Make ls command work for BasicObjects

[eikes]

When working with the builder gem I noticed that the irb inspection of the Builder::XmlMarkup instances was not working as expected. Upon further investigation it turns out, that the reason is that this class inherits from BasicObject directly and not from the more common Object.

You can see the problem here:

4.0.1 :001 > ls BasicObject.new
/gems/irb-1.17.0/lib/irb/command/ls.rb:58:in 'IRB::Command::Ls#execute': undefined method 'class' for an instance of BasicObject (NoMethodError)

        klass  = (obj.class == Class || obj.class == Module ? obj : obj.class)
                     ^^^^^^

I have also created a new ls command test file containing a failing test which you can see below: https://github.com/ruby/irb/actions/runs/22390651625/job/64811518726

The test is fixed with the second commit of this PR by using a slightly different way to inspect the class. singleton_class and instance_variables of an object.

PS: The prism-latest test failure is because the syntax of ruby 4.1 allows trailing commas in method definitions and this change is addressed here: #1178

[st0012]

Maybe we can just do Kernel.instance_method(:is_a?).bind(obj).call(Module)? If an object is a Class, it's definitely a Module as well.

[eikes]

I didn't think about that, but it's true! I just kept it as it was but I'll change it.

[eikes]

It's not necessarily easier to read though:

-        is_class_or_module = klass == Class || klass == Module
+        is_class_or_module = Kernel.instance_method(:is_a?).bind(obj).call(Module)

[tompng]

How about Module === obj

[eikes]

That's neat! I changed it 👍

[eikes]

Just rebased it on master to make the prism test pass...

[eikes]

@tompng @st0012 anything else you'd like to see so you can merge this PR?

[tompng]

Thank you 👍