Values for --unhandled-rejection flag added in v15 are not in --help (and default value is not indicated)

[glasser]

• Version: v15.12.0 (issue exists on main and has existed since v15.0.0)
• Platform: Darwin dsg-mbp 18.7.0 Darwin Kernel Version 18.7.0: Tue Nov 10 00:07:31 PST 2020; root:xnu-4903.278.51~1/RELEASE_X86_64 x86_64 (but issue is not platform-specific)
• Subsystem: src/node_options.cc

What steps will reproduce the bug?

In #33475, @dfabulich added two new legal values for --unhandled-rejection: throw and warn-with-error-code. These new values are not listed in the help string in node --help. Additionally, the help string doesn't explain which is the default value.

$ node --version
v15.12.0
$ node --help | grep -A4 unhandled-rejections
  --unhandled-rejections=...  define unhandled rejections behavior.
  Options are 'strict' (raise an error),
  'warn' (enforce warnings) or 'none'
  (silence warnings)
  --use-bundled-ca            use bundled CA store (default)
$ node --unhandled-rejections=an-unknown-value -e ''
node: invalid value for --unhandled-rejections
$ node --unhandled-rejections=throw -e ''
$ node --unhandled-rejections=warn-with-error-code -e ''

How often does it reproduce? Is there a required condition?

Always.

What is the expected behavior?

The documentation of --unhandled-rejections in --help should list all legal values or not attempt to provide a list of legal values, and it should say what the default value is.

What do you see instead?

Only strict, warn, and none, as shown above.

Additional information

I'd file a PR but I'm not sure I know how to describe the two new values in a concise way. (One option would be to remove the parenthesized explanations and just link to the docs for more details.)

[aduh95]

Maybe we could reuse the wording in the documentation: https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode
That'd be awesome if you could make a PR to fix that.

[dfabulich]

There's not gonna be a three-word explanation of throw. Here's my attempt:

Options are 'strict' (always raise an error), 'throw' (raise an error unless 'unhandledRejection' hook is set; this is the default), 'warn' (log a warning), 'none' (silence warnings), 'warn-with-error-code' (log a warning and set exit code 1 unless 'unhandledRejection' hook is set)

[glasser]

Thanks. I've filed #37899 with @dfabulich's text.