Editor: Consider single unmodified default block as empty content

packages/editor/src/hooks/index.js

@@ -7,3 +7,4 @@ import './custom-class-name';
 import './default-autocompleters';
 import './generated-class-name';
 import './layout';
+import './process-content';

packages/editor/src/hooks/process-content.js

@@ -0,0 +1,91 @@
+/**
+ * WordPress dependencies
+ */
+import { addFilter } from '@wordpress/hooks';
+import { removep } from '@wordpress/autop';
+import {
+	isUnmodifiedDefaultBlock,
+	getUnknownTypeHandlerName,
+} from '@wordpress/blocks';
+
+/**
+ * Returns true if the given array of blocks consists of a single block of the
+ * unknown type, or false otherwise.
+ *
+ * @param {WPBlock[]} blocks Array of block objects.
+ *
+ * @return {boolean} Whether array consists of single unknown block.
+ */
+export function isSingleUnknownBlock( blocks ) {
+	return (
+		blocks.length === 1 &&
+		blocks[ 0 ].name === getUnknownTypeHandlerName()
+	);
+}
+
+/**
+ * Returns true if the given array of blocks consists of a single unmodified
+ * default block, or false otherwise.
+ *
+ * @param {WPBlock[]} blocks Array of block objects.
+ *
+ * @return {boolean} Whether array consists of single unmodified default block.
+ */
+export function isSingleUnmodifiedDefaultBlock( blocks ) {
+	return (
+		blocks.length === 1 &&
+		isUnmodifiedDefaultBlock( blocks[ 0 ] )
+	);
+}
+
+/**
+ * Given an array of blocks, returns either an empty array if the blocks
+ * consist only of a single unmodified default block. Otherwise returns the
+ * original array unmodified.
+ *
+ * @param {WPBlock[]} blocks Array of blocks.
+ *
+ * @return {WPBlock[]} Empty array, or original passed set of blocks.
+ */
+export function omitSingleUnmodifiedDefaultBlock( blocks ) {
+	if ( isSingleUnmodifiedDefaultBlock( blocks ) ) {
+		blocks = [];
+	}
+
+	return blocks;
+}
+
+/**
+ * Given an HTML string and array of blocks, returns a formatted HTML string
+ * with paragraph tags removed via `removep` behavior if the array of blocks
+ * consists only of a single block of the unknown type.
+ *
+ * @link https://www.npmjs.com/package/@wordpress/autop
+ *
+ * @param {string}    content HTML content.
+ * @param {WPBlock[]} blocks  Array of blocks from which HTML content has been
+ *                            generated.
+ *
+ * @return {string} HTML content, with `removep` filtering applied if the array
+ *                  of blocks from which it was generated consists only of a
+ *                  single block of the unknown type.
+ */
+export function removepSingleUnknownBlock( content, blocks ) {
+	if ( isSingleUnknownBlock( blocks ) ) {
+		content = removep( content );
+	}
+
+	return content;
+}
+
+addFilter(
+	'editor.selectors.getBlockContent',
+	'core/processContent/removepSingleUnknownBlock',
+	removepSingleUnknownBlock
+);
+
+addFilter(
+	'editor.selectors.getBlocksForSave',
+	'core/processContent/omitSingleUnmodifiedDefaultBlock',
+	omitSingleUnmodifiedDefaultBlock
+);

