fix: Clearing empty Set&Map should be noop (#682). Fixes #680

__tests__/map-set.js

@@ -266,5 +266,19 @@ function runBaseTest(name, useProxies, autoFreeze, useListener) {
 				]
 			])
 		})
+
+		test("#680 - Clearing empty Set&Map should be noop", () => {
+			const map = new Map()
+			let result = produce(map, draft => {
+				draft.clear()
+			})
+			expect(result).toBe(map)
+
+			const set = new Set()
+			result = produce(set, draft => {
+				draft.clear()
+			})
+			expect(result).toBe(set)
+		})
 	})
 }

src/plugins/mapset.ts

@@ -108,13 +108,15 @@ export function enableMapSet() {
 		p.clear = function() {
 			const state: MapState = this[DRAFT_STATE]
 			assertUnrevoked(state)
-			prepareMapCopy(state)
-			markChanged(state)
-			state.assigned_ = new Map()
-			each(state.base_, key => {
-				state.assigned_!.set(key, false)
-			})
-			return state.copy_!.clear()
+			if (latest(state).size) {
+				prepareMapCopy(state)
+				markChanged(state)
+				state.assigned_ = new Map()
+				each(state.base_, key => {
+					state.assigned_!.set(key, false)
+				})
+				state.copy_!.clear()
+			}
 		}
 
 		p.forEach = function(
@@ -273,9 +275,11 @@ export function enableMapSet() {
 		p.clear = function() {
 			const state: SetState = this[DRAFT_STATE]
 			assertUnrevoked(state)
-			prepareSetCopy(state)
-			markChanged(state)
-			return state.copy_!.clear()
+			if (latest(state).size) {
+				prepareSetCopy(state)
+				markChanged(state)
+				state.copy_!.clear()
+			}
 		}
 
 		p.values = function(): IterableIterator<any> {