Commander unsafely allows commands with duplicate `name`s to be registered

[huntie]

We ran into an issue recently in a project that depends on commander, which dynamically defines commands based on plugins. Commander's internal array data structure for commands, and the Array.find based lookup on name, meant that repeat calls to command() produced unexpected behaviour (the most recent call does not redeclare the command).

At minimum, I believe this should error.

• breaking: Fix ability to override commands via config react-native-community/cli#1999

Example

const { Command } = require('commander');
const program = new Command();
program.command('split').action((str, options) => console.log('1st'));
program.command('split').action((str, options) => console.log('2nd'));
program.parse();

Output will always be the first.

$ node example
Usage: example [options] [command]
Options:
  -h, --help      display help for command
Commands:
  split
  split
  help [command]  display help for command
$ node example split
1st

Expectation

Shouldn't allow duplicates and should throw an exception if a name already exists.

[shadowspawn]

Commander does not have tests for all possible mistakes/accidental-misuse by the "author", but willing to consider more as they come up. Mixing in plugins does make it possible for the issue to come up for the end-user rather than for the author as such.

The duplicate primary name does have a dubious outcome. I am less worried about aliases clashing, but could perhaps actually handle this and ignore clashing alias when command is added.

[aweebit]

Opened #1924 with a fix.

[shadowspawn]

Reworked PR in #2059.

[shadowspawn]

Released in Commander v12.0.0.