From: "Earlopain (Earlopain _) via ruby-core" <ruby-core@...>
Date: 2025-11-28T11:41:27+00:00
Subject: [ruby-core:123932] [Ruby Bug#21718] TypeError:wrong argument type ... (expected Array)

Issue #21718 has been updated by Earlopain (Earlopain _).


I only checked minimagick, this looks caused by https://bugs.ruby-lang.org/issues/21219

`MiniMagick::Tool` defines `method_missing` and returns itself: https://github.com/minimagick/minimagick/blob/ddcbfe9632667876be10373e1e01252617e74057/lib/mini_magick/tool.rb#L257-L262

The test passes if I explicitly return an array on like `return [] if name == :instance_variables_to_inspect`. Rspec code is not comprehensible to me but it looks like it might use `inspect` to match yielded arguments or something along those lines?

Basically, it boils down to this:
```rb
class Foo
  def method_missing(...)
    self
  end
end

Foo.new.inspect # 'Kernel#inspect': wrong argument type Foo (expected Array) (TypeError)
```

----------------------------------------
Bug #21718: TypeError:wrong argument type ... (expected Array)
https://bugs.ruby-lang.org/issues/21718#change-115331

* Author: vo.x (Vit Ondruch)
* Status: Open
* ruby -v: ruby 4.0.0dev (2025-11-18 master 85abc59c32) +PRISM [x86_64-linux]
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
Testing Ruby 4.0 on Fedora, we observe these errors in [MiniMagick](https://github.com/minimagick/minimagick/)

~~~
1) MiniMagick::Image#composite yields an optional block
      Failure/Error: yield composite if block_given?

TypeError:
        wrong argument type MiniMagick::Tool (expected Array)
      # ./lib/mini_magick/image.rb:515:in 'block in MiniMagick::Image#composite'
      # ./lib/mini_magick/tool.rb:34:in 'MiniMagick::Tool.new'
      # ./lib/mini_magick.rb:28:in 'block (2 levels) in module:MiniMagick'
      # ./lib/mini_magick/image.rb:514:in 'MiniMagick::Image#composite'
      # ./spec/lib/mini_magick/image_spec.rb:609:in 'block (4 levels) in <top (required)>'
      # ./spec/lib/mini_magick/image_spec.rb:610:in 'block (3 levels) in <top (required)>'
~~~

and [Vagrant](https://github.com/hashicorp/vagrant) / [vagrant-libvirt](https://github.com/vagrant-libvirt/vagrant-libvirt)

~~~
340) VagrantPlugins::ProviderLibvirt::Util::NetworkUtil #libvirt_networks should retrieve the list of networks
        Failure/Error: let(:machine)          { iso_env.machine(:test, :libvirt) }

TypeError:
          wrong argument type Vagrant::Config::V2::DummyConfig (expected Array)
        # /usr/share/vagrant/gems/gems/vagrant-2.3.4/plugins/kernel_v2/config/vm.rb:713:in 'Kernel#inspect'
        # /usr/share/vagrant/gems/gems/vagrant-2.3.4/plugins/kernel_v2/config/vm.rb:713:in 'VagrantPlugins::Kernel_V2::VMConfig#get_provider_config'
        # /usr/share/vagrant/gems/gems/vagrant-2.3.4/lib/vagrant/vagrantfile.rb:75:in 'Vagrant::Vagrantfile#machine'
        # /usr/share/vagrant/gems/gems/vagrant-2.3.4/lib/vagrant/environment.rb:740:in 'Vagrant::Environment#machine'
        # ./spec/support/unit_context.rb:26:in 'block (2 levels) in <top (required)>'
        # ./spec/support/unit_context.rb:37:in 'block (2 levels) in <top (required)>'
        # ./spec/support/unit_context.rb:51:in 'block (3 levels) in <top (required)>'
        # ./spec/support/unit_context.rb:43:in 'block (2 levels) in <top (required)>'
        # /usr/share/rubygems/rubygems.rb:303:in 'Kernel#load'
        # /usr/share/rubygems/rubygems.rb:303:in 'Gem.activate_and_load_bin_path'
~~~

Trying to investigate closer the vagrant-libvirt case, I really cannot wrap my head around it, because it fails with innocently looking `result.inspect` [1]. The image_magick fails at `yield composite if block_given?` line, so I suspect that the `yield composite` is the specific place.

Since this does not make any sense to me, I have grepped the Ruby source code for:

~~~
$ grep -R -e TypeError | grep "wrong argument type.*Array"

... snip ...

prism/extension.c:        rb_raise(rb_eTypeError, "wrong argument type %"PRIsVALUE" (expected Array)", rb_obj_class(scopes));
prism/extension.c:                rb_raise(rb_eTypeError, "wrong argument type %"PRIsVALUE" (expected Array)", rb_obj_class(locals));
prism/extension.c:                rb_raise(rb_eTypeError, "wrong argument type %"PRIsVALUE" (expected Array)", rb_obj_class(names));
~~~

This seems to come from https://github.com/ruby/prism/commit/21abb6b7c499b41a951eba7c8219c336a656da40 . So is it the reason? Not sure.

[1]: https://github.com/hashicorp/vagrant/blob/986a01734f008d62897bb66085381090e4fcabfc/plugins/kernel_v2/config/vm.rb#L712
[2]: https://github.com/minimagick/minimagick/blob/ddcbfe9632667876be10373e1e01252617e74057/lib/mini_magick/image.rb#L515



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