Fix imprecise types after assignment when strict-types=1

Author: staabm

tests/PHPStan/Analyser/nsrt/bug-12902.php

@@ -0,0 +1,40 @@
+<?php declare(strict_types = 1);
+
+use function PHPStan\Testing\assertNativeType;
+use function PHPStan\Testing\assertType;
+
+class NarrowsNativeUnion {
+	private readonly int|float $i;
+
+	public function __construct()
+	{
+		$this->i = getInt();
+		assertType('int', $this->i);
+		assertNativeType('int', $this->i);
+	}
+
+	public function doFoo(): void {
+		assertType('int', $this->i);
+		assertNativeType('int', $this->i);
+	}
+}
+
+class NarrowsStaticNativeUnion {
+	private static int|float $i;
+
+	public function __construct()
+	{
+		self::$i = getInt();
+		assertType('int', self::$i);
+		assertNativeType('int', self::$i);
+	}
+
+	public function doFoo(): void {
+		assertType('float|int', self::$i);
+		assertNativeType('float|int', self::$i);
+	}
+}
+
+function getInt(): int {
+	return 1;
+}