SoapClient can't convert BackedEnum to scalar value

[MrMeshok]

Description

The following code:

<?php
enum TestBackedEnum: string
{
    case First = 'first';
}

$client = new SoapClient('https://raw.githubusercontent.com/php/php-src/master/ext/soap/tests/classmap.wsdl');

$book = new stdClass();
$book->a = TestBackedEnum::First;
$book->b = '';

$client->dotest($book);

Resulted in this output:

PHP Fatal error:  Uncaught Error: Object of class TestBackedEnum could not be converted to string

But I expected this output instead:

No errors

PHP Version

PHP 8.3.11

Operating System

No response

[cmb69]

Somewhat related to #15650. Quoting from there:

In general, enums are not their backing values, and conversion is explicit. This was a deliberate design decision of enums.

So this is not a bug, but might be a legit feature request.

[cmb69]

cc @Crell and @iluuu1994

[Crell]

I think the main question here would be if we consider SOAPClient to be a serialization context. serialize(), json_encode(), etc. are, and so use the backing value. Would SOAPClient fall into that category? If so, pulling the backing value makes sense. If not, it doesn't.

[cmb69]

I think the main question here would be if we consider SOAPClient to be a serialization context.

I think, we do. @nielsdos can possibly clarify.

However, I'm not sure where to draw the line about what we support. https://pecl.php.net/package/xmlrpc is likely of no concern any longer, although XMLRPC can be regarded as precursor to SOAP. But there are likely more relevant packages, e.g. https://pecl.php.net/package/yaml. Well, not bundled extension probably need to decide for themselves, but what about XMLWriter and FFI (not really serialization, but somewhat related), for instance?

[nielsdos]

What's the definition of "serialization context"? I guess it depends on that.
In any case, this error comes from zval_get_string_func called from to_xml_string when trying to convert the field to a string. So to me, it is casting, not serialization, and therefore, there is nothing to do here.

[MrMeshok]

Let me show you how I got to this issue.
I have WSDL with this definition of enum

<xsd:simpleType name="AuthMethod">
    <xsd:restriction base="xsd:string">
        <xsd:enumeration value="SessionToken"/>
        <xsd:enumeration value="LoginProductAndPassword"/>
    </xsd:restriction>
</xsd:simpleType>

So I created Enum and DTO which I will pass to SoapClient

enum AuthMethod: string
{
    case SessionToken = 'SessionToken';
    case LoginProductAndPassword = 'LoginProductAndPassword';
}

class AuthRequest
{
    public function __construct(
        public AuthMethod $AuthMethod,
        public ?string $SessionToken = null,
        public ?int $ProductId = null,
        public ?string $Login = null,
        public ?string $Password = null,
    ) {}
}

For me it's seems reasonable, to expect for it to just work.

If instead of SOAP it was some JSON RPC API I would just json_encode my DTO and it will work how I expected it.

{
    "AuthMethod": "SessionToken",
    "SessionToken": "123345"
}