fix(util, datePicker): support $compileProvider.debugInfoEnabled(false);

add `$mdUtil.validateScope( )` to confirm availability of scope value.

Fixes angular#4532.

>  [$compileProvider](https://docs.angularjs.org/guide/production) explains that `$compileProvider.debugInfoEnabled(false)` will make the `scope()` function return undefined: @see angular/angular.js@dbbe6b3

src/components/datepicker/datePicker.js

@@ -294,9 +294,13 @@
  if (this.$attrs['ngDisabled']) {
  // The expression is to be evaluated against the directive element's scope and not
  // the directive's isolate scope.
- this.$element.scope().$watch(this.$attrs['ngDisabled'], function(isDisabled) {
- self.setDisabled(isDisabled);
- });
+ var scope = this.$mdUtil.validateScope(this.$element) ? this.$element.scope() : null;
+
+ if ( scope ) {
+ scope.$watch(this.$attrs['ngDisabled'], function(isDisabled) {
+ self.setDisabled(isDisabled);
+ });
+ }
  }
 
  Object.defineProperty(this, 'placeholder', {

src/core/util/util.js

@@ -141,7 +141,8 @@ function UtilFactory($document, $timeout, $compile, $rootScope, $$mdAnimate, $in
 
  // If the expression evaluates to FALSE, then it is not focusable target
  var focusExpression = it[0].getAttribute(attribute);
- var isFocusable = focusExpression ? (it.scope().$eval(focusExpression) !== false ) : true;
+ var isFocusable = !focusExpression || !$mdUtil.validateScope(it) ? true :
+ (it.scope().$eval(focusExpression) !== false );
 
  if (isFocusable) elFound = it;
  });
@@ -404,6 +405,22 @@ function UtilFactory($document, $timeout, $compile, $rootScope, $$mdAnimate, $in
  return '' + nextUniqueId++;
  },
 
+ /**
+ * By default AngularJS attaches information about binding and scopes to DOM nodes,
+ * and adds CSS classes to data-bound elements. But this information is NOT available
+ * when `$compileProvider.debugInfoEnabled(false);`
+ *
+ * @see https://docs.angularjs.org/guide/production
+ */
+ validateScope : function(element) {
+ var hasScope = element && angular.isDefined(element.scope());
+ if ( !hasScope ) {
+ $log.warn("element.scope() is not available when 'debug mode' == false. @see https://docs.angularjs.org/guide/production!");
+ }
+
+ return hasScope;
+ },
+
  // Stop watchers and events from firing on a scope without destroying it,
  // by disconnecting it from its parent and its siblings' linked lists.
  disconnectScope: function disconnectScope(scope) {

src/core/util/util.spec.js

@@ -1,5 +1,39 @@
 describe('util', function() {
 
+ describe('validateScope',function() {
+
+ it("should not find a valid scope when debug is disabled", function() {
+ module(function($compileProvider) {
+ $compileProvider.debugInfoEnabled(false);
+ });
+
+ inject(function($compile, $rootScope, $mdUtil) {
+ var widget = angular.element($compile('<div><button><img></button></div>')($rootScope));
+ var button = angular.element(widget.children()[0]);
+
+ $rootScope.$apply();
+ expect(button.scope()).toBe(undefined);
+ expect($mdUtil.validateScope(button)).toBe(false);
+
+ });
+ });
+
+ it("should find a valid scope when debug is enabled", function() {
+ module(function($compileProvider) {
+ $compileProvider.debugInfoEnabled(true);
+ });
+
+ inject(function($compile, $rootScope, $mdUtil) {
+ var widget = angular.element($compile('<div><button><img></button></div>')($rootScope));
+ var button = angular.element(widget.children()[0]);
+
+ $rootScope.$apply();
+ expect(button.scope()).toBeDefined();
+ expect($mdUtil.validateScope(button)).toBe(true);
+ });
+ });
+ });
+
  describe('with no overrides', function() {
  beforeEach(module('material.core'));