avoid empty where clauses

Author: RalfJung

compiler/rustc_builtin_macros/src/deriving/generic/mod.rs

@@ -724,15 +724,17 @@ impl<'a> TraitDef<'a> {
                             ));
                         }
 
-                        let predicate = ast::WhereBoundPredicate {
-                            span: self.span,
-                            bound_generic_params: field_ty_param.bound_generic_params,
-                            bounded_ty: field_ty_param.ty,
-                            bounds,
-                        };
-
-                        let predicate = ast::WherePredicate::BoundPredicate(predicate);
-                        where_clause.predicates.push(predicate);
+                        if !bounds.is_empty() {
+                            let predicate = ast::WhereBoundPredicate {
+                                span: self.span,
+                                bound_generic_params: field_ty_param.bound_generic_params,
+                                bounded_ty: field_ty_param.ty,
+                                bounds,
+                            };
+
+                            let predicate = ast::WherePredicate::BoundPredicate(predicate);
+                            where_clause.predicates.push(predicate);
+                        }
                     }
                 }
             }

tests/ui/deriving/deriving-all-codegen.stdout

@@ -598,9 +598,7 @@ impl<T: ::core::hash::Hash + Trait, U: ::core::hash::Hash> ::core::hash::Hash
     }
 }
 #[automatically_derived]
-impl<T: Trait, U> ::core::marker::StructuralPartialEq for Generic<T, U> where
-    T::A: {
-}
+impl<T: Trait, U> ::core::marker::StructuralPartialEq for Generic<T, U> { }
 #[automatically_derived]
 impl<T: ::core::cmp::PartialEq + Trait, U: ::core::cmp::PartialEq>
     ::core::cmp::PartialEq for Generic<T, U> where
@@ -611,8 +609,7 @@ impl<T: ::core::cmp::PartialEq + Trait, U: ::core::cmp::PartialEq>
     }
 }
 #[automatically_derived]
-impl<T: Trait, U> ::core::marker::StructuralEq for Generic<T, U> where T::A: {
-}
+impl<T: Trait, U> ::core::marker::StructuralEq for Generic<T, U> { }
 #[automatically_derived]
 impl<T: ::core::cmp::Eq + Trait, U: ::core::cmp::Eq> ::core::cmp::Eq for
     Generic<T, U> where T::A: ::core::cmp::Eq {
@@ -720,7 +717,7 @@ impl<T: ::core::hash::Hash + ::core::marker::Copy + Trait,
 }
 #[automatically_derived]
 impl<T: Trait, U> ::core::marker::StructuralPartialEq for PackedGeneric<T, U>
-    where T::A: {
+    {
 }
 #[automatically_derived]
 impl<T: ::core::cmp::PartialEq + ::core::marker::Copy + Trait,
@@ -734,9 +731,7 @@ impl<T: ::core::cmp::PartialEq + ::core::marker::Copy + Trait,
     }
 }
 #[automatically_derived]
-impl<T: Trait, U> ::core::marker::StructuralEq for PackedGeneric<T, U> where
-    T::A: {
-}
+impl<T: Trait, U> ::core::marker::StructuralEq for PackedGeneric<T, U> { }
 #[automatically_derived]
 impl<T: ::core::cmp::Eq + ::core::marker::Copy + Trait, U: ::core::cmp::Eq +
     ::core::marker::Copy> ::core::cmp::Eq for PackedGeneric<T, U> where