fix(assert): Call out the action in positional assert

Brought up in #5135

Author: epage

clap_builder/src/builder/debug_asserts.rs

@@ -746,8 +746,9 @@ fn assert_arg(arg: &Arg) {
         );
         assert!(
             arg.is_takes_value_set(),
-            "Argument '{}` is positional, it must take a value{}",
+            "Argument '{}` is positional and it must take a value but action is {:?}{}",
             arg.get_id(),
+            arg.get_action(),
             if arg.get_id() == Id::HELP {
                 " (`mut_arg` no longer works with implicit `--help`)"
             } else if arg.get_id() == Id::VERSION {

tests/builder/multiple_values.rs

@@ -1730,7 +1730,7 @@ fn issue_2229() {
 }
 
 #[test]
-#[should_panic = "Argument 'pos` is positional, it must take a value"]
+#[should_panic = "Argument 'pos` is positional and it must take a value but action is SetTrue"]
 fn disallow_positionals_without_values() {
     let cmd = Command::new("test").arg(Arg::new("pos").num_args(0));
     cmd.debug_assert();