Narrow enum_exists() arg to UnitEnum

src/Type/Php/ClassExistsFunctionTypeSpecifyingExtension.php

@@ -16,6 +16,8 @@
 use PHPStan\Type\Constant\ConstantBooleanType;
 use PHPStan\Type\Constant\ConstantStringType;
 use PHPStan\Type\FunctionTypeSpecifyingExtension;
+use PHPStan\Type\Generic\GenericClassStringType;
+use PHPStan\Type\ObjectType;
 use function in_array;
 use function ltrim;
 
@@ -41,7 +43,6 @@ public function isFunctionSupported(
 	public function specifyTypes(FunctionReflection $functionReflection, FuncCall $node, Scope $scope, TypeSpecifierContext $context): SpecifiedTypes
 	{
 		$argType = $scope->getType($node->getArgs()[0]->value);
-		$classStringType = new ClassStringType();
 		if ($argType instanceof ConstantStringType) {
 			return $this->typeSpecifier->create(
 				new FuncCall(new FullyQualified('class_exists'), [
@@ -54,6 +55,17 @@ public function specifyTypes(FunctionReflection $functionReflection, FuncCall $n
 			);
 		}
 
+		if ($functionReflection->getName() === 'enum_exists') {
+			return $this->typeSpecifier->create(
+				$node->getArgs()[0]->value,
+				new GenericClassStringType(new ObjectType('UnitEnum')),
+				$context,
+				false,
+				$scope,
+			);
+		}
+
+		$classStringType = new ClassStringType();
 		return $this->typeSpecifier->create(
 			$node->getArgs()[0]->value,
 			$classStringType,

tests/PHPStan/Analyser/NodeScopeResolverTest.php

@@ -1372,6 +1372,7 @@ public function dataFileAsserts(): iterable
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-9963.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/str-shuffle.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-9995.php');
+		yield from $this->gatherAssertTypes(__DIR__ . '/data/enum_exists.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-9867.php');
 	}
 

tests/PHPStan/Analyser/data/enum_exists.php

@@ -0,0 +1,28 @@
+<?php
+
+namespace EnumExists;
+
+use function PHPStan\Testing\assertType;
+
+function getEnumValue(string $enumFqcn, string $name): mixed {
+	if (enum_exists($enumFqcn)) {
+		assertType('class-string<UnitEnum>', $enumFqcn);
+		return (new \ReflectionEnum($enumFqcn))->getCase($name)->getValue();
+	}
+	assertType('string', $enumFqcn);
+
+	return null;
+}
+
+/**
+ * @param class-string $enumFqcn
+ */
+function getEnumValueFromClassString(string $enumFqcn, string $name): mixed {
+	if (enum_exists($enumFqcn)) {
+		assertType('class-string<UnitEnum>', $enumFqcn);
+		return (new \ReflectionEnum($enumFqcn))->getCase($name)->getValue();
+	}
+	assertType('class-string', $enumFqcn);
+
+	return null;
+}

tests/PHPStan/Analyser/data/generic-enum-class-string.php

@@ -8,7 +8,7 @@ function testEnumExists(string $str)
 {
 	assertType('string', $str);
 	if (enum_exists($str)) {
-		assertType('class-string', $str);
+		assertType('class-string<UnitEnum>', $str);
 	}
 }