added regression test

Author: staabm

tests/PHPStan/Rules/Comparison/StrictComparisonOfDifferentTypesRuleTest.php

@@ -1034,4 +1034,10 @@ public function testBug11035(): void
 		]);
 	}
 
+	public function testBug9804(): void
+	{
+		$this->checkAlwaysTrueStrictComparison = true;
+		$this->analyse([__DIR__ . '/data/bug-9804.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Comparison/data/bug-9804.php

@@ -0,0 +1,34 @@
+<?php
+
+namespace Bug9804;
+
+class Test
+{
+	public function error(?string $someString): void
+	{
+		// Line below is the only difference to "pass" method
+		if (!$someString) {
+			return;
+		}
+
+		// Strict comparison using === between int<min, -1>|int<1, max> and 0 will always evaluate to false.
+		$firstLetterAsInt = (int)substr($someString, 0, 1);
+		if ($firstLetterAsInt === 0) {
+			return;
+		}
+	}
+
+	public function pass(?string $someString): void
+	{
+		// Line below is the only difference to "error" method
+		if ($someString === null) {
+			return;
+		}
+
+		// All ok
+		$firstLetterAsInt = (int)substr($someString, 0, 1);
+		if ($firstLetterAsInt === 0) {
+			return;
+		}
+	}
+}