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//! Routines to check for relations between fully inferred types.
//!
//! FIXME: Move this to a more general place. The utility of this extends to
//! other areas of the compiler as well.
use rustc_infer::infer::{DefiningAnchor, TyCtxtInferExt};
use rustc_infer::traits::ObligationCause;
use rustc_middle::ty::{ParamEnv, Ty, TyCtxt};
use rustc_trait_selection::traits::ObligationCtxt;
/// Returns whether the two types are equal up to subtyping.
///
/// This is used in case we don't know the expected subtyping direction
/// and still want to check whether anything is broken.
pub fn is_equal_up_to_subtyping<'tcx>(
tcx: TyCtxt<'tcx>,
param_env: ParamEnv<'tcx>,
src: Ty<'tcx>,
dest: Ty<'tcx>,
) -> bool {
// Fast path.
if src == dest {
return true;
}
// Check for subtyping in either direction.
is_subtype(tcx, param_env, src, dest) || is_subtype(tcx, param_env, dest, src)
}
/// Returns whether `src` is a subtype of `dest`, i.e. `src <: dest`.
///
/// This mostly ignores opaque types as it can be used in constraining contexts
/// while still computing the final underlying type.
pub fn is_subtype<'tcx>(
tcx: TyCtxt<'tcx>,
param_env: ParamEnv<'tcx>,
src: Ty<'tcx>,
dest: Ty<'tcx>,
) -> bool {
if src == dest {
return true;
}
let mut builder =
tcx.infer_ctxt().ignoring_regions().with_opaque_type_inference(DefiningAnchor::Bubble);
let infcx = builder.build();
let ocx = ObligationCtxt::new(&infcx);
let cause = ObligationCause::dummy();
let src = ocx.normalize(&cause, param_env, src);
let dest = ocx.normalize(&cause, param_env, dest);
match ocx.sub(&cause, param_env, src, dest) {
Ok(()) => {}
Err(_) => return false,
};
let errors = ocx.select_all_or_error();
// With `Reveal::All`, opaque types get normalized away, with `Reveal::UserFacing`
// we would get unification errors because we're unable to look into opaque types,
// even if they're constrained in our current function.
//
// It seems very unlikely that this hides any bugs.
let _ = infcx.inner.borrow_mut().opaque_type_storage.take_opaque_types();
errors.is_empty()
}
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