feat(sidenav): configurable scroll prevent target (#9338)

* Adds the ability to select which element's scrolling will be disabled when a sidenav is open. This can be useful in the cases where the scrollable container isn't the direct parent of the sidenav.
* Adds unit tests for the parent scroll prevention.

Fixes #8634

src/components/sidenav/sidenav.js

@@ -232,6 +232,8 @@ function SidenavFocusDirective() {
  * @param {expression=} md-is-locked-open When this expression evaluates to true,
  * the sidenav 'locks open': it falls into the content's flow instead
  * of appearing over it. This overrides the `md-is-open` attribute.
+ * @param {string=} md-disable-scroll-target Selector, pointing to an element, whose scrolling will
+ * be disabled when the sidenav is opened. By default this is the sidenav's direct parent.
  *
 * The $mdMedia() service is exposed to the is-locked-open attribute, which
  * can be given a media query or one of the `sm`, `gt-sm`, `md`, `gt-md`, `lg` or `gt-lg` presets.
@@ -261,6 +263,7 @@ function SidenavDirective($mdMedia, $mdUtil, $mdConstant, $mdTheming, $animate,
   function postLink(scope, element, attr, sidenavCtrl) {
     var lastParentOverFlow;
     var backdrop;
+    var disableScrollTarget = null;
     var triggeringElement = null;
     var previousContainerStyles;
     var promise = $q.when(true);
@@ -275,8 +278,23 @@ function SidenavDirective($mdMedia, $mdUtil, $mdConstant, $mdTheming, $animate,
       });
     };
 
+    if (attr.mdDisableScrollTarget) {
+      disableScrollTarget = $document[0].querySelector(attr.mdDisableScrollTarget);
+
+      if (disableScrollTarget) {
+        disableScrollTarget = angular.element(disableScrollTarget);
+      } else {
+        $log.warn($mdUtil.supplant('mdSidenav: couldn\'t find element matching ' +
+          'selector "{selector}". Falling back to parent.', { selector: attr.mdDisableScrollTarget }));
+      }
+    }
+
+    if (!disableScrollTarget) {
+      disableScrollTarget = element.parent();
+    }
+
     // Only create the backdrop if the backdrop isn't disabled.
-    if (!angular.isDefined(attr.mdDisableBackdrop)) {
+    if (!attr.hasOwnProperty('mdDisableBackdrop')) {
       backdrop = $mdUtil.createBackdrop(scope, "md-sidenav-backdrop md-opaque ng-enter");
     }
 
@@ -393,25 +411,20 @@ function SidenavDirective($mdMedia, $mdUtil, $mdConstant, $mdTheming, $animate,
           backdrop[0].style.height = null;
 
           previousContainerStyles = null;
-        }
+        };
       }
     }
 
     /**
      * Prevent parent scrolling (when the SideNav is open)
      */
     function disableParentScroll(disabled) {
-      var parent = element.parent();
       if ( disabled && !lastParentOverFlow ) {
-
-        lastParentOverFlow = parent.css('overflow');
-        parent.css('overflow', 'hidden');
-
+        lastParentOverFlow = disableScrollTarget.css('overflow');
+        disableScrollTarget.css('overflow', 'hidden');
       } else if (angular.isDefined(lastParentOverFlow)) {
-
-        parent.css('overflow', lastParentOverFlow);
+        disableScrollTarget.css('overflow', lastParentOverFlow);
         lastParentOverFlow = undefined;
-
       }
     }
 

src/components/sidenav/sidenav.spec.js

@@ -164,6 +164,47 @@ describe('mdSidenav', function() {
       });
     });
 
+    describe('parent scroll prevention', function() {
+      it('should prevent scrolling on the parent element', inject(function($rootScope) {
+        var parent = setup('md-is-open="isOpen"').parent()[0];
+
+        expect(parent.style.overflow).toBeFalsy();
+        $rootScope.$apply('isOpen = true');
+        expect(parent.style.overflow).toBe('hidden');
+      }));
+
+      it('should prevent scrolling on a custom element', inject(function($compile, $rootScope) {
+        var preventScrollTarget = angular.element('<div id="prevent-scroll-target"></div>');
+        var parent = angular.element(
+          '<div>' +
+            '<md-sidenav md-disable-scroll-target="#prevent-scroll-target" md-is-open="isOpen"></md-sidenav>' +
+          '</div>'
+        );
+
+        preventScrollTarget.append(parent);
+        angular.element(document.body).append(preventScrollTarget);
+        $compile(preventScrollTarget)($rootScope);
+
+        expect(preventScrollTarget[0].style.overflow).toBeFalsy();
+        expect(parent[0].style.overflow).toBeFalsy();
+
+        $rootScope.$apply('isOpen = true');
+        expect(preventScrollTarget[0].style.overflow).toBe('hidden');
+        expect(parent[0].style.overflow).toBeFalsy();
+        preventScrollTarget.remove();
+      }));
+
+      it('should log a warning and fall back to the parent if the custom scroll target does not exist',
+        inject(function($rootScope, $log) {
+          spyOn($log, 'warn');
+          var parent = setup('md-is-open="isOpen" md-disable-scroll-target="does-not-exist"').parent()[0];
+
+          $rootScope.$apply('isOpen = true');
+          expect($log.warn).toHaveBeenCalled();
+          expect(parent.style.overflow).toBe('hidden');
+        }));
+    });
+
   });
 
   describe('controller', function() {