cli: Explicitly add a Help command to accept the early args after it

The default clap's help command doesn't have the ability to accept flags
(e.g --no-pager). The recommended way[1] to solve this is to manually
implement it.

[1]: clap-rs/clap#5332

Fixes: #4501

cli/src/commands/help.rs

@@ -0,0 +1,66 @@
+// Copyright 2024 The Jujutsu Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use tracing::instrument;
+
+use crate::cli_util::CommandHelper;
+use crate::command_error;
+use crate::command_error::CommandError;
+use crate::ui::Ui;
+
+/// Print this message or the help of the given subcommand(s)
+#[derive(clap::Args, Clone, Debug)]
+pub(crate) struct HelpArgs {
+    /// The command to show help
+    command: Option<Vec<String>>,
+}
+
+#[instrument(skip_all)]
+pub(crate) fn cmd_help(
+    _ui: &mut Ui,
+    command: &CommandHelper,
+    args: &HelpArgs,
+) -> Result<(), CommandError> {
+    let cmd_names = if let Some(cmd_to_show_help) = &args.command {
+        let mut ret = vec![];
+        let mut curr_command = command.app();
+
+        for cmd_to_show_help in cmd_to_show_help {
+            curr_command = curr_command
+                .find_subcommand(cmd_to_show_help.clone())
+                .ok_or(command.app().clone().error(
+                    clap::error::ErrorKind::InvalidValue,
+                    format!("no subcomand with name {}", cmd_to_show_help),
+                ))?;
+
+            ret.push(curr_command.get_name());
+        }
+
+        ret
+    } else {
+        vec![]
+    };
+
+    let mut args_to_show_help = vec![command.app().get_name()];
+    args_to_show_help.extend(cmd_names);
+    args_to_show_help.push("--help");
+
+    let help_err = command
+        .app()
+        .clone()
+        .try_get_matches_from(args_to_show_help)
+        .expect_err("Clap library should return a DisplayHelp error in this context");
+
+    Err(command_error::cli_error(help_err))
+}

cli/src/commands/mod.rs

@@ -30,6 +30,7 @@ mod evolog;
 mod file;
 mod fix;
 mod git;
+mod help;
 mod init;
 mod interdiff;
 mod log;
@@ -109,6 +110,7 @@ enum Command {
     Fix(fix::FixArgs),
     #[command(subcommand)]
     Git(git::GitCommand),
+    Help(help::HelpArgs),
     Init(init::InitArgs),
     Interdiff(interdiff::InterdiffArgs),
     Log(log::LogArgs),
@@ -173,7 +175,7 @@ struct DummyCommandArgs {
 }
 
 pub fn default_app() -> clap::Command {
-    Command::augment_subcommands(Args::command())
+    Command::augment_subcommands(Args::command()).disable_help_subcommand(true)
 }
 
 #[instrument(skip_all)]
@@ -213,6 +215,7 @@ pub fn run_command(ui: &mut Ui, command_helper: &CommandHelper) -> Result<(), Co
         }
         Command::Fix(args) => fix::cmd_fix(ui, command_helper, args),
         Command::Git(args) => git::cmd_git(ui, command_helper, args),
+        Command::Help(args) => help::cmd_help(ui, command_helper, args),
         Command::Init(args) => init::cmd_init(ui, command_helper, args),
         Command::Interdiff(args) => interdiff::cmd_interdiff(ui, command_helper, args),
         Command::Log(args) => log::cmd_log(ui, command_helper, args),

cli/tests/cli-reference@.md.snap

@@ -56,6 +56,7 @@ This document contains the help content for the `jj` command-line program.
 * [`jj git remote remove`↴](#jj-git-remote-remove)
 * [`jj git remote rename`↴](#jj-git-remote-rename)
 * [`jj git remote set-url`↴](#jj-git-remote-set-url)
+* [`jj help`↴](#jj-help)
 * [`jj init`↴](#jj-init)
 * [`jj interdiff`↴](#jj-interdiff)
 * [`jj log`↴](#jj-log)
@@ -126,6 +127,7 @@ To get started, see the tutorial at https://martinvonz.github.io/jj/latest/tutor
 * `file` — File operations
 * `fix` — Update files with formatting fixes or other changes
 * `git` — Commands for working with Git remotes and the underlying Git repo
+* `help` — Print this message or the help of the given subcommand(s)
 * `init` — Create a new repo in the given directory
 * `interdiff` — Compare the changes of two commits
 * `log` — Show revision history
@@ -1150,6 +1152,18 @@ Set the URL of a Git remote
 
 
 
+## `jj help`
+
+Print this message or the help of the given subcommand(s)
+
+**Usage:** `jj help [COMMAND]...`
+
+###### **Arguments:**
+
+* `<COMMAND>` — The command to show help
+
+
+
 ## `jj init`
 
 Create a new repo in the given directory

cli/tests/test_global_opts.rs

@@ -530,6 +530,10 @@ fn test_early_args() {
     let stdout = test_env.jj_cmd_success(test_env.env_root(), &["--color=always", "help"]);
     insta::assert_snapshot!(stdout.lines().find(|l| l.contains("Commands:")).unwrap(), @"Commands:");
 
+    // Check that early args are accepted after the help command
+    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:");
+
     // 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.