mirror
/
rustc-dev-guide
mirror of https://github.com/rust-lang/rustc-dev-guide.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

add names to the trait lowering rules 

This allows cross-references from the code.
This commit is contained in:
Niko Matsakis 2018-03-15 14:26:09 -04:00 committed by Who? Me?!
parent 80fa5ad68d
commit 7dea4167cf
1 changed files with 21 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

21
src/traits-lowering-rules.md
View File

@ -20,6 +20,16 @@ the [notation given in this section](./traits-goals-and-clauses.html).
We sometimes insert "macros" like `LowerWhereClause!` into these We sometimes insert "macros" like `LowerWhereClause!` into these
definitions; these macros reference other sections within this chapter. definitions; these macros reference other sections within this chapter.
## Rule names and cross-references
Each of these lowering rules is given a name, documented with a
comment like so:
// Rule Foo-Bar-Baz
you can also search through the `librustc_traits` crate in rustc
to find the corresponding rules from the implementation.
## Lowering where clauses ## Lowering where clauses
When used in a goal position, where clauses can be mapped directly to When used in a goal position, where clauses can be mapped directly to
@ -76,6 +86,7 @@ relationships between different kinds of domain goals. The first such
rule from the trait header creates the mapping between the `FromEnv` rule from the trait header creates the mapping between the `FromEnv`
and `Implemented` predicates: and `Implemented` predicates:
// Rule Implemented-From-Env
forall<Self, P1..Pn> { forall<Self, P1..Pn> {
Implemented(Self: Trait<P1..Pn>) :- FromEnv(Self: Trait<P1..Pn>) Implemented(Self: Trait<P1..Pn>) :- FromEnv(Self: Trait<P1..Pn>)
} }
@ -89,6 +100,8 @@ The next few clauses have to do with implied bounds (see also
[RFC 2089]: https://rust-lang.github.io/rfcs/2089-implied-bounds.html [RFC 2089]: https://rust-lang.github.io/rfcs/2089-implied-bounds.html
// Rule Implied-Bound-From-Trait
//
// For each where clause WC: // For each where clause WC:
forall<Self, P1..Pn> { forall<Self, P1..Pn> {
FromEnv(WC) :- FromEnv(Self: Trait<P1..Pn) FromEnv(WC) :- FromEnv(Self: Trait<P1..Pn)
@ -112,6 +125,8 @@ clauses** but also things that follow from them.
The next rule is related; it defines what it means for a trait reference The next rule is related; it defines what it means for a trait reference
to be **well-formed**: to be **well-formed**:
// Rule WellFormed-TraitRef
//
// For each where clause WC: // For each where clause WC:
forall<Self, P1..Pn> { forall<Self, P1..Pn> {
WellFormed(Self: Trait<P1..Pn>) :- Implemented(Self: Trait<P1..Pn>) && WellFormed(WC) WellFormed(Self: Trait<P1..Pn>) :- Implemented(Self: Trait<P1..Pn>) && WellFormed(WC)
@ -175,12 +190,16 @@ the rules by which `ProjectionEq` can succeed; these two clauses are discussed
in detail in the [section on associated types](./traits-associated-types.html),, in detail in the [section on associated types](./traits-associated-types.html),,
but reproduced here for reference: but reproduced here for reference:
// Rule ProjectionEq-Normalize
//
// ProjectionEq can succeed by normalizing: // ProjectionEq can succeed by normalizing:
forall<Self, P1..Pn, Pn+1..Pm, U> { forall<Self, P1..Pn, Pn+1..Pm, U> {
ProjectionEq(<Self as Trait<P1..Pn>>::AssocType<Pn+1..Pm> = U) :- ProjectionEq(<Self as Trait<P1..Pn>>::AssocType<Pn+1..Pm> = U) :-
Normalize(<Self as Trait<P1..Pn>>::AssocType<Pn+1..Pm> -> U) Normalize(<Self as Trait<P1..Pn>>::AssocType<Pn+1..Pm> -> U)
} }
// Rule ProjectionEq-Skolemize
//
// ProjectionEq can succeed by skolemizing, see "associated type" // ProjectionEq can succeed by skolemizing, see "associated type"
// chapter for more: // chapter for more:
forall<Self, P1..Pn, Pn+1..Pm> { forall<Self, P1..Pn, Pn+1..Pm> {
@ -223,6 +242,7 @@ where WC
Let `TraitRef` be the trait reference `A0: Trait<A1..An>`. Then we Let `TraitRef` be the trait reference `A0: Trait<A1..An>`. Then we
will create the following rules: will create the following rules:
// Rule Implemented-From-Impl
forall<P0..Pn> { forall<P0..Pn> {
Implemented(TraitRef) :- WC Implemented(TraitRef) :- WC
} }
@ -245,6 +265,7 @@ where WC
We produce the following rule: We produce the following rule:
// Rule Normalize-From-Impl
forall<P0..Pm> { forall<P0..Pm> {
forall<Pn+1..Pm> { forall<Pn+1..Pm> {
Normalize(<A0 as Trait<A1..An>>::AssocType<Pn+1..Pm> -> T) :- Normalize(<A0 as Trait<A1..An>>::AssocType<Pn+1..Pm> -> T) :-