Propagate Expectation around binop typeck code to construct more precise trait obligations for binops.

2 files changed, 14 insertions, 3 deletions

diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
index 39fce3cf769..c1af1a05972 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
@@ -665,6 +665,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                             self.suggest_restricting_param_bound(
                                 &mut err,
                                 trait_predicate,
+                                None,
                                 obligation.cause.body_id,
                             );
                         } else if !suggested {
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
index 57d5e5436a6..469436ff0db 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
@@ -24,7 +24,8 @@ use rustc_middle::hir::map;
 use rustc_middle::ty::{
     self, suggest_arbitrary_trait_bound, suggest_constraining_type_param, AdtKind, DefIdTree,
     GeneratorDiagnosticData, GeneratorInteriorTypeCause, Infer, InferTy, IsSuggestable,
-    ToPredicate, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable, TypeVisitable,
+    ProjectionPredicate, ToPredicate, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable,
+    TypeVisitable,
 };
 use rustc_middle::ty::{TypeAndMut, TypeckResults};
 use rustc_session::Limit;
@@ -172,6 +173,7 @@ pub trait InferCtxtExt<'tcx> {
         &self,
         err: &mut Diagnostic,
         trait_pred: ty::PolyTraitPredicate<'tcx>,
+        proj_pred: Option<ty::PolyProjectionPredicate<'tcx>>,
         body_id: hir::HirId,
     );
 
@@ -457,6 +459,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
         &self,
         mut err: &mut Diagnostic,
         trait_pred: ty::PolyTraitPredicate<'tcx>,
+        proj_pred: Option<ty::PolyProjectionPredicate<'tcx>>,
         body_id: hir::HirId,
     ) {
         let trait_pred = self.resolve_numeric_literals_with_default(trait_pred);
@@ -589,9 +592,16 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                     }
                     // Missing generic type parameter bound.
                     let param_name = self_ty.to_string();
-                    let constraint = with_no_trimmed_paths!(
+                    let mut constraint = with_no_trimmed_paths!(
                         trait_pred.print_modifiers_and_trait_path().to_string()
                     );
+
+                    if let Some(proj_pred) = proj_pred {
+                        let ProjectionPredicate { projection_ty, term } = proj_pred.skip_binder();
+                        let item = self.tcx.associated_item(projection_ty.item_def_id);
+                        constraint.push_str(&format!("<{}={}>", item.name, term.to_string()));
+                    }
+
                     if suggest_constraining_type_param(
                         self.tcx,
                         generics,
@@ -2825,7 +2835,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
         trait_ref: &ty::PolyTraitRef<'tcx>,
     ) {
         let rhs_span = match obligation.cause.code() {
-            ObligationCauseCode::BinOp { rhs_span: Some(span), is_lit } if *is_lit => span,
+            ObligationCauseCode::BinOp { rhs_span: Some(span), is_lit, .. } if *is_lit => span,
             _ => return,
         };
         match (