UndefRefError for keyword methods with anonymous type variable in where bound #173

Hi, apologies if this issue should be in Revise.jl instead of here. I encountered this issue and worked around it in QuantumKitHub/MPSKit.jl#540.

Somehow, when a keyword argument method has an anonymous type variable inside the bound of a static parameter (in my specific case a where bound), the keyword-body function can't be resolved and raises a warning of the form

┌ Warning: skipping callee Main.:(var"#f#2") (called by Main.f) due to UndefRefError()
└ @ LoweredCodeUtils ~/.julia/packages/LoweredCodeUtils/WbxFQ/src/signatures.jl:344

When Revise attempts to rerun this signature, it freezes my REPL. I'm on Julia v1.12.6, Windows 11 if that matters.

Edit: I found a second trigger, namely anonymous type variables in the type of callable objects. MWE for the 2nd case:

struct Foo{T} end
(h::Foo{<:Integer})(x; kw...) = 1 # warns
(::Type{<:Foo})(x; kw...) = 1  # warns
(h::Foo{T})(x; kw...) where {T <: Integer} = 1 # fine
(h::Foo{<:Integer})(x) = 1 # fine (no keyword arguments)
(h::Foo)(x::Vector{<:Integer}; kw...) = 1 # fine (<: only in an argument type)