Fallback to regular subscribe if the store doesn't exist in useSelect (…

…#27466)

packages/data/src/components/use-select/test/index.js

@@ -283,6 +283,9 @@ describe( 'useSelect', () => {
 			expect( selectCount2 ).toHaveBeenCalledTimes( 3 );
 			expect( TestComponent ).toHaveBeenCalledTimes( 3 );
 			expect( testInstance.findByType( 'div' ).props.data ).toBe( 1 );
+
+			// Test if the unsubscribers get called correctly.
+			renderer.unmount();
 		} );
 
 		it( 'can subscribe to multiple stores at once', () => {
@@ -565,5 +568,156 @@ describe( 'useSelect', () => {
 				childCount: 0,
 			} );
 		} );
+
+		it( 'handles non-existing stores', () => {
+			registry.registerStore( 'store-1', counterStore );
+
+			let renderer;
+
+			const TestComponent = jest.fn( () => {
+				const state = useSelect(
+					( select ) => ( {
+						count1: select( 'store-1' ).getCounter(),
+						blank: select( 'non-existing-store' )?.getCounter(),
+					} ),
+					[]
+				);
+
+				return <div data={ state } />;
+			} );
+
+			act( () => {
+				renderer = TestRenderer.create(
+					<RegistryProvider value={ registry }>
+						<TestComponent />
+					</RegistryProvider>
+				);
+			} );
+
+			const testInstance = renderer.root;
+
+			expect( testInstance.findByType( 'div' ).props.data ).toEqual( {
+				count1: 0,
+				blank: undefined,
+			} );
+
+			act( () => {
+				registry.dispatch( 'store-1' ).increment();
+			} );
+
+			expect( testInstance.findByType( 'div' ).props.data ).toEqual( {
+				count1: 1,
+				blank: undefined,
+			} );
+
+			// Test if the unsubscribers get called correctly.
+			renderer.unmount();
+		} );
+
+		it( 'handles registration of a non-existing store during rendering', () => {
+			let renderer;
+
+			const TestComponent = jest.fn( () => {
+				const state = useSelect(
+					( select ) =>
+						select( 'not-yet-registered-store' )?.getCounter(),
+					[]
+				);
+
+				return <div data={ state } />;
+			} );
+
+			act( () => {
+				renderer = TestRenderer.create(
+					<RegistryProvider value={ registry }>
+						<TestComponent />
+					</RegistryProvider>
+				);
+			} );
+
+			const testInstance = renderer.root;
+
+			expect( testInstance.findByType( 'div' ).props.data ).toBe(
+				undefined
+			);
+
+			act( () => {
+				registry.registerStore(
+					'not-yet-registered-store',
+					counterStore
+				);
+			} );
+
+			// This is not ideal, but is the way it's working before and we want to prevent breaking changes.
+			expect( testInstance.findByType( 'div' ).props.data ).toBe(
+				undefined
+			);
+
+			act( () => {
+				registry.dispatch( 'not-yet-registered-store' ).increment();
+			} );
+
+			expect( testInstance.findByType( 'div' ).props.data ).toBe( 1 );
+
+			// Test if the unsubscribers get called correctly.
+			renderer.unmount();
+		} );
+
+		it( 'handles registration of a non-existing store of sub-registry during rendering', () => {
+			let renderer;
+
+			const subRegistry = createRegistry( {}, registry );
+
+			const TestComponent = jest.fn( () => {
+				const state = useSelect(
+					( select ) =>
+						select(
+							'not-yet-registered-child-store'
+						)?.getCounter(),
+					[]
+				);
+
+				return <div data={ state } />;
+			} );
+
+			act( () => {
+				renderer = TestRenderer.create(
+					<RegistryProvider value={ registry }>
+						<RegistryProvider value={ subRegistry }>
+							<TestComponent />
+						</RegistryProvider>
+					</RegistryProvider>
+				);
+			} );
+
+			const testInstance = renderer.root;
+
+			expect( testInstance.findByType( 'div' ).props.data ).toBe(
+				undefined
+			);
+
+			act( () => {
+				registry.registerStore(
+					'not-yet-registered-child-store',
+					counterStore
+				);
+			} );
+
+			// This is not ideal, but is the way it's working before and we want to prevent breaking changes.
+			expect( testInstance.findByType( 'div' ).props.data ).toBe(
+				undefined
+			);
+
+			act( () => {
+				registry
+					.dispatch( 'not-yet-registered-child-store' )
+					.increment();
+			} );
+
+			expect( testInstance.findByType( 'div' ).props.data ).toBe( 1 );
+
+			// Test if the unsubscribers get called correctly.
+			renderer.unmount();
+		} );
 	} );
 } );

packages/data/src/registry.js

@@ -234,6 +234,14 @@ export function createRegistry( storeConfigs = {}, parent = null ) {
 			return stores[ storeName ].subscribe( handler );
 		}
 
+		// Trying to access a store that hasn't been registered,
+		// this is a pattern rarely used but seen in some places.
+		// We fallback to regular `subscribe` here for backward-compatibility for now.
+		// See https://github.com/WordPress/gutenberg/pull/27466 for more info.
+		if ( ! parent ) {
+			return subscribe( handler );
+		}
+
 		return parent.__experimentalSubscribeStore( storeName, handler );
 	}