Further simplifications

compiler/rustc_middle/src/ty/error.rs

@@ -32,7 +32,7 @@ impl<T> ExpectedFound<T> {
 pub enum TypeError<'tcx> {
     Mismatch,
     ConstnessMismatch(ExpectedFound<ty::BoundConstness>),
-    PolarityMismatch(ExpectedFound<ty::ImplPolarity>),
+    PolarityMismatch(ExpectedFound<ty::PredicatePolarity>),
     UnsafetyMismatch(ExpectedFound<hir::Unsafety>),
     AbiMismatch(ExpectedFound<abi::Abi>),
     Mutability,

compiler/rustc_middle/src/ty/mod.rs

@@ -280,17 +280,6 @@ pub enum ImplPolarity {
     Reservation,
 }
 
-impl ImplPolarity {
-    /// Flips polarity by turning `Positive` into `Negative` and `Negative` into `Positive`.
-    pub fn flip(&self) -> Option<ImplPolarity> {
-        match self {
-            ImplPolarity::Positive => Some(ImplPolarity::Negative),
-            ImplPolarity::Negative => Some(ImplPolarity::Positive),
-            ImplPolarity::Reservation => None,
-        }
-    }
-}
-
 impl fmt::Display for ImplPolarity {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
@@ -301,15 +290,9 @@ impl fmt::Display for ImplPolarity {
     }
 }
 
-impl From<PredicatePolarity> for ImplPolarity {
-    fn from(value: PredicatePolarity) -> Self {
-        match value {
-            PredicatePolarity::Positive => ImplPolarity::Positive,
-            PredicatePolarity::Negative => ImplPolarity::Negative,
-        }
-    }
-}
-
+/// Polarity for a trait predicate. May either be negative or positive.
+/// Distinguished from [`ImplPolarity`] since we never compute goals with
+/// "reservation" level.
 #[derive(Copy, Clone, PartialEq, Eq, Hash, TyEncodable, TyDecodable, HashStable, Debug)]
 #[derive(TypeFoldable, TypeVisitable)]
 pub enum PredicatePolarity {

compiler/rustc_middle/src/ty/relate.rs

@@ -769,27 +769,13 @@ impl<'tcx> Relate<'tcx> for GenericArg<'tcx> {
     }
 }
 
-impl<'tcx> Relate<'tcx> for ty::ImplPolarity {
-    fn relate<R: TypeRelation<'tcx>>(
-        _relation: &mut R,
-        a: ty::ImplPolarity,
-        b: ty::ImplPolarity,
-    ) -> RelateResult<'tcx, ty::ImplPolarity> {
-        if a != b { Err(TypeError::PolarityMismatch(expected_found(a, b))) } else { Ok(a) }
-    }
-}
-
 impl<'tcx> Relate<'tcx> for ty::PredicatePolarity {
     fn relate<R: TypeRelation<'tcx>>(
         _relation: &mut R,
         a: ty::PredicatePolarity,
         b: ty::PredicatePolarity,
     ) -> RelateResult<'tcx, ty::PredicatePolarity> {
-        if a != b {
-            Err(TypeError::PolarityMismatch(expected_found(a.into(), b.into())))
-        } else {
-            Ok(a)
-        }
+        if a != b { Err(TypeError::PolarityMismatch(expected_found(a, b))) } else { Ok(a) }
     }
 }