Sync with changes made in master.

lib/legacy/class.html

@@ -153,24 +153,6 @@
           return info.observers;
         }
 
-        /**
-         * @return {HTMLTemplateElement} template for this class
-         */
-        static get template() {
-          if (!this.hasOwnProperty(JSCompiler_renameProperty('_template', this))) {
-            this._template =                  
-              // Accept template: _null to short-circuit dom-module lookup
-              info._template !== undefined ? info._template : 
-              // Look in dom-module associated with this element's is
-              this._getTemplateFromDomModule() ||
-              // Look up in the chain
-              Base.template ||
-              // Use any template set on the prototype via registered callback
-              this.prototype._template;
-          }
-          return this._template;
-        }
-
         /**
          * @return {void}
          */

lib/mixins/element-mixin.html

@@ -130,7 +130,7 @@
     }
 
     /**
-     * Returns a memoized version of the the `observers` array.
+     * Returns a memoized version of the `observers` array.
      * @param {PolymerElementConstructor} constructor Element class
      * @return {Array} Array containing own observers for the given class
      * @protected
@@ -154,7 +154,7 @@
      * alter these settings. However, additional `observers` may be added
      * by subclasses.
      *
-     * The info object should may contain property metadata as follows:
+     * The info object should contain property metadata as follows:
      *
      * * `type`: {function} type to which an attribute matching the property
      * is deserialized. Note the property is camel-cased from a dash-cased
@@ -166,7 +166,7 @@
      * property 'foo',
      *
      * * `computed`: {string} creates a computed property. A computed property
-     * also automatically is set to `readOnly: true`. The value is calculated
+     * is also automatically set to `readOnly: true`. The value is calculated
      * by running a method and arguments parsed from the given string. For
      * example 'compute(foo)' will compute a given property when the
      * 'foo' property changes by executing the 'compute' method. This method
@@ -277,6 +277,27 @@
     }
 
     /**
+     * Look up template from dom-module for element
+     *
+     * @param {!string} is Element name to look up
+     * @return {!HTMLTemplateElement} Template found in dom module, or
+     *   undefined if not found
+     * @protected
+     */
+    function getTemplateFromDomModule(is) {
+      let template = null;
+      if (is && Polymer.DomModule) {
+        template = Polymer.DomModule.import(is, 'template');
+        // Under strictTemplatePolicy, require any element with an `is`
+        // specified to have a dom-module
+        if (Polymer.strictTemplatePolicy && !template) {
+          throw new Error(`strictTemplatePolicy: expecting dom-module or null template for ${is}`);
+        }
+      }
+      return template;
+    }
+
+  /**
      * @polymer
      * @mixinClass
      * @unrestricted
@@ -348,30 +369,6 @@
         }
       }
 
