fix(command): help callback not working with global options and comma…

…nds (#149)

command/command.ts

@@ -69,6 +69,8 @@ interface IDefaultOption<O = any, A extends Array<any> = any> {
 
 type ITypeMap = Map<string, IType>;
 
+type IHelpHandler = (this: Command) => string;
+
 // deno-lint-ignore no-explicit-any
 export class Command<O = any, A extends Array<any> = any> {
   private types: ITypeMap = new Map<string, IType>([
@@ -106,7 +108,7 @@ export class Command<O = any, A extends Array<any> = any> {
   private hasDefaults = false;
   private _versionOption?: IDefaultOption<O, A> | false;
   private _helpOption?: IDefaultOption<O, A> | false;
-  private _help?: (this: Command<O, A>) => string;
+  private _help?: IHelpHandler;
 
   /** Disable version option. */
   public versionOption(enable: false): this;
@@ -1163,7 +1165,12 @@ export class Command<O = any, A extends Array<any> = any> {
   /** Get generated help. */
   public getHelp(): string {
     this.registerDefaults();
-    return (this._help!)();
+    return this.getHelpHandler().call(this);
+  }
+
+  /** Get generated help. */
+  private getHelpHandler(): IHelpHandler {
+    return this._help ?? this._parent?.getHelpHandler() as IHelpHandler;
   }
 
   /*****************************************************************************

command/test/command/help_test.ts

@@ -0,0 +1,36 @@
+import { assertEquals } from "../../../dev_deps.ts";
+import { Command } from "../../command.ts";
+
+Deno.test("command help handler", () => {
+  const cmd = new Command()
+    .throwErrors()
+    .name("main")
+    .help(function () {
+      return `help: ${this.getName()}`;
+    })
+    .command("foo")
+    .command("bar")
+    .reset();
+
+  assertEquals(cmd.getHelp(), "help: main");
+  assertEquals(cmd.getCommand("foo")?.getHelp(), "help: foo");
+  assertEquals(cmd.getCommand("bar")?.getHelp(), "help: bar");
+});
+
+Deno.test("command help handler override", () => {
+  const cmd = new Command()
+    .throwErrors()
+    .name("main")
+    .help(function () {
+      return `help: ${this.getName()}`;
+    })
+    .command("foo")
+    .help(`foo help`)
+    .command("bar")
+    .help(() => `bar help`)
+    .reset();
+
+  assertEquals(cmd.getHelp(), "help: main");
+  assertEquals(cmd.getCommand("foo")?.getHelp(), "foo help");
+  assertEquals(cmd.getCommand("bar")?.getHelp(), "bar help");
+});