Writing Flow: Avoid horizontal writing flow navigation in native inputs

packages/editor/src/components/writing-flow/index.js

@@ -49,6 +49,29 @@ const isTabbableTextField = overEvery( [
 	focus.tabbable.isTabbableIndex,
 ] );
 
+/**
+ * Returns true if the element should consider edge navigation upon a keyboard
+ * event of the given directional key code, or false otherwise.
+ *
+ * @param {Element} element     HTML element to test.
+ * @param {number}  keyCode     KeyboardEvent keyCode to test.
+ * @param {boolean} hasModifier Whether a modifier is pressed.
+ *
+ * @return {boolean} Whether element should consider edge navigation.
+ */
+export function isNavigationCandidate( element, keyCode, hasModifier ) {
+	const isVertical = ( keyCode === UP || keyCode === DOWN );
+
+	// Currently, all elements support unmodified vertical navigation.
+	if ( isVertical && ! hasModifier ) {
+		return true;
+	}
+
+	// Native inputs should not navigate horizontally.
+	const { tagName } = element;
+	return tagName !== 'INPUT' && tagName !== 'TEXTAREA';
+}
+
 class WritingFlow extends Component {
 	constructor() {
 		super( ...arguments );
@@ -209,6 +232,7 @@ class WritingFlow extends Component {
 		const isVertical = isUp || isDown;
 		const isNav = isHorizontal || isVertical;
 		const isShift = event.shiftKey;
+		const hasModifier = isShift || event.ctrlKey || event.altKey || event.metaKey;
 		const isNavEdge = isVertical ? isVerticalEdge : isHorizontalEdge;
 
 		// This logic inside this condition needs to be checked before
@@ -243,6 +267,12 @@ class WritingFlow extends Component {
 			return;
 		}
 
+		// Abort if our current target is not a candidate for navigation (e.g.
+		// preserve native input behaviors).
+		if ( ! isNavigationCandidate( target, keyCode, hasModifier ) ) {
+			return;
+		}
+
 		if ( ! isVertical ) {
 			this.verticalRect = null;
 		} else if ( ! this.verticalRect ) {

packages/editor/src/components/writing-flow/test/index.js

@@ -0,0 +1,51 @@
+/**
+ * WordPress dependencies
+ */
+import { UP, DOWN, LEFT, RIGHT } from '@wordpress/keycodes';
+
+/**
+ * Internal dependencies
+ */
+import { isNavigationCandidate } from '../';
+
+describe( 'isNavigationCandidate', () => {
+	let elements;
+	beforeAll( () => {
+		elements = {};
+		elements.input = document.createElement( 'input' );
+		elements.contentEditable = document.createElement( 'p' );
+		elements.contentEditable.contentEditable = true;
+	} );
+
+	it( 'should return true if vertically navigating input without modifier', () => {
+		[ UP, DOWN ].forEach( ( keyCode ) => {
+			const result = isNavigationCandidate( elements.input, keyCode, false );
+
+			expect( result ).toBe( true );
+		} );
+	} );
+
+	it( 'should return false if vertically navigating input with modifier', () => {
+		[ UP, DOWN ].forEach( ( keyCode ) => {
+			const result = isNavigationCandidate( elements.input, keyCode, true );
+
+			expect( result ).toBe( false );
+		} );
+	} );
+
+	it( 'should return false if horizontally navigating input', () => {
+		[ LEFT, RIGHT ].forEach( ( keyCode ) => {
+			const result = isNavigationCandidate( elements.input, keyCode, false );
+
+			expect( result ).toBe( false );
+		} );
+	} );
+
+	it( 'should return true if horizontally navigating non-input', () => {
+		[ LEFT, RIGHT ].forEach( ( keyCode ) => {
+			const result = isNavigationCandidate( elements.contentEditable, keyCode, false );
+
+			expect( result ).toBe( true );
+		} );
+	} );
+} );

test/e2e/specs/writing-flow.test.js

@@ -195,4 +195,32 @@ describe( 'adding blocks', () => {
 		await pressWithModifier( 'Shift', 'Enter' );
 		expect( await getEditedPostContent() ).toMatchSnapshot();
 	} );
+
+	it( 'should navigate native inputs vertically, not horizontally', async () => {
+		// See: https://github.com/WordPress/gutenberg/issues/9626
+
+		// Title is within the editor's writing flow, and is a <textarea>
+		await page.click( '.editor-post-title' );
+
+		// Should remain in title upon ArrowRight:
+		await page.keyboard.press( 'ArrowRight' );
+		let isInTitle = await page.evaluate( () => (
+			!! document.activeElement.closest( '.editor-post-title' )
+		) );
+		expect( isInTitle ).toBe( true );
+
+		// Should remain in title upon modifier + ArrowDown:
+		await pressWithModifier( META_KEY, 'ArrowDown' );
+		isInTitle = await page.evaluate( () => (
+			!! document.activeElement.closest( '.editor-post-title' )
+		) );
+		expect( isInTitle ).toBe( true );
+
+		// Should navigate into blocks list upon ArrowDown:
+		await page.keyboard.press( 'ArrowDown' );
+		const isInBlock = await page.evaluate( () => (
+			!! document.activeElement.closest( '[data-type]' )
+		) );
+		expect( isInBlock ).toBe( true );
+	} );
 } );