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Diffstat (limited to '')
-rw-r--r-- | compiler/rustc_const_eval/src/util/compare_types.rs | 63 |
1 files changed, 63 insertions, 0 deletions
diff --git a/compiler/rustc_const_eval/src/util/compare_types.rs b/compiler/rustc_const_eval/src/util/compare_types.rs new file mode 100644 index 000000000..be786569c --- /dev/null +++ b/compiler/rustc_const_eval/src/util/compare_types.rs @@ -0,0 +1,63 @@ +//! 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() +} |