fix(parser): Ensure subcommand flags can conflict

Fixes #5297

clap_builder/src/parser/parser.rs

@@ -454,6 +454,17 @@ impl<'cmd> Parser<'cmd> {
         }
 
         if let Some(ref pos_sc_name) = subcmd_name {
+            if self.cmd.is_args_conflicts_with_subcommands_set() && valid_arg_found {
+                return Err(ClapError::subcommand_conflict(
+                    self.cmd,
+                    pos_sc_name.clone(),
+                    matcher
+                        .arg_ids()
+                        .map(|id| self.cmd.find(id).unwrap().to_string())
+                        .collect(),
+                    Usage::new(self.cmd).create_usage_with_title(&[]),
+                ));
+            }
             let sc_name = self
                 .cmd
                 .find_subcommand(pos_sc_name)

tests/builder/conflicts.rs

@@ -727,25 +727,41 @@ For more information, try '--help'.
 #[test]
 #[cfg(feature = "error-context")]
 fn flag_conflicts_with_subcommand_long_flag() {
+    static CONFLICT_ERR: &str = "\
+error: the subcommand 'sub' cannot be used with '--hello'
+
+Usage: test [OPTIONS]
+       test <COMMAND>
+
+For more information, try '--help'.
+";
+
     let cmd = Command::new("test")
         .args_conflicts_with_subcommands(true)
         .arg(arg!(--hello))
         .subcommand(Command::new("sub").long_flag("sub"));
 
-    let res = cmd.try_get_matches_from(vec!["", "--hello", "--sub"]);
-    assert!(res.is_ok(), "error: {:?}", res.unwrap_err().kind());
+    utils::assert_output(cmd, "test --hello --sub", CONFLICT_ERR, true);
 }
 
 #[test]
 #[cfg(feature = "error-context")]
 fn flag_conflicts_with_subcommand_short_flag() {
+    static CONFLICT_ERR: &str = "\
+error: the subcommand 'sub' cannot be used with '--hello'
+
+Usage: test [OPTIONS]
+       test <COMMAND>
+
+For more information, try '--help'.
+";
+
     let cmd = Command::new("test")
         .args_conflicts_with_subcommands(true)
         .arg(arg!(--hello))
         .subcommand(Command::new("sub").short_flag('s'));
 
-    let res = cmd.try_get_matches_from(vec!["", "--hello", "-s"]);
-    assert!(res.is_ok(), "error: {:?}", res.unwrap_err().kind());
+    utils::assert_output(cmd, "test --hello -s", CONFLICT_ERR, true);
 }
 
 #[test]