serializer for external classes

app_config_config.yml

# app/config/config.yml

jms_serializer:
    metadata:
        directories:
            my-file:
                namespace_prefix: "My\\Ns"
                path: "@MyNsBundle/Resources/config/serializer"

File.php

<?php

// My/Ns/File
namespace My\Ns;

class File
{
  
}

My_Ns_Bundle_Resources_config_serializer_My_Ns_File.xml

<!-- My/Ns/Bundle/Resources/config/serializer/My.Ns.File.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<serializer>
    <class name="My\Ns\File" exclusion-policy="ALL">
    </class>
</serializer>    
        

@stof this should be correct or?

Try removing the \ at the end of the namespace prefix to see whether it fixes it (I don't use a trailing backslash in my working config, I don't know whether it is important)

tried it in all variations :/

got it working:

jms_serializer:
    metadata:
        directories:
            issues:
                namespace_prefix: "Rs\\Issues"
                path: "@RsIssuesBundle/Resources/config/serializer/issues"

 ls -la vendor/digitalkaoz/issues-bundle/Resources/config/serializer/issues
Github.GithubIssue.xml
Github.GithubProject.xml

<?xml version="1.0" encoding="UTF-8" ?>
<serializer>
    <class name="Rs\Issues\Github\GithubProject" exclusion-policy="ALL">
    <!-- ... -->
    </class>