Support subclassing Command

[ngocdaothanh]

Currently, the return type of the methods in class Command is Command:

public command(name: string, desc?: string, opts?: commander.CommandOptions): Command;

I cannot extend Command to add more methods, like this:

class MyCommandWithUtilities extends Command {
  public util1(): this {
     // ...
     return this;
  }
}

const cmd = new MyCommandWithUtilities();
cmd
  .command('foo')
  .util1()  // Syntax error, because `command` returns `Command`, not `MyCommandWithUtilities`
  .option(...);

So, please change the return type of the methods in Command to this.

public command(name: string, desc?: string, opts?: commander.CommandOptions): this;

It seems that simply changing the definitions in index.d.ts is not enough. The main source code must also be changed.

See:
microsoft/TypeScript#4910

[ngocdaothanh]

public command(name: string, desc?: string, opts?: commander.CommandOptions): this;

It's not that simple, because the current design is to return a new Command instance, unless desc is specified; the return type is Command | this.

So to support subclassing, we need to change the design of command.

[shadowspawn]

Yes, for action handler based subcommands (no description), .command returns a new object representing the new command. (That might be doable using a factory method to create the new object, but definitely more complicated than just changing the TypeScript definition for .command.)

[ngocdaothanh]

Workaround: use a wrapper.

Example (TypeScript):

export class MyCommand {
  private readonly cmd: commander.Command;

  constructor(cmd?: commander.Command) {
    this.cmd = cmd ? cmd : new commander.Command();
  }

  public command(name: string): MyCommand {
    const cmd = this.cmd.command(name);
    return new MyCommand(cmd);
  }

  public description(desc: string): this {
    this.cmd.description(desc);
    return this;
  }

  public util1(): this {
     // ...
     return this;
  }

  ...
}

[shadowspawn]

See #1191 for work in progress which resolves this issue.