Fix settype() not handled properly for non-constant type strings

- When settype()'s second argument is a non-constant string, broaden the variable type to all possible settype outcomes (bool|int|float|string|array|object|null)
- Previously, non-constant type strings caused the extension to return empty SpecifiedTypes, leaving the variable type unchanged
- New regression test in tests/PHPStan/Analyser/nsrt/bug-3250.php

Author: VincentLanglet

src/Type/Php/SetTypeFunctionTypeSpecifyingExtension.php

@@ -10,10 +10,16 @@
 use PHPStan\Analyser\TypeSpecifierContext;
 use PHPStan\DependencyInjection\AutowiredService;
 use PHPStan\Reflection\FunctionReflection;
+use PHPStan\Type\ArrayType;
+use PHPStan\Type\BooleanType;
 use PHPStan\Type\ErrorType;
+use PHPStan\Type\FloatType;
 use PHPStan\Type\FunctionTypeSpecifyingExtension;
+use PHPStan\Type\IntegerType;
+use PHPStan\Type\MixedType;
 use PHPStan\Type\NullType;
 use PHPStan\Type\ObjectType;
+use PHPStan\Type\StringType;
 use PHPStan\Type\TypeCombinator;
 use stdClass;
 use function count;
@@ -41,7 +47,20 @@ public function specifyTypes(FunctionReflection $functionReflection, FuncCall $n
 
 		$constantStrings = $castType->getConstantStrings();
 		if (count($constantStrings) < 1) {
-			return new SpecifiedTypes();
+			return $this->typeSpecifier->create(
+				$value,
+				TypeCombinator::union(
+					new BooleanType(),
+					new IntegerType(),
+					new FloatType(),
+					new StringType(),
+					new ArrayType(new MixedType(), new MixedType()),
+					new ObjectType(stdClass::class),
+					new NullType(),
+				),
+				TypeSpecifierContext::createTruthy(),
+				$scope,
+			)->setAlwaysOverwriteTypes();
 		}
 
 		$types = [];

tests/PHPStan/Analyser/nsrt/bug-3250.php

@@ -0,0 +1,33 @@
+<?php declare(strict_types = 1);
+
+namespace Bug3250;
+
+use stdClass;
+use function PHPStan\Testing\assertType;
+
+function castTo(string $value, string $castTo): void
+{
+	$newValue = $value;
+	settype($newValue, $castTo);
+
+	assertType('array|bool|float|int|stdClass|string|null', $newValue);
+}
+
+function castToInt(string $value): void
+{
+	$newValue = $value;
+	settype($newValue, 'int');
+
+	assertType('int', $newValue);
+}
+
+/**
+ * @param 'int'|'float' $castTo
+ */
+function castToIntOrFloat(string $value, string $castTo): void
+{
+	$newValue = $value;
+	settype($newValue, $castTo);
+
+	assertType('float|int', $newValue);
+}