Correct arity for instrumented methods w/o args

This ensures that an instrumented method that doesn't take arguments
reports an arity of 0, instead of -1.

If Ruby had a proper method for finding out the required arguments of a
method (e.g. Method#required_arguments) this would not have been an
issue. Sadly the only two methods we have are Method#parameters and
Method#arity, and both are equally painful to use.

Fixes gitlab-org/gitlab-ce#12450

1 files changed, 10 insertions, 0 deletions

diff --git a/spec/lib/gitlab/metrics/instrumentation_spec.rb b/spec/lib/gitlab/metrics/instrumentation_spec.rb
index 2a37cd40dde..ad4290c43bb 100644
--- a/spec/lib/gitlab/metrics/instrumentation_spec.rb
+++ b/spec/lib/gitlab/metrics/instrumentation_spec.rb
@@ -66,6 +66,16 @@ describe Gitlab::Metrics::Instrumentation do
 
         @dummy.foo
       end
+
+      it 'generates a method with the correct arity when using methods without arguments' do
+        dummy = Class.new do
+          def self.test; end
+        end
+
+        described_class.instrument_method(dummy, :test)
+
+        expect(dummy.method(:test).arity).to eq(0)
+      end
     end
 
     describe 'with metrics disabled' do