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​​2018.03.08 — Lowering Planning

​​Goals

​​

• ​​Enough structure for people to find tasks and execute on them

• ​​Figure out question around GAT

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​​Compiler data structures

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• ​​Can represent types and regions

• ​​No representation for Program Clauses

• ​​Predicate type

• ​​similar to domain goal but:

• ​​it includes binders

• ​​doesn’t have FromEnv​

• ​​Rather than re-use, we will introduce types modeled on chalk

• ​​probably into librustc_traits​ crate

• ​​enum DomainGoal​

• ​​enum Goal​

• ​​enum ProgramClause​

• ​​new rustc queries oriented around lowering that produce those data structures

• ​​program_clauses_implementing(DefId)​ — where def-id names a trait and this gives impls for that trait

• ​​program_clauses_for(DefId)​ — how is this structured?

• ​​the def-id might name a trait, impl, etc

• ​​all_program_clauses()​ root query ← probably start here for now but later refine

• ​​may want to try and avoid *this*

• ​​can start by unit testing these

• ​​#[rustc_dump_program_clause]​ attached to an item

• ​​emit to stderr or something, telling you what program clauses came out

• ​​MVP:

• ​​unit testing framework

• ​​the basic queries and types

• ​​given an impl, give back the program clauses

• ​​hold off then and have others do the rest of the rules

• ​​SLG crate interface

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​​Other work items:

• ​​universe transition and canonicalization

• ​​rental inference context thing

• ​​ InferCtxtBuilder::new().enter(|infcx| { .. })​ // only valid during this closure

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​​Moving trait selection into a query:

• ​​evaluate_obligation​ query https://github.com/rust-lang/rust/issues/48537

• ​​FulfillmentContext​ is used directly by typeck

• ​​can we make it private to librustc::traits​

• ​​maybe make a new wrapper TraitSolver​

​​

​​// in normal mode:

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​​rustc_typeck -uses-> TraitSolver -delegates-to-> FulfillmentCtxt

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