Add non-regression tests for #6663 and #4090

- #6663: nsrt test for type narrowing in nested if with || condition
- #4090: nsrt + rule test verifying no "trim expects string, string|false
  given" error when array count is checked via elseif/switch

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: 2 people

tests/PHPStan/Analyser/nsrt/bug-4090.php

@@ -0,0 +1,46 @@
+<?php
+
+declare(strict_types = 1);
+
+namespace Bug4090;
+
+use function PHPStan\Testing\assertType;
+
+/** @param string[] $a */
+function foo(array $a): void
+{
+	if (count($a) > 1) {
+		echo implode(',', $a);
+	} elseif (count($a) === 1) {
+		assertType('string', current($a));
+		echo trim(current($a));
+	}
+}
+
+/** @param string[] $a */
+function bar(array $a): void
+{
+	$count = count($a);
+	if ($count > 1) {
+		echo implode(',', $a);
+	} elseif ($count === 1) {
+		assertType('string', current($a));
+		echo trim(current($a));
+	}
+}
+
+/** @param string[] $a */
+function qux(array $a): void
+{
+	switch (count($a)) {
+		case 0:
+			break;
+		case 1:
+			assertType('string', current($a));
+			echo trim(current($a));
+			break;
+		default:
+			echo implode(',', $a);
+			break;
+	}
+}

tests/PHPStan/Analyser/nsrt/bug-6663.php

@@ -0,0 +1,24 @@
+<?php
+
+declare(strict_types = 1);
+
+namespace Bug6663;
+
+use function PHPStan\Testing\assertType;
+
+class X {}
+class Y {}
+
+function test(mixed $xy, mixed $ab): void
+{
+	if ($xy instanceof X || $ab instanceof X) {
+		if ($xy instanceof Y) {
+			assertType('Bug6663\Y', $xy);
+			assertType('Bug6663\X', $ab);
+		}
+		if ($ab instanceof Y) {
+			assertType('Bug6663\X', $xy);
+			assertType('Bug6663\Y', $ab);
+		}
+	}
+}