raise exception on Vararg-arguments in subtype rather than abort

fix #44735

Author: aviatesk

src/subtype.c

@@ -1258,7 +1258,8 @@ static int subtype(jl_value_t *x, jl_value_t *y, jl_stenv_t *e, int param)
     }
     if (jl_is_unionall(y))
         return subtype_unionall(x, (jl_unionall_t*)y, e, 1, param);
-    assert(!jl_is_vararg(x) && !jl_is_vararg(y));
+    else if (jl_is_vararg(x) || jl_is_vararg(y))
+        jl_errorf("invalid subtyping with Vararg");
     if (jl_is_datatype(x) && jl_is_datatype(y)) {
         if (x == y) return 1;
         if (y == (jl_value_t*)jl_any_type) return 1;

test/subtype.jl

@@ -1976,3 +1976,7 @@ 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)
+
+# https://github.com/JuliaLang/julia/issues/44735
+@test_throws ErrorException("invalid subtyping with Vararg") typeintersect(Vararg{Int}, Int)
+@test_throws ErrorException("invalid subtyping with Vararg") typeintersect(Int, Vararg{Int})