fix #44735, assert typeintersect arguments on Julia level

Author: aviatesk

base/reflection.jl

@@ -680,7 +680,11 @@ issingletontype(@nospecialize(t)) = (@_pure_meta; isa(t, DataType) && isdefined(
 Compute a type that contains the intersection of `T` and `S`. Usually this will be the
 smallest such type or one close to it.
 """
-typeintersect(@nospecialize(a), @nospecialize(b)) = (@_pure_meta; ccall(:jl_type_intersection, Any, (Any, Any), a, b))
+function typeintersect(@nospecialize(a), @nospecialize(b))
+    @_pure_meta
+    (!isvarargtype(a) && !isvarargtype(b)) || throw(ArgumentError("invalid typeintersect with Vararg"))
+    return ccall(:jl_type_intersection, Any, (Any, Any), a, b)
+end
 
 morespecific(@nospecialize(a), @nospecialize(b)) = ccall(:jl_type_morespecific, Cint, (Any, Any), a, b) != 0
 

test/subtype.jl

@@ -1976,3 +1976,6 @@ end
 @testintersect(Tuple{Type{Pair{_A, S} where S<:AbstractArray{<:_A, 2}}, Dict} where _A,
                Tuple{Type{Pair{_A, S} where S<:AbstractArray{<:_A, 2}} where _A, Union{Array, Pair}},
                Bottom)
+
+@test_throws ArgumentError typeintersect(Vararg{Int}, Int)
+@test_throws ArgumentError typeintersect(Int, Vararg{Int})