Fix suggestions for &&T == &T

Author: sjwang05

compiler/rustc_middle/src/traits/mod.rs

@@ -512,6 +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)),

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -838,14 +838,16 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                     }
                 }
             }
-        } else if let ObligationCauseCode::BinOp { lhs_hir_id, .. } = code
+        } else if let (ObligationCauseCode::BinOp { lhs_hir_id, .. }, predicate) =
+            code.peel_derives_with_predicate()
             && let hir::Node::Expr(lhs) = self.tcx.hir().get(*lhs_hir_id)
         {
+            let trait_pred = predicate.unwrap_or(trait_pred);
             let lhs_ty = self.tcx.instantiate_bound_regions_with_erased(trait_pred.self_ty());
             if let ty::Ref(..) = *lhs_ty.kind() {
-                let autoderef = (self.autoderef_steps)(lhs_ty);
+                let lhs_autoderef = (self.autoderef_steps)(lhs_ty);
                 if let Some(steps) =
-                    autoderef.into_iter().enumerate().find_map(|(steps, (ty, obligations))| {
+                    lhs_autoderef.into_iter().enumerate().find_map(|(steps, (ty, obligations))| {
                         // Remapping bound vars here
                         let trait_pred_and_ty =
                             trait_pred.map_bound(|inner_trait_pred| (inner_trait_pred, ty));
@@ -890,7 +892,6 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                 }
             }
         }
-
         false
     }