Add ability to define importMeta on legacy elements. Fixes #5163

Author: kevinpschaaf

lib/legacy/legacy-element-mixin.html

@@ -86,6 +86,16 @@
         this._applyListeners();
       }
 
+      /**
+       * Forwards `importMeta` from the prototype (i.e. from the info object
+       * passed to `Polymer({...})`) to the static API.
+       *
+       * @return {!Object} The `import.meta` object set on the prototype
+       */
+      static get importMeta() {
+        return this.prototype.importMeta;
+      }
+
       /**
        * Legacy callback called during the `constructor`, for overriding
        * by the user.

lib/mixins/element-mixin.html

@@ -402,11 +402,13 @@
        * This path is used to resolve url's in template style cssText.
        * The `importPath` property is also set on element instances and can be
        * used to create bindings relative to the import path.
-       * For elements defined in ES modules, users should implement `importMeta`
-       * and this getter will return `import.meta.url`'s path. For elements
-       * defined in HTML imports, this getter will return the path to the
-       * document containing a `dom-module` element matching this element's
-       * static `is` property.
+       *
+       * For elements defined in ES modules, users should implement 
+       * `static get importMeta() { return import.meta; }` and the default
+       * implementation of `importPath` will  return `import.meta.url`'s path.
+       * For elements defined in HTML imports, this getter will return the path
+       * to the document containing a `dom-module` element matching this
+       * element's static `is` property.
        *
        * Note, this path should contain a trailing `/`.
        *
@@ -426,18 +428,6 @@
         return this._importPath;
       }
 
-      /**
-       * When an element definition is being loaded from an ES module, users
-       * may override this getter to return the `import.meta` object from that
-       * module, which will be used to derive the `importPath` for the element.
-       * When implementing `importMeta`, users should not implement `importPath`.
-       *
-       * @return {!Object} The `import.meta` object for the element's module
-       */
-      static get importMeta() {
-        return null;
-      }
-
       constructor() {
         super();
         /** @type {HTMLTemplateElement} */

test/unit/resolveurl.html

@@ -82,7 +82,9 @@
 
       test('Urls in styles and attributes', testStylesAndAttributes('p-r', 'sub'));
 
-      test('Urls in styles and attributes (importMeta)', testStylesAndAttributes('p-r-im', 'http://foo.com/mymodule'));
+      test('Urls in styles and attributes (importMeta)', testStylesAndAttributes('p-r-im', 'http://class.com/mymodule'));
+
+      test('Urls in styles and attributes (importMeta, hybrid)', testStylesAndAttributes('p-r-hybrid', 'http://hybrid.com/mymodule'));
 
       test('url changes via setting importPath/rootPath on element instance', function() {
         var el = document.createElement('p-r');

test/unit/sub/resolveurl-elements.html

@@ -39,14 +39,26 @@
   }
   customElements.define(PR.is, PR);
 
-  class PRImportMeta extends PR {
+  class PRImportMeta extends Polymer.Element {
+    static get template() {
+      return Polymer.DomModule.import('p-r', 'template').cloneNode(true);
+    }
     static get importMeta() {
       // Idiomatically, this would be `return import.meta`, but for purposes
       // of stubbing the test without actual modules, it's shimmed
-      return { url: 'http://foo.com/mymodule/index.js' }
+      return { url: 'http://class.com/mymodule/index.js' };
     }
   }
   customElements.define('p-r-im', PRImportMeta);
+
+  const PRHybrid = Polymer({
+    is: 'p-r-hybrid',
+    _template: Polymer.DomModule.import('p-r', 'template').cloneNode(true),
+    // Idiomatically, this would be `return import.meta`, but for purposes
+    // of stubbing the test without actual modules, it's shimmed
+    importMeta: { url: 'http://hybrid.com/mymodule/index.js' }
+  });
+
 </script>
 
 <dom-module id="p-r-ap" assetpath="../../assets/"></dom-module>