Adds check for attributes in block settings (#15959)

* Adds check for attributes in block settings

* Adds unit test

* Addresses PR feedback

packages/block-editor/src/hooks/anchor.js

@@ -1,7 +1,7 @@
 /**
  * External dependencies
  */
-import { assign } from 'lodash';
+import { assign, has } from 'lodash';
 
 /**
  * WordPress dependencies
@@ -33,6 +33,10 @@ const ANCHOR_REGEX = /[\s#]/g;
  * @return {Object} Filtered block settings.
  */
 export function addAttribute( settings ) {
+	// allow blocks to specify their own attribute definition with default values if needed.
+	if ( has( settings.attributes, [ 'anchor', 'type' ] ) ) {
+		return settings;
+	}
 	if ( hasBlockSupport( settings, 'anchor' ) ) {
 		// Use Lodash's assign to gracefully handle if attributes are undefined
 		settings.attributes = assign( settings.attributes, {

packages/block-editor/src/hooks/test/anchor.js

@@ -39,6 +39,23 @@ describe( 'anchor', () => {
 
 			expect( settings.attributes ).toHaveProperty( 'anchor' );
 		} );
+
+		it( 'should not override attributes defined in settings', () => {
+			const settings = registerBlockType( {
+				...blockSettings,
+				supports: {
+					anchor: true,
+				},
+				attributes: {
+					anchor: {
+						type: 'string',
+						default: 'testAnchor',
+					},
+				},
+			} );
+
+			expect( settings.attributes.anchor ).toEqual( { type: 'string', default: 'testAnchor' } );
+		} );
 	} );
 
 	describe( 'addSaveProps', () => {