Running mocha with istanbul ignores the --use_strict option

[vitorbaptista]

I have the following structure:

test
    mocha.opts
    sum.js
package.json

mocha.opts just has --use_strict. sum.js has:

const assert = require('assert');

it('foo', () => {
  let result = 4;
  assert(2 + 2 == result);
});

In my package.json, I've added:

"scripts": {
    "test": "mocha",
    "coverage": "istanbul cover _mocha"
}

If I run npm test, everything works fine. If I run npm run coverage, I get:

> [email protected] coverage /tmp/foo
> istanbul cover _mocha

No coverage information was collected, exit without writing coverage information
/tmp/foo/test/sum.js:4
  let result = 4;
  ^^^

SyntaxError: Block-scoped declarations (let, const, function, class) not yet supported outside strict mode
    at exports.runInThisContext (vm.js:53:16)
    at Module._compile (module.js:387:25)
    at Object.Module._extensions..js (module.js:422:10)
    at Object.Module._extensions.(anonymous function) [as .js] (/tmp/foo/node_modules/istanbul/lib/hook.js:109:37)
    at Module.load (module.js:357:32)
    at Function.Module._load (module.js:314:12)
    at Module.require (module.js:367:17)
    at require (internal/module.js:16:19)
    at /tmp/foo/node_modules/mocha/lib/mocha.js:219:27
    at Array.forEach (native)
    at Mocha.loadFiles (/tmp/foo/node_modules/mocha/lib/mocha.js:216:14)
    at Mocha.run (/tmp/foo/node_modules/mocha/lib/mocha.js:468:10)
    at Object.<anonymous> (/tmp/foo/node_modules/mocha/bin/_mocha:403:18)
    at Module._compile (module.js:413:34)
    at Object.Module._extensions..js (module.js:422:10)
    at Object.Module._extensions.(anonymous function) [as .js] (/tmp/foo/node_modules/istanbul/lib/hook.js:109:37)
    at Module.load (module.js:357:32)
    at Function.Module._load (module.js:314:12)
    at Function.Module.runMain (module.js:447:10)
    at runFn (/tmp/foo/node_modules/istanbul/lib/command/common/run-with-cover.js:122:16)
    at /tmp/foo/node_modules/istanbul/lib/command/common/run-with-cover.js:251:17
    at /tmp/foo/node_modules/istanbul/lib/util/file-matcher.js:68:16
    at /tmp/foo/node_modules/async/lib/async.js:52:16
    at /tmp/foo/node_modules/async/lib/async.js:361:13
    at /tmp/foo/node_modules/async/lib/async.js:52:16
    at async.forEachOf.async.eachOf (/tmp/foo/node_modules/async/lib/async.js:236:30)
    at _asyncMap (/tmp/foo/node_modules/async/lib/async.js:355:9)
    at Object.map (/tmp/foo/node_modules/async/lib/async.js:337:20)
    at /tmp/foo/node_modules/istanbul/lib/util/file-matcher.js:44:15
    at Object.next (/tmp/foo/node_modules/fileset/lib/fileset.js:43:14)
    at emitOne (events.js:90:13)
    at Fileset.emit (events.js:182:7)
    at Fileset.Glob._finish (/tmp/foo/node_modules/glob/glob.js:172:8)
    at done (/tmp/foo/node_modules/glob/glob.js:159:12)
    at Fileset.Glob._processGlobStar2 (/tmp/foo/node_modules/glob/glob.js:601:12)
    at /tmp/foo/node_modules/glob/glob.js:590:10
    at RES (/tmp/foo/node_modules/inflight/inflight.js:23:14)
    at f (/tmp/foo/node_modules/once/once.js:17:25)
    at lstatcb_ (/tmp/foo/node_modules/glob/glob.js:491:7)
    at RES (/tmp/foo/node_modules/inflight/inflight.js:23:14)
    at f (/tmp/foo/node_modules/once/once.js:17:25)
    at FSReqWrap.oncomplete (fs.js:82:15)

I'm running [email protected] and [email protected] with NodeJS 5.5.0.

If I change my coverage script to run node --use_strict ./node_modules/.bin/istanbul cover _mocha, everything runs fine.

This seems related to #44.

[gotwarlost]

Yup, that's the correct fix. And not, it's not a bug. The way mocha works is that it accepts all sorts of options and then launches a subprocess with those options enabled for the node executable.

istanbul doesn't do any of that.

[vitorbaptista]

Fair enough. Thanks for the quick answer 👍_