perf(copy): only validate/clear user specified destination

Closes #12068

Author: jbedard

src/Angular.js

@@ -794,100 +794,111 @@ function arrayRemove(array, value) {
  </file>
  </example>
  */
-function copy(source, destination, stackSource, stackDest) {
-  if (isWindow(source) || isScope(source)) {
-    throw ngMinErr('cpws',
-      "Can't copy! Making copies of Window or Scope instances is not supported.");
-  }
-  if (isTypedArray(destination)) {
-    throw ngMinErr('cpta',
-      "Can't copy! TypedArray destination cannot be mutated.");
-  }
-
-  if (!destination) {
-    destination = source;
-    if (isObject(source)) {
-      var index;
-      if (stackSource && (index = stackSource.indexOf(source)) !== -1) {
-        return stackDest[index];
-      }
+function copy(source, destination) {
+  var stackSource = [];
+  var stackDest = [];
 
-      // TypedArray, Date and RegExp have specific copy functionality and must be
-      // pushed onto the stack before returning.
-      // Array and other objects create the base object and recurse to copy child
-      // objects. The array/object will be pushed onto the stack when recursed.
-      if (isArray(source)) {
-        return copy(source, [], stackSource, stackDest);
-      } else if (isTypedArray(source)) {
-        destination = new source.constructor(source);
-      } else if (isDate(source)) {
-        destination = new Date(source.getTime());
-      } else if (isRegExp(source)) {
-        destination = new RegExp(source.source, source.toString().match(/[^\/]*$/)[0]);
-        destination.lastIndex = source.lastIndex;
-      } else if (isFunction(source.cloneNode)) {
-          destination = source.cloneNode(true);
-      } else {
-        var emptyObject = Object.create(getPrototypeOf(source));
-        return copy(source, emptyObject, stackSource, stackDest);
-      }
+  if (destination) {
+    if (isTypedArray(destination)) {
+      throw ngMinErr('cpta', "Can't copy! TypedArray destination cannot be mutated.");
+    }
+    if (source === destination) {
+      throw ngMinErr('cpi', "Can't copy! Source and destination are identical.");
+    }
 
-      if (stackDest) {
-        stackSource.push(source);
-        stackDest.push(destination);
-      }
+    // Empty the destination object
+    if (isArray(destination)) {
+      destination.length = 0;
+    } else {
+      forEach(destination, function(value, key) {
+        if (key !== '$$hashKey') {
+          delete destination[key];
+        }
+      });
     }
-  } else {
-    if (source === destination) throw ngMinErr('cpi',
-      "Can't copy! Source and destination are identical.");
 
-    stackSource = stackSource || [];
-    stackDest = stackDest || [];
+    stackSource.push(source);
+    stackDest.push(destination);
+    return copyRecurse(source, destination);
+  }
 
-    if (isObject(source)) {
-      stackSource.push(source);
-      stackDest.push(destination);
-    }
+  return copyElement(source);
 
