Added option to load/save build diff stats

[kuldeepkeshwar]

With this developer can load the stats & save them back.

stats format:(As mentioned here)

{
  timestamp: 123456789,
  files: [
    {
     filename: 'foo/foo.a1e6f.chunk.js',
     previous: 1000,
     size: 1024,
     diff: 24
    },
    // .. etc ..
  ]
}

Example:

new SizePlugin({
  async load() {
    return JSON.parse(await someDb.get('stats'));
  },
  async save(stats) {
    await someDb.set('stats', JSON.stringify(stats));
  }
})

This should solve #15 & #6

[kuldeepkeshwar]

Seems like we have out-dated snapshots.
@developit should I update snapshots?

[developit]

@kuldeepkeshwar yup, good to update!

[kuldeepkeshwar]

By default, when Webpack runs with mode equals to production, it writes to disk(size-plugin.json).
example:

          new SizePlugin({
            filename: "stats-lock.json" // 🙃 optional, default is size-plugin.json
          })

[kuldeepkeshwar]

This also resolves #22

[kuldeepkeshwar]

@developit can you please review it

[kuldeepkeshwar]

@developit summarizing the final changes:

• options.filename: filename to save filesizes to disk, default size-plugin.json
• options.publish: option to publish filesizes to size-plugin-store, default true
• options.writeFile: option to save filesizes to disk, default true
• include deleted files in diff process.

[marvinhagemeister]

LGTM 🎉

[developit]

Only thing I think we should consider is defaulting options.publish to false. Most folks using this plugin (via other CLI's, etc) would not expect it to publish to a remote server by default.

[marvinhagemeister]

Good point, it should definitely be opt-in instead of opt-out 👍

[kuldeepkeshwar]

@developit, addressed the review comments & updated code accordingly

[kuldeepkeshwar]

@developit should we also make options.writeFile opt-in ?

[developit]

@kuldeepkeshwar Not sure on that one actually. One option here that might help simplify would be if we removed options.writeFile, and simply had options.filename trigger the writing of stats files. It could be undefined by default, which means when the user specifies filename:'xx' they get the stats file.

options.publish:true could also detect when options.filename is unset and assign it to some internal value like .size-plugin.json since it needs that file on disk.

[kuldeepkeshwar]

@developit, can we merge this? let me know if you have other thoughts in mind.