Document how to use --harmony* flags with _mocha

[BrandonZacharie]

I expect these flags to work because

➜ node_modules/.bin/_mocha --help               

  ...

  Options:

    ...
    --harmony<_classes,_generators,...>     all node --harmony* flags are available

However, as of

➜ node_modules/.bin/_mocha --version
3.2.0

I get

➜ node_modules/.bin/_mocha --harmony_async_await

  error: unknown option `--harmony_async_await'

[ScottFreeCode]

I'm not sure off the top of my head whether there's a way to give mocha and _mocha separate help messages. I am fairly sure that the main reason for the two separate files is specifically so that mocha can pass the Node flags (such as --harmony*) to Node while calling the actual _mocha under the hood. This would presumably be improved/fixed by #2517... Or, depending on why you're using _mocha, we may be able to figure out how to call it so as to get the --harmony* flags to Node directly, rather than sending them through Mocha at all.

[BrandonZacharie]

If there's any other way to get --harmony_async_await working, i'm for it. I'm using _mocha with istanbul.

[ScottFreeCode]

Does node --harmony_async_await node_modules/istanbul/lib/cli.js <command> node_modules/mocha/bin/_mocha still work? (Found here: gotwarlost/istanbul#44 (comment) the next thing after that on google is https://www.npmjs.com/package/istanbul-harmony...)

[BrandonZacharie]

➜ node --harmony_async_await node_modules/.bin/istanbul cover node_modules/.bin/_mocha
node_modules/mocha/lib/mocha.js:79
  this.files = [];
             ^

TypeError: Cannot set property 'files' of undefined
    at Mocha (node_modules/mocha/lib/mocha.js:79:14)
    at Object.<anonymous> (test/index.js:10:13)
    at Module._compile (module.js:571:32)
    at Object.Module._extensions..js (module.js:580:10)
    at Object.Module._extensions.(anonymous function) [as .js] (node_modules/istanbul/lib/hook.js:109:37)
    ...

[BrandonZacharie]

I think I understand now... I tried your script on other repos that use istanbul and it worked perfectly. The one i'm working with now spills out a bunch of errors like

Transformation error; return original code
{ Error: Line 26: Unexpected token =>
    at constructError (node_modules/esprima/esprima.js:2407:21)
    at createError (node_modules/esprima/esprima.js:2426:17)
    at unexpectedTokenError (node_modules/esprima/esprima.js:2500:13)
    ...
  lineNumber: 26,
  description: 'Unexpected token =>',
  index: 560 }

I believe this is related to istanbul and ES8 syntax. The others that tested fine with your script, like this one, only use ES6 syntax.

With that said, I think it would still be A Good Idea™ to go forward with #2517 and maybe document this workaround somewhere in the meantime.

[ScottFreeCode]

With that said, I think it would still be A Good Idea™ to go forward with #2517 and maybe document this workaround somewhere in the meantime.

Yeah, I'm a little surprised myself that it's this tricky, so we should definitely document this until we can test that #2517 doesn't break anything (depending on how it works, it might have the same problem running Istanbul as using mocha rather than _mocha does now...). Since we've got issue #2517 to track the potential simplification, mind if we use this ticket to track the lack of documentation for the workaround?

[BrandonZacharie]

Sounds good. On that note, is the Wiki the appropriate place to put something like this? If so, maybe we could add a Known Issues section and put this there.

[ScottFreeCode]

It should be in theory, but I don't know how up to date it is.

[Munter]

@BrandonZacharie You might have better luck with using nyc for code coverage rather than istanbul

[sabakugaara]

I just use node --harmony ./node_modules/.bin/istanbul cover ./node_modules/.bin/_mocha -- tests/*, it works well

istanbul ^1.0.0-alpha.2
mocha ^3.2.0

[juergba]

The _mocha executable does not support Node flags and there are no plans to do so in future.

You have two options:

• use the mocha executable which detects the Node flags and spawns a child-process.
• pass the Node flags directly to Node (not via Mocha) as shown above by @sabakugaara

see docu