In order to avoid reference cycles and repeat printing of data, stringForPrintObject maintains a list of references it has encountered and skips printing them

Bridging was causing an issue where some value types were being bridged into references and ending up randomly causing collisions which would make certain data not be printed when it should have

Make it so that we only tuck away references we know are natively references for uniqueness purposes

Fixes rdar://problem/27319054

Author: Enrico Granata

stdlib/public/core/DebuggerSupport.swift

@@ -38,20 +38,36 @@ public enum _DebuggerSupport {
     }
   }
 
-  internal static func asObjectIdentifier(_ value: Any) -> ObjectIdentifier? {
-    if let ao = value as? AnyObject {
-      return ObjectIdentifier(ao)
-    } else {
-      return nil
+  internal static func isClass(_ value: Any) -> Bool {
+    if let _ = value.dynamicType as? AnyClass {
+      return true
+    }
+    return false
+  }
+  
+  internal static func checkValue<T>(
+    _ value: Any,
+    ifClass: (AnyObject)->T,
+    otherwise: ()->T
+  ) -> T {
+    if isClass(value) {
+      if let ao = value as? AnyObject {
+        return ifClass(ao)
+      }
     }
+    return otherwise()
+  }
+
+  internal static func asObjectIdentifier(_ value: Any) -> ObjectIdentifier? {
+    return checkValue(value,
+      ifClass: { return ObjectIdentifier($0) },
+      otherwise: { return nil })
   }
 
   internal static func asNumericValue(_ value: Any) -> Int {
-    if let ao = value as? AnyObject {
-      return unsafeBitCast(ao, to: Int.self)
-    } else {
-      return 0
-    }
+    return checkValue(value,
+      ifClass: { return unsafeBitCast($0, to: Int.self) },
+      otherwise: { return 0 })
   }
 
   internal static func asStringRepresentation(

test/1_stdlib/DebuggerSupport.swift

@@ -19,6 +19,42 @@ class ClassWithMirror: CustomReflectable {
   }
 }
 
+#if _runtime(_ObjC)
+struct DontBridgeThisStruct {
+  var message = "Hello World"
+}
+
+extension DontBridgeThisStruct : _ObjectiveCBridgeable {
+  typealias _ObjectiveCType = AnyObject
+
+  static func _isBridgedToObjectiveC() -> Bool { return true }
+
+  func _bridgeToObjectiveC() -> _ObjectiveCType {
+    fatalError("tried to bridge DontBridgeThisStruct")
+  }
+
+  static func _forceBridgeFromObjectiveC(
+    _ source: _ObjectiveCType,
+    result: inout DontBridgeThisStruct?
+  ) {
+    result = nil
+  }
+
+  static func _conditionallyBridgeFromObjectiveC(
+    _ source: _ObjectiveCType,
+    result: inout DontBridgeThisStruct?
+  ) -> Bool {
+    result = nil
+    return false
+  }
+
+  static func _unconditionallyBridgeFromObjectiveC(_ source: _ObjectiveCType?)
+      -> DontBridgeThisStruct {
+    return DontBridgeThisStruct()
+  }
+}
+#endif
+
 let StringForPrintObjectTests = TestSuite("StringForPrintObject")
 StringForPrintObjectTests.test("StructWithMembers") {
   let printed = _DebuggerSupport.stringForPrintObject(StructWithMembers())
@@ -57,4 +93,11 @@ StringForPrintObjectTests.test("SomeOptional") {
   expectEqual(printed, "▿ Optional<Int>\n  - some : 3\n")
 }
 
+#if _runtime(_ObjC)
+StringForPrintObjectTests.test("DontBridgeThisStruct") {
+  let printed = _DebuggerSupport.stringForPrintObject(DontBridgeThisStruct())
+  expectEqual(printed, "▿ DontBridgeThisStruct\n  - message : \"Hello World\"\n")
+}
+#endif
+
 runAllTests()