wg-traits meeting agenda and dev log

Instructions

During the week, find the section for the upcoming meeting. Add into the "Log of notable events" any interesting things that you did – PRs opened, notes made, problems encountered. Then add to the Agenda possible topics for focused discussion. During the meeting we'll focus on some of the agenda items, and we'll add a link to the Zulip topic so you can read the details.

Current sprint

The current sprint runs from 2020.05.26 to 2020.07.07. You can find our sprint goals here.

Upcoming meeting topics

Previous meeting topics

[2021.03.30]

Type library and planning

[2020.10.20]

To discuss

In progress work
- Binder refactor (rust#76814)
- ~~Binder map_bound_ref (rust#77685)~~
- TyKind -> TyData (rust#77768)
- Subtyping/variance (chalk#609)
- Sem/syn equality (chalk#589)
- Const evaluation (chalk#596)

[2020.09.29]

To discuss

Issue #77187: What do we need to do for >1 type parameters on fundamental types?
Issue #76814: Is it potentially worth it to have a prelim PR that adds a rebind function to Binder?
- dummy: adds a level of binding without allowing capturing escaping vars (enforced)
- bind: potentially captures escaping vars
- rebind: (potentially) recaptures escaping vars
  - would rather use map/map_ref, but this isn't possible in a lot of cases currently
- wrap_nonbinding: adds a level of binding, shifting vars to avoid captures
Design meeting: Wellformed

Action items

Open issue for coherence rules with >1 param (Jack)
Open PR to import coherence doc into book (Jack)
Open PR for new coherence rules with >1 param (anyone, Jack)
Prepare discussion points for WF design meeting (Jack)
Post a summary of Kind changes to MCP topic (Jack)

[2020.09.22]

Topic: placeholder canonicalization

[2020.09.15]

Action Items

File issue for adding ReStatic (Jack)
Review conversation on placeholder canonicalization (Niko, all)

2020.09.08

Meeting notes

Sprint planning
- https://hackmd.io/s1MfBn4bRjyir-aqHZzbKQ

2020.09.01

Action Items

Review Chalk upgrade PR (#75173) (Niko)
Add rustc-chalk integration tracking issue (Jack)
Elaborate on opaque types WF w/ implied bounds (detrumi)
File issue for auto and builtin traits with builtin types (Jack)
Update well known traits table for closures extern types (Jack)
Update skill tree (Niko)

Meeting notes

Catching up from the summer
- chalk/rustc integration (no issue)
  - rust#75173 – needs review
  - next steps:
    - variance
    - placeholder canonicalization
    - params
- chalk-ty lib extraction (rust-lang/wg-traits#16)
  - rust#75077 – basically ready to land, but blocked on the question of whether to return &TyKind; we hit some complications trying to do so
- builtin traits (rust-lang/chalk#363)
  - need Unpin, CoerceUnsied, DispatchFromDyn
- builtin types([rust-lang/chalk#368])
  * generators (chalk#593) and extern types
- recursive solver
- opaque types (tracking issue)
  - chalk#559 – needs tests fixed so it can be merged
  - chalk#579 – waiting for r+
- auto traits with builtin types
  - good starter issue
- builtin traits with builtin types
- sem-syn inequality
  - pending PR chalk#589 but causes some perf regressions in rust-analyzer that will require investigation
- variance and subtyping
  - chalk#520 – needs some testing

2020.06.02

Notes from meeting

chalk 0.11.0 was published last week
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also some crate structure refactors
some talk about making the solver more parallel
opaque types are getting close
discussion on subtyping, variance

2020.05.26

Agenda and possible topics

Possible future meeting topics
- implied bounds – continuing from last meeting
- how to manage consts in chalk writer
- shared type library next steps
- wf checks on types
- chalk's support for coherence

2020.05.12

Agenda and possible topics

Minutes updating on rust-lang/wg-traits (last is 2020.03.03)
- Will also close meeting issues
Sprint overview
- Blog post?
Next sprint planning

