add test for fix bug 7937

Author: schlndh

tests/PHPStan/Rules/Comparison/BooleanNotConstantConditionRuleTest.php

@@ -146,6 +146,12 @@ public function testBug8797(): void
 		$this->analyse([__DIR__ . '/data/bug-8797.php'], []);
 	}
 
+	public function testBug7937(): void
+	{
+		$this->treatPhpDocTypesAsCertain = true;
+		$this->analyse([__DIR__ . '/data/bug-7937.php'], []);
+	}
+
 	public function dataReportAlwaysTrueInLastCondition(): iterable
 	{
 		yield [false, [

tests/PHPStan/Rules/Comparison/data/bug-7937.php

@@ -0,0 +1,31 @@
+<?php declare(strict_types = 1);
+
+namespace Bug7937;
+
+class HelloWorld
+{
+	public function f(int $a, int $b)
+	{
+		if (!$a && !$b) {
+			return "";
+		}
+
+		$output = " ";
+
+		if ($a) {
+			$output .= "$a";
+		}
+
+		\PHPStan\dumpType($a);
+
+		if ($b) {
+			\PHPStan\dumpType($a);
+
+			if (!$a) {
+				$output .= "_";
+			}
+		}
+
+		return $output;
+	}
+}