Add a safe API for NSValue and migrate NSValue value fetching to the size variants for validation (#22265)

Author: phausler

stdlib/public/Darwin/Foundation/NSValue.swift.gyb

@@ -23,3 +23,31 @@ ${ ObjectiveCBridgeableImplementationForNSValue("CGVector") }
 ${ ObjectiveCBridgeableImplementationForNSValue("CGSize") }
 ${ ObjectiveCBridgeableImplementationForNSValue("CGAffineTransform") }
 
+extension NSValue {
+    public func value<StoredType>(of type: StoredType.Type) -> StoredType? {
+        if StoredType.self is AnyObject.Type {
+            let encoding = String(cString: objCType)
+            // some subclasses of NSValue can return @ and the default initialized variant returns ^v for encoding
+            guard encoding == "^v" || encoding == "@" else {
+                return nil
+            }
+            return nonretainedObjectValue as? StoredType
+        } else if _isPOD(StoredType.self) {
+            var storedSize = 0
+            var storedAlignment = 0
+            NSGetSizeAndAlignment(objCType, &storedSize, &storedAlignment)
+            guard MemoryLayout<StoredType>.size == storedSize && MemoryLayout<StoredType>.alignment == storedAlignment else {
+                return nil
+            }
+            let allocated = UnsafeMutablePointer<StoredType>.allocate(capacity: 1)
+            defer { allocated.deallocate() }
+            if #available(OSX 10.13, iOS 11.0, tvOS 11.0, watchOS 4.0, *) {
+            	getValue(allocated, size: storedSize)
+        	} else {
+        		getValue(allocated)
+        	}
+            return allocated.pointee
+        }
+        return nil
+    }
+}

test/stdlib/NSValueBridging.swift.gyb

@@ -91,4 +91,31 @@ nsValueBridging.test("NSValue can only be cast back to its original type") {
   _ = rangeObject as! CGRect
 }
 
+nsValueBridging.test("NSValue fetching method should be able to convert constructed values safely") {
+  let range = NSRange(location: 17, length: 38)
+  let value = NSValue(range: range)
+  expectEqual(value.value(of: NSRange.self)?.location, range.location)
+  expectEqual(value.value(of: NSRange.self)?.length, range.length)
+  expectEqual(value.value(of: CGRect.self), .none)
+  expectEqual(value.value(of: String.self), .none)
+  expectTrue(value.value(of: AnyObject.self) == nil)
+
+
+  class GenericThingNotRootedInObjC<T> {
+    init() { }
+  }
+
+  let obj = GenericThingNotRootedInObjC<String>()
+  // extend the lifetime to ensure that the non retained pointer is valid for the test duration
+  withExtendedLifetime(obj) { () -> Void in
+    let value = NSValue(nonretainedObject: obj)
+    let resString = value.value(of: GenericThingNotRootedInObjC<String>.self)
+    expectEqual(resString === obj, true) // ensure the value is exactly the same
+    
+    let resInt = value.value(of: GenericThingNotRootedInObjC<Int>.self)
+    expectTrue(resInt == nil)
+  }
+
+}
+
 runAllTests()

utils/gyb_foundation_support.py

@@ -12,7 +12,11 @@ def ObjectiveCBridgeableImplementationForNSValue(Type):
                         _getObjCTypeEncoding({Type}.self)) == 0,
                  "NSValue does not contain the right type to bridge to {Type}")
     result = {Type}()
-    source.getValue(&result!)
+    if #available(OSX 10.13, iOS 11.0, tvOS 11.0, watchOS 4.0, *) {{
+      source.getValue(&result!, size: MemoryLayout<{Type}>.size)
+    }} else {{
+      source.getValue(&result!)
+    }}
   }}
 
   public static func _conditionallyBridgeFromObjectiveC(_ source: NSValue,
@@ -23,7 +27,11 @@ def ObjectiveCBridgeableImplementationForNSValue(Type):
       return false
     }}
     result = {Type}()
-    source.getValue(&result!)
+    if #available(OSX 10.13, iOS 11.0, tvOS 11.0, watchOS 4.0, *) {{
+      source.getValue(&result!, size: MemoryLayout<{Type}>.size)
+    }} else {{
+      source.getValue(&result!)
+    }}
     return true
   }}
 
@@ -34,7 +42,11 @@ def ObjectiveCBridgeableImplementationForNSValue(Type):
                         _getObjCTypeEncoding({Type}.self)) == 0,
                  "NSValue does not contain the right type to bridge to {Type}")
     var result = {Type}()
-    unwrappedSource.getValue(&result)
+    if #available(OSX 10.13, iOS 11.0, tvOS 11.0, watchOS 4.0, *) {{
+      unwrappedSource.getValue(&result, size: MemoryLayout<{Type}>.size)
+    }} else {{
+      unwrappedSource.getValue(&result)
+    }}
     return result
   }}
 }}