fix inference of Tuple{unknown}, where the parameter can be a Vararg

Author: JeffBezanson

base/inference.jl

@@ -838,7 +838,11 @@ function apply_type_tfunc(headtypetype::ANY, args::ANY...)
             #end
             uncertain = true
             if istuple
-                push!(tparams, Any)
+                if i == largs
+                    push!(tparams, Vararg)
+                else
+                    push!(tparams, Any)
+                end
             else
                 # TODO: use rewrap_unionall to skip only the unknown parameters
                 #push!(tparams, headtype.parameters[i-1])

test/inference.jl

@@ -466,6 +466,18 @@ function g19348(x)
 end
 test_inferred_static(@code_typed g19348((1, 2.0)))
 
+# make sure Tuple{unknown} handles the possibility that `unknown` is a Vararg
+function maybe_vararg_tuple_1()
+    x = Any[Vararg{Int}][1]
+    Tuple{x}
+end
+@test Type{Tuple{Vararg{Int}}} <: Base.return_types(maybe_vararg_tuple_1, ())[1]
+function maybe_vararg_tuple_2()
+    x = Type[Vararg{Int}][1]
+    Tuple{x}
+end
+@test Type{Tuple{Vararg{Int}}} <: Base.return_types(maybe_vararg_tuple_2, ())[1]
+
 # Issue 19641
 foo19641() = let a = 1.0
     Core.Inference.return_type(x -> x + a, Tuple{Float64})