-      /**
-       * Look up template from dom-module for element
-       * 
-       * @param {!string} is Element name to look up
-       * @return {!HTMLTemplateElement} Template found in dom module, or
-       *   undefined if not found
-       * @protected
-       */
-      static _getTemplateFromDomModule() {
-        let template = null;
-        const is = /** @type {PolymerElementConstructor}*/ (this).is;
-        // Under strictTemplatePolicy in 3.x+, dom-module lookup is only allowed
-        // when opted-in via allowTemplateFromDomModule
-        if (is && Polymer.DomModule) {
-          template = Polymer.DomModule.import(is, 'template');
-          // Under strictTemplatePolicy, require any element with an `is`
-          // specified to have a dom-module
-          if (Polymer.strictTemplatePolicy && !template) {
-            throw new Error(`strictTemplatePolicy: expecting dom-module or null template for ${is}`);
-          }
-        }
-        return template;
-      }
-
       /**
        * Returns the template that will be stamped into this element's shadow root.
        *
@@ -410,25 +407,51 @@
        * @return {HTMLTemplateElement|string} Template to be stamped
        */
       static get template() {
+        // Explanation of template-related properties:
+        // - constructor.template (this getter): the template for the class.
+        //     This can come from the prototype (for legacy elements), from a
+        //     dom-module, or from the super class's template (or can be overridden
+        //     altogether by the user)
+        // - constructor._template: memoized version of constructor.template
+        // - prototype._template: working template for the element, which will be
+        //     parsed and modified in place. It is a cloned version of
+        //     constructor.template, saved in _finalizeClass(). Note that before
+        //     this getter is called, for legacy elements this could be from a
+        //     _template field on the info object passed to Polymer(), a behavior,
+        //     or set in registered(); once the static getter runs, a clone of it
+        //     will overwrite it on the prototype as the working template.
         if (!this.hasOwnProperty(JSCompiler_renameProperty('_template', this))) {
           this._template =
+            // If user has put template on prototype (e.g. in legacy via registered
+            // callback or info object), prefer that first
+            this.prototype.hasOwnProperty(JSCompiler_renameProperty('_template', this.prototype)) ?
+            this.prototype._template :
             // Look in dom-module associated with this element's is
-            this._getTemplateFromDomModule() ||
+            (getTemplateFromDomModule(/** @type {PolymerElementConstructor}*/ (this).is) ||
             // Next look for superclass template (call the super impl this
             // way so that `this` points to the superclass)
-            Object.getPrototypeOf(/** @type {PolymerElementConstructor}*/ (this).prototype).constructor.template;
+            Object.getPrototypeOf(/** @type {PolymerElementConstructor}*/ (this).prototype).constructor.template);
         }
         return this._template;
       }
 
+      /**
+       * Set the template.
+       *
+       * @param {!HTMLTemplateElement|string} value Template to set.
+       */
+      static set template(value) {
+        this._template = value;
+      }
+
       /**
        * Path matching the url from which the element was imported.
        *
        * 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 
+       * 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

test/unit/strict-template-policy.html

@@ -222,7 +222,7 @@
         assertThrows(function() {
           el = document.createElement('trusted-element');
           document.getElementById('target').appendChild(el);
-        }, /expecting dom-module or null template/);
+        }, /expecting dom-module or null template for trusted-element/);
         assert.notOk(el && el.shadowRoot);
         assert.notOk(document.getElementById('injected'));
       });
@@ -238,7 +238,7 @@
         }, /trusted-element re-registered/);
         const el = document.createElement('trusted-element');
         document.getElementById('target').appendChild(el);
-        assert.notOk(el && el.shadowRoot);
+        assert.notOk(el.shadowRoot);
         assert.notOk(document.getElementById('injected'));
       });
 
@@ -273,7 +273,7 @@
         assertThrows(function() {
           el = document.createElement('trusted-element-legacy');
           document.getElementById('target').appendChild(el);
-        }, /expecting dom-module or null template/);
+        }, /expecting dom-module or null template for trusted-element-legacy/);
         assert.notOk(el && el.shadowRoot);
         assert.notOk(document.getElementById('injected'));
       });
@@ -287,9 +287,9 @@
             '  </template>`' +
             '</dom-module>';
         }, /trusted-element-legacy re-registered/);
-        const el = document.createElement('trusted-element');
+        const el = document.createElement('trusted-element-legacy');
         document.getElementById('target').appendChild(el);
-        assert.notOk(el && el.shadowRoot);
+        assert.notOk(el.shadowRoot);
         assert.notOk(document.getElementById('injected'));
       });
 
@@ -303,7 +303,7 @@
         Polymer({
           is: 'has-no-template-legacy',
           _template: null
-        }, /expecting dom-module or null template/);
+        });
         let el = document.createElement('has-no-template-legacy');
         document.getElementById('target').appendChild(el);
         assert.notOk(el.shadowRoot);
@@ -331,7 +331,7 @@
         }, /expecting dom-module or null template/);
       });
 
-      test('template helpers in trusted templates work', function() {
+      test('template helpers in trusted templates work', function() {        
         var el = document.createElement('trusted-templates');
         document.getElementById('target').appendChild(el);
         Polymer.flush();
@@ -352,6 +352,7 @@
       });
 
     });
+
   </script>
 
 </body>