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'), [
@@ -54,9 +55,14 @@ public function specifyTypes(FunctionReflection $functionReflection, FuncCall $n
 );
 }
 
+$narrowedType = new ClassStringType();
+if ($functionReflection->getName() === 'enum_exists') {
+$narrowedType = new GenericClassStringType(new ObjectType('UnitEnum'));
+}
+
 return $this->typeSpecifier->create(
 $node->getArgs()[0]->value,
-$classStringType,
+$narrowedType,
 $context,
 false,
 $scope,

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);
 }
 }