[Bug]: Invalid type checking for service declarations with union service types

[MaryamZi]

Description

$title.

Steps to Reproduce

import ballerina/io;

type Foo distinct service object {
    isolated function get() returns string|error;
};

type Bar distinct service object {
    
};

public class Listener {

    public function 'start() returns error? {
    }

    public function gracefulStop() returns error? {
    }

    public function immediateStop() returns error? {
    }

    public function detach(Foo|Bar s) returns error? {
    }

    public function attach(Foo|Bar s, string[]|string|() name = ()) returns error? {
        io:println(s is Foo);
        io:println(s is Bar);
        io:println(s is Foo|Bar);
    }
}


service on new Listener() {

    isolated function get() returns string|error {
        return "";
    }

}

All the is checks evaluate to false. This particular example should probably fail at compile-time due to ambiguity anyway.

But, even for the following types, prints false for both.

type Foo distinct service object {
    isolated function get() returns string|error;
};

type Bar distinct service object {
    isolated function get() returns int|error;
};

Affected Version(s)

No response

OS, DB, other environment details and versions

No response

Related area

-> Compilation

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