Regression in output of an error throw by a -r module throws (within yargs)

[alexjeffburke]

Prerequisites

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Description

When a module loaded with -r throws in the current version of mocha 7, the call made to yargs.showHelp() after the error is printed (https://github.com/mochajs/mocha/blob/v7.2.0/lib/cli/cli.js#L53) seems to throw with the following stack trace:

(node:10708) UnhandledPromiseRejectionWarning: TypeError: Cannot convert undefined or null to object
    at Function.keys (<anonymous>)
    at Object.help (/path/to/mocha-dominate/node_modules/mocha/node_modules/yargs/lib/usage.js:242:22)
    at Object.self.showHelp (/path/to/mocha-dominate/node_modules/mocha/node_modules/yargs/lib/usage.js:434:15)
    at Array.yargs.scriptName.command.command.updateStrings.fail (/path/to/mocha-dominate/node_modules/mocha/lib/cli/cli.js:54:13)
    at Object.fail (/path/to/mocha-dominate/node_modules/mocha/node_modules/yargs/lib/usage.js:41:17)
    at handlerResult.catch.error (/path/to/mocha-dominate/node_modules/mocha/node_modules/yargs/lib/command.js:246:36)
    at process._tickCallback (internal/process/next_tick.js:68:7)
    at Function.Module.runMain (internal/modules/cjs/loader.js:834:11)
    at findNodeScript.then.existing (/Users/alex/.nvm/versions/node/v10.19.0/lib/node_modules/npm/node_modules/libnpx/index.js:268:14)

Having looked into the yargs code at line 240 in yargs/lib/usage.js mentioned above, the problem seems to be that at this point yargs.parsed is false, which means the dereference of newAliases returns undefined and then Object.keys() wrapped around it throws a null or undefined error.

Steps to Reproduce

This error can be reproducued by saving the following in a file called "thrower.js":

throw new Error('some error');

and mocha executed as follows:

npx mocha -r ./thrower.js

Expected behavior:
The error thrown by the require hook is printed to the console.

Actual behavior:
Before the error can be thrown an internal error is created from within yargs.
Reproduces how often: [What percentage of the time does it reproduce?]
This is consistently reproducible.

Versions

Mocha version 7.2.0

[boneskull]

sorry got confused. #4311

[boneskull]

duplicate of #4310

[boneskull]

a fix will land in v8.0.0

[alexjeffburke]

@boneskull thanks for looking at this - did look around for other issues but didn't quite make the connection this would be solved by the one you linked to.

Btw, this came up when I was trying to port a mocha plugin to the new exports.mochaHooks = {} mechanism. It does some validation and throws when things are out of whack which is how I stumbled on this. But this aside, hooks worked really well and looks like it will be very useful :)

[boneskull]

@alexjeffburke Thanks for the kind words. Yes, this was kind of buried (the fix landed as part of something else), so I don't fault you for not being able to find it.