InputControl: Fix acceptance of falsy values in controlled updates

packages/components/CHANGELOG.md

@@ -13,6 +13,7 @@
 -   `ColorPalette`: Fix background image in RTL mode ([#42510](https://github.com/WordPress/gutenberg/pull/42510)).
 -   `RangeControl`: clamp initialPosition between min and max values ([#42571](https://github.com/WordPress/gutenberg/pull/42571)).
 -   `Tooltip`: avoid unnecessary re-renders of select child elements ([#42483](https://github.com/WordPress/gutenberg/pull/42483)).
+-   `InputControl`: Fix acceptance of falsy values in controlled updates ([#42484](https://github.com/WordPress/gutenberg/pull/42484/)).
 
 ### Enhancements
 

packages/components/src/input-control/reducer/actions.ts

@@ -10,6 +10,7 @@ import type { DragProps } from '../types';
 
 export const CHANGE = 'CHANGE';
 export const COMMIT = 'COMMIT';
+export const CONTROL = 'CONTROL';
 export const DRAG_END = 'DRAG_END';
 export const DRAG_START = 'DRAG_START';
 export const DRAG = 'DRAG';
@@ -23,7 +24,7 @@ interface EventPayload {
 	event?: SyntheticEvent;
 }
 
-interface Action< Type, ExtraPayload = {} > {
+export interface Action< Type = string, ExtraPayload = {} > {
 	type: Type;
 	payload: EventPayload & ExtraPayload;
 }
@@ -34,6 +35,7 @@ interface ValuePayload {
 
 export type ChangeAction = Action< typeof CHANGE, ValuePayload >;
 export type CommitAction = Action< typeof COMMIT, ValuePayload >;
+export type ControlAction = Action< typeof CONTROL, ValuePayload >;
 export type PressUpAction = Action< typeof PRESS_UP >;
 export type PressDownAction = Action< typeof PRESS_DOWN >;
 export type PressEnterAction = Action< typeof PRESS_ENTER >;

packages/components/src/input-control/reducer/reducer.ts

@@ -39,22 +39,32 @@ function mergeInitialState(
 }
 
 /**
- * Creates a reducer that opens the channel for external state subscription
- * and modification.
+ * Creates the base reducer which may be coupled to a specializing reducer.
+ * As its final step, for all actions other than CONTROL, the base reducer
+ * passes the state and action on through the specializing reducer. The
+ * exception for CONTROL actions is because they represent controlled updates
+ * from props and no case has yet presented for their specialization.
  *
- * This technique uses the "stateReducer" design pattern:
- * https://kentcdodds.com/blog/the-state-reducer-pattern/
- *
- * @param  composedStateReducers A custom reducer that can subscribe and modify state.
+ * @param  composedStateReducers A reducer to specialize state changes.
  * @return The reducer.
  */
 function inputControlStateReducer(
 	composedStateReducers: StateReducer
-): StateReducer {
+): StateReducer< actions.ControlAction > {
 	return ( state, action ) => {
 		const nextState = { ...state };
 
 		switch ( action.type ) {
+			/*
+			 * Controlled updates
+			 */
+			case actions.CONTROL:
+				nextState.value = action.payload.value;
+				nextState.isDirty = false;
+				nextState._event = undefined;
+				// Returns immediately to avoid invoking additional reducers.
+				return nextState;
+
 			/**
 			 * Keyboard events
 			 */
@@ -140,7 +150,7 @@ export function useInputControlStateReducer(
 	initialState: Partial< InputState > = initialInputControlState,
 	onChangeHandler: InputChangeCallback
 ) {
-	const [ state, dispatch ] = useReducer< StateReducer >(
+	const [ state, dispatch ] = useReducer(
 		inputControlStateReducer( stateReducer ),
 		mergeInitialState( initialState )
 	);
@@ -188,10 +198,15 @@ export function useInputControlStateReducer(
 
