Fix Types.DeepMutable mapping over functions (#5752)

Author: janglad

.changeset/gold-swans-camp.md

@@ -0,0 +1,5 @@
+---
+"effect": patch
+---
+
+Fix Types.DeepMutable mapping over functions

packages/effect/dtslint/Types.tst.ts

@@ -144,6 +144,25 @@ describe("Types", () => {
       >().type.toBe<[string, number, boolean, bigint, symbol, never, null, "a", 1, true]>()
     })
 
+    it("functions", () => {
+      expect<Types.DeepMutable<(arg: 1) => 2>>().type.toBe<(arg: 1) => 2>()
+    })
+
+    it("built in objects", () => {
+      expect<
+        [
+          Types.DeepMutable<String>,
+          Types.DeepMutable<Number>,
+          Types.DeepMutable<Boolean>,
+          Types.DeepMutable<BigInt>,
+          Types.DeepMutable<Symbol>,
+          Types.DeepMutable<Date>,
+          Types.DeepMutable<RegExp>,
+          Types.DeepMutable<Generator>
+        ]
+      >().type.toBeAssignableTo<[String, Number, Boolean, BigInt, Symbol, Date, RegExp, Generator]>()
+    })
+
     describe("Branded", () => {
       it("should leave a string brand unchanged", () => {
         type T = string & Brand.Brand<"mybrand">

packages/effect/src/Types.ts

@@ -261,7 +261,7 @@ export type Mutable<T> = {
  */
 export type DeepMutable<T> = T extends ReadonlyMap<infer K, infer V> ? Map<DeepMutable<K>, DeepMutable<V>>
   : T extends ReadonlySet<infer V> ? Set<DeepMutable<V>>
-  : T extends string | number | boolean | bigint | symbol ? T
+  : T extends string | number | boolean | bigint | symbol | Function ? T
   : { -readonly [K in keyof T]: DeepMutable<T[K]> }
 
 /**