feat(esl-utils): add provider to default value in attr

(cherry picked from commit e482aaf)

src/modules/esl-utils/decorators/attr.ts

@@ -1,7 +1,8 @@
-import {identity} from '../misc/functions';
+import {identity, resolveProperty} from '../misc/functions';
 import {parseString, toKebabCase} from '../misc/format';
 import {getAttr, setAttr} from '../dom/attr';
 
+import type {PropertyProvider} from '../misc/functions';
 import type {ESLAttributeDecorator} from '../dom/attr';
 import type {ESLDomElementTarget} from '../abstract/dom-target';
 
@@ -17,7 +18,7 @@ type AttrDescriptor<T = string> = {
   /** Use data-* attribute */
   dataAttr?: boolean;
   /** Default property value. Used if no attribute is present on the element. Empty string by default. */
-  defaultValue?: T;
+  defaultValue?: T | PropertyProvider<T>;
   /** Parser from attribute value */
   parser?: AttrParser<T>;
   /** Serializer to transform passed value to attribute value */
@@ -38,7 +39,9 @@ export const attr = <T = string>(config: AttrDescriptor<T> = {}): ESLAttributeDe
 
     function get(): T | null {
       const val = getAttr(this, attrName);
-      if (val === null && 'defaultValue' in config) return config.defaultValue as T;
+      if (val === null && 'defaultValue' in config) {
+        return resolveProperty(config.defaultValue, this) as T;
+      }
       return (config.parser || parseString as AttrParser<any>)(val);
     }
     function set(value: T): void {

src/modules/esl-utils/decorators/test/attr.test.ts

@@ -18,6 +18,8 @@ describe('Decorator: attr', () => {
     public readonlyField: string | null;
     @attr({defaultValue: 'def'})
     public defField: string | boolean;
+    @attr({defaultValue: () => 'test-provider'})
+    public defProvider: string;
   }
   customElements.define('test-el-attr', TestElement);
   const el = new TestElement();
@@ -99,6 +101,9 @@ describe('Decorator: attr', () => {
     el.defField = false;
     expect(el.defField).toBe('def');
     expect(el.hasAttribute('def-field')).toBe(false);
+    expect(el.defProvider).toBe('test-provider');
+    el.defProvider = '';
+    expect(el.defProvider).toBe('');
   });
 
   afterAll(() => {