Visual revisions: Add a code diff view inside the editor

packages/editor/CHANGELOG.md

@@ -10,6 +10,10 @@
 
 -   The "Apply globally" control now opens a review modal so you can choose which of a block's modified styles are pushed to Global Styles, showing each style's current and new value ([#79839](https://github.com/WordPress/gutenberg/pull/79839)).
 
+### Enhancements
+
+-   Add a read-only code diff to the revisions screen ([#80314](https://github.com/WordPress/gutenberg/pull/80314)).
+
 ### Bug Fixes
 
 -   `mediaUpload`: Add an `isTransportOnly` parameter, set by the `@wordpress/upload-media` queue, which owns progress tracking and save locking for its own items and uses this function only as its server transport. Fixes the progress snackbar showing "1 of 2" for a single HEIC upload in Safari ([#80369](https://github.com/WordPress/gutenberg/issues/80369)).

packages/editor/src/components/editor-interface/index.js

@@ -30,7 +30,11 @@ import TemplateValidationNotice from '../template-validation-notice';
 import Header from '../header';
 import InserterSidebar from '../inserter-sidebar';
 import ListViewSidebar from '../list-view-sidebar';
-import { RevisionsHeader, RevisionsCanvas } from '../post-revisions-preview';
+import {
+	RevisionsHeader,
+	RevisionsCanvas,
+	RevisionsCodeDiff,
+} from '../post-revisions-preview';
 import { CollaboratorsOverlay } from '../collaborators-overlay';
 import { useCollaboratorNotifications } from '../collaborators-presence/use-collaborator-notifications';
 import SavePublishPanels from '../save-publish-panels';
@@ -174,7 +178,13 @@ export default function EditorInterface( {
 						onToggleDiff={ () => setShowRevisionDiff( ! showDiff ) }
 					/>
 				}
-				content={ <RevisionsCanvas /> }
+				content={
+					mode === 'text' ? (
+						<RevisionsCodeDiff />
+					) : (
+						<RevisionsCanvas />
+					)
+				}
 				sidebar={ <ComplementaryArea.Slot scope="core" /> }
 			/>
 		);

packages/editor/src/components/more-menu/index.js

@@ -22,7 +22,7 @@ import ToolsMoreMenuGroup from './tools-more-menu-group';
 import ViewMoreMenuGroup from './view-more-menu-group';
 import { store as editorStore } from '../../store';
 
-export default function MoreMenu( { disabled = false } ) {
+export default function MoreMenu( { isRevisionMode = false } ) {
 	const { openModal } = useDispatch( interfaceStore );
 	const { set: setPreference } = useDispatch( preferencesStore );
 	const { toggleDistractionFree } = useDispatch( editorStore );
@@ -35,24 +35,32 @@ export default function MoreMenu( { disabled = false } ) {
 	const turnOffDistractionFree = () => {
 		setPreference( 'core', 'distractionFree', false );
 	};
+	const dropdownProps = {
+		icon: moreVertical,
+		label: __( 'Options' ),
+		popoverProps: {
+			placement: 'bottom-end',
+			className: 'more-menu-dropdown__content',
+		},
+		toggleProps: {
+			showTooltip: ! showIconLabels,
+			...( showIconLabels && { variant: 'tertiary' } ),
+			tooltipPosition: 'bottom',
+			size: 'compact',
+		},
+	};
+
+	if ( isRevisionMode ) {
+		return (
+			<DropdownMenu { ...dropdownProps }>
+				{ () => <ModeSwitcher /> }
+			</DropdownMenu>
+		);
+	}
 
 	return (
 		<>
-			<DropdownMenu
-				icon={ moreVertical }
-				label={ __( 'Options' ) }
-				popoverProps={ {
-					placement: 'bottom-end',
-					className: 'more-menu-dropdown__content',
-				} }
-				toggleProps={ {
-					showTooltip: ! showIconLabels,
-					...( showIconLabels && { variant: 'tertiary' } ),
-					tooltipPosition: 'bottom',
-					size: 'compact',
-					disabled,
-				} }
-			>
+			<DropdownMenu { ...dropdownProps }>
 				{ ( { onClose } ) => (
 					<>
 						<MenuGroup label={ _x( 'View', 'noun' ) }>

