Parser: Refactor meta parsing as filtered external source

blocks/api/parser.js

@@ -8,6 +8,7 @@ import { mapValues, omit } from 'lodash';
  * WordPress dependencies
  */
 import { autop } from '@wordpress/autop';
+import { applyFilters } from '@wordpress/hooks';
 
 /**
  * Internal dependencies
@@ -118,7 +119,15 @@ export function getBlockAttribute( attributeKey, attributeSchema, innerHTML, com
 			break;
 	}
 
-	return value === undefined ? attributeSchema.default : asType( value, attributeSchema.type );
+	value = applyFilters( 'blocks.getBlockAttribute.source', value, attributeSchema, innerHTML, commentAttributes );
+
+	if ( value === undefined ) {
+		value = attributeSchema.default;
+	} else {
+		value = asType( value, attributeSchema.type );
+	}
+
+	return applyFilters( 'blocks.getBlockAttribute', value, attributeSchema, innerHTML, commentAttributes );
 }
 
 /**

edit-post/hooks/index.js

@@ -0,0 +1,4 @@
+/**
+ * Internal dependencies
+ */
+import './meta';

edit-post/hooks/meta/index.js

@@ -0,0 +1,28 @@
+/**
+ * WordPress dependencies
+ */
+import { addFilter } from '@wordpress/hooks';
+import { select } from '@wordpress/data';
+
+const editor = select( 'core/editor' );
+
+/**
+ * Filters an attribute value during parse to inject post properties from meta.
+ *
+ * @param {*}      value  Parsed value.
+ * @param {Object} schema Attribute schema.
+ *
+ * @return {*} Filtered value with meta substitute if applicable.
+ */
+function getMetaAttributeFromPost( value, schema ) {
+	if ( schema.source === 'meta' ) {
+		const meta = editor.getCurrentPost().meta;
+		if ( meta && meta.hasOwnProperty( schema.meta ) ) {
+			return meta[ schema.meta ];
+		}
+	}
+
+	return value;
+}
+
+addFilter( 'blocks.getBlockAttribute', 'core/edit-post/meta/getMetaAttributeFromPost', getMetaAttributeFromPost );

edit-post/index.js

@@ -18,6 +18,7 @@ import { EditorProvider, ErrorBoundary } from '@wordpress/editor';
 import './assets/stylesheets/main.scss';
 import Layout from './components/layout';
 import store from './store';
+import './hooks';
 
 // Configure moment globally
 moment.locale( dateSettings.l10n.locale );

editor/store/effects.js

@@ -292,10 +292,21 @@ export default {
 
 		dispatch( savePost() );
 	},
-	SETUP_EDITOR( action ) {
+	SETUP_EDITOR( action, store ) {
 		const { post, settings } = action;
 		const effects = [];
 
+		// Dispatch must occur immediately, as subsequent block parse filtering
+		// may rely on post properties.
+		store.dispatch( resetPost( post ) );
+
+		// Include auto draft title in edits while not flagging post as dirty
+		if ( post.status === 'auto-draft' ) {
+			effects.push( setupNewPost( {
+				title: post.title.raw,
+			} ) );
+		}
+
 		// Parse content as blocks
 		if ( post.content.raw ) {
 			effects.push( resetBlocks( parse( post.content.raw ) ) );
@@ -311,17 +322,6 @@ export default {
 			effects.push( resetBlocks( blocks ) );
 		}
 
-		// Resetting post should occur after blocks have been reset, since it's
-		// the post reset that restarts history (used in dirty detection).
-		effects.push( resetPost( post ) );
-
-		// Include auto draft title in edits while not flagging post as dirty
-		if ( post.status === 'auto-draft' ) {
-			effects.push( setupNewPost( {
-				title: post.title.raw,
-			} ) );
-		}
-
 		return effects;
 	},
 	FETCH_REUSABLE_BLOCKS( action, store ) {

editor/store/index.js

@@ -11,6 +11,7 @@ import applyMiddlewares from './middlewares';
 import {
 	getBlockCount,
 	getBlocks,
+	getCurrentPost,
 	getEditedPostAttribute,
 	getLastMultiSelectedBlockUid,
 	getSelectedBlockCount,
@@ -30,6 +31,7 @@ loadAndPersist( store, reducer, 'preferences', STORAGE_KEY );
 registerSelectors( MODULE_KEY, {
 	getBlockCount,
 	getBlocks,
+	getCurrentPost,
 	getEditedPostAttribute,
 	getLastMultiSelectedBlockUid,
 	getSelectedBlockCount,

editor/store/reducer.js

@@ -114,12 +114,12 @@ function getFlattenedBlocks( blocks ) {
 export const editor = flow( [
 	combineReducers,
 
-	// Track undo history, starting at editor initialization.
-	partialRight( withHistory, { resetTypes: [ 'SETUP_NEW_POST', 'SETUP_EDITOR' ] } ),
+	// Track undo history, starting at editor initialization of blocks. Assumes
+	// one of either block resetting, new post setup occurs in initialization.
+	partialRight( withHistory, { resetTypes: [ 'SETUP_NEW_POST', 'RESET_BLOCKS' ] } ),
 
-	// Track whether changes exist, resetting at each post save. Relies on
-	// editor initialization firing post reset as an effect.
-	partialRight( withChangeDetection, { resetTypes: [ 'SETUP_NEW_POST', 'RESET_POST' ] } ),
+	// Track whether changes exist, resetting at initialization and each save.
+	partialRight( withChangeDetection, { resetTypes: [ 'RESET_POST', 'SETUP_NEW_POST', 'RESET_BLOCKS' ] } ),
 ] )( {
 	edits( state = {}, action ) {
 		switch ( action.type ) {

editor/store/selectors.js

@@ -6,9 +6,7 @@ import {
 	map,
 	first,
 	get,
-	has,
 	last,
-	reduce,
 	compact,
 	find,
 	some,
@@ -422,47 +420,17 @@ export const getBlock = createSelector(
 			return null;
 		}
 
-		let { attributes } = block;
-
-		// Inject custom source attribute values.
-		//
-		// TODO: Create generic external sourcing pattern, not explicitly
-		// targeting meta attributes.
-		const type = getBlockType( block.name );
-		if ( type ) {
-			attributes = reduce( type.attributes, ( result, value, key ) => {
-				if ( value.source === 'meta' ) {
-					if ( result === attributes ) {
-						result = { ...result };
-					}
-
-					result[ key ] = getPostMeta( state, value.meta );
-				}
-
-				return result;
-			}, attributes );
-		}
-
 		return {
 			...block,
-			attributes,
 			innerBlocks: getBlocks( state, uid ),
 		};
 	},
 	( state, uid ) => [
 		get( state, [ 'editor', 'present', 'blocksByUid', uid ] ),
 		getBlockDependantsCacheBust( state, uid ),
-		get( state, [ 'editor', 'present', 'edits', 'meta' ] ),
-		get( state, 'currentPost.meta' ),
 	]
 );
 
-function getPostMeta( state, key ) {
-	return has( state, [ 'editor', 'present', 'edits', 'meta', key ] ) ?
-		get( state, [ 'editor', 'present', 'edits', 'meta', key ] ) :
-		get( state, [ 'currentPost', 'meta', key ] );
-}
-
 /**
  * Returns all block objects for the current post being edited as an array in
  * the order they appear in the post.