build: refactor build script

[filipesilva]

Following a conversation with @benlesh, I'm taking a look at the tooling in RxJS to see where things can be simplified or removed.

I wanted to put this PR while it's still in progress to see if I'm missing important things or changing stuff I really shouldn't.

With the current changes, the dist/ folder has a slightly different layout:

/dist
├── /ajax
|  ├── LICENSE.txt
|  └── package.json
├── /fetch
|  ├── LICENSE.txt
|  └── package.json
├── /operators
|  ├── LICENSE.txt
|  └── package.json
├── /testing
|  ├── LICENSE.txt
|  └── package.json
├──/webSocket
|  ├── LICENSE.txt
|  └── package.json
├── /formats
|  ├── /cjs
|  ├── /esm2015
|  ├── /esm5
|  └── /typings
├── /bundles
|  ├── rxjs.umd.js
|  └── rxjs.umd.min.js
├── LICENSE.txt
├── package.json
└── README.md

The ajax, fetch, operators, testing, and webSocket folders remain mostly the same. They are secondary entry points and just point to the format specific files. There's no index.js in them anymore though.

{
  "name": "rxjs/ajax",
  "main": "../formats/cjs/ajax/index.js",
  "module": "../formats/esm5/ajax/index.js",
  "es2015": "../formats/esm2015/ajax/index.js",
  "typings": "../formats/typings/ajax/index.d.ts",
  "sideEffects": false
}

The formats folder contains all the different supported formats: cjs, esm2015, esm5, and typings. The UMD bundles are inside bundles. Maybe they should also be inside formats but since users do deep imports for them today, I left them in the same place.

Then there's the license, package.json and readme in the top level.

I think this format still caters to all the same consumers are before, but is simpler and requires moving less stuff around. Along the way I tried to remove scripts that weren't needed anymore. .make-packages.js is now much smaller and does all the build/packaging tasks.

I still have more scripts to look at and try to simplify but this is a start.

@benlesh (and others) please let me know what you think.

[filipesilva]

I'm not sure what to do about sourcemaps. I think the current ones are a bit weird and work only because the TS sourcefiles are bundled. We could inline sourcemaps but I'm not sure if that impacts parsing performance.

[filipesilva]

Does RxJS still need to ship TS for Bazel support? I thought this wasn't needed anymore.

[filipesilva]

Running Build Optimizer over both ESM5 and ESM2015 should enable tree shaking for both (and prevent rollup/rollup#2415).

[benlesh]

Hey, @filipesilva, this is old, and probably fell through the cracks when I left Google. I appreciate the effort, but I think we've got other solutions in place for now. Is it okay if we close this one? Or do you still see opportunity to improve what we have?

[filipesilva]

SGTM Ben, no worries at all.