Also verify if extending would override a class method

Since extending a class means including on the singleton class of the
class, this should now complain this:

``` ruby
module M
  extend Gitlab::Utils::Override

  override :f
  def f
    super.succ
  end
end

class C
  extend M

  def self.f
    0
  end
end
```

It should complain because `C.f` wasn't calling `M#f`.
This should pass verification:

``` ruby
module M
  extend Gitlab::Utils::Override

  override :f
  def f
    super.succ
  end
end

class B
  def self.f
    0
  end
end

class C < B
  extend M
end
```

Because `C.f` would now call `M#f`, and `M#f` does override something.

1 files changed, 13 insertions, 3 deletions

diff --git a/lib/gitlab/utils/override.rb b/lib/gitlab/utils/override.rb
index 8bf6bcb1fe2..7b2a62fed48 100644
--- a/lib/gitlab/utils/override.rb
+++ b/lib/gitlab/utils/override.rb
@@ -87,18 +87,28 @@ module Gitlab
       end
 
       def included(base = nil)
-        return super if base.nil? # Rails concern, ignoring it
+        super
+
+        queue_verification(base)
+      end
 
+      alias_method :prepended, :included
+
+      def extended(mod)
         super
 
+        queue_verification(mod.singleton_class)
+      end
+
+      def queue_verification(base)
+        return unless ENV['STATIC_VERIFICATION']
+
         if base.is_a?(Class) # We could check for Class in `override`
           # This could be `nil` if `override` was never called
           Override.extensions[self]&.add_class(base)
         end
       end
 
-      alias_method :prepended, :included
-
       def self.extensions
         @extensions ||= {}
       end