Auto merge of #47804 - retep007:recursive-requirements, r=pnkfelix

[rust.git] / src / librustc / traits / error_reporting.rs

diff --git a/src/librustc/traits/error_reporting.rs b/src/librustc/traits/error_reporting.rs
index a290839425ebe2051947c32eeaf4ae0d23560a39..214d8ec325f2b16ce72bb39953f941b921471a91 100644 (file)
--- a/src/librustc/traits/error_reporting.rs
+++ b/src/librustc/traits/error_reporting.rs
@@ -1224,13 +1224,15 @@ fn note_obligation_cause<T>(&self,
     {
         self.note_obligation_cause_code(err,
                                         &obligation.predicate,
-                                        &obligation.cause.code);
+                                        &obligation.cause.code,
+                                        &mut vec![]);
     }
 
     fn note_obligation_cause_code<T>(&self,
                                      err: &mut DiagnosticBuilder,
                                      predicate: &T,
-                                     cause_code: &ObligationCauseCode<'tcx>)
+                                     cause_code: &ObligationCauseCode<'tcx>,
+                                     obligated_types: &mut Vec<&ty::TyS<'tcx>>)
         where T: fmt::Display
     {
         let tcx = self.tcx;
@@ -1326,12 +1328,17 @@ fn note_obligation_cause_code<T>(&self,
             }
             ObligationCauseCode::BuiltinDerivedObligation(ref data) => {
                 let parent_trait_ref = self.resolve_type_vars_if_possible(&data.parent_trait_ref);
-                err.note(&format!("required because it appears within the type `{}`",
-                                  parent_trait_ref.0.self_ty()));
+                let ty = parent_trait_ref.0.self_ty();
+                err.note(&format!("required because it appears within the type `{}`", ty));
+                obligated_types.push(ty);
+
                 let parent_predicate = parent_trait_ref.to_predicate();
-                self.note_obligation_cause_code(err,
-                                                &parent_predicate,
-                                                &data.parent_code);
+                if !self.is_recursive_obligation(obligated_types, &data.parent_code) {
+                    self.note_obligation_cause_code(err,
+                                                    &parent_predicate,
+                                                    &data.parent_code,
+                                                    obligated_types);
+                }
             }
             ObligationCauseCode::ImplDerivedObligation(ref data) => {
                 let parent_trait_ref = self.resolve_type_vars_if_possible(&data.parent_trait_ref);
@@ -1341,8 +1348,9 @@ fn note_obligation_cause_code<T>(&self,
                              parent_trait_ref.0.self_ty()));
                 let parent_predicate = parent_trait_ref.to_predicate();
                 self.note_obligation_cause_code(err,
-                                                &parent_predicate,
-                                                &data.parent_code);
+                                            &parent_predicate,
+                                            &data.parent_code,
+                                            obligated_types);
             }
             ObligationCauseCode::CompareImplMethodObligation { .. } => {
                 err.note(
@@ -1361,6 +1369,20 @@ fn suggest_new_overflow_limit(&self, err: &mut DiagnosticBuilder) {
         err.help(&format!("consider adding a `#![recursion_limit=\"{}\"]` attribute to your crate",
                           suggested_limit));
     }
+
+    fn is_recursive_obligation(&self,
+                                   obligated_types: &mut Vec<&ty::TyS<'tcx>>,
+                                   cause_code: &ObligationCauseCode<'tcx>) -> bool {
+        if let ObligationCauseCode::BuiltinDerivedObligation(ref data) = cause_code {
+            let parent_trait_ref = self.resolve_type_vars_if_possible(&data.parent_trait_ref);
+            for obligated_type in obligated_types {
+                if obligated_type == &parent_trait_ref.0.self_ty() {
+                    return true;
+                }
+            }
+        }
+        return false;
+    }
 }
 
 enum ArgKind {