Log of notable events, please feel free to add

rustc Chalk integration MVP PR landed

2020.05.05

Agenda and possible topics

Decide on the approach for dealing with const types
ObjectSafe(Trait)

Log of notable events, please feel free to add

2020.04.28

Agenda and possible topics

Sprint progress - 2 weeks left
Release?
Mdbook linkcheck - should we block
from_fallible on Interner list-like types
Implied bounds

2020.04.21

Agenda and possible topics

Design meeting: discuss implied bounds (tracking issue)

Log of notable events, please feel free to add

The recursive solver was added as an alternative to the existing solver
Basic support for impl Trait landed
Added support for the Copy, Clone and Drop traits
The new-style trait solving chapter was moved from rustc-dev-guide to the chalk book

2020.04.14

Agenda and possible topics

crate.io release
Where should "builtin" types go? chalk-ir or chalk-rust-ir? (#368 and #371)
- If in chalk-rust-ir, chalk_ir::ApplicationType.name would have to an associated type on Interner. And then chalk_solve would have to have some way to constrain this for a fixed set of types.
rustc integration
- RegionOutlives, TypeOutlives
  - We need some way to register Constraints.
  - LifetimeEq -> Outlives?
- Subtype
  - What to do here? How do we handle super traits currently?
State of "old" PRs
Not enough sprint issues for the many new contributors

Log of notable events, please feel free to add

8 PRs merged (11 if you include those merged last Tuesday)
- 11(!) open now too

2020.04.07

Agenda and possible topics

Discuss what to do about const generics (tracking issue)

Notes from meeting

created hackmd with notes

Log of notable events, please feel free to add

rustc integration is getting close
many Chalk PRs in a lot of areas
- extending TypeName
- built-in traits like Sized, Drop, Copy, and Clone
- adding a Visitor
- an open PR for the recursive solver
- impl Trait
Progress towards leak check removal in rustc

2020.03.31

Agenda and possible topics

We discussed the sprint goals, got into more details, and enumerated planned meetings

Notes from meeting

Log of notable events, please feel free to add

Sprint start
Landed PR to count binders, not variables
Landed initial work on builtin traits
Landed stopgap measure for builtin traits

2020.03.24

Agenda and possible topics

Sprint is over - retrospective
Next sprint - March 31st to May 12th?
- Goals/Topic
  - Goal: Rustc integration MVP
    - In this version:
      - rustc types are converted to chalk types deeply and eagerly
      - region integration is basically ignored, so not sound
      - chalk is responsible for generating builtin trait rules, and those may be approximated in some cases
      - constants are not handled, they are translated to () type for now
      - closures and the fn traits are "reach items"
      - unsizing is out of scope
    - Work items (required):
      - Write code to eagerly, deeply convert rustc types to chalk types
      - Define builtin traits mechanism
        
        Implement rules for Sized
        
        Implement rules for Clone
        
        Implement rules for Copy
      - Some kind of interim solution *Outlives and Subtype
      - Land Jack's branch :)
    - Work items (reach):
      - Implement rules for Fn traits as applied to fn-def and closures
  - Goal: Plan for what const integration looks like
    - Hold a design meeting, or multiple
  - Goal: Move towards alignment of rustc and chalk types, and towards extracting a shared library
    - Adopt "count binder"-style debruijn indices (in progress, carried over)
    - Adapt rustc to support binder lists and (perhaps) indices in late-bound regions (discussion)
    - Extend chalk with types like Rustc's FnDef and Closure
    - In some order:
      - Adapt rustc to use ty.kind(tcx) instead of ty.kind
      - Align names of rustc and chalk types (eg., GenericArg)
      - Extract or identify items from rustc that would ultimately live in the new library
  - Goal: basic support for impl Trait
    - Land existing PR
    - Accomodatic generic opaque types fully
    - Lazy access of hidden type
    - Well-formedness rules for opaque types
  - Goal: progress towards removing leak check in rustc
    - Next step: extend NLL solver with the notion of
  - Goal: exploration and research
    - exploring recursive solver (flodiebold)
    - explore converting semantic-to-syntactic equality
    - create a chalk file from any given program
  - Goal: increase Chalk performance (very open-ended)
    - Create a set of benchmarks
    - Add tracing support (in progress)
    - Track memory usage and try to decrease as necessary
    - Creating a .chalk from a given program for reproducing
See https://rust-lang.zulipchat.com/#narrow/stream/144729-wg-traits/topic/.22skill.20tree.22/near/190652842 to add to skill-tree?
rustc integration: TypeOutlives, RegionOutlives, Subtype
- *Outlives are WhereClause variants, Subtype is GoalKind
Possible issue with any_future_answer/MayInvalidate: https://github.com/rust-lang/chalk/pull/331