+  function copyRecurse(source, destination) {
+    var h = destination.$$hashKey;
     var result, key;
     if (isArray(source)) {
-      destination.length = 0;
-      for (var i = 0; i < source.length; i++) {
-        destination.push(copy(source[i], null, stackSource, stackDest));
+      for (var i = 0, ii = source.length; i < ii; i++) {
+        destination.push(copyElement(source[i]));
       }
-    } else {
-      var h = destination.$$hashKey;
-      if (isArray(destination)) {
-        destination.length = 0;
-      } else {
-        forEach(destination, function(value, key) {
-          delete destination[key];
-        });
+    } else if (isBlankObject(source)) {
+      // createMap() fast path --- Safe to avoid hasOwnProperty check because prototype chain is empty
+      for (key in source) {
+        destination[key] = copyElement(source[key]);
       }
-      if (isBlankObject(source)) {
-        // createMap() fast path --- Safe to avoid hasOwnProperty check because prototype chain is empty
-        for (key in source) {
-          destination[key] = copy(source[key], null, stackSource, stackDest);
-        }
-      } else if (source && typeof source.hasOwnProperty === 'function') {
-        // Slow path, which must rely on hasOwnProperty
-        for (key in source) {
-          if (source.hasOwnProperty(key)) {
-            destination[key] = copy(source[key], null, stackSource, stackDest);
-          }
+    } else if (source && typeof source.hasOwnProperty === 'function') {
+      // Slow path, which must rely on hasOwnProperty
+      for (key in source) {
+        if (source.hasOwnProperty(key)) {
+          destination[key] = copyElement(source[key]);
         }
-      } else {
-        // Slowest path --- hasOwnProperty can't be called as a method
-        for (key in source) {
-          if (hasOwnProperty.call(source, key)) {
-            destination[key] = copy(source[key], null, stackSource, stackDest);
-          }
+      }
+    } else {
+      // Slowest path --- hasOwnProperty can't be called as a method
+      for (key in source) {
+        if (hasOwnProperty.call(source, key)) {
+          destination[key] = copyElement(source[key]);
         }
       }
-      setHashKey(destination,h);
     }
+    setHashKey(destination, h);
+    return destination;
+  }
+
+  function copyElement(source) {
+    // Simple values
+    if (!isObject(source)) {
+      return source;
+    }
+
+    // Already copied values
+    var index = stackSource.indexOf(source);
+    if (index !== -1) {
+      return stackDest[index];
+    }
+
+    if (isWindow(source) || isScope(source)) {
+      throw ngMinErr('cpws',
+        "Can't copy! Making copies of Window or Scope instances is not supported.");
+    }
+
+    var needsRecurse = false;
+    var destination;
+
+    if (isArray(source)) {
+      destination = [];
+      needsRecurse = true;
+    } else if (isTypedArray(source)) {
+      destination = new source.constructor(source);
+    } else if (isDate(source)) {
+      destination = new Date(source.getTime());
+    } else if (isRegExp(source)) {
+      destination = new RegExp(source.source, source.toString().match(/[^\/]*$/)[0]);
+      destination.lastIndex = source.lastIndex;
+    } else if (isFunction(source.cloneNode)) {
+        destination = source.cloneNode(true);
+    } else {
+      destination = Object.create(getPrototypeOf(source));
+      needsRecurse = true;
+    }
+
+    stackSource.push(source);
+    stackDest.push(destination);
+
+    return needsRecurse
+      ? copyRecurse(source, destination)
+      : destination;
   }
-  return destination;
 }
 
 /**

test/AngularSpec.js

@@ -313,11 +313,19 @@ describe('angular', function() {
     it('should throw an exception if a Scope is being copied', inject(function($rootScope) {
       expect(function() { copy($rootScope.$new()); }).
           toThrowMinErr("ng", "cpws", "Can't copy! Making copies of Window or Scope instances is not supported.");
+      expect(function() { copy({child: $rootScope.$new()}, {}); }).
+          toThrowMinErr("ng", "cpws", "Can't copy! Making copies of Window or Scope instances is not supported.");
+      expect(function() { copy([$rootScope.$new()]); }).
+          toThrowMinErr("ng", "cpws", "Can't copy! Making copies of Window or Scope instances is not supported.");
     }));
 
     it('should throw an exception if a Window is being copied', function() {
       expect(function() { copy(window); }).
           toThrowMinErr("ng", "cpws", "Can't copy! Making copies of Window or Scope instances is not supported.");
+      expect(function() { copy({child: window}); }).
+          toThrowMinErr("ng", "cpws", "Can't copy! Making copies of Window or Scope instances is not supported.");
+      expect(function() { copy([window], []); }).
+          toThrowMinErr("ng", "cpws", "Can't copy! Making copies of Window or Scope instances is not supported.");
     });
 
     it('should throw an exception when source and destination are equivalent', function() {
@@ -334,6 +342,11 @@ describe('angular', function() {
       hashKey(src);
       dst = copy(src);
       expect(hashKey(dst)).not.toEqual(hashKey(src));
+
+      src = {foo: {}};
+      hashKey(src.foo);
+      dst = copy(src);
+      expect(hashKey(src.foo)).not.toEqual(hashKey(dst.foo));
     });
 
     it('should retain the previous $$hashKey when copying object with hashKey', function() {