Provide better suggestions for T == &T and &T == T

compiler/rustc_middle/src/traits/mod.rs

@@ -429,8 +429,10 @@ pub enum ObligationCauseCode<'tcx> {
     MatchImpl(ObligationCause<'tcx>, DefId),
 
     BinOp {
+        lhs_hir_id: hir::HirId,
+        rhs_hir_id: Option<hir::HirId>,
         rhs_span: Option<Span>,
-        is_lit: bool,
+        rhs_is_lit: bool,
         output_ty: Option<Ty<'tcx>>,
     },
 
@@ -510,6 +512,21 @@ impl<'tcx> ObligationCauseCode<'tcx> {
         base_cause
     }
 
+    /// Returns the base obligation and the base trait predicate, if any, ignoring
+    /// derived obligations.
+    pub fn peel_derives_with_predicate(&self) -> (&Self, Option<ty::PolyTraitPredicate<'tcx>>) {
+        let mut base_cause = self;
+        let mut base_trait_pred = None;
+        while let Some((parent_code, parent_pred)) = base_cause.parent() {
+            base_cause = parent_code;
+            if let Some(parent_pred) = parent_pred {
+                base_trait_pred = Some(parent_pred);
+            }
+        }
+
+        (base_cause, base_trait_pred)
+    }
+
     pub fn parent(&self) -> Option<(&Self, Option<ty::PolyTraitPredicate<'tcx>>)> {
         match self {
             FunctionArgumentObligation { parent_code, .. } => Some((parent_code, None)),