Added regression test

Author: staabm

tests/PHPStan/Rules/Comparison/ImpossibleCheckTypeFunctionCallRuleTest.php

@@ -1038,10 +1038,26 @@ public function testBug6788(): void
 		$this->analyse([__DIR__ . '/data/bug-6788.php'], []);
 	}
 
+	#[RequiresPhp('>= 8.0')]
 	public function testBug13268(): void
 	{
 		$this->treatPhpDocTypesAsCertain = true;
 		$this->analyse([__DIR__ . '/data/bug-13268.php'], []);
 	}
 
+	#[RequiresPhp('>= 8.0')]
+	public function testBug12087(): void
+	{
+		$tipText = 'Because the type is coming from a PHPDoc, you can turn off this check by setting <fg=cyan>treatPhpDocTypesAsCertain: false</> in your <fg=cyan>%configurationFile%</>.';
+
+		$this->treatPhpDocTypesAsCertain = true;
+		$this->analyse([__DIR__ . '/data/bug-12087.php'], [
+			[
+				'Call to function is_null() with null will always evaluate to true.',
+				14,
+				$tipText,
+			],
+		]);
+	}
+
 }

tests/PHPStan/Rules/Comparison/data/bug-12087.php

@@ -0,0 +1,15 @@
+<?php declare(strict_types=1);
+
+namespace Bug12087;
+
+enum Button: int
+{
+	case On = 1;
+
+	case Off = 0;
+}
+
+$value = 10;
+
+is_null($value = Button::tryFrom($value));
+