Implement "Control Flow Collections"

[munificent]

The "Control Flow Collections" proposal (#78) has been accepted and is being implemented (yay!). This is the parent issue to track all of the specific issues for implementing the feature across various tools and libraries.

Phase 0: Prerequisite

• Experimental flag
• Language tests

Phase 1: Foundation

• Implementation in CFE/Kernel (CFE: Implement "Control Flow Collections" sdk#36333)
• Implementation in analyzer (Analyzer: control flow collections phase 1 sdk#35566)

Phase 2: Tool implementation

• Implementation in dart2js (dart2js backend support for spreads and control flow features [meta bug] sdk#36313)
• Implementation in dartdevc (dartdevc: Implement "Control Flow Collections" sdk#36005)
• Implementation in dartfmt (Implement control flow collections dart_style#779)
• Implementation in IntelliJ (TODO)
• Implementation in Grok (TODO)
• Implementation in analyzer (Analyzer: control flow collections phase 2 sdk#35567)
• Implementation in Atom plugin (TODO)
• Implementation in VM (VM: Implement "Control Flow Collections" sdk#36214)
• Co19 tests
• Usability validation

Phase 3: Release

• Enable (TODO)
• Use in SDK and team-maintained packages (TODO)
• Documentation (https://medium.com/dartlang/making-dart-a-better-language-for-ui-f1ccaf9f546c)

Phase 4: Clean-up

• Remove flag (TODO)

[munificent]

dartfmt support is landed in the dart_style repo, but not published and rolled into the SDK yet. I'll do that once, I can upgrade it to analyzer 0.36.0.

[leafpetersen]

Is this complete? Can we close this?

[natebosch]

Is this complete? Can we close this?

I don't think so: One of the steps is use in the SDK and/or team owned packages. Can you point to a usage?

We also need to add a step to validate behavior in codegen like angular. That is currently broken. Where is the template for these issues so I can add a step?

[natebosch]

The template has mentioned angular since August 2018. This issue was filed in January.

Why didn't we use the template?
If we did use the template, why did we delete the angular step?

[munificent]

I probably copy/pasted from an existing bug instead of from the template. I may not have known we even had the template. Sorry.

[munificent]

This has shipped!