Added ability to add custom tags to transactions

CHANGELOG

@@ -2,6 +2,7 @@ Please view this file on the master branch, on stable branches it's out of date.
 
 v 8.7.0 (unreleased)
   - All service classes (those residing in app/services) are now instrumented (Yorick Peterse)
+  - Developers can now add custom tags to transactions (Yorick Peterse)
   - Enable gzip for assets, makes the page size significantly smaller. !3544 / !3632 (Connor Shea)
   - Load award emoji images separately unless opening the full picker. Saves several hundred KBs of data for most pages. (Connor Shea)
   - All images in discussions and wikis now link to their source files !3464 (Connor Shea).

lib/gitlab/metrics.rb

@@ -104,6 +104,16 @@ module Gitlab
       retval
     end
 
+    # Adds a tag to the current transaction (if any)
+    #
+    # name - The name of the tag to add.
+    # value - The value of the tag.
+    def self.tag_transaction(name, value)
+      trans = current_transaction
+
+      trans.add_tag(name, value) if trans
+    end
+
     # When enabled this should be set before being used as the usual pattern
     # "@foo ||= bar" is _not_ thread-safe.
     if enabled?

spec/lib/gitlab/metrics_spec.rb

@@ -98,4 +98,29 @@ describe Gitlab::Metrics do
       end
     end
   end
+
+  describe '.tag_transaction' do
+    context 'without a transaction' do
+      it 'does nothing' do
+        expect_any_instance_of(Gitlab::Metrics::Transaction).
+          not_to receive(:add_tag)
+
+        Gitlab::Metrics.tag_transaction(:foo, 'bar')
+      end
+    end
+
+    context 'with a transaction' do
+      let(:transaction) { Gitlab::Metrics::Transaction.new }
+
+      it 'adds the tag to the transaction' do
+        expect(Gitlab::Metrics).to receive(:current_transaction).
+          and_return(transaction)
+
+        expect(transaction).to receive(:add_tag).
+          with(:foo, 'bar')
+
+        Gitlab::Metrics.tag_transaction(:foo, 'bar')
+      end
+    end
+  end
 end