set thiscontext (#2197)

Author: matthyk

typings/index.d.ts

@@ -544,7 +544,7 @@ export class Command {
    *
    * @returns `this` command for chaining
    */
-  action(fn: (...args: any[]) => void | Promise<void>): this;
+  action(fn: (this: this, ...args: any[]) => void | Promise<void>): this;
 
   /**
    * Define option with `flags`, `description`, and optional argument parsing function or `defaultValue` or both.

typings/index.test-d.ts

@@ -148,6 +148,10 @@ expectType<commander.Command>(
 // action
 expectType<commander.Command>(program.action(() => {}));
 expectType<commander.Command>(program.action(async () => {}));
+program
+  .action(function () {
+    expectType<typeof program>(this)
+  })
 
 // option
 expectType<commander.Command>(program.option('-a,--alpha'));