 	const currentState = useRef( state );
 	const refProps = useRef( { value: initialState.value, onChangeHandler } );
+
+	// Freshens refs to props and state so that subsequent effects have access
+	// to their latest values without their changes causing effect runs.
 	useLayoutEffect( () => {
 		currentState.current = state;
 		refProps.current = { value: initialState.value, onChangeHandler };
 	} );
+
+	// Propagates the latest state through onChange.
 	useLayoutEffect( () => {
 		if (
 			currentState.current._event !== undefined &&
@@ -205,14 +220,16 @@ export function useInputControlStateReducer(
 			} );
 		}
 	}, [ state.value, state.isDirty ] );
+
+	// Updates the state from props.
 	useLayoutEffect( () => {
 		if (
 			initialState.value !== currentState.current.value &&
 			! currentState.current.isDirty
 		) {
 			dispatch( {
-				type: actions.RESET,
-				payload: { value: initialState.value },
+				type: actions.CONTROL,
+				payload: { value: initialState.value ?? '' },
 			} );
 		}
 	}, [ initialState.value ] );

packages/components/src/input-control/reducer/state.ts

@@ -6,7 +6,7 @@ import type { Reducer, SyntheticEvent } from 'react';
 /**
  * Internal dependencies
  */
-import type { InputAction } from './actions';
+import type { Action, InputAction } from './actions';
 
 export interface InputState {
 	_event?: SyntheticEvent;
@@ -19,7 +19,12 @@ export interface InputState {
 	value?: string;
 }
 
-export type StateReducer = Reducer< InputState, InputAction >;
+export type StateReducer< SpecializedAction = {} > = Reducer<
+	InputState,
+	SpecializedAction extends Action
+		? InputAction | SpecializedAction
+		: InputAction
+>;
 
 export const initialStateReducer: StateReducer = ( state: InputState ) => state;
 

packages/components/src/input-control/test/index.js

@@ -85,34 +85,50 @@ describe( 'InputControl', () => {
 			expect( spy ).toHaveBeenLastCalledWith( 'Hello there' );
 		} );
 
-		it( 'should work as a controlled component', async () => {
+		it( 'should work as a controlled component given normal, falsy or nullish values', async () => {
 			const user = setupUser();
 			const spy = jest.fn();
+			const heldKeySet = new Set();
 			const Example = () => {
 				const [ state, setState ] = useState( 'one' );
 				const onChange = ( value ) => {
 					setState( value );
 					spy( value );
 				};
 				const onKeyDown = ( { key } ) => {
-					if ( key === 'Escape' ) setState( 'three' );
+					heldKeySet.add( key );
+					if ( key === 'Escape' ) {
+						if ( heldKeySet.has( 'Meta' ) ) setState( 'qux' );
+						else if ( heldKeySet.has( 'Alt' ) )
+							setState( undefined );
+						else setState( '' );
+					}
 				};
+				const onKeyUp = ( { key } ) => heldKeySet.delete( key );
 				return (
 					<InputControl
 						value={ state }
 						onChange={ onChange }
 						onKeyDown={ onKeyDown }
+						onKeyUp={ onKeyUp }
 					/>
 				);
 			};
 			render( <Example /> );
 			const input = getInput();
 
 			await user.type( input, '2' );
-			// Make a controlled update.
+			// Make a controlled update with a falsy value.
 			await user.keyboard( '{Escape}' );
+			expect( input ).toHaveValue( '' );
 
-			expect( input ).toHaveValue( 'three' );
+			// Make a controlled update with a normal value.
+			await user.keyboard( '{Meta>}{Escape}{/Meta}' );
+			expect( input ).toHaveValue( 'qux' );
+
+			// Make a controlled update with a nullish value.
+			await user.keyboard( '{Alt>}{Escape}{/Alt}' );
+			expect( input ).toHaveValue( '' );
 			/*
 			 * onChange called only once. onChange is not called when a
 			 * parent component explicitly passed a (new value) change down to