packages/editor/src/hooks/test/process-content.js

@@ -0,0 +1,179 @@
+/**
+ * WordPress dependencies
+ */
+import {
+	getBlockTypes,
+	unregisterBlockType,
+	registerBlockType,
+	createBlock,
+	getDefaultBlockName,
+	setDefaultBlockName,
+	getUnknownTypeHandlerName,
+	setUnknownTypeHandlerName,
+} from '@wordpress/blocks';
+
+/**
+ * Internal dependencies
+ */
+import {
+	isSingleUnknownBlock,
+	isSingleUnmodifiedDefaultBlock,
+	omitSingleUnmodifiedDefaultBlock,
+	removepSingleUnknownBlock,
+} from '../process-content';
+
+describe( 'processContent', () => {
+	let originalDefaultBlockName, originalUnknownTypeHandlerName;
+
+	beforeAll( () => {
+		originalDefaultBlockName = getDefaultBlockName();
+		originalUnknownTypeHandlerName = getUnknownTypeHandlerName();
+
+		registerBlockType( 'core/default', {
+			category: 'common',
+			title: 'default',
+			attributes: {
+				modified: {
+					type: 'boolean',
+					default: false,
+				},
+			},
+			save: () => null,
+		} );
+		registerBlockType( 'core/unknown', {
+			category: 'common',
+			title: 'unknown',
+			save: () => null,
+		} );
+		setDefaultBlockName( 'core/default' );
+		setUnknownTypeHandlerName( 'core/unknown' );
+	} );
+
+	afterAll( () => {
+		setDefaultBlockName( originalDefaultBlockName );
+		setUnknownTypeHandlerName( originalUnknownTypeHandlerName );
+		getBlockTypes().forEach( ( block ) => {
+			unregisterBlockType( block.name );
+		} );
+	} );
+
+	describe( 'isSingleUnknownBlock', () => {
+		it( 'returns false if multiple blocks passed', () => {
+			const blocks = [
+				createBlock( getUnknownTypeHandlerName() ),
+				createBlock( getUnknownTypeHandlerName() ),
+			];
+
+			const result = isSingleUnknownBlock( blocks );
+
+			expect( result ).toBe( false );
+		} );
+
+		it( 'returns false if single block not of unknown type', () => {
+			const blocks = [
+				createBlock( getDefaultBlockName() ),
+			];
+
+			const result = isSingleUnknownBlock( blocks );
+
+			expect( result ).toBe( false );
+		} );
+
+		it( 'returns true if single block of unknown type', () => {
+			const blocks = [
+				createBlock( getUnknownTypeHandlerName() ),
+			];
+
+			const result = isSingleUnknownBlock( blocks );
+
+			expect( result ).toBe( true );
+		} );
+	} );
+
+	describe( 'isSingleUnmodifiedDefaultBlock', () => {
+		it( 'returns false if multiple blocks passed', () => {
+			const blocks = [
+				createBlock( getDefaultBlockName() ),
+				createBlock( getDefaultBlockName() ),
+			];
+
+			const result = isSingleUnmodifiedDefaultBlock( blocks );
+
+			expect( result ).toBe( false );
+		} );
+
+		it( 'returns false if single non-default block', () => {
+			const blocks = [
+				createBlock( getUnknownTypeHandlerName() ),
+			];
+
+			const result = isSingleUnmodifiedDefaultBlock( blocks );
+
+			expect( result ).toBe( false );
+		} );
+
+		it( 'returns false if single modified default block', () => {
+			const blocks = [
+				createBlock( getDefaultBlockName(), { modified: true } ),
+			];
+
+			const result = isSingleUnmodifiedDefaultBlock( blocks );
+
+			expect( result ).toBe( false );
+		} );
+
+		it( 'returns true if single unmodified default block', () => {
+			const blocks = [
+				createBlock( getDefaultBlockName() ),
+			];
+
+			const result = isSingleUnmodifiedDefaultBlock( blocks );
+
+			expect( result ).toBe( true );
+		} );
+	} );
+
+	describe( 'omitSingleUnmodifiedDefaultBlock', () => {
+		it( 'returns original array of blocks if not single unmodified default block', () => {
+			const blocks = [
+				createBlock( getUnknownTypeHandlerName() ),
+			];
+
+			const result = omitSingleUnmodifiedDefaultBlock( blocks );
+
+			expect( result ).toBe( blocks );
+		} );
+
+		it( 'returns an empty array if single unmodified default block', () => {
+			const blocks = [
+				createBlock( getDefaultBlockName() ),
+			];
+
+			const result = omitSingleUnmodifiedDefaultBlock( blocks );
+
+			expect( result ).toEqual( [] );
+		} );
+	} );
+
+	describe( 'removepSingleUnknownBlock', () => {
+		it( 'returns original content if not single block of unknown type', () => {
+			const blocks = [
+				createBlock( getDefaultBlockName() ),
+			];
+
+			const result = removepSingleUnknownBlock( '<p>foo</p>', blocks );
+
+			expect( result ).toBe( '<p>foo</p>' );
+		} );
+
+		it( 'returns removep-formatted content if single block of unknown type', () => {
+			const blocks = [
+				createBlock( getUnknownTypeHandlerName() ),
+			];
+
+			const result = removepSingleUnknownBlock( '<p>foo</p>', blocks );
+
+			expect( result ).toBe( 'foo' );
+		} );
+	} );
+} );

