Enum rustc_trait_selection::traits::project::ProjectAndUnifyResult

pub(super) enum ProjectAndUnifyResult<'tcx> {
    Holds(Vec<PredicateObligation<'tcx>>),
    FailedNormalization,
    Recursive,
    MismatchedProjectionTypes(MismatchedProjectionTypes<'tcx>),
}

States returned from poly_project_and_unify_type. Takes the place of the old return type, which was:

Result<
    Result<Option<Vec<PredicateObligation<'tcx>>>, InProgress>,
    MismatchedProjectionTypes<'tcx>,
>

Variants

Holds(Vec<PredicateObligation<'tcx>>)

The projection bound holds subject to the given obligations. If the projection cannot be normalized because the required trait bound does not hold, this is returned, with obligations being a predicate that cannot be proven.

FailedNormalization

The projection cannot be normalized due to ambiguity. Resolving some inference variables in the projection may fix this.

Recursive

The project cannot be normalized because poly_project_and_unify_type is called recursively while normalizing the same projection.

MismatchedProjectionTypes(MismatchedProjectionTypes<'tcx>)

Layout

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain repr(...) attributes. Please see the Rust Reference's “Type Layout” chapter for details on type layout guarantees.

Size: 32 bytes

Size for each variant:

• Holds: 32 bytes
• FailedNormalization: 0 bytes
• Recursive: 0 bytes
• MismatchedProjectionTypes: 32 bytes