Expose before filter hook in useSettings and the block metadata for C…

…SS classes generation (#45089)

packages/block-editor/src/components/use-setting/index.js

@@ -11,6 +11,7 @@ import {
 	__EXPERIMENTAL_PATHS_WITH_MERGE as PATHS_WITH_MERGE,
 	hasBlockSupport,
 } from '@wordpress/blocks';
+import { applyFilters } from '@wordpress/hooks';
 
 /**
  * Internal dependencies
@@ -122,7 +123,18 @@ export default function useSetting( path ) {
 				return undefined;
 			}
 
-			let result;
+			// 0. Allow third parties to filter the block's settings at runtime.
+			let result = applyFilters(
+				'blockEditor.useSetting.before',
+				undefined,
+				path,
+				clientId,
+				blockName
+			);
+
+			if ( undefined !== result ) {
+				return result;
+			}
 
 			const normalizedPath = removeCustomPrefixes( path );
 

packages/block-editor/src/components/use-setting/test/index.js

@@ -0,0 +1,99 @@
+/**
+ * WordPress dependencies
+ */
+import { addFilter, removeFilter } from '@wordpress/hooks';
+import { useSelect } from '@wordpress/data';
+
+/**
+ * Internal dependencies
+ */
+import useSetting from '..';
+import * as BlockEditContext from '../../block-edit/context';
+
+// Mock useSelect() functions used by useSetting()
+jest.mock( '@wordpress/data/src/components/use-select' );
+
+let selectMock = {};
+const setupSelectMock = () => {
+	selectMock = {
+		getSettings: () => ( {} ),
+		getBlockParents: () => [],
+		getBlockName: () => '',
+	};
+};
+
+useSelect.mockImplementation( ( callback ) => callback( () => selectMock ) );
+
+const mockSettings = ( settings ) => {
+	selectMock.getSettings = () => ( {
+		__experimentalFeatures: settings,
+	} );
+};
+
+const mockCurrentBlockContext = (
+	blockContext = { name: '', isSelected: false }
+) => {
+	jest.spyOn( BlockEditContext, 'useBlockEditContext' ).mockReturnValue(
+		blockContext
+	);
+};
+
+describe( 'useSetting', () => {
+	beforeEach( () => {
+		setupSelectMock();
+		mockCurrentBlockContext();
+	} );
+
+	it( 'uses block setting', () => {
+		mockSettings( {
+			blocks: {
+				'core/test-block': {
+					layout: {
+						contentSize: '840px',
+					},
+				},
+			},
+		} );
+
+		mockCurrentBlockContext( {
+			name: 'core/test-block',
+		} );
+
+		expect( useSetting( 'layout.contentSize' ) ).toBe( '840px' );
+	} );
+
+	it( 'uses blockEditor.useSetting.before hook override', () => {
+		mockSettings( {
+			blocks: {
+				'core/test-block': {
+					layout: {
+						contentSize: '840px',
+					},
+				},
+			},
+		} );
+
+		mockCurrentBlockContext( {
+			name: 'core/test-block',
+		} );
+
+		addFilter(
+			'blockEditor.useSetting.before',
+			'test/useSetting.before',
+			( result, path, clientId, blockName ) => {
+				if ( blockName === 'core/test-block' ) {
+					return '960px';
+				}
+
+				return result;
+			}
+		);
+
+		expect( useSetting( 'layout.contentSize' ) ).toBe( '960px' );
+
+		removeFilter(
+			'blockEditor.useSetting.before',
+			'test/useSetting.before'
+		);
+	} );
+} );