Enum ConstraintCategory

pub enum ConstraintCategory<'tcx> {
    Return(ReturnConstraint),
    Yield,
    UseAsConst,
    UseAsStatic,
    TypeAnnotation,
    Cast {
        is_implicit_coercion: bool,
        unsize_to: Option<Ty<'tcx>>,
    },
    ClosureBounds,
    CallArgument(Option<Ty<'tcx>>),
    CopyBound,
    SizedBound,
    Assignment,
    Usage,
    OpaqueType,
    ClosureUpvar(FieldIdx),
    Predicate(Span),
    Boring,
    BoringNoLocation,
    Internal,
    IllegalUniverse,
}

Outlives-constraints can be categorized to determine whether and why they are interesting (for error reporting). Order of variants indicates sort order of the category, thereby influencing diagnostic output.

See also rustc_const_eval::borrow_check::constraints.

Variants

Return(ReturnConstraint)

Yield

UseAsConst

UseAsStatic

TypeAnnotation

Cast

Fields

is_implicit_coercion: bool

Whether this cast is a coercion that was automatically inserted by the compiler.

unsize_to: Option<Ty<'tcx>>

Whether this is an unsizing coercion and if yes, this contains the target type. Region variables are erased to ReErased.

ClosureBounds

A constraint that came from checking the body of a closure.

We try to get the category that the closure used when reporting this.

CallArgument(Option<Ty<'tcx>>)

Contains the function type if available.

CopyBound

SizedBound

Assignment

Usage

A constraint that came from a usage of a variable (e.g. in an ADT expression like Foo { field: my_val })

OpaqueType

ClosureUpvar(FieldIdx)

Predicate(Span)

A constraint from a user-written predicate with the provided span, written on the item with the given DefId

Boring

A “boring” constraint (caused by the given location) is one that the user probably doesn’t want to see described in diagnostics, because it is kind of an artifact of the type system setup.

BoringNoLocation

Internal

A constraint that doesn’t correspond to anything the user sees.

IllegalUniverse

An internal constraint derived from an illegal universe relation.