chore: SlotRerenderObject aligned with reactive cycle (docs + changelog) (#1999)

.changeset/slot-mixin-reactivity-align.md

@@ -0,0 +1,7 @@
+---
+'@lion/ui': minor
+---
+
+fix(ui): align light dom with internal [reactivity cycle of LitElement/ReactiveElement](https://lit.dev/docs/components/lifecycle/#reactive-update-cycle).
+Since light dom render is now aligned inside `update` instead of `updated` (like it already was for shadow dom),
+we can rely on the fact that all dom (light and shadow) has rendered inside our `updated` loop.

docs/fundamentals/systems/core/SlotMixin.md

@@ -74,7 +74,6 @@ class MyAccessibleControl extends SlotMixin(LitElement) {
      'rerenderable-slot': () => {
        return {
          template: html`<w-c>${this.litProperty}</w-c>`,
-         afterRender: () => { /** sync some state */ },
        }
      },
      // undefined (conditional slot)
@@ -105,14 +104,11 @@ A `SlotRerenderObject` looks like this:
 ```ts
 {
   template: TemplateResult;
- afterRender?: Function;
-};
+}
 ```
 
-It is meant for complex templates that need rerenders. Normally - when rendering into shadow dom via `LitElement.render` - we get rerenders
-"for free" via [property effects](https://lit.dev/docs/components/properties/#when-properties-change).
-When we configure `SlotFunctionResult` to return a `SlotRerenderObject`, we get the same behavior for light dom.
-For this rerendering to work predictably (no focus and other interaction issues), the slot will be created with a wrapper div.
+It is meant for complex templates that need rerenders and are bound to the [reactive update cycle](https://lit.dev/docs/components/lifecycle/#reactive-update-cycle). The same lifecycle hooks (for instance `updated`) can be used as with templates rendered to the shadow root (via the regular render function).
+For rerendering to work predictably (no focus and other interaction issues), the slot will be created within a wrapper div.
 
 ### Undefined
 

packages/ui/components/core/src/SlotMixin.js

@@ -83,6 +83,7 @@ const SlotMixinImplementation = superclass =>
         slotName,
         shouldRerender: true,
       });
+      // TODO: this is deprecated, remove later
       slotFunctionResult.afterRender?.();
     }
 

packages/ui/components/core/test/SlotMixin.test.js

@@ -383,7 +383,7 @@ describe('SlotMixin', () => {
       expect(slot.tagName).to.equal('SPAN');
     });
 
-    it('supports afterRender logic (type "{ template:TemplateResults; afterRender: Function}" )', async () => {
+    it('supports (deprecated) afterRender logic (type "{ template:TemplateResults; afterRender: Function}" )', async () => {
       let varThatProvesAfterRenderIsCalled = 'not called';
 
       const tag = defineCE(

packages/ui/components/core/types/SlotMixinTypes.ts

@@ -6,7 +6,10 @@ import { TemplateResult, LitElement } from 'lit';
  */
 export type SlotRerenderObject = {
   template: TemplateResult;
-  /* Add logic that will be performed after the render */
+  /**
+   * Add logic that will be performed after the render
+   * @deprecated
+   */
   afterRender?: Function;
 };
 

packages/ui/components/input-tel-dropdown/src/LionInputTelDropdown.js

@@ -180,7 +180,6 @@ export class LionInputTelDropdown extends LionInputTel {
 
         return {
           template: templates.dropdown(this._templateDataDropdown),
-          afterRender: this.__syncRegionWithDropdown,
         };
       },
     };
@@ -274,9 +273,7 @@ export class LionInputTelDropdown extends LionInputTel {
   updated(changedProperties) {
     super.updated(changedProperties);
 
-    if (changedProperties.has('activeRegion')) {
     this.__syncRegionWithDropdown();
-    }
 
     if (changedProperties.has('disabled') || changedProperties.has('readOnly')) {
       if (this.disabled || this.readOnly) {