packages/editor/src/store/selectors.js

@@ -23,9 +23,15 @@ import createSelector from 'rememo';
 /**
  * WordPress dependencies
  */
-import { serialize, getBlockType, getBlockTypes, hasBlockSupport, hasChildBlocks, getUnknownTypeHandlerName } from '@wordpress/blocks';
+import {
+	serialize,
+	getBlockType,
+	getBlockTypes,
+	hasBlockSupport,
+	hasChildBlocks,
+} from '@wordpress/blocks';
 import { moment } from '@wordpress/date';
-import { removep } from '@wordpress/autop';
+import { applyFilters } from '@wordpress/hooks';
 
 /***
  * Module constants
@@ -349,15 +355,20 @@ export function isEditedPostSaveable( state ) {
 
 /**
  * Returns true if the edited post has content. A post has content if it has at
- * least one block or otherwise has a non-empty content property assigned.
+ * least one saveable block or otherwise has a non-empty content property
+ * assigned.
  *
  * @param {Object} state Global application state.
  *
  * @return {boolean} Whether post has content.
  */
 export function isEditedPostEmpty( state ) {
+	// While the condition of truthy content string would be sufficient for
+	// determining emptiness, testing saveable blocks length is a trivial
+	// operation by comparison. Since this function can be called frequently,
+	// optimize for the fast case where saveable blocks are non-empty.
 	return (
-		! getBlockCount( state ) &&
+		! getBlocksForSave( state ).length &&
 		! getEditedPostAttribute( state, 'content' )
 	);
 }
@@ -1346,6 +1357,50 @@ export function getSuggestedPostFormat( state ) {
 	return null;
 }
 
+/**
+ * Returns a filtered set of blocks which are assumed to be used in
+ * consideration of the post's generated save content.
+ *
+ * @param {Object} state Editor state.
+ *
+ * @return {WPBlock[]} Filtered set of blocks for save.
+ */
+export function getBlocksForSave( state ) {
+	/**
+	 * Filters the set of blocks assumed to be used in consideration of the
+	 * post's generated save content.
+	 *
+	 * @param {Object[]} blocks Original editor state blocks.
+	 */
+	return applyFilters(
+		'editor.selectors.getBlocksForSave',
+		getBlocks( state ),
+	);
+}
+
+/**
+ * Returns a filtered HTML string for serialized given array of blocks.
+ *
+ * @param {Object}    state  Editor state.
+ * @param {WPBlock[]} blocks Array of blocks from which to generate content.
+ *
+ * @return {string} Filtered HTML string for serialized blocks.
+ */
+export function getBlockContent( state, blocks ) {
+	/**
+	 * Filters the serialized content result of blocks.
+	 *
+	 * @param {string}    content Original serialized value.
+	 * @param {WPBlock[]} blocks  Blocks from which serialized value is
+	 *                            generated.
+	 */
+	return applyFilters(
+		'editor.selectors.getBlockContent',
+		serialize( blocks ),
+		blocks
+	);
+}
+
 /**
  * Returns the content of the post being edited, preferring raw string edit
  * before falling back to serialization of block state.
@@ -1361,13 +1416,7 @@ export const getEditedPostContent = createSelector(
 			return edits.content;
 		}
 
-		const blocks = getBlocks( state );
-
-		if ( blocks.length === 1 && blocks[ 0 ].name === getUnknownTypeHandlerName() ) {
-			return removep( serialize( blocks ) );
-		}
-
-		return serialize( blocks );
+		return getBlockContent( state, getBlocksForSave( state ) );
 	},
 	( state ) => [
 		state.editor.present.edits.content,