype(typeof(g)), kwargs, ::typeof(g), args...), which calls overdub(ctx::Ctx, ::typeof(g), args...; kwargs...), which once again hits that recurse. So infinite recursion is justified.

The real solution here is to somehow be able to pass keywords to recurse. Is there a way that we can define a method of recurse that accepts keywords, similar to what we can do with overdub?