Function ptrauth_clone_discriminated_schema_for 

pub fn ptrauth_clone_discriminated_schema_for<'tcx, S>(
    tcx: TyCtxt<'tcx>,
    schema: Option<PointerAuthSchema>,
    source: S,
) -> Option<PointerAuthSchema>
where
    S: FnPtrDiscriminatorSource<'tcx>,

Clones a pointer authentication schema and updates its constant discriminator.

If schema is Some, the function computes a function pointer type discriminator from source and stores it in the cloned schema’s constant_discriminator field.

If no discriminator can be computed (for example, because source does not represent a function pointer type), the schema is returned unchanged.

This is intended as a convenience helper for code generation sites that need to attach function pointer type discrimination to a generic schema before calling get_fn_addr.