Invert dependency between core and readable-stream

00X-streams.md

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+| Title  | Invert dependency of readable-stream |
+|--------|--------------------------------------|
+| Author | @mcollina                            |
+| Status | DRAFT                                |
+| Date   | 2017-01-26 12:00:00                  |
+
+## Description
+
+The `readable-stream` module is one of the most popular modules on NPM,
+with 33 million downloads per month. `readable-stream` is the basis of
+most of the ecosystem utilities for manipulating streams, as it provides
+a consistent API across all the different versions of Node.js and the
+browser: from Node.js v0.8, and IE 9 and Safari 5 as the oldest browsers.
+
+`readable-stream` was introduced to help module authors build the
+streams ecosystem across the different versions of Node.js, backporting
+v0.10 streams to v0.8.
+The code for the `'stream'` module in core *depends on the version of
+core* that is being used, and because streams users inherits from
+classes like `Readable`, `Writable` or `Transform` a tiny difference
+might make a program work on a version of Node but not in another.
+Module authors appreciate the stability `readable-stream` provides,
+and it is currently in the dependency tree of gulp, mysql, mongodb, webpack
+and many other highly-popular libraries.
+A good article for what `readable-stream` provides can be found at
+https://r.va.gg/2014/06/why-i-dont-use-nodes-core-stream-module.html.
+
+`readable-stream` is an export of the latest stream API from the Node.js,
+done via a mixture of babel transpiling and regular expressions. The export
+means that `readable-stream` has to follow the Node.js release cycle, and it
+is not versioned independently. Specifically, versioning of `readable-stream`
+is extremely hard, as *we are currently not bumping major*
+to avoid breaking many packages and maintaining multiple lines. The current
+situation is not ideal, as `readable-stream` passively follows what is merged
+in Node.js.
+
+At the moment `readable-stream` does not have its own documentation, it is the
+documentation of whichever version of Node.js is built from. This creates confusion,
+as the latest `stream` from Node.js supports some features that cannot be ported
+to all versions of Node.js.
+
+This EP proposes to invert that dependency, and have Node.js include
+readable-stream from the `deps` folder.
+
+## SEMVER for streams
+
+As things stands right now, `readable-stream` support Node.js from v0.8
+upwards, and fairly ancient browsers versions as well. Because of this,
+we are currently using babel (and a bunch of regexps) before release,
+to support ES5-based vendors. Dropping support for any of those is a
+semver-major change, and given the massive amount of dependencies, it
+might have a semver-major ripple effect throughout the ecosystem.
+In order to avoid a lot of work for maintainers, we aim to minimize those.
+At the time of this writing, we plan __not to bump__ semver-major in 2017.
+
+We recognize that the ecosystem is changing at a fast pace, and at some
+point we would have to bump the major. If we decide to do that, we would
+have to manage two release lines (or more), and backport changes from
+Node.js streams to **both**. As things are now, this is highly
+impractical to do, and it would be much easier to manage if `readable-streams`
+could manage its own versioning.
+
+## Process / Timeline
+
+1. move the code of streams into `readable-stream`
+2. amend the build script for the NPM/ecosystem build
+3. rewrite the tests to easily check against both the node
+   source folder and old versions of Node.js and the browser.
+4. port the Node streams documentation to `readable-stream`; a _copy_
+   of the docs will be maintained in Node.js.
+4. merge back all changes that happened in the meanwhile, and sync up
+5. add `nodejs/readable-stream` inside deps of Node.js, and remove the streams
+   implementation; to avoid any possible disruption, this will be a
+   _semver-major_ change for Node.js.
+6. bump *minor* version of `readable-stream`.
+
+## Challenges
+
+1. export git history from node.js
+2. handling issues between the two repositories
+
+These challenges need to be adressed with the rest of the node collaborators.
+
+## Role of the Streams WG
+
+The Streams Working Group will still be responsible for maintaining
+`readable-stream` and `'streams'` in core, and this EP does not change
+anything. However, the role of `readable-stream` is to
+`'port stream to older node versions and browsers'`, while after the
+inversion of dependency, it would change to `'support Node.js streams in
+throughout the different versions of Node and browsers'`.
+As it is right now, the Streams WG commits in maintaining the
+performance of streams within Node.js.
+
+## Target version of Node
+
+We think we should target this to be shipped in Node 8.