Traits working group meeting minutes

compiler traits working group
2

Triage meeting on 2019-02-24

Info

Zulip thread.

Summary

The goal of the meeting was to try and figure out, in somewhat more detail, how we want to organize the traits working group itself. We’ve been doing work on enumerating and triaging the set of things we hope to do, but in this meeting we were basically trying to come up with some concrete next steps.

Ultimately we identified the following next steps:

  • Schedule a meeting to dig into some of the lifetime problems around async-await. This is kind of an “intersecting” issue between async await and the traigs WG, but seems high priority. (nikomatsakis)
  • Explore the use cases for lazy normalization, trying to create a summary of exactly which test cases are causing problems and why, and what it might take to fix them (can it be done without a full chalk transition?). (nikomatsakis)
  • Explore the use cases for GATs, trying to find a set of specific examples from async-await and other contexts. It seems likely that we could do an initial impl of GATs in rustc without chalk, but would it be enough? (aturon, centril)
  • Schedule a meeting to dig into the chalk transition – what is current status and what are the possible future routes, what should we be exploring? (nikomatsakis, scalexm)
  • Get tests plus FCP around type Foo = impl Bar (centril)

In general, we’re trying to get a sense for what the initial set of active ‘subprojects’ will be (basically, the things that the WG is focusing on). Ideally, each of them will have a distinct “lead” (or, better, leads!) who is driving the effort (in collaboration with the rest of us).

A likely set of initial subprojects will contain:

  • some amount of hacking on rustc (GATs, lazy norm) in an effort to “relieve the pressure”
  • some amount of hacking on chalk itself and on chalk integration
  • some amount of work on defining the semantics of other features like specialization by lowering them to chalk predicates

but that is not certain. A key drive is both the set of people we have involved and also what seems to be highest priority in terms of unblocking other things within Rust.

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