cli: insert dummy -h/--help flag when parsing early args

Fixes jj-vcs#4746

cli/src/cli_util.rs

@@ -3032,7 +3032,16 @@ fn handle_early_args(
     let early_matches = app
         .clone()
         .disable_version_flag(true)
+        // Do not emit DisplayHelp error
         .disable_help_flag(true)
+        // Do not stop parsing at -h/--help
+        .arg(
+            clap::Arg::new("help")
+                .short('h')
+                .long("help")
+                .global(true)
+                .action(ArgAction::Count),
+        )
         .ignore_errors(true)
         .try_get_matches_from(args)?;
     let mut args: EarlyArgs = EarlyArgs::from_arg_matches(&early_matches).unwrap();

cli/tests/test_global_opts.rs

@@ -559,6 +559,16 @@ fn test_early_args() {
     let stdout = test_env.jj_cmd_success(test_env.env_root(), &["help", "--color=always"]);
     insta::assert_snapshot!(stdout.lines().find(|l| l.contains("Commands:")).unwrap(), @"Commands:");
 
+    // Check that early args are accepted after -h/--help
+    let stdout = test_env.jj_cmd_success(test_env.env_root(), &["-h", "--color=always"]);
+    insta::assert_snapshot!(
+        stdout.lines().find(|l| l.contains("Usage:")).unwrap(),
+        @"Usage: jj [OPTIONS] <COMMAND>");
+    let stdout = test_env.jj_cmd_success(test_env.env_root(), &["log", "--help", "--color=always"]);
+    insta::assert_snapshot!(
+        stdout.lines().find(|l| l.contains("Usage:")).unwrap(),
+        @"Usage: jj log [OPTIONS] [PATHS]...");
+
     // Early args are parsed with clap's ignore_errors(), but there is a known
     // bug that causes defaults to be unpopulated. Test that the early args are
     // tolerant of this bug and don't cause a crash.