Ensure newly created traces have the correct tags set

We currently have the rails_pages span, which is just floating around by itself because it's not properly tagged to get connected to other spans.

README.md

@@ -56,10 +56,15 @@ DegicaDatadog::Tracing.span!("hats.process_payment") do
   # Process a payment.
 end
 
+# Optionally specify a resource and/or tags.
+resource = webhook.provider.name
 tags = {
     "merchant_uuid" => merchant.uuid,
     "merchant_name" => merchant.name,
 }
+DegicaDatadog::Tracing.span!("hats.send_webhook", resource: resource, tags: tags) do
+  # Process a payment.
+end
 
 # Add tags to the current span.
 DegicaDatadog::Tracing.span_tags!(**tags)

lib/degica_datadog/tracing.rb

@@ -41,6 +41,7 @@ def init # rubocop:disable Metrics/AbcSize,Metrics/MethodLength
 
       # Start a new span.
       def span!(name, **options, &block)
+        enrich_span_options!(options)
         Datadog::Tracing.trace(name, **options, &block)
       end
 
@@ -84,6 +85,27 @@ def flatten_hash_for_span(hsh, key = nil) # rubocop:disable Metrics/MethodLength
 
         flattened_hash
       end
+
+      # Merge in default tags and service name.
+      def enrich_span_options!(options)
+        options[:service] = Config.service
+
+        if options[:tags]
+          options[:tags].merge!(default_span_tags)
+        else
+          options[:tags] = default_span_tags
+        end
+      end
+
+      def default_span_tags
+        {
+          "env" => Config.environment,
+          "version" => Config.version,
+          "service" => Config.service,
+          "git.commit.sha" => Config.version,
+          "git.repository_url" => Config.repository_url
+        }
+      end
     end
   end
 end

spec/tracing_spec.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+RSpec.describe DegicaDatadog::Tracing do
+  describe ".enrich_span_options!" do
+    it "adds the service name" do
+      options = {}
+      described_class.enrich_span_options!(options)
+      expect(options[:service]).to eq(DegicaDatadog::Config.service)
+    end
+
+    it "adds the default tags if none are present" do
+      options = {}
+      described_class.enrich_span_options!(options)
+      expect(options[:tags]).to eq(DegicaDatadog::Tracing.default_span_tags)
+    end
+
+    it "merges the default tags with the provided tags" do
+      options = { tags: { "foo" => "bar" } }
+      described_class.enrich_span_options!(options)
+      expect(options[:tags]).to eq(DegicaDatadog::Tracing.default_span_tags.merge("foo" => "bar"))
+    end
+
+    it "overrides the provided tags with default tags" do
+      options = { tags: { "env" => "test" } }
+      described_class.enrich_span_options!(options)
+      expect(options[:tags]).to eq(DegicaDatadog::Tracing.default_span_tags)
+    end
+  end
+end