[Fizz] Add FB specific streaming API and build

[sebmarkbage]

We don't have either Browser nor Node streams at FB WWW. This adds a specific ServerStreamConfig and exported API for this purpose. It's not necessarily optimal. E.g. this doesn't take advantage of back pressure, sharing buffers with the underlying sink and doesn't support TypedArrays. It's just closest to what we already have but we can iterate on this independently.

We also happen to import React with custom builds instead of npm. So I build it separately without an entry point.

It's kinds of similar to what we do with Flight for Relay so I just added it under that folder and it's flow typed under the "dom-relay" flag to avoid having too many Flow passes.

I made a new build that builds to ReactDOMServer.js but only in EXPERIMENTAL which is actually "modern" builds. So the net effect will be that ReactDOMServer.modern.js is Fizz.

I plan on moving Fizz onto the main react-dom/server export but it's difficult because we need it to export multiple builds which goes against the grain of our system atm. But the idea is to export both and then remove legacy. So this is just jumping ahead to the last step for FB.

This structure probably doesn't make much sense overall but it is what it is.

[sizebot]

Comparing: c3cb2c2...05075f7

Critical size changes

Includes critical production bundles, as well as any change greater than 2%:

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-stable/react-dom/cjs/react-dom.production.min.js	=	122.72 kB	122.72 kB	=	39.39 kB	39.39 kB
oss-experimental/react-dom/cjs/react-dom.production.min.js	=	129.30 kB	129.30 kB	=	41.47 kB	41.48 kB
facebook-www/ReactDOM-prod.classic.js	=	412.22 kB	412.22 kB	=	76.23 kB	76.24 kB
facebook-www/ReactDOM-prod.modern.js	=	400.29 kB	400.29 kB	=	74.32 kB	74.32 kB
facebook-www/ReactDOMForked-prod.classic.js	=	412.22 kB	412.22 kB	=	76.24 kB	76.24 kB
facebook-www/ReactDOMServer-prod.modern.js	+50.86%	47.54 kB	71.72 kB	+33.92%	11.06 kB	14.81 kB
facebook-www/ReactDOMServer-dev.modern.js	+38.75%	145.85 kB	202.36 kB	+27.27%	37.44 kB	47.65 kB

Significant size changes

Includes any change greater than 0.2%:

Expand to show

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
facebook-www/ReactDOMServer-prod.modern.js	+50.86%	47.54 kB	71.72 kB	+33.92%	11.06 kB	14.81 kB
facebook-www/ReactDOMServer-dev.modern.js	+38.75%	145.85 kB	202.36 kB	+27.27%	37.44 kB	47.65 kB

Generated by 🚫 dangerJS against 05075f7

[bvaughn]

I wonder how this PR was able to land given that packages/react-server-dom-relay/package.json doesn't define a files field and the build scripts seem to enforce this:

react/scripts/rollup/packaging.js

Lines 149 to 152 in 50263d3

	let files = packageJSON.files;
	if (!Array.isArray(files)) {
	throw new Error('expected all package.json files to contain a files field');
	}

The build script also throws if there's no README file, since it tries to copy unconditionally:

react/scripts/rollup/packaging.js

Lines 193 to 196 in 50263d3

	asyncCopyTo(
	`packages/${name}/README.md`,
	`build/node_modules/${name}/README.md`
	),

Are we filtering out private packages somewhere?

[sebmarkbage]

Seems we don’t get there if there wasn’t a node_modules built which there wouldn’t be for FB-only builds. Like if there’s no NODE_PROD.

react/scripts/rollup/packaging.js

Line 213 in cae6350

const builtPackageFolders = readdirSync('build/node_modules').filter(

[bvaughn]

Hm. When I build all packages locally, build/node_module includes 'react-server-dom-relay' (which is why I noticed this in the first place).