Log of notable events, please feel free to add

Niko pushed more on debruijn branch, making some progress

2020.03.17

Agenda and possible topics

Design meeting of compiler to discuss extracting a rust-ty library – nikomatsakis
- How does this work interact with this group? Maybe a good thing for next sprint
Rustc integration blocking items (for next sprint?)
- Sized and other built-in Traits
- Fn and closures
Next sprint planning?

Notes from meeting

Ongoing things from this sprint

modeling impl Trait
making the Interner a value that gets passed around (probably.. 75% done)
exploring the recursive solver (yay @Florian Diebold)
exploring rustc integration (the most nebuluous, but we've definitely made progress)
tracing (added:)

Discussing next sprint topics

Goal: extending the interner data methods to have &self
- yaahc has made great progress here, we need to land and maybe tweak it
Goal: implement the "builtin traits"
Possible goal: rustc refactors to move closer to chalk-ir model
- e.g., ty.kind to ty.kind(tcx)
Goal: continue exploration of recursive solver
- flodiebold has made great progress here
Goal: explore equivalence edges
Goal: move to tracing
Possible goal: refactor NLL solver in rustc to further the work in removing the leak check (is this really wg-traits?? maybe not. –niko)
Goal: complete the chalk part of impl Trait modeling
- i.e., given that some other layer is managing the inference of the hidden type

Log of notable events, please feel free to add

Niko updated a gist exploring how to the "debruijn index" question
Niko was updating roadmap slightly to account for function/closure types, which are baked into rustc's trait matching just a it

2020.03.10

Agenda and possible topics

Design meeting of compiler to discuss extracting a rust-ty library – nikomatsakis
- How does this work interact with this group? Maybe a good thing for next sprint
How to handle debruijn and type parameter indexing? – nikomatsakis
- building on the gist that I wrote, I'm not sure what to do
Expected pattern for integrating impl Trait into rust-analyzer etc – nikomatsakis
- I'd like to understand better what detrumi + flodiebold were discussing – nikomatsakis
rustc integration: TypeOutlives, RegionOutlives, Subtype

Log of notable events, please feel free to add

yaahc made a number of PRs related to chalk#340, adding &self to all the other interning methods besides typing
yaahc opened a "WIP" PR
flodiebold resurrected the recursive trait solver from older versions of chalk
flodiebold + detrumi explored integration of impl Trait into rust-analyzer
nikomatsakis pursued debruijn interation and encountered some questions, started writing a gist that explains how things work today
- goal is to eventually produce a proposal :)

Syntax	Example	Reference
# Header	Header	基本排版
- Unordered List	Unordered List
1. Ordered List	Ordered List
- [ ] Todo List	Todo List
> Blockquote	Blockquote
Bold font	Bold font
Italics font	Italics font
~~Strikethrough~~	~~Strikethrough~~
19^th^	19^th
H~2~O	H₂O
++Inserted text++	Inserted text
==Marked text==	Marked text
[link text](https:// "title")	Link
![image alt](https:// "title")	Image
`Code`	`Code`	在筆記中貼入程式碼
```javascript var i = 0; ```	`var i = 0;`	在筆記中貼入程式碼
:smile:		Emoji list
{%youtube youtube_id %}	Externals
$L^aT_eX$	L^aT_eX
:::info This is a alert area. :::	This is a alert area.