fix: Append to array when key is "-" (#872)

* Appends to array when key is "-"

* Avoids unnecessary copy of patches in applyPatches

__tests__/patch.js

@@ -720,6 +720,22 @@ describe("arrays - delete", () => {
 	)
 })
 
+describe("arrays - append", () => {
+	test("appends to array when last part of path is '-'", () => {
+		const state = {
+			list: [1, 2, 3]
+		}
+		const patch = {
+			op: "add",
+			value: 4,
+			path: ["list", "-"]
+		}
+		expect(applyPatches(state, [patch])).toEqual({
+			list: [1, 2, 3, 4]
+		})
+	})
+})
+
 describe("sets - add - 1", () => {
 	runPatchTest(
 		new Set([1]),

src/core/immerClass.ts

@@ -196,16 +196,21 @@ export class Immer implements ProducersFns {
 				break
 			}
 		}
+		// If there was a patch that replaced the entire state, start from the
+		// patch after that.
+		if (i > -1) {
+			patches = patches.slice(i + 1)
+		}
 
 		const applyPatchesImpl = getPlugin("Patches").applyPatches_
 		if (isDraft(base)) {
 			// N.B: never hits if some patch a replacement, patches are never drafts
-			return applyPatchesImpl(base, patches) as any
+			return applyPatchesImpl(base, patches)
 		}
 		// Otherwise, produce a copy of the base state.
 		return this.produce(base, (draft: Drafted) =>
-			applyPatchesImpl(draft, patches.slice(i + 1))
-		) as any
+			applyPatchesImpl(draft, patches)
+		)
 	}
 }
 

src/plugins/patches.ts

@@ -240,7 +240,9 @@ export function enablePatches() {
 				case ADD:
 					switch (type) {
 						case Archtype.Array:
-							return base.splice(key as any, 0, value)
+							return key === "-"
+								? base.push(value)
+								: base.splice(key as any, 0, value)
 						case Archtype.Map:
 							return base.set(key, value)
 						case Archtype.Set: