fix: SimplifyDeep should not skip arrays

Author: som-sm

source/simplify-deep.d.ts

@@ -1,5 +1,6 @@
 import type {ConditionalSimplifyDeep} from './conditional-simplify-deep.d.ts';
 import type {MapsSetsOrArrays, NonRecursiveType} from './internal/index.d.ts';
+import type {UnknownArray} from './unknown-array.d.ts';
 
 /**
 Deeply simplifies an object type.
@@ -109,7 +110,7 @@ type SimplifyDeepProperties = SimplifyDeep<Properties1 & Properties2, ComplexTyp
 export type SimplifyDeep<Type, ExcludeType = never> =
 	ConditionalSimplifyDeep<
 		Type,
-	ExcludeType | NonRecursiveType | MapsSetsOrArrays,
+	ExcludeType | NonRecursiveType | Exclude<MapsSetsOrArrays, UnknownArray>,
 	object
 	>;
 

test-d/simplify-deep.ts

@@ -42,3 +42,15 @@ declare const flattenProperties2: {
 	}>;
 };
 expectType<SimplifyDeep<{arrayType: ArrayType}>>(flattenProperties2);
+
+declare function testArraySimplification(arg: {foo: Array<{[x: string]: string}>}): void;
+
+// eslint-disable-next-line @typescript-eslint/consistent-type-definitions
+interface BarBaz {
+	bar: string;
+	baz: string;
+}
+
+// This would fail if `SimplifyDeep` did not simplify arrays,
+// because interfaces being open are not compatible with index signatures.
+testArraySimplification({} as SimplifyDeep<{foo: BarBaz[]}>);