cgen: fix cgen for thread wrappers, when spawning fns with with anon-…

…fn array args and mut interfaces (fix #19425) (#20241)

vlib/v/gen/c/spawn_and_go.v

@@ -252,6 +252,19 @@ fn (mut g Gen) spawn_and_go_expr(node ast.SpawnExpr, mode SpawnGoMode) {
 					mut arg_types := f.params.map(it.typ)
 					arg_types = arg_types.map(muttable.resolve_generic_to_concrete(it,
 						f.generic_names, node.call_expr.concrete_types) or { it })
+					for i, typ in arg_types {
+						mut typ_sym := g.table.sym(typ)
+						for {
+							if mut typ_sym.info is ast.Array {
+								typ_sym = g.table.sym(typ_sym.info.elem_type)
+							} else {
+								if typ_sym.info is ast.FnType {
+									arg_types[i] = expr.args[i].typ
+								}
+								break
+							}
+						}
+					}
 					fn_var = g.fn_var_signature(return_type, arg_types, 'fn')
 				}
 			}

vlib/v/tests/go_call_fn_with_anon_fn_array_arg_test.v

@@ -0,0 +1,12 @@
+// for issue 19425
+interface MyInterface {}
+
+type Func = fn () int
+
+fn handle_fns(fns []Func, mut w MyInterface) {}
+
+fn test_main() {
+	mut w := &MyInterface(123)
+	spawn handle_fns([], mut w)
+	assert true
+}