Distributing a library with es6-* deps without requiring users to install typings

[alexeagle]

Had a ts-typings slack conversation with @mhegazy just now, regarding angular2 changing our typings to stop polluting the type-checker with our dependencies.
(details on that change: https://docs.google.com/document/d/1vgepQPkuHS4P3rzANQpoMIDIXe0Rl9Z2QyTtb8dpMoI/edit# )

While correct, this makes the getting started experience worse for Angular 2 users (many of whom are new to TypeScript and even JavaScript).

The major stumbling block is our dependency on es6-promise and es6-collections. For users with --target=es5 (the majority and default case), they need these two .d.ts files presented to the compiler. When --target=es6, we must avoid Duplicate identifier errors. We would prefer not to have the typings tool involved in our first five minutes, since we may lose some audience from the complexity and possibility of a mistake ruining their first app.

To make it really seamless we need two things:

• If the user has a dependency on angular2, we want the compiler to add es6-promise and es6-collections typings. Imagine if angular2/package.json could declare "ambientTypingsDependencies": ["es6-promise","es6-collections"]. (We don't care what the right-hand side means - it could mean any typing discoverable by typings search but that has versioning issues. It should probably instead be done by splitting lib.es6.d.ts in the TypeScript distro into smaller files, then the option "typingDeps":["XXX"] causes reference to lib.XXX.d.ts and this does not become a general-purpose mechanism. This is really similar to --target=es5+es6-promise+es6-collections except that the user doesn't need to specify it, rather it appears via the dependency on angular2)
• No Duplicate identifier errors based on the --target setting. This could be either a fix for New APIs added to lib.d.ts may break client codes. Allow duplicated members in interfaces? Make lib.d.ts overridable? #3215, or else avoiding the addition of those typings for --target=es6, maybe with something like "typingsDependencies__ButEs5Only": ["es6-promise","es6-collections"]

[alexeagle]

Another detail here: you should start putting together the parts of lib.es7.d.ts - we should be able to depend on es7-reflect-metadata this way rather than an external channel for distribution.

cc @IgorMinar

[mhegazy]

Just a quick note, it is not ES7/ES2016 now. Only proposals at stage 4 can make it to the ES7 train at this point, so it is got to be ES8+.

[mhegazy]

Should be addressed by #9851

[RyanCavanaugh]

This is implemented as much as we know how to with /// <reference lib= directives