fix(pacts for verification): return the pacts for the branch heads wh…

…en using the branch selector

Rather than returning the latest pacts for the versions that had pacts.

The impact of this is that you can now decomission an integration by publishing a consumer version that does not have a pact any more.

lib/pact_broker/pacts/pact_publication_dataset_module.rb

@@ -111,7 +111,37 @@ def overall_latest_for_consumer_id_and_provider_id(consumer_id, provider_id)
           .limit(1)
       end
 
+      # Return the pacts (if they exist) for the branch heads.
+      # This uses the new logic of finding the branch head and returning any associated pacts,
+      # rather than the old logic of returning the pact for the latest version
+      # on the branch that had a pact.
+      def for_branch_heads(branch_name)
+        branch_head_join = {
+          Sequel[:pact_publications][:consumer_version_id] => Sequel[:branch_heads][:version_id],
+        }
+
+        base_query = self
+        if no_columns_selected?
+          base_query = base_query.select_all_qualified.select_append(Sequel[:branch_heads][:branch_name].as(:branch_name))
+        end
+
+        base_query
+          .join(:branch_heads, branch_head_join) do
+            name_like(Sequel[:branch_heads][:branch_name], branch_name)
+          end
+          .remove_overridden_revisions_from_complete_query
+      end
+
       def latest_for_consumer_branch(branch_name)
+        # Keep this flag for a little whle in case we need to disable the new logic
+        if PactBroker.feature_enabled?(:disable_use_branch_heads_for_latest_branch_pacts, true)
+          old_latest_for_consumer_branch(branch_name)
+        else
+          for_branch_heads(branch_name)
+        end
+      end
+
+      def old_latest_for_consumer_branch(branch_name)
         branch_versions_join = {
           Sequel[:pact_publications][:consumer_version_id] => Sequel[:branch_versions][:version_id]
         }

spec/lib/pact_broker/pacts/pact_publication_dataset_module_spec.rb

@@ -104,6 +104,28 @@ module Pacts
           expect(subject.first.values.keys.sort).to eq (PactPublication.columns + [:branch_name]).sort
         end
 
+        context "when there is no pact for the branch head" do
+          before do
+            td.create_consumer_version("12", branch: "main")
+          end
+
+          it "does not return a pact" do
+            all = subject.all_allowing_lazy_load
+            expect(all.size).to eq 1
+          end
+
+          context "when the new logic is disabled" do
+            before do
+              allow(PactBroker). to receive(:feature_enabled?).with(:disable_use_branch_heads_for_latest_branch_pacts, true).and_return(true)
+            end
+
+            it "does return a pact for the branch" do
+              all = subject.all_allowing_lazy_load
+              expect(all.size).to eq 2
+            end
+          end
+        end
+
         context "when columns are already selected" do
           subject { PactPublication.select(Sequel[:pact_publications][:id]).latest_for_consumer_branch("main") }