Remove optional peer dependencies

[j0k3r]

What did you implement:

When fetching peer dependencies we now remove those which are optional.

And optional dependencies can be defined using Yarn (only at the moment) when using the peerDependenciesMeta field:

"peerDependenciesMeta": {
  "peer-deps": {
    "optional": true
  }
}

I got that issue because jsdom recently added a peer dependency as optional: jsdom/jsdom#2605

The peerDependenciesMeta exist in Yarn since almost a year now: yarnpkg/yarn#6671

How did you implement it:

If the peer dependency is defined as optional, I removed it from the peer dependencies.

How can we verify it:

Build a project which contains the jsdom deps as of 15.2.0.
It'll try to fetch the canvas deps which is defined as peer dependency but optional.
You should get that error when build the package using serverless:

Serverless: Bundling with Webpack...
   XX modules
Serverless: Fetch dependency graph from /Users/jeremy/project/package.json
...
Serverless: Adding explicit peers for dependency jsdom
Serverless: WARNING: Could not determine version of module canvas
Serverless: Package lock found - Using locked versions
Serverless: Packing external modules: jsdom@^15.2.0, canvas

  Error --------------------------------------------------

  Error: yarn install --frozen-lockfile --non-interactive --ignore-scripts failed with code 1
      at ChildProcess.child.on.exitCode (/Users/jeremy/Sites/project/node_modules/serverless-webpack/lib/utils.js:92:16)
      at emitTwo (events.js:126:13)
      at ChildProcess.emit (events.js:214:7)
      at maybeClose (internal/child_process.js:925:16)
      at Process.ChildProcess._handle.onexit (internal/child_process.js:209:5)

     For debugging logs, run again after setting the "SLS_DEBUG=*" environment variable.

With that PR the optional peer dependency will be ignored:

Serverless: Bundling with Webpack...
   XX modules
Serverless: Fetch dependency graph from /Users/jeremy/project/package.json
...
Serverless: Adding explicit peers for dependency jsdom
Serverless: Skipping peers dependency canvas for dependency jsdom because it's optional
Serverless: Package lock found - Using locked versions
Serverless: Packing external modules: jsdom@^15.2.0
Serverless: Package took [3123 ms]

Todos:

• Write tests
• Write documentation
• Fix linting errors
• Make sure code coverage hasn't dropped
• Provide verification config / commands / resources
• Enable "Allow edits from maintainers" for this PR
• Update the messages below

Is this ready for review?: YES
Is it a breaking change?: NO

[miguel-a-calles-mba]

Code coverage decreased significantly.

[j0k3r]

I’ll take a look!

[j0k3r]

I force pushed to remove the merge commit from master and rebased against the master so the branch is clean and up to date.

I've also added more test to cover each scenarii: with & without optional peer deps.

I've duplicated the whole peer dependencies tests because I didn't know how to achieve same test with a different package.json.

[j0k3r]

Force pushed to make the PR up-to-date with the master branch.

Also coverage dropped because there is an issue on Travis. The Node 6 build generate a good coverage while the Node 8 build generate less coverage:

• Node 8: https://travis-ci.org/github/serverless-heaven/serverless-webpack/jobs/683232428#L523
• Node 6 https://travis-ci.org/github/serverless-heaven/serverless-webpack/jobs/683232427#L507

[j0k3r]

Rebased again from master so it's tested on Node 10 & 12.

[miguel-a-calles-mba]

@j0k3r Would you be interested in joining the Serverless Webpack team?

[j0k3r]

@miguel-a-calles-mba Sure!
I can help you manage issues & PRs from time to time