From 0d5fc691c1a4a8d1e6ad4e345ca187b9089dfc7a Mon Sep 17 00:00:00 2001
From: Masahiko Shin <contact@shin-translation.com>
Date: Tue, 21 Jun 2022 17:30:12 +0900
Subject: [PATCH] Improve type inference.

Type inferences for some kind of values(functions, records, promises,.etc) are not correct when deep option is enabled. It is because CamelCaseKeys type accepts Record<string, any> and then accepts some object-like types such as functions or promises.
---
 index.d.ts      | 38 +++++++++++++++++++++-----------------
 index.test-d.ts | 24 ++++++++++++++++++++++++
 2 files changed, 45 insertions(+), 17 deletions(-)

diff --git a/index.d.ts b/index.d.ts
index e1e9416..3ed41af 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -45,13 +45,15 @@ export type CamelCaseKeys<
 > = T extends readonly any[]
 	// Handle arrays or tuples.
 	? {
-		[P in keyof T]: CamelCaseKeys<
-		T[P],
-		Deep,
-		IsPascalCase,
-		Exclude,
-		StopPaths
-		>;
+		[P in keyof T]: Record<string, unknown> extends CamelCaseKeys<T[P]>
+			? T[P]
+			: CamelCaseKeys<
+			T[P],
+			Deep,
+			IsPascalCase,
+			Exclude,
+			StopPaths
+			>;
 	}
 	: T extends Record<string, any>
 		// Handle objects.
@@ -64,16 +66,18 @@ export type CamelCaseKeys<
 				true,
 			]
 				? T[P]
-				: [Deep] extends [true]
-					? CamelCaseKeys<
-					T[P],
-					Deep,
-					IsPascalCase,
-					Exclude,
-					StopPaths,
-					AppendPath<Path, P & string>
-					>
-					: T[P];
+				: Record<string, unknown> extends CamelCaseKeys<T[P]>
+					? T[P]
+					: [Deep] extends [true]
+						? CamelCaseKeys<
+						T[P],
+						Deep,
+						IsPascalCase,
+						Exclude,
+						StopPaths,
+						AppendPath<Path, P & string>
+						>
+						: T[P];
 		}
 		// Return anything else as-is.
 		: T;
diff --git a/index.test-d.ts b/index.test-d.ts
index f2b2f99..2ee6076 100644
--- a/index.test-d.ts
+++ b/index.test-d.ts
@@ -350,3 +350,27 @@ expectNotType<InvalidConvertedExcludeObjectDataType>(
 		exclude,
 	}),
 );
+
+expectType<{
+	funcFoo: () => 'foo';
+	recordBar: {foo: string};
+	promiseBaz: Promise<unknown>;
+}>(camelcaseKeys({
+			func_foo: () => 'foo',
+			record_bar: {foo: 'bar'},
+			promise_baz: new Promise(resolve => {
+				resolve(true);
+			}),
+		}));
+
+expectType<[
+	() => 'foo',
+	{foo: string},
+	Promise<unknown>,
+]>(camelcaseKeys([
+			() => 'foo',
+			{foo: 'bar'},
+			new Promise(resolve => {
+				resolve(true);
+			}),
+		]));