From d677a2d73b87926c5fa359b47830de39ab0e9626 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Thu, 21 Mar 2024 15:53:21 -0400
Subject: [PATCH] Further simplifications

---
 compiler/rustc_middle/src/ty/error.rs  |  2 +-
 compiler/rustc_middle/src/ty/mod.rs    | 23 +++--------------------
 compiler/rustc_middle/src/ty/relate.rs | 16 +---------------
 3 files changed, 5 insertions(+), 36 deletions(-)

diff --git a/compiler/rustc_middle/src/ty/error.rs b/compiler/rustc_middle/src/ty/error.rs
index e15f03788464e..a2d674b9c4402 100644
--- a/compiler/rustc_middle/src/ty/error.rs
+++ b/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,
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index b2fa944b34fe3..6ce53ccc8cd7a 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/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 {
diff --git a/compiler/rustc_middle/src/ty/relate.rs b/compiler/rustc_middle/src/ty/relate.rs
index cb43ae93c8dcd..f523fd7b75a1d 100644
--- a/compiler/rustc_middle/src/ty/relate.rs
+++ b/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) }
     }
 }