packages/editor/src/components/post-revisions-preview/index.js

@@ -1,2 +1,3 @@
 export { default as RevisionsHeader } from './revisions-header';
 export { default as RevisionsCanvas } from './revisions-canvas';
+export { default as RevisionsCodeDiff } from './revisions-code-diff';

packages/editor/src/components/post-revisions-preview/revisions-code-diff.js

@@ -0,0 +1,236 @@
+/**
+ * External dependencies
+ */
+import { diffLines } from 'diff';
+
+/**
+ * WordPress dependencies
+ */
+import { Spinner } from '@wordpress/components';
+import { useSelect } from '@wordpress/data';
+import { useMemo } from '@wordpress/element';
+import { __ } from '@wordpress/i18n';
+import { VisuallyHidden } from '@wordpress/ui';
+
+/**
+ * Internal dependencies
+ */
+import { store as editorStore } from '../../store';
+import { unlock } from '../../lock-unlock';
+
+const MAX_DIFF_EDIT_LENGTH = 1000;
+const DIFF_TIMEOUT = 100;
+
+/**
+ * Diff parts often end in a newline. Remove the trailing empty item so it is
+ * not rendered as another source line.
+ *
+ * @param {string} value Diff part value.
+ * @return {string[]} Lines in the diff part.
+ */
+function splitLines( value ) {
+	const lines = value.split( '\n' );
+	if ( lines[ lines.length - 1 ] === '' ) {
+		lines.pop();
+	}
+	return lines;
+}
+
+/**
+ * Creates the rows shown in the code diff and adds line numbers for both
+ * revisions.
+ *
+ * @param {string}  previousContent Previous revision content.
+ * @param {string}  currentContent  Selected revision content.
+ * @param {boolean} showDiff        Whether changes should be highlighted.
+ * @return {Array<Object>} Code-diff rows.
+ */
+export function getCodeDiffRows( previousContent, currentContent, showDiff ) {
+	let parts = [ { value: currentContent } ];
+	if ( showDiff ) {
+		parts = diffLines( previousContent, currentContent, {
+			maxEditLength: MAX_DIFF_EDIT_LENGTH,
+			timeout: DIFF_TIMEOUT,
+		} );
+
+		// Line diffing can be quadratic for unrelated revisions. If it exceeds
+		// either limit, mark every old and new line instead.
+		if ( ! parts ) {
+			parts = [
+				{ value: previousContent, removed: true },
+				{ value: currentContent, added: true },
+			];
+		}
+	}
+	let previousLineNumber = 1;
+	let currentLineNumber = 1;
+
+	return parts.flatMap( ( part ) => {
+		let status = 'unchanged';
+		if ( part.added ) {
+			status = 'added';
+		} else if ( part.removed ) {
+			status = 'removed';
+		}
+
+		return splitLines( part.value ).map( ( value ) => {
+			const row = {
+				value,
+				status,
+				previousLineNumber: null,
+				currentLineNumber: null,
+			};
+
+			if ( status !== 'added' && showDiff ) {
+				row.previousLineNumber = previousLineNumber++;
+			}
+			if ( status !== 'removed' ) {
+				row.currentLineNumber = currentLineNumber++;
+			}
+
+			return row;
+		} );
+	} );
+}
+
+export default function ConnectedRevisionsCodeDiff() {
+	const revisionDiff = useSelect( ( select ) => {
+		const editorSelectors = select( editorStore );
+		const {
+			getCurrentRevision,
+			getPreviousRevision,
+			getRevisionPage,
+			getRevisionsPerPage,
+			isShowingRevisionDiff,
+		} = unlock( editorSelectors );
+		const _previousRevision = getPreviousRevision();
+		const _showDiff = isShowingRevisionDiff();
+		const totalPages =
+			Math.ceil(
+				editorSelectors.getCurrentPostRevisionsCount() /
+					getRevisionsPerPage()
+			) || 1;
+
+		return {
+			revision: getCurrentRevision(),
+			previousRevision: _previousRevision,
+			showDiff: _showDiff,
+			isPreviousRevisionLoading:
+				_showDiff &&
+				_previousRevision === null &&
