fix(icon): handle icons as <symbol> nodes

Fixes icons not being rendered if they're defined as a `<symbol>` inside the source file.

Fixes angular#4680.

src/lib/icon/fake-svgs.ts

@@ -30,6 +30,14 @@ const FAKE_SVGS = (() => {
       </svg>
   `);
 
+  svgs.set('farm-set-3.svg', `
+      <svg>
+        <symbol id="duck">
+          <path id="quack"></path>
+        </symbol>
+      </svg>
+  `);
+
   svgs.set('arrow-set.svg', `
       <svg>
         <defs>

src/lib/icon/icon-registry.ts

@@ -327,14 +327,24 @@ export class MdIconRegistry {
    */
   private _extractSvgIconFromSet(iconSet: SVGElement, iconName: string): SVGElement {
     const iconNode = iconSet.querySelector('#' + iconName);
+
     if (!iconNode) {
       return null;
     }
+
     // If the icon node is itself an <svg> node, clone and return it directly. If not, set it as
     // the content of a new <svg> node.
-    if (iconNode.tagName.toLowerCase() == 'svg') {
+    if (iconNode.tagName.toLowerCase() === 'svg') {
       return this._setSvgAttributes(iconNode.cloneNode(true) as SVGElement);
     }
+
+    // If the node is a <symbol>, it won't be rendered so we have to convert it into <svg>. Note
+    // that the same could be achieved by referring to it via <use href="#id">, however the <use>
+    // tag is problematic on Firefox, because it needs to include the current page path.
+    if (iconNode.nodeName.toLowerCase() === 'symbol') {
+      return this._setSvgAttributes(this._toSvgElement(iconNode));
+    }
+
     // createElement('SVG') doesn't work as expected; the DOM ends up with
     // the correct nodes, but the SVG content doesn't render. Instead we
     // have to create an empty SVG node using innerHTML and append its content.
@@ -343,6 +353,7 @@ export class MdIconRegistry {
     const svg = this._svgElementFromString('<svg></svg>');
     // Clone the node so we don't remove it from the parent icon set element.
     svg.appendChild(iconNode.cloneNode(true));
+
     return this._setSvgAttributes(svg);
   }
 
@@ -361,6 +372,19 @@ export class MdIconRegistry {
     return svg;
   }
 
+  /**
+   * Converts an element into an SVG node by cloning all of its children.
+   */
+  private _toSvgElement(element: Element): SVGElement {
+    let svg = this._svgElementFromString('<svg></svg>');
+
+    for (let i = 0; i < element.children.length; i++) {
+      svg.appendChild(element.children[i].cloneNode(true));
+    }
+
+    return svg;
+  }
+
   /**
    * Sets the default attributes for an SVG element to be used as an icon.
    */

src/lib/icon/icon.spec.ts

@@ -10,28 +10,31 @@ import {wrappedErrorMessage} from '../core/testing/wrapped-error-message';
 
 
 /** Returns the CSS classes assigned to an element as a sorted array. */
-const sortedClassNames = (elem: Element) => elem.className.split(' ').sort();
+function sortedClassNames(element: Element): string[] {
+  return element.className.split(' ').sort();
+}
 
 /**
  * Verifies that an element contains a single <svg> child element, and returns that child.
  */
-const verifyAndGetSingleSvgChild = (element: SVGElement): any => {
+function verifyAndGetSingleSvgChild(element: SVGElement): SVGElement {
   expect(element.childNodes.length).toBe(1);
-  const svgChild = <Element>element.childNodes[0];
+  const svgChild = element.childNodes[0] as SVGElement;
   expect(svgChild.tagName.toLowerCase()).toBe('svg');
   return svgChild;
-};
+}
 
 /**
  * Verifies that an element contains a single <path> child element whose "id" attribute has
  * the specified value.
  */
-const verifyPathChildElement = (element: Element, attributeValue: string) => {
+function verifyPathChildElement(element: Element, attributeValue: string): void {
   expect(element.childNodes.length).toBe(1);
-  const pathElement = <Element>element.childNodes[0];
+  const pathElement = element.childNodes[0] as SVGPathElement;
   expect(pathElement.tagName.toLowerCase()).toBe('path');
   expect(pathElement.getAttribute('id')).toBe(attributeValue);
-};
+}
+
 
 describe('MdIcon', () => {
 
@@ -240,6 +243,25 @@ describe('MdIcon', () => {
       expect(httpRequestUrls.sort()).toEqual(['farm-set-1.svg', 'farm-set-2.svg']);
     });
 
+    it('should unwrap <symbol> nodes', () => {
+      mdIconRegistry.addSvgIconSetInNamespace('farm', trust('farm-set-3.svg'));
+
+      const fixture = TestBed.createComponent(MdIconFromSvgNameTestApp);
+      const testComponent = fixture.componentInstance;
+      const mdIconElement = fixture.debugElement.nativeElement.querySelector('md-icon');
+
+      testComponent.iconName = 'farm:duck';
+      fixture.detectChanges();
+
+      const svgElement = verifyAndGetSingleSvgChild(mdIconElement);
+      const firstChild = svgElement.children[0];
+
+      expect(svgElement.querySelector('symbol')).toBeFalsy();
+      expect(svgElement.children.length).toBe(1);
+      expect(firstChild.nodeName.toLowerCase()).toBe('path');
+      expect(firstChild.getAttribute('id')).toBe('quack');
+    });
+
     it('should not wrap <svg> elements in icon sets in another svg tag', () => {
       mdIconRegistry.addSvgIconSet(trust('arrow-set.svg'));