Merge remote-tracking branch 'origin/swift-4.0-branch' into stable
diff --git a/lib/AST/DeclObjC.cpp b/lib/AST/DeclObjC.cpp
index 5d894c5..03eaaab 100644
--- a/lib/AST/DeclObjC.cpp
+++ b/lib/AST/DeclObjC.cpp
@@ -162,10 +162,10 @@
         return nullptr;
   }
 
-  // If context is class, then lookup property in its extensions.
+  // If context is class, then lookup property in its visible extensions.
   // This comes before property is looked up in primary class.
   if (auto *IDecl = dyn_cast<ObjCInterfaceDecl>(DC)) {
-    for (const auto *Ext : IDecl->known_extensions())
+    for (const auto *Ext : IDecl->visible_extensions())
       if (ObjCPropertyDecl *PD = ObjCPropertyDecl::findPropertyDecl(Ext,
                                                        propertyID,
                                                        queryKind))
diff --git a/test/Modules/Inputs/category_right_sub.h b/test/Modules/Inputs/category_right_sub.h
index 231f65f..c8ba793 100644
--- a/test/Modules/Inputs/category_right_sub.h
+++ b/test/Modules/Inputs/category_right_sub.h
@@ -15,3 +15,8 @@
 
 @interface Foo(LeftP4) <P4>
 @end
+
+// A hidden extension
+@interface Foo ()
+@property (assign) int hiddenPropertyFromExtension;
+@end
diff --git a/test/Modules/objc-categories.m b/test/Modules/objc-categories.m
index 42baf35..fcffe3c 100644
--- a/test/Modules/objc-categories.m
+++ b/test/Modules/objc-categories.m
@@ -53,6 +53,9 @@
   p3p = foo.p3_prop; // expected-error{{property 'p3_prop' not found on object of type 'Foo *'}}
   id p4p = p4.p4_prop; // expected-error{{property 'p4_prop' not found on object of type 'id<P4>'}}
   p4p = foo.p4_prop; // expected-error{{property 'p4_prop' not found on object of type 'Foo *'}}
+
+  if (foo.hiddenPropertyFromExtension) { // expected-error {{property 'hiddenPropertyFromExtension' not found on object of type 'Foo *'}}
+  }
 }
 
 @import category_left.sub;
@@ -74,6 +77,7 @@
   id p4p = p4.p4_prop; // expected-error{{property 'p4_prop' not found on object of type 'id<P4>'}}
   p4p = foo.p4_prop; // expected-error{{property 'p4_prop' not found on object of type 'Foo *'; did you mean 'p3_prop'?}}
   // expected-note@Inputs/category_left_sub.h:7{{'p3_prop' declared here}}
+  int hiddenFromExtension = foo.hiddenPropertyFromExtension; // expected-error {{property 'hiddenPropertyFromExtension' not found on object of type 'Foo *'}}
 }
 
 @import category_right.sub;
@@ -92,4 +96,6 @@
   p3p = foo.p3_prop;
   id p4p = p4.p4_prop;
   p4p = foo.p4_prop;
+  if (foo.hiddenPropertyFromExtension) {
+  }
 }