+				getRevisionPage() < totalPages,
+		};
+	}, [] );
+
+	return <RevisionsCodeDiff { ...revisionDiff } />;
+}
+
+/**
+ * Shows the selected revision's raw block markup as a read-only diff.
+ *
+ * @param {Object}      props                           Component props.
+ * @param {Object}      props.revision                  Selected revision.
+ * @param {Object|null} props.previousRevision          Previous revision.
+ * @param {boolean}     props.showDiff                  Whether to show changes.
+ * @param {boolean}     props.isPreviousRevisionLoading Whether the previous revision is loading.
+ * @return {React.JSX.Element} The revision code diff.
+ */
+export function RevisionsCodeDiff( {
+	revision,
+	previousRevision,
+	showDiff,
+	isPreviousRevisionLoading,
+} ) {
+	const rows = useMemo( () => {
+		if ( ! revision || isPreviousRevisionLoading ) {
+			return [];
+		}
+
+		return getCodeDiffRows(
+			previousRevision?.content?.raw ?? '',
+			revision.content?.raw ?? '',
+			showDiff
+		);
+	}, [ revision, previousRevision, showDiff, isPreviousRevisionLoading ] );
+
+	if ( ! revision || isPreviousRevisionLoading ) {
+		return (
+			<div className="editor-revisions-canvas__loading">
+				<Spinner />
+			</div>
+		);
+	}
+
+	const label = showDiff ? __( 'Code changes' ) : __( 'Revision code' );
+
+	return (
+		<div
+			className="editor-revisions-code-diff"
+			role="region"
+			aria-label={ label }
+			tabIndex={ 0 }
+		>
+			{ rows.length ? (
+				<table className="editor-revisions-code-diff__table">
+					<VisuallyHidden render={ <caption /> }>
+						{ label }
+					</VisuallyHidden>
+					<VisuallyHidden render={ <thead /> }>
+						<tr>
+							{ showDiff && <th>{ __( 'Previous line' ) }</th> }
+							<th>{ __( 'Current line' ) }</th>
+							{ showDiff && <th>{ __( 'Change' ) }</th> }
+							<th>{ __( 'Code' ) }</th>
+						</tr>
+					</VisuallyHidden>
+					<tbody>
+						{ rows.map( ( row, index ) => {
+							let marker = '';
+							let statusLabel = __( 'Unchanged' );
+							if ( row.status === 'added' ) {
+								marker = '+';
+								statusLabel = __( 'Added' );
+							} else if ( row.status === 'removed' ) {
+								marker = '−';
+								statusLabel = __( 'Removed' );
+							}
+
+							return (
+								<tr
+									key={ index }
+									className={ `editor-revisions-code-diff__line is-${ row.status }` }
+								>
+									{ showDiff && (
+										<td className="editor-revisions-code-diff__line-number is-previous">
+											{ row.previousLineNumber }
+										</td>
+									) }
+									<td className="editor-revisions-code-diff__line-number is-current">
+										{ row.currentLineNumber }
+									</td>
+									{ showDiff && (
+										<td className="editor-revisions-code-diff__marker">
+											<VisuallyHidden>
+												{ statusLabel }
+											</VisuallyHidden>
+											<span aria-hidden="true">
+												{ marker }
+											</span>
+										</td>
+									) }
+									<td className="editor-revisions-code-diff__code">
+										<code>{ row.value }</code>
+									</td>
+								</tr>
+							);
+						} ) }
+					</tbody>
+				</table>
+			) : (
+				<p className="editor-revisions-code-diff__empty">
+					{ __( 'This revision is empty.' ) }
+				</p>
+			) }
+		</div>
+	);
+}

packages/editor/src/components/post-revisions-preview/revisions-header.js

@@ -110,7 +110,7 @@ function RevisionsHeader( { showDiff, onToggleDiff } ) {
 					>
 						{ __( 'Restore' ) }
 					</Button>
-					<MoreMenu disabled />
+					<MoreMenu isRevisionMode />
 				</>
 			}
 		/>