Enum rustc_trait_selection::infer::NllRegionVariableOrigin

pub enum NllRegionVariableOrigin {
    FreeRegion,
    Placeholder(Placeholder<BoundRegionKind>),
    RootEmptyRegion,
    Existential {
        from_forall: bool,
    },
}

Variants

FreeRegion

During NLL region processing, we create variables for free regions that we encounter in the function signature and elsewhere. This origin indices we’ve got one of those.

Placeholder(Placeholder<BoundRegionKind>)

“Universal” instantiation of a higher-ranked region (e.g., from a for<'a> T binder). Meant to represent “any region”.

RootEmptyRegion

The variable we create to represent 'empty(U0).

Existential

Fields of Existential

from_forall: bool

If this is true, then this variable was created to represent a lifetime bound in a for binder. For example, it might have been created to represent the lifetime 'a in a type like for<'a> fn(&'a u32). Such variables are created when we are trying to figure out if there is any valid instantiation of 'a that could fit into some scenario.

This is used to inform error reporting: in the case that we are trying to determine whether there is any valid instantiation of a 'a variable that meets some constraint C, we want to blame the “source” of that for type, rather than blaming the source of the constraint C.