fix: error out if a valid flag is passed before a subcommand

cli/args/flags.rs

@@ -1236,6 +1236,51 @@ pub fn flags_from_vec(args: Vec<OsString>) -> clap::error::Result<Flags> {
   }
 
   if let Some((subcommand, mut m)) = matches.remove_subcommand() {
+    let pre_subcommand_arg = app
+      .get_arguments()
+      .filter(|arg| !arg.is_global_set())
+      .find(|arg| {
+        matches
+          .value_source(arg.get_id().as_str())
+          .is_some_and(|value| value == clap::parser::ValueSource::CommandLine)
+      })
+      .map(|arg| {
+        format!(
+          "--{}",
+          arg.get_long().unwrap_or_else(|| arg.get_id().as_str())
+        )
+      });
+
+    if let Some(arg) = pre_subcommand_arg {
+      let usage = app.find_subcommand_mut(&subcommand).unwrap().render_usage();
+
+      let mut err =
+        clap::error::Error::new(ErrorKind::UnknownArgument).with_cmd(&app);
+      err.insert(
+        clap::error::ContextKind::InvalidArg,
+        clap::error::ContextValue::String(arg.clone()),
+      );
+
+      let valid = app.get_styles().get_valid();
+
+      let styled_suggestion = clap::builder::StyledStr::from(format!(
+        "'{}{subcommand} {arg}{}' exists",
+        valid.render(),
+        valid.render_reset()
+      ));
+
+      err.insert(
+        clap::error::ContextKind::Suggested,
+        clap::error::ContextValue::StyledStrs(vec![styled_suggestion]),
+      );
+      err.insert(
+        clap::error::ContextKind::Usage,
+        clap::error::ContextValue::StyledStr(usage),
+      );
+
+      return Err(err);
+    }
+
     match subcommand.as_str() {
       "add" => add_parse(&mut flags, &mut m),
       "remove" => remove_parse(&mut flags, &mut m),
@@ -4701,16 +4746,10 @@ fn run_parse(
       "[SCRIPT_ARG] may only be omitted with --v8-flags=--help, else to use the repl with arguments, please use the `deno repl` subcommand",
     ));
   } else {
-    return Err(
-      app
-        .get_subcommands_mut()
-        .find(|subcommand| subcommand.get_name() == "run")
-        .unwrap()
-        .error(
-          clap::error::ErrorKind::MissingRequiredArgument,
-          "[SCRIPT_ARG] may only be omitted with --v8-flags=--help",
-        ),
-    );
+    return Err(app.find_subcommand_mut("run").unwrap().error(
+      clap::error::ErrorKind::MissingRequiredArgument,
+      "[SCRIPT_ARG] may only be omitted with --v8-flags=--help",
+    ));
   }
 
   Ok(())
@@ -10835,4 +10874,17 @@ mod tests {
       }
     )
   }
+
+  #[test]
+  fn flag_before_subcommand() {
+    let r = flags_from_vec(svec!["deno", "--allow-net", "repl"]);
+    assert_eq!(
+      r.unwrap_err().to_string(),
+      "error: unexpected argument '--allow-net' found
+
+  tip: 'repl --allow-net' exists
+
+Usage: deno repl [OPTIONS] [-- [ARGS]...]\n"
+    )
+  }
 }