Fix dor help <command> to show the command's help

dor/src/cli.ts

@@ -98,7 +98,7 @@ interface CaptureProcess extends StricliProcess {
 
 export async function runCli(argv: string[], options: CliOptions = {}): Promise<CliResult> {
   const helpTarget = getHelpTarget(argv);
-  const [commandName, ...args] = argv[0] === 'help' ? ['--help'] : argv;
+  const [commandName, ...args] = rewriteHelpArgv(argv);
 
   if (commandName === 'ensure' && !args.includes('-h') && !args.includes('--help')) {
     const delimiterCheck = validateEnsureDelimiter(args);
@@ -126,7 +126,13 @@ type HelpTarget =
   | { scope: 'command'; commandName: string };
 
 function getHelpTarget(argv: string[]): HelpTarget | undefined {
-  if (argv.length === 0 || argv[0] === 'help' || (argv.length === 1 && (argv[0] === '--help' || argv[0] === '-h'))) {
+  if (argv[0] === 'help') {
+    const subject = argv[1];
+    return subject && isCommandName(subject)
+      ? { scope: 'command', commandName: subject }
+      : { scope: 'root' };
+  }
+  if (argv.length === 0 || (argv.length === 1 && (argv[0] === '--help' || argv[0] === '-h'))) {
     return { scope: 'root' };
   }
 
@@ -138,6 +144,12 @@ function getHelpTarget(argv: string[]): HelpTarget | undefined {
   return undefined;
 }
 
+function rewriteHelpArgv(argv: string[]): string[] {
+  if (argv[0] !== 'help') return argv;
+  const subject = argv[1];
+  return subject && isCommandName(subject) ? [subject, '--help'] : ['--help'];
+}
+
 function isCommandName(value: string): value is keyof typeof ROUTES {
   return value in ROUTES;
 }

dor/test/cli-help.test.mjs

@@ -15,6 +15,11 @@ test('help snapshots cover every command in global help', async (t) => {
 
   assert.deepEqual(await runCli([]), globalHelp, 'no-arg dor should print root help');
   assert.deepEqual(await runCli(['help']), globalHelp, 'dor help should print root help');
+  assert.deepEqual(
+    await runCli(['help', 'not-a-command']),
+    globalHelp,
+    'dor help <unknown> should print root help',
+  );
 
   await t.test('dor', async () => {
     await snapshotHelp({
@@ -26,14 +31,20 @@ test('help snapshots cover every command in global help', async (t) => {
   });
 
   for (const command of commandNames) {
+    const commandHelp = await runCli([command, '--help']);
     await t.test(`dor ${command}`, async () => {
       await snapshotHelp({
         file: command,
         title: `dor ${command}`,
         invocation: `dor ${command} --help`,
-        result: await runCli([command, '--help']),
+        result: commandHelp,
       });
     });
+    assert.deepEqual(
+      await runCli(['help', command]),
+      commandHelp,
+      `dor help ${command} should match dor ${command} --help`,
+    );
   }
 
   await assertSnapshotInventory(['dor', ...commandNames]);