Module utils

Each item can involve three kinds of predicates:

• input aka required predicates: the predicates required to mention the item. These are usually where clauses (or equivalent) on the item:

struct Foo<T: Clone> { ... }
trait Foo<T> where T: Clone { ... }
fn function<I>() where I: Iterator, I::Item: Clone { ... }

• output aka implied predicates: the predicates that are implied by the presence of this item in a signature. This is mostly trait parent predicates:

trait Foo: Clone { ... }
fn bar<T: Foo>() {
  // from `T: Foo` we can deduce `T: Clone`
}

This could also include implied predicates such as &'a T implying T: 'a but we don’t consider these.

• “self” predicate: that’s the special Self: Trait predicate in scope within a trait declaration or implementation for trait Trait.

Note that within a given item the polarity is reversed: input predicates are the ones that can be assumed to hold and output predicates must be proven to hold. The “self” predicate is both assumed and proven within an impl block, and just assumed within a trait declaration block.

The current implementation considers all predicates on traits to be outputs, which has the benefit of reducing the size of signatures. Moreover, the rules on which bounds are required vs implied are subtle. We may change this if this proves to be a problem.

Functions

• erase_all_regions
  Erase all regions. Largely copied from tcx.erase_regions.
• erase_and_norm
• implied_predicates
  The predicates that can be deduced from the presence of this item in a signature. We only consider predicates implied by traits here, not implied bounds such as &'a T implying T: 'a.
• predicates_defined_on
  Returns a list of type predicates for the definition with ID def_id, including inferred lifetime constraints. This is the basic list of predicates we use for essentially all items.
• required_predicates
  The predicates that must hold to mention this item.
• self_predicate
  The special “self” predicate on a trait.