Added rack-lineprof for development

This can be used to measure the time (roughly) spent on a per line
basis. This can also be used to measure timings for views, for example
by adding the following to a URL:

   ?lineprof=app/views/projects/notes/_note

rack-lineprof is only enabled when:

1. The application runs in development mode
2. The used Ruby is MRI
3. The environment variable ENABLE_LINEPROF is set to a non-empty value

1 files changed, 31 insertions, 0 deletions

diff --git a/config/initializers/rack_lineprof.rb b/config/initializers/rack_lineprof.rb
new file mode 100644
index 00000000000..80d232c3d36
--- /dev/null
+++ b/config/initializers/rack_lineprof.rb
@@ -0,0 +1,31 @@
+# The default colors of rack-lineprof can be very hard to look at in terminals
+# with darker backgrounds. This patch tweaks the colors a bit so the output is
+# actually readable.
+if Rails.env.development? and RUBY_ENGINE == 'ruby' and ENV['ENABLE_LINEPROF']
+  Gitlab::Application.config.middleware.use(Rack::Lineprof)
+
+  module Rack
+    class Lineprof
+      class Sample < Rack::Lineprof::Sample.superclass
+        def format(*)
+          formatted = if level == CONTEXT
+            sprintf "                 | % 3i  %s", line, code
+          else
+            sprintf "% 8.1fms %5i | % 3i  %s", ms, calls, line, code
+          end
+
+          case level
+          when CRITICAL
+            color.red formatted
+          when WARNING
+            color.yellow formatted
+          when NOMINAL
+            color.white formatted
+          else # CONTEXT
+            formatted
+          end
+        end
+      end
+    end
+  end
+end