Revert to legacy template getter, update tests.

lib/legacy/class.js

@@ -148,6 +148,24 @@ function GenerateClassFromInfo(info, Base) {
       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.js

@@ -270,29 +270,6 @@ export const ElementMixin = dedupingMixin(base => {
     }
   }
 
-  /**
-   * 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
-   * @private
-   */
-  function getTemplateFromDomModule(is) {
-    let template = null;
-    // Under strictTemplatePolicy in 3.x+, dom-module lookup is only allowed
-    // when opted-in via allowTemplateFromDomModule
-    if (is && (!strictTemplatePolicy || allowTemplateFromDomModule)) {
-      template = DomModule.import(is, 'template');
-      // Under strictTemplatePolicy, require any element with an `is`
-      // specified to have a dom-module
-      if (strictTemplatePolicy && !template) {
-        throw new Error(`strictTemplatePolicy: expecting dom-module or null template for ${is}`);
-      }
-    }
-    return template;
-  }
-
   /**
    * @polymer
    * @mixinClass
@@ -364,6 +341,30 @@ export const ElementMixin = dedupingMixin(base => {
       }
     }
 
+    /**
+     * 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 && (!strictTemplatePolicy || allowTemplateFromDomModule)) {
+        template = DomModule.import(is, 'template');
+        // Under strictTemplatePolicy, require any element with an `is`
+        // specified to have a dom-module
+        if (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.
      *
@@ -403,17 +404,14 @@ export const ElementMixin = dedupingMixin(base => {
     static get template() {
       if (!this.hasOwnProperty(JSCompiler_renameProperty('_template', this))) {
         this._template =
-          // Take any template set on the prototype, including null (for legacy
-          // support, setting in registered callback, etc.)
-          this.prototype._template !== undefined ? this.prototype._template :
           // Look in dom-module associated with this element's is
-          getTemplateFromDomModule(/** @type {PolymerElementConstructor}*/ (this).is) ||
+          this._getTemplateFromDomModule() ||
           // 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;
       }
       return this._template;
-  }
+    }
 
     /**
      * Path matching the url from which the element was imported.

test/unit/behaviors.html

@@ -23,7 +23,7 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
     </template>
   </dom-module>
 
-  <dom-module id="template-from-behavior">
+  <dom-module id="template-from-base">
     <template>
       <div id="from-base">should not be used</div>
     </template>
@@ -299,9 +299,9 @@ window.templateBehavior2 = {
   _template: html`<div id="from-behavior2"></div>`
 };
 
-window.templateBehaviorFromRegister = {
+window.templateBehaviorFromRegistered = {
   registered: function() {
-    this._template = html`<div id="behavior-from-register"></div>`;
+    this._template = html`<div id="behavior-from-registered"></div>`;
   }
 };
 
@@ -312,6 +312,13 @@ Polymer({
   }
 });
 
+Polymer({
+  is: 'template-from-base',
+  behaviors: [
+    window.templateBehavior1
+  ]
+});
+
 Polymer({
   is: 'template-from-behavior',
   behaviors: [
@@ -330,8 +337,7 @@ Polymer({
 Polymer({
   is: 'template-from-behavior-registered',
   behaviors: [
-    window.templateBehavior1,
-    window.templateBehaviorFromRegister
+    window.templateBehaviorFromRegistered
   ]
 });
 </script>
@@ -366,6 +372,12 @@ Polymer({
     </template>
   </test-fixture>
 
+  <test-fixture id="from-base">
+    <template>
+      <template-from-base></template-from-base>
+    </template>
+  </test-fixture>
+
   <test-fixture id="from-behavior">
     <template>
       <template-from-behavior></template-from-behavior>
@@ -588,9 +600,14 @@ suite('templates from behaviors', function() {
     assert.ok(el.shadowRoot.querySelector('#from-registered'));
   });
 
+  test('template from base', function() {
+    var el = fixture('from-base');
+    assert.ok(el.shadowRoot.querySelector('#from-base'));
+    assert.notOk(el.shadowRoot.querySelector('#from-behavior1'));
+  });
+
   test('template from behavior', function() {
     var el = fixture('from-behavior');
-    assert.notOk(el.shadowRoot.querySelector('#from-base'));
     assert.ok(el.shadowRoot.querySelector('#from-behavior1'));
   });
 
@@ -602,8 +619,7 @@ suite('templates from behaviors', function() {
 
   test('template from behavior registered callback', function() {
     var el = fixture('from-behavior-registered');
-    assert.notOk(el.shadowRoot.querySelector('#from-behavior1'));
-    assert.ok(el.shadowRoot.querySelector('#behavior-from-register'));
+    assert.ok(el.shadowRoot.querySelector('#behavior-from-registered'));
   });
 
 });

test/unit/strict-template-policy.html

@@ -85,8 +85,12 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
 
     suite('strictTemplatePolicy', function() {
 
-      teardown(function() {
+      function restoreOnError() {
         window.uncaughtErrorFilter = window.top.uncaughtErrorFilter = null;
+      }
+
+      teardown(function() {
+        restoreOnError();
         document.getElementById('target').textContent = '';
       });
 
@@ -117,6 +121,7 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
             throw new Error(uncaughtError.message);
           }
         }, re);
+        restoreOnError();
       }
 
       test('dom-bind', function() {
@@ -181,9 +186,12 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
             '  </template>`' +
             '</dom-module>';
         }, /trusted-element re-registered/);
-        const el = document.createElement('trusted-element');
-        document.getElementById('target').appendChild(el);
-        assert.notOk(el.shadowRoot);
+        let el;
+        assertThrows(function() {
+          el = document.createElement('trusted-element');
+          document.getElementById('target').appendChild(el);
+        }, /expecting dom-module or null template for trusted-element/);
+        assert.notOk(el && el.shadowRoot);
         assert.notOk(document.getElementById('injected'));
       });
       
@@ -229,9 +237,12 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
             '  </template>`' +
             '</dom-module>';
         }, /trusted-element-legacy re-registered/);
-        const el = document.createElement('trusted-element-legacy');
-        document.getElementById('target').appendChild(el);
-        assert.notOk(el.shadowRoot);
+        let el;
+        assertThrows(function() {
+          el = document.createElement('trusted-element-legacy');
+          document.getElementById('target').appendChild(el);
+        }, /expecting dom-module or null template for trusted-element-legacy/);
+        assert.notOk(el && el.shadowRoot);
         assert.notOk(document.getElementById('injected'));
       });