From 33a305b116dec7871bcfeab706ea3f4f86efb423 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rgvin=20Ragnarsson?=
 <201388+nifgraup@users.noreply.github.com>
Date: Tue, 20 Oct 2020 22:28:03 +0300
Subject: [PATCH] fix: Clearing empty Set&Map should be noop (#682). Fixes #680

---
 __tests__/map-set.js  | 14 ++++++++++++++
 src/plugins/mapset.ts | 24 ++++++++++++++----------
 2 files changed, 28 insertions(+), 10 deletions(-)

diff --git a/__tests__/map-set.js b/__tests__/map-set.js
index bbe9d479..cdcc5725 100644
--- a/__tests__/map-set.js
+++ b/__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)
+		})
 	})
 }
diff --git a/src/plugins/mapset.ts b/src/plugins/mapset.ts
index 6dd579a7..0be2ef67 100644
--- a/src/plugins/mapset.ts
+++ b/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> {