Reflection functions should handle `UnionAll`

[yuyichao]

From #20869

julia> foo{N}(::Val{N}, ::Type{Val{N}}) = true
foo (generic function with 1 method)

julia> Method[m[3] for m in Base._methods_by_ftype(Tuple{typeof(foo),Val{N},Type{Val{N}}} where N, -1, typemax(UInt))]
1-element Array{Method,1}:
 foo(::Val{N}, ::Type{Val{N}}) where N in Main at REPL[1]:1

julia> methods(foo, Tuple{Val{N},Type{Val{N}}} where N)
ERROR: type UnionAll has no field parameters
Stacktrace:
 [1] to_tuple_type(::Any) at ./reflection.jl:466
 [2] methods(::Any, ::Any) at ./reflection.jl:582

[ssfrr]

For some user-facing context - this issue is causing errors to be thrown whenever Atom tries to run auto-completion if PlotlyJS is loaded, using 0.6.0 (unless there's something weird on my machine specifically). Is there a fix/backport that seems likely soon, or would it make sense to try to work around it in Atom or PlotlyJS?

@pfitzseb @MikeInnes @sglyon

[vtjnash]

also related to #22051?

[sglyon]

Hey @ssfrr I've noticed it too, but didn't narrow it down to only arising after loading PlotlyJS. That's super weird.

The good news is that it looks like @pfitzseb made a fix in CodeTools.jl. have you tried that yet?

[tkoolen]

This issue partially breaks DocStringExtensions on 0.6: JuliaDocs/DocStringExtensions.jl#32.

[tkoolen]

See JuliaDocs/DocStringExtensions.jl#38 for my workaround for this issue in DocStringExtensions.

As I was implementing this workaround, I realized that DocStringExtensions' getmethods! function was already working around a couple of corner cases of Base.methods that one could argue aren't handled properly; I was merely adding another. Should DocStringExtensions.getmethods just form the basis for a new Base.methods implementation?