fix: do not re-render when setting sync property to same value

packages/component-base/src/polylit-mixin.js

@@ -4,6 +4,7 @@
  * This program is available under Apache License Version 2.0, available at https://vaadin.com/license/
  */
 import { dedupeMixin } from '@open-wc/dedupe-mixin';
+import { notEqual } from 'lit';
 import { get, set } from './path-utils.js';
 
 const caseMap = {};
@@ -101,12 +102,15 @@ const PolylitMixinImplementation = (superclass) => {
           get: defaultDescriptor.get,
           set(value) {
             const oldValue = this[name];
-            this[key] = value;
-            this.requestUpdate(name, oldValue, options);
 
-            // Enforce synchronous update
-            if (this.hasUpdated) {
-              this.performUpdate();
+            if (notEqual(value, oldValue)) {
+              this[key] = value;
+              this.requestUpdate(name, oldValue, options);
+
+              // Enforce synchronous update
+              if (this.hasUpdated) {
+                this.performUpdate();
+              }
             }
           },
           configurable: true,
@@ -115,21 +119,17 @@ const PolylitMixinImplementation = (superclass) => {
       }
 
       if (options.readOnly) {
-        const setter = defaultDescriptor.set;
+        const setter = result.set;
 
         this.addCheckedInitializer((instance) => {
           // This is run during construction of the element
           instance[`_set${upper(name)}`] = function (value) {
             setter.call(instance, value);
-
-            if (options.sync) {
-              this.performUpdate();
-            }
           };
         });
 
         result = {
-          get: defaultDescriptor.get,
+          get: result.get,
           set() {
             // Do nothing, property is read-only.
           },

packages/component-base/src/resize-mixin.js

@@ -8,6 +8,10 @@ import { dedupingMixin } from '@polymer/polymer/lib/utils/mixin.js';
 const observer = new ResizeObserver((entries) => {
   setTimeout(() => {
     entries.forEach((entry) => {
+      if (!entry.target.isConnected) {
+        return;
+      }
+
       // Notify child resizables, if any
       if (entry.target.resizables) {
         entry.target.resizables.forEach((resizable) => {

packages/component-base/test/polylit-mixin.test.js

@@ -1079,6 +1079,20 @@ describe('PolylitMixin', () => {
       expect(element.hasAttribute('helper')).to.be.true;
     });
 
+    it('should not reflect immediately when setting a read-only sync property to the same value', () => {
+      element._setOpened(true);
+      element._setHelper('foo'); // async property
+      element._setOpened(true); // sync property
+      expect(element.hasAttribute('helper')).to.be.false;
+    });
+
+    it('should not reflect immediately when setting sync property to the same value', () => {
+      element.disabled = true;
+      element._setHelper('foo'); // async property
+      element.disabled = true; // sync property
+      expect(element.hasAttribute('helper')).to.be.false;
+    });
+
     it('should only call ready callback once during initialization', () => {
       expect(element.count).to.equal(1);
     });

packages/date-picker/src/vaadin-date-picker-mixin.js

@@ -1211,10 +1211,7 @@ export const DatePickerMixin = (subclass) =>
         if (!dateEquals(this.__enteredDate, date)) {
           this.__enteredDate = date;
         }
-      } else if (this.__enteredDate != null) {
-        // Do not override initial undefined value with null
-        // to avoid triggering a Lit update that can cause
-        // other scheduled properties to flush too early.
+      } else {
         this.__enteredDate = null;
       }
     }

packages/field-base/src/input-mixin.js

@@ -63,6 +63,7 @@ export const InputMixin = dedupingMixin(
             type: Boolean,
             value: false,
             observer: '_hasInputValueChanged',
+            sync: true,
           },
         };
       }

packages/grid/src/vaadin-grid-column-group-mixin.js

@@ -41,6 +41,7 @@ export const GridColumnGroupMixin = (superClass) =>
         width: {
           type: String,
           readOnly: true,
+          sync: true,
         },
 
         /** @private */

packages/grid/src/vaadin-grid-column-mixin.js

@@ -177,10 +177,16 @@ export const ColumnBaseMixin = (superClass) =>
         _emptyCells: Array,
 
         /** @private */
-        _headerCell: Object,
+        _headerCell: {
+          type: Object,
+          sync: true,
+        },
 
         /** @private */
-        _footerCell: Object,
+        _footerCell: {
+          type: Object,
+          sync: true,
+        },
 
         /** @protected */
         _grid: Object,

packages/grid/src/vaadin-grid-sorter-mixin.js

@@ -117,6 +117,14 @@ export const GridSorterMixin = (superClass) =>
     /** @protected */
     connectedCallback() {
       super.connectedCallback();
+
+      if (this.performUpdate) {
+        // Force Lit's first render to be synchronous to ensure
+        // _pathOrDirectionChanged is triggered before grid's
+        // __applySorters, as it is in Polymer.
+        this.performUpdate();
+      }
+
       if (this._grid) {
         this._grid.__applySorters();
       } else {

packages/item/src/vaadin-item-mixin.js

@@ -38,6 +38,7 @@ export const ItemMixin = (superClass) =>
           value: false,
           reflectToAttribute: true,
           observer: '_selectedChanged',
+          sync: true,
         },
 
         /** @private */

packages/select/src/vaadin-select-base-mixin.js

@@ -97,6 +97,7 @@ export const SelectBaseMixin = (superClass) =>
           value: '',
           notify: true,
           observer: '_valueChanged',
+          sync: true,
         },
 
         /**