fix(icon): rename nodes id's from cache to prevent duplicates.

Currently we always rename the icons id's on cache initialization, but that causes problems, when using the cached icon multiple times in the app.
A super elegant solution, is to transform the ids, when the icon is requested from the cache.

Closes #7468

src/components/icon/icon.spec.js

@@ -478,6 +478,41 @@ describe('mdIcon service', function() {
       });
     });
 
+    describe('icon is cached', function() {
+
+      it('should prevent duplicate ids', function() {
+        var firstId;
+
+        $mdIcon('android.svg').then(function(el) {
+          // First child is in our case always the node with an id.
+          firstId = el.firstChild.id;
+        });
+
+        $scope.$digest();
+
+        $mdIcon('android.svg').then(function(el) {
+          expect(el.firstChild.id).not.toBe(firstId);
+        });
+
+        $scope.$digest();
+
+      });
+
+      it('should suffix duplicated ids', function() {
+        // Just request the icon to be stored in the cache.
+        $mdIcon('android.svg');
+
+        $scope.$digest();
+
+        $mdIcon('android.svg').then(function(el) {
+          expect(el.firstChild.id).toMatch(/.+_cache[0-9]+/g);
+        });
+
+        $scope.$digest();
+      });
+
+    });
+
     describe('icon group is not found', function() {
       it('should log Error', function() {
         var msg;
@@ -509,11 +544,6 @@ describe('mdIcon service', function() {
   function updateDefaults(svg) {
     svg = angular.element(svg)[0];
 
-    svg.removeAttribute('id');
-    angular.forEach(svg.querySelectorAll('[id]'), function(item) {
-      item.removeAttribute('id');
-    });
-
     angular.forEach({
       'xmlns' : 'http://www.w3.org/2000/svg',
       'fit'   : '',

src/components/icon/js/iconService.js

@@ -316,9 +316,9 @@
 
    },
 
-   $get : ['$http', '$q', '$log', '$templateCache', function($http, $q, $log, $templateCache) {
+   $get : ['$http', '$q', '$log', '$templateCache', '$mdUtil', function($http, $q, $log, $templateCache, $mdUtil) {
      this.preloadIcons($templateCache);
-     return MdIconService(config, $http, $q, $log, $templateCache);
+     return MdIconService(config, $http, $q, $log, $templateCache, $mdUtil);
    }]
  };
 
@@ -373,7 +373,7 @@
   */
 
   /* @ngInject */
- function MdIconService(config, $http, $q, $log, $templateCache) {
+ function MdIconService(config, $http, $q, $log, $templateCache, $mdUtil) {
    var iconCache = {};
    var urlRegex = /[-\w@:%\+.~#?&//=]{2,}\.[a-z]{2,4}\b(\/[-\w@:%\+.~#?&//=]*)?/i;
    var dataUrlRegex = /^data:image\/svg\+xml[\s*;\w\-\=]*?(base64)?,(.*)$/i;
@@ -393,7 +393,7 @@
      // If already loaded and cached, use a clone of the cached icon.
      // Otherwise either load by URL, or lookup in the registry and then load by URL, and cache.
 
-     if ( iconCache[id] ) return $q.when( iconCache[id].clone() );
+     if ( iconCache[id] ) return $q.when( transformClone(iconCache[id]) );
      if ( urlRegex.test(id) || dataUrlRegex.test(id) ) return loadByURL(id).then( cacheIcon(id) );
      if ( id.indexOf(':') == -1 ) id = '$default:' + id;
 
@@ -418,24 +418,28 @@
       return result;
    }
 
+   function transformClone(cacheElement) {
+     var clone = cacheElement.clone();
+     var cacheSuffix = '_cache' + $mdUtil.nextUid();
+
+     // We need to modify for each cached icon the id attributes.
+     // This is needed because SVG id's are treated as normal DOM ids
+     // and should not have a duplicated id.
+     if (clone.id) clone.id += cacheSuffix;
+     angular.forEach(clone.querySelectorAll('[id]'), function (item) {
+       item.id += cacheSuffix;
+     });
+
+     return clone;
+   }
+
    /**
     * Prepare and cache the loaded icon for the specified `id`
     */
    function cacheIcon( id ) {
 
-     return function updateCache( _icon ) {
-       var icon = isIcon(_icon) ? _icon : new Icon(_icon, config[id]);
-
-       //clear id attributes to prevent aria issues
-       var elem = icon.element;
-       elem.removeAttribute('id');
-
-       angular.forEach(elem.querySelectorAll('[id]'), function(item) {
-         item.removeAttribute('id');
-       });
-
-       iconCache[id] = icon;
-
+     return function updateCache( icon ) {
+       iconCache[id] = isIcon(icon) ? icon : new Icon(icon, config[id]);
 
        return iconCache[id].clone();
      };