Add deprecation for Route#render method

packages/@ember/-internals/glimmer/tests/integration/application/debug-render-tree-test.ts

@@ -222,10 +222,13 @@ if (ENV._DEBUG_RENDER_TREE) {
             }
 
             renderTemplate(_: Controller, { showHeader }: Model): void {
-              this.render();
+              expectDeprecation(() => this.render(), 'Usage of `render` is deprecated.');
 
               if (showHeader) {
-                this.render('header', { outlet: 'header' });
+                expectDeprecation(
+                  () => this.render('header', { outlet: 'header' }),
+                  'Usage of `render` is deprecated.'
+                );
               } else {
                 expectDeprecation(
                   () => this.disconnectOutlet('header'),

packages/@ember/-internals/glimmer/tests/integration/application/rendering-test.js

@@ -464,11 +464,13 @@ moduleFor(
         'route:application',
         Route.extend({
           renderTemplate() {
-            this.render();
-            this.render('nav', {
-              into: 'application',
-              outlet: 'nav',
-            });
+            expectDeprecation(() => {
+              this.render();
+              this.render('nav', {
+                into: 'application',
+                outlet: 'nav',
+              });
+            }, 'Usage of `render` is deprecated.');
           },
         })
       );
@@ -613,7 +615,10 @@ moduleFor(
           },
 
           renderTemplate(controller, model) {
-            this.render({ controller: model.color, model });
+            expectDeprecation(
+              () => this.render({ controller: model.color, model }),
+              'Usage of `render` is deprecated.'
+            );
           },
         })
       );
@@ -659,7 +664,10 @@ moduleFor(
           },
 
           renderTemplate(controller, model) {
-            this.render('common', { controller: 'common', model });
+            expectDeprecation(
+              () => this.render('common', { controller: 'common', model }),
+              'Usage of `render` is deprecated.'
+            );
           },
         })
       );
@@ -672,7 +680,10 @@ moduleFor(
           },
 
           renderTemplate(controller, model) {
-            this.render('common', { controller: 'common', model });
+            expectDeprecation(
+              () => this.render('common', { controller: 'common', model }),
+              'Usage of `render` is deprecated.'
+            );
           },
         })
       );

packages/@ember/-internals/routing/lib/system/route.ts

@@ -1485,6 +1485,29 @@ class Route extends EmberObject implements IRoute {
     return route && route.currentModel;
   }
 
+  /**
+    `_render` is used to render a template into a region of another template
+    (indicated by an `{{outlet}}`).
+
+    @method _render
+    @param {String} name the name of the template to render
+    @param {Object} [options] the options
+    @param {String} [options.into] the template to render into,
+                    referenced by name. Defaults to the parent template
+    @param {String} [options.outlet] the outlet inside `options.into` to render into.
+                    Defaults to 'main'
+    @param {String|Object} [options.controller] the controller to use for this template,
+                    referenced by name or as a controller instance. Defaults to the Route's paired controller
+    @param {Object} [options.model] the model object to set on `options.controller`.
+                    Defaults to the return value of the Route's model hook
+    @private
+   */
+  _render(name?: string, options?: PartialRenderOptions) {
+    let renderOptions = buildRenderOptions(this, name, options);
+    ROUTE_CONNECTIONS.get(this).push(renderOptions);
+    once(this._router, '_setOutlets');
+  }
+
   /**
     A hook you can use to render the template for the current route.
 
@@ -1521,7 +1544,7 @@ class Route extends EmberObject implements IRoute {
   */
   renderTemplate(_controller: any, _model: {}) {
     // eslint-disable-line no-unused-vars
-    this.render();
+    this._render();
   }
 
   /**
@@ -1652,9 +1675,16 @@ class Route extends EmberObject implements IRoute {
     @public
   */
   render(name?: string, options?: PartialRenderOptions) {
-    let renderOptions = buildRenderOptions(this, name, options);
-    ROUTE_CONNECTIONS.get(this).push(renderOptions);
-    once(this._router, '_setOutlets');
+    deprecate('Usage of `render` is deprecated.', false, {
+      id: 'route-render-template',
+      until: '4.0.0',
+      url: 'https://deprecations.emberjs.com/v3.x/#toc_route-render-template',
+      for: 'ember-source',
+      since: {
+        enabled: '3.27.0',
+      },
+    });
+    this._render(name, options);
   }
 
   /**

packages/ember/tests/routing/model_loading_test.js

@@ -214,7 +214,10 @@ moduleFor(
         Route.extend({
           controllerName: 'myController',
           renderTemplate() {
-            this.render('alternative_home');
+            expectDeprecation(
+              () => this.render('alternative_home'),
+              'Usage of `render` is deprecated.'
+            );
           },
         })
       );