Add map state test to forEach

src/vs/base/common/map.ts

@@ -580,7 +580,9 @@ export const enum Touch {
 	AsNew = 2
 }
 
-export class LinkedMap<K, V> {
+export class LinkedMap<K, V> implements Map<K, V> {
+
+	readonly [Symbol.toStringTag] = 'LinkedMap';
 
 	private _map: Map<K, Item<K, V>>;
 	private _head: Item<K, V> | undefined;
@@ -636,7 +638,7 @@ export class LinkedMap<K, V> {
 		return item.value;
 	}
 
-	set(key: K, value: V, touch: Touch = Touch.None): void {
+	set(key: K, value: V, touch: Touch = Touch.None): this {
 		let item = this._map.get(key);
 		if (item) {
 			item.value = value;
@@ -662,6 +664,7 @@ export class LinkedMap<K, V> {
 			this._map.set(key, item);
 			this._size++;
 		}
+		return this;
 	}
 
 	delete(key: K): boolean {
@@ -694,6 +697,7 @@ export class LinkedMap<K, V> {
 	}
 
 	forEach(callbackfn: (value: V, key: K, map: LinkedMap<K, V>) => void, thisArg?: any): void {
+		const state = this._state;
 		let current = this._head;
 		while (current) {
 			if (thisArg) {
@@ -701,6 +705,9 @@ export class LinkedMap<K, V> {
 			} else {
 				callbackfn(current.value, current.key, this);
 			}
+			if (this._state !== state) {
+				throw new Error(`LinkedMap got modified during iteration.`);
+			}
 			current = current.next;
 		}
 	}
@@ -987,9 +994,10 @@ export class LRUCache<K, V> extends LinkedMap<K, V> {
 		return super.get(key, Touch.None);
 	}
 
-	set(key: K, value: V): void {
+	set(key: K, value: V): this {
 		super.set(key, value, Touch.AsNew);
 		this.checkTrim();
+		return this;
 	}
 
 	private checkTrim() {