Switch to nyc, babel-plugin-istanbul & codecov-node for code coverage

[motiz88]

Q	A
Bug fix?	no
Breaking change?	no
New feature?	no
Deprecations?	no
Spec compliancy?	no
Tests added/pass?	no (well they pass)
License	MIT

The key benefit of this setup, apart from using the newer tools (same as Babylon has used for a while) is that coverage is now referenced to src/ rather than lib/, so the correct source shows up on Codecov, hopefully getting us to #1851 faster 😉

Thanks @bcoe for releasing istanbuljs-archived-repos/istanbul-lib-instrument#26 so quickly!

---

As I've mentioned on Slack - this currently causes a double build on CI, once during make bootstrap and once during make test-cov. This is not ideal and I'm hoping someone can weigh in on whether we need to build in make bootstrap at all.

[codecov-io]

Current coverage is 89.95% (diff: 100%)

Merging #4740 into master will increase coverage by 0.63%

@@             master      #4740   diff @@
==========================================
  Files           196        196           
  Lines         13784      10227   -3557   
  Methods        1434       1122    -312   
  Messages          0          0           
  Branches       3199       2691    -508   
==========================================
- Hits          12312       9200   -3112   
+ Misses         1472       1027    -445   
  Partials          0          0           

Powered by Codecov. Last update 2b6ff53...3421983

[danez]

The only big problem that we have then (and we currently also have in babylon) is that not all files show up in the reports. Only the files that are required at least once.
istanbuljs/babel-plugin-istanbul#4
So it could be that we reach 100% but still have uncovered files.

[motiz88]

@danez Oh. I think I knew about that problem and then forgot about it. Gonna have a look.

[motiz88]

Just a quick update - I'm doing some work on nyc and istanbul-lib-instrument (also been back full-circle to Babel with #4746 😄) to fix the problem @danez mentioned above. My test repo motiz88/nyc-all-demo ties everything together and has links to the gory details.

[bcoe]

@motiz88 @danez @hzoo, we've landed changes to istanbul-lib-instrument and nyc, such that --all should now work for babel-plugin-istanbul 👍

This is currently published to the next branch on npm, and I would love the extra help testing:

npm cache clear; npm i nyc@next babel-plugin-istanbul@latest

My configuration and test-script look like this, in the testing project I've been using:

cross-env NODE_ENV=test nyc --all --show-process-tree --silent mocha test/*.js

  {"babel": {
    "presets": [
      "es2015"
    ],
    "env": {
      "test": {
        "plugins": [
          "istanbul"
        ]
      }
    }
  },
  "nyc": {
    "include": [
      "src/**/*.js"
    ],
    "exclude": [
      "node_modules"
    ],
    "require": [
      "babel-register"
    ],
    "sourceMap": false,
    "instrument": false
  }}

Thanks for everyone's help and feedback regarding this feature; it will be awesome to babel using nyc, which I think will in turn help make nyc significantly better.

[bcoe]

@motiz88 @danez everything necessary to land this with --all support should now be landed;

You might find yourself wanting to fiddle with cache settings for a large codebase like this though.

[hzoo]

Merged this via #4885