Fixes type InvertPatternForExcludeInternal to work with readonly array

src/types/InvertPattern.ts

@@ -318,7 +318,10 @@ type InvertPatternForExcludeInternal<p, i, empty = never> =
     ? {
         select: InvertPatternForExcludeInternal<subpattern, i, empty>;
         array: i extends readonly (infer ii)[]
-          ? InvertPatternForExcludeInternal<subpattern, ii, empty>[]
+          ? MaybeAddReadonly<
+              InvertPatternForExcludeInternal<subpattern, ii, empty>[],
+              IsReadonlyArray<i>
+            >
           : empty;
         map: subpattern extends [infer pk, infer pv]
           ? i extends Map<infer ik, infer iv>

tests/exhaustive-match.test.ts

@@ -979,4 +979,15 @@ describe('exhaustive()', () => {
       expect(withoutTypo({ sex: 'b', age: 'c' })).toBe(1);
     });
   });
+
+  it('issue #271: P.array should support readonly arrays as its input', () => {
+    type Input = string | Date | readonly string[];
+    const input = ['a', 'b', 'c'] as Input;
+
+    const output = match(input)
+      .with(P.array(P.string), (value) => 1)
+      .with(P.string, (value) => 2)
+      .with(P.instanceOf(Date), (value) => 3)
+      .exhaustive();
+  });
 });