feat: add methods to make setting invalid overridable (#1043)

src/vaadin-combo-box-mixin.html

@@ -1093,6 +1093,27 @@
       this._clear();
     }
 
+    /**
+     * @param {boolean} invalid
+     * @protected
+     */
+    _setInvalid(invalid) {
+      if (this._shouldSetInvalid(invalid)) {
+        this.invalid = invalid;
+      }
+    }
+
+    /**
+     * Override this method to define whether the given `invalid` state should be set.
+     *
+     * @param {boolean} _invalid
+     * @return {boolean}
+     * @protected
+     */
+    _shouldSetInvalid(_invalid) {
+      return true;
+    }
+
     /**
      * Validates the field and sets the `invalid` property based on the result.
      *
@@ -1102,7 +1123,7 @@
      */
     validate() {
       const isValid = this.checkValidity();
-      this.invalid = !isValid;
+      this._setInvalid(!isValid);
       this.dispatchEvent(new CustomEvent('validated', {detail: {valid: isValid}}));
       return isValid;
     }

test/validation.html

@@ -82,6 +82,24 @@
       expect(event.detail.valid).to.be.false;
     });
   });
+  describe('invalid cannot be set to false', () => {
+    let comboBox;
+
+    beforeEach(async() => {
+      comboBox = fixture('combo-box');
+      comboBox._shouldSetInvalid = (invalid) => invalid;
+      await nextRender();
+    });
+
+    it('should set invalid only when it is true', async() => {
+      comboBox.required = true;
+      comboBox.validate();
+      expect(comboBox.invalid).to.be.true;
+      comboBox.value = 'foo';
+      comboBox.validate();
+      expect(comboBox.invalid).to.be.true;
+    });
+  });
   </script>
 
 </body>