Suggest help when unknown command (#1179)

* Suggest help when unknown command

* Use custom help flag in message

Author: shadowspawn

index.js

@@ -1124,7 +1124,12 @@ class Command extends EventEmitter {
    */
 
   unknownCommand() {
-    const message = `error: unknown command '${this.args[0]}'`;
+    const partCommands = [this.name()];
+    for (let parentCmd = this.parent; parentCmd; parentCmd = parentCmd.parent) {
+      partCommands.unshift(parentCmd.name());
+    }
+    const fullCommand = partCommands.join(' ');
+    const message = `error: unknown command '${this.args[0]}'. See '${fullCommand} ${this._helpLongFlag}'.`;
     console.error(message);
     this._exit(1, 'commander.unknownCommand', message);
   };

tests/command.exitOverride.test.js

@@ -54,6 +54,7 @@ describe('.exitOverride and error details', () => {
   test('when specify unknown command then throw CommanderError', () => {
     const program = new commander.Command();
     program
+      .name('prog')
       .exitOverride()
       .command('sub');
 
@@ -65,7 +66,7 @@ describe('.exitOverride and error details', () => {
     }
 
     expect(consoleErrorSpy).toHaveBeenCalled();
-    expectCommanderError(caughtErr, 1, 'commander.unknownCommand', "error: unknown command 'oops'");
+    expectCommanderError(caughtErr, 1, 'commander.unknownCommand', "error: unknown command 'oops'. See 'prog --help'.");
   });
 
   // Same error as above, but with custom handler.