Enable loose transformation for object spread operator to improve per…

[wurstbonbon]

Problem

Upgrading to babel 7 has significantly worsened the normalization performance, which is part of the reason for https://github.com/paularmstrong/normalizr/issues/383. With Babel 7 the transpilation of the spread operator changed from a simple Object.assign to a more complicate logic https://babeljs.io/docs/en/v7-migration#babel-plugin-proposal-object-rest-spread. Spreading is used as processStrategy and mergeStrategy which became a lot more expensive.

Solution

Enable "loose" transformation for object spreading.

Performance comparison

Setup

const mySchema = new schema.Entity('tacos');
const data = [];
for (let i = 0; i < N; i++) {
  data.push({ id: i, type: `foo-${i}` });
}
normalize(data, [mySchema]);

Normalization times in milliseconds for 5 runs

N = 10,000 entities
current	27	22	22	22	21
loose transformation	17	9	11	9	12

N = 100,000 entities
current	210	201	200	200	198
loose transformation	97	111	97	97	94

TODO

• Add & update tests
• Ensure CI is passing (lint, tests, flow)
• Update relevant documentation

[coveralls]

Coverage remained the same at 100.0% when pulling 8a2eaaa on wurstbonbon:babel-spread into 3df7d07 on paularmstrong:master.

[paularmstrong]

🎉 Thanks @wurstbonbon @ntucker

[wurstbonbon]

@paularmstrong Any chance to get this released soon?