Regression test

Closes phpstan/phpstan#6947

Author: ondrejmirtes

tests/PHPStan/Rules/Comparison/ElseIfConstantConditionRuleTest.php

@@ -140,4 +140,20 @@ public function testBug11674(): void
 		]);
 	}
 
+	public function testBug6947(): void
+	{
+		if (PHP_VERSION_ID < 80000) {
+			$this->markTestSkipped('Test requires PHP 8.0');
+		}
+
+		$this->treatPhpDocTypesAsCertain = true;
+		$this->analyse([__DIR__ . '/data/bug-6947.php'], [
+			[
+				'Elseif condition is always false.',
+				11,
+				'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%</>.',
+			],
+		]);
+	}
+
 }

tests/PHPStan/Rules/Comparison/data/bug-6947.php

@@ -0,0 +1,17 @@
+<?php declare(strict_types = 1);
+
+namespace Bug6947;
+
+abstract class HelloWorld
+{
+	public function sayHello(): void
+	{
+		if (is_string($this->getValue())) {
+
+		} elseif (is_array($this->getValue())) {
+
+		}
+	}
+
+	abstract public function getValue():int|float|string|null;
+}