Struct GoalEvaluation 

pub struct GoalEvaluation<I>
where
    I: Interner,
{
    pub goal: Goal<I, <I as Interner>::Predicate>,
    pub certainty: Certainty,
    pub has_changed: HasChanged,
    pub stalled_on: Option<GoalStalledOn<I>>,
}

The result of evaluating a goal.

Fields

goal: Goal<I, <I as Interner>::Predicate>

The goal we’ve evaluated. This is the input goal, but potentially with its inference variables resolved. This never applies any inference constraints from evaluating the goal.

We rely on this to check whether root goals in HIR typeck had an unresolved type inference variable in the input. We must not resolve this after evaluating the goal as even if the inference variable has been resolved by evaluating the goal itself, this goal may still end up failing due to region uniquification later on.

This is used as a minor optimization to avoid re-resolving inference variables when reevaluating ambiguous goals. E.g. if we’ve got a goal ?x: Trait with ?x already being constrained to Vec<?y>, then the first evaluation resolves it to Vec<?y>: Trait. If this goal is still ambiguous and we later resolve ?y to u32, then reevaluating this goal now only needs to resolve ?y while it would otherwise have to resolve both ?x and ?y,

certainty: Certainty

has_changed: HasChanged

stalled_on: Option<GoalStalledOn<I>>

If the Certainty was Maybe, then keep track of whether the goal has changed before rerunning it.

Layout

Note: Unable to compute type layout, possibly due to this type having generic parameters. Layout can only be computed for concrete, fully-instantiated types.