Don't modify state when setting identical selection

packages/block-editor/src/store/reducer.js

@@ -1336,14 +1336,14 @@ function selectionHelper( state = {}, action ) {
 			if (
 				! action.clientIds ||
 				! action.clientIds.length ||
-				action.clientIds.indexOf( state.clientId ) === -1
+				! action.clientIds.includes( state.clientId )
 			) {
 				return state;
 			}
 
 			return {};
 		case 'REPLACE_BLOCKS': {
-			if ( action.clientIds.indexOf( state.clientId ) === -1 ) {
+			if ( ! action.clientIds.includes( state.clientId ) ) {
 				return state;
 			}
 
@@ -1366,6 +1366,20 @@ function selectionHelper( state = {}, action ) {
 	return state;
 }
 
+function selectionEqual( sel1, sel2 ) {
+	if ( sel1 === sel2 ) {
+		return true;
+	}
+	if ( ! sel1 || ! sel2 ) {
+		return false;
+	}
+	return (
+		sel1.clientId === sel2.clientId &&
+		sel1.attributeKey === sel2.attributeKey &&
+		sel1.offset === sel2.offset
+	);
+}
+
 /**
  * Reducer returning the selection state.
  *
@@ -1375,33 +1389,30 @@ function selectionHelper( state = {}, action ) {
  * @return {boolean} Updated state.
  */
 export function selection( state = {}, action ) {
+	let { selectionStart, selectionEnd } = state;
+
 	switch ( action.type ) {
 		case 'SELECTION_CHANGE':
 			if ( action.clientId ) {
-				return {
-					selectionStart: {
-						clientId: action.clientId,
-						attributeKey: action.attributeKey,
-						offset: action.startOffset,
-					},
-					selectionEnd: {
-						clientId: action.clientId,
-						attributeKey: action.attributeKey,
-						offset: action.endOffset,
-					},
+				selectionStart = {
+					clientId: action.clientId,
+					attributeKey: action.attributeKey,
+					offset: action.startOffset,
+				};
+				selectionEnd = {
+					clientId: action.clientId,
+					attributeKey: action.attributeKey,
+					offset: action.endOffset,
 				};
+			} else {
+				selectionStart = action.start || selectionStart;
+				selectionEnd = action.end || selectionEnd;
 			}
-
-			return {
-				selectionStart: action.start || state.selectionStart,
-				selectionEnd: action.end || state.selectionEnd,
-			};
+			break;
 		case 'RESET_SELECTION':
-			const { selectionStart, selectionEnd } = action;
-			return {
-				selectionStart,
-				selectionEnd,
-			};
+			selectionStart = action.selectionStart;
+			selectionEnd = action.selectionEnd;
+			break;
 		case 'MULTI_SELECT':
 			const { start, end } = action;
 
@@ -1412,10 +1423,9 @@ export function selection( state = {}, action ) {
 				return state;
 			}
 
-			return {
-				selectionStart: { clientId: start },
-				selectionEnd: { clientId: end },
-			};
+			selectionStart = { clientId: start };
+			selectionEnd = { clientId: end };
+			break;
 		case 'RESET_BLOCKS':
 			const startClientId = state?.selectionStart?.clientId;
 			const endClientId = state?.selectionEnd?.clientId;
@@ -1431,31 +1441,26 @@ export function selection( state = {}, action ) {
 					( block ) => block.clientId === startClientId
 				)
 			) {
-				return {
-					selectionStart: {},
-					selectionEnd: {},
-				};
+				selectionStart = {};
+				selectionEnd = {};
 			}
-
 			// If the end of the selection won't exist after reset, collapse selection.
-			if (
+			else if (
 				! action.blocks.some(
 					( block ) => block.clientId === endClientId
 				)
 			) {
-				return {
-					...state,
-					selectionEnd: state.selectionStart,
-				};
+				selectionEnd = selectionStart;
 			}
+			break;
+		default:
+			selectionStart = selectionHelper( state.selectionStart, action );
+			selectionEnd = selectionHelper( state.selectionEnd, action );
 	}
 
-	const selectionStart = selectionHelper( state.selectionStart, action );
-	const selectionEnd = selectionHelper( state.selectionEnd, action );
-
 	if (
-		selectionStart === state.selectionStart &&
-		selectionEnd === state.selectionEnd
+		selectionEqual( selectionStart, state.selectionStart ) &&
+		selectionEqual( selectionEnd, state.selectionEnd )
 	) {
 		return state;
 	}