Struct rustc_type_ir::search_graph::StackEntry

struct StackEntry<X: Cx> {
    input: X::Input,
    available_depth: AvailableDepth,
    reached_depth: StackDepth,
    non_root_cycle_participant: Option<StackDepth>,
    encountered_overflow: bool,
    has_been_used: Option<UsageKind>,
    nested_goals: HashSet<X::Input>,
    provisional_result: Option<X::Result>,
}

Fields

input: X::Input

available_depth: AvailableDepth

reached_depth: StackDepth

The maximum depth reached by this stack entry, only up-to date for the top of the stack and lazily updated for the rest.

non_root_cycle_participant: Option<StackDepth>

Whether this entry is a non-root cycle participant.

We must not move the result of non-root cycle participants to the global cache. We store the highest stack depth of a head of a cycle this goal is involved in. This necessary to soundly cache its provisional result.

encountered_overflow: bool

has_been_used: Option<UsageKind>

nested_goals: HashSet<X::Input>

We put only the root goal of a coinductive cycle into the global cache.

If we were to use that result when later trying to prove another cycle participant, we can end up with unstable query results.

See tests/ui/next-solver/coinduction/incompleteness-unstable-result.rs for an example of where this is needed.

There can be multiple roots on the same stack, so we need to track cycle participants per root:

A :- B
B :- A, C
C :- D
D :- C

provisional_result: Option<X::Result>

Starts out as None and gets set when rerunning this goal in case we encounter a cycle.

Trait Implementations

impl<X: Cx> Debug for StackEntry<X>

fn fmt(&self, __f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

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.