typeintersect: conservative typevar subtitution during finish_unionall (#54465)

This commit adds a nothrow path for type instantiation, which eliminates
the bad `Union` elements from the result rather than returns the bottom
type.
close #54404

(cherry picked from commit a946631)

Author: N5N3

src/builtins.c

@@ -1564,11 +1564,11 @@ JL_CALLABLE(jl_f_apply_type)
         jl_vararg_t *vm = (jl_vararg_t*)args[0];
         if (!vm->T) {
             JL_NARGS(apply_type, 2, 3);
-            return (jl_value_t*)jl_wrap_vararg(args[1], nargs == 3 ? args[2] : NULL, 1);
+            return (jl_value_t*)jl_wrap_vararg(args[1], nargs == 3 ? args[2] : NULL, 1, 0);
         }
         else if (!vm->N) {
             JL_NARGS(apply_type, 2, 2);
-            return (jl_value_t*)jl_wrap_vararg(vm->T, args[1], 1);
+            return (jl_value_t*)jl_wrap_vararg(vm->T, args[1], 1, 0);
         }
     }
     else if (jl_is_unionall(args[0])) {
@@ -2474,7 +2474,7 @@ void jl_init_primitives(void) JL_GC_DISABLED
     add_builtin("Tuple", (jl_value_t*)jl_anytuple_type);
     add_builtin("TypeofVararg", (jl_value_t*)jl_vararg_type);
     add_builtin("SimpleVector", (jl_value_t*)jl_simplevector_type);
-    add_builtin("Vararg", (jl_value_t*)jl_wrap_vararg(NULL, NULL, 0));
+    add_builtin("Vararg", (jl_value_t*)jl_wrap_vararg(NULL, NULL, 0, 0));
 
     add_builtin("Module", (jl_value_t*)jl_module_type);
     add_builtin("MethodTable", (jl_value_t*)jl_methtable_type);

src/gf.c

@@ -767,7 +767,7 @@ static jl_value_t *inst_varargp_in_env(jl_value_t *decl, jl_svec_t *sparams)
                 vm = T_has_tv ? jl_type_unionall(v, T) : T;
                 if (N_has_tv)
                     N = NULL;
-                vm = (jl_value_t*)jl_wrap_vararg(vm, N, 1); // this cannot throw for these inputs
+                vm = (jl_value_t*)jl_wrap_vararg(vm, N, 1, 0); // this cannot throw for these inputs
             }
             sp++;
             decl = ((jl_unionall_t*)decl)->body;
@@ -1016,7 +1016,7 @@ static void jl_compilation_sig(
             // avoid Vararg{Type{Type{...}}}
             if (jl_is_type_type(type_i) && jl_is_type_type(jl_tparam0(type_i)))
                 type_i = (jl_value_t*)jl_type_type;
-            type_i = (jl_value_t*)jl_wrap_vararg(type_i, (jl_value_t*)NULL, 1); // this cannot throw for these inputs
+            type_i = (jl_value_t*)jl_wrap_vararg(type_i, (jl_value_t*)NULL, 1, 0); // this cannot throw for these inputs
         }
         else {
             type_i = inst_varargp_in_env(decl, sparams);