Adapt JRuby arity workaround to BlockSignature

The workaround looking up the corresponding Java class and looking at its methods only works for methods, and doesn't work for Proc, where there isn't a direct API to access the proxied Java class.

While the same problem exists for Proc's, until jruby/jruby#2817 has been resolved, there isn't much that can be done for that case. However, the current code fails to run for all blocks with arity -1, so this tweak is necessary to ensure normal blocks work again.

I couldn't find any specs for BlockSignature, so wasn't sure where it would be appropriate to add a test for this.

Author: grddev

lib/rspec/support/method_signature_verifier.rb

@@ -180,13 +180,19 @@ def classify_parameters
       # aliases to make method names look more Rubyesque). If there is only a
       # single match, we can use that methods arity directly instead of the
       # default -1 arity.
+      #
+      # This workaround only works for Java proxy methods, and in order to
+      # support regular methods and blocks, we need to be careful about calling
+      # owner and java_class as they might not be available
       if Java::JavaLang::String.instance_method(:char_at).arity == -1
         class MethodSignature < remove_const(:MethodSignature)
         private
 
           def classify_parameters
             super
-            return unless @method.arity == -1 && @method.owner.respond_to?(:java_class)
+            return unless @method.arity == -1
+            return unless @method.respond_to?(:owner)
+            return unless @method.owner.respond_to?(:java_class)
             java_instance_methods = @method.owner.java_class.java_instance_methods
             compatible_overloads = java_instance_methods.select do |java_method|
               @method == @method.owner.instance_method(java_method.name)