nyc trying to cover babel plugin even though it's excluded via config

[NiGhTTraX]

In a project that uses babel-istanbul and babel-register AND a custom babel plugin, nyc instruments the custom plugin even though it's in a folder excluded from coverage via .nycrc:exclude.

Expected Behavior

100% coverage on src/foobar.js and nothing else because nyc is set to exclude the tests/ folder which includes the babel-plugin defined in .babelrc.

Observed Behavior

Bonus Points! Code (or Repository) that Reproduces Issue

https://github.com/NiGhTTraX/nyc-exclude-bug

{
  "include": [
    "src/**/*.js"
  ],
  "exclude": [
    "tests/**/*.js"
  ],
  "all": true,

  "sourceMap": false,
  "instrument": false,

  "reporter": ["html"],
  "report-dir": "tests/unit/results/coverage",

  "lines": 100,
  "branches": 100,
  "check-coverage": true
}

Forensic Information

Operating System: Ubuntu 16.04
Environment Information:

Node: v6.9.5
npm: 3.10.10

[bcoe]

@NiGhTTraX thanks for the great reproduction, and sorry for the slow reply have been trying to gradually catch up on old GitHub issues.

I did a tiny bit of digging using your example repo, and the issue seems to be an interaction between the exclude rules and he --all functionality. My hunch is that the walk of files that takes place during the --all step isn't having the include and exclude rules applied.

If you feel like contributing to the project, this is probably a pretty straight forward fix; I think it will be in nyc/index.js.

[NiGhTTraX]

So I found the real problem: the plugin is instrumented by babel-plugin-istanbul when it's required by Babel while transpiling a source file with babel-register. Deep breath. Here's how it happens:

1. if (config.all) nyc.addAllFiles() - entry point for when all: true
2. glob.sync(pattern, {cwd: dir, nodir: true, ignore: this.exclude.exclude}) - this correctly excludes the plugin; let's assume that it emits todo.jsx for now
3. NYC.prototype._readTranspiledSource requires the source file
4. babel-register handler will pick the require and compile it
5. Doing so it will apply the plugins in .babelrc over it
6. my-custom-babel-plugin is part of .babelrc so Babel will fetch it by doing a require call
7. babel-register sees that require and tries to compile the plugin
8. It will again use the plugins in .babelrc
9. At this point babel-plugin-istanbul will instrument my-custom-babel-plugin
10. That instrumented plugin will report coverage to nyc

So yeah, not really a nyc bug. Maybe babel-plugin-istanbul could read the same excludes and bail out if it's attempting to instrument an excluded file?

#649 would work around the problem, but I'd like to have the code not emit coverage reports in case other tools will read it instead of nyc.

A foolproof workaround is to put the plugin in a separate folder and add a .babelrc there that removes babel-plugin-istanbul. This is the solution I've went with and it's working as expected. I had to duplicate the .babelrc file, but eh...