From 2c27133d45729667b4871ea4db835589a6b9cba3 Mon Sep 17 00:00:00 2001
From: Alec Larson <alec.stanford.larson@gmail.com>
Date: Thu, 7 Mar 2019 08:39:20 -0500
Subject: [PATCH] fix(ts): Immutable<T> / read-only arrays in TS 3.4+

---
 src/immer.d.ts | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/immer.d.ts b/src/immer.d.ts
index d2b30a9b..aa370e94 100644
--- a/src/immer.d.ts
+++ b/src/immer.d.ts
@@ -53,6 +53,10 @@ export type Produced<Base, Return> = Return extends void
     ? Promise<Result extends void ? Base : FromNothing<Result>>
     : FromNothing<Return>
 
+type ImmutableArray<T extends ReadonlyArray<any>> = {
+    [P in Extract<keyof T, number>]: ReadonlyArray<Immutable<T[number]>>
+}[Extract<keyof T, number>]
+
 type ImmutableTuple<T extends ReadonlyArray<any>> = {
     readonly [P in keyof T]: Immutable<T[P]>
 }
@@ -63,7 +67,7 @@ export type Immutable<T> = T extends object
         ? T
         : T extends ReadonlyArray<any>
         ? Array<T[number]> extends T
-            ? {[P in keyof T]: ReadonlyArray<Immutable<T[number]>>}[keyof T]
+            ? ImmutableArray<T>
             : ImmutableTuple<T>
         : {readonly [P in keyof T]: Immutable<T[P]>}
     : T