fix vararg unionall handling

Author: pfitzseb

src/construct.jl

@@ -206,7 +206,8 @@ function prepare_call(@nospecialize(f), allargs; enter_generated = false)
     # Can happen for thunks created by generated functions
     if isa(f, Core.Builtin) || isa(f, Core.IntrinsicFunction)
         return nothing
-    elseif any(x->isa(x, Type) && x <: Vararg, allargs)
+    elseif any(x -> isa(x, Type) &&
+                    (x <: Vararg || (typeof(x) in (UnionAll, DataType) && nameof(x) == :Vararg)), allargs)
         return nothing  # https://github.com/JuliaLang/julia/issues/30995
     end
     argtypes = Tuple{map(_Typeof,allargs)...}

test/interpret.jl

@@ -370,3 +370,11 @@ end
     end
     @test @interpret h_gf() == 2
 end
+
+# https://github.com/JuliaDebug/JuliaInterpreter.jl/issues/130
+@testset "vararg handling" begin
+    method_c1(x::Float64, s::AbstractString...) = true
+    buf = IOBuffer()
+    me = Base.MethodError(method_c1,(1, 1, ""))
+    @test (@interpret Base.show_method_candidates(buf, me)) == nothing
+end