Jsonify: Fix handling of nested objects with only a name property (…

…#691)

Co-authored-by: Sindre Sorhus <sindresorhus@gmail.com>

source/internal.d.ts

@@ -189,9 +189,16 @@ type BaseKeyFilter<Type, Key extends keyof Type> = Key extends symbol
 	? never
 	: Type[Key] extends symbol
 		? never
-		: [(...arguments_: any[]) => any] extends [Type[Key]]
-			? never
-			: Key;
+		/*
+		To prevent a problem where an object with only a `name` property is incorrectly treated as assignable to a function, we first check if the property is a record.
+		This check is necessary, because without it, if we don't verify whether the property is a record, an object with a type of `{name: any}` would return `never` due to its potential assignability to a function.
+		See: https://github.com/sindresorhus/type-fest/issues/657
+		*/
+		: Type[Key] extends Record<string, unknown>
+			? Key
+			: [(...arguments_: any[]) => any] extends [Type[Key]]
+				? never
+				: Key;
 
 /**
 Returns the required keys.

test-d/jsonify.ts

@@ -327,6 +327,17 @@ expectType<{a: any}>(objectWithAnyProperty);
 declare const objectWithAnyProperties: Jsonify<Record<string, any>>;
 expectType<Record<string, any>>(objectWithAnyProperties);
 
+// Test for `Jsonify` support for nested objects with _only_ a name property.
+// See https://github.com/sindresorhus/type-fest/issues/657
+declare const nestedObjectWithNameProperty: {
+	first: {
+		name: string;
+	};
+};
+declare const jsonifiedNestedObjectWithNameProperty: Jsonify<typeof nestedObjectWithNameProperty>;
+
+expectType<typeof nestedObjectWithNameProperty>(jsonifiedNestedObjectWithNameProperty);
+
 /// #629
 // declare const readonlyTuple: Jsonify<readonly [1, 2, 3]>;
 // expectType<readonly [1, 2, 3]>(readonlyTuple);