Fix force-push message in push emails

`after_sha` maps to the source branch, as it's the head of our compare,
so these were just the wrong way around.

app/workers/emails_on_push_worker.rb

@@ -33,13 +33,13 @@ class EmailsOnPushWorker
     reverse_compare = false
 
     if action == :push
-      compare = CompareService.new.execute(project, before_sha, project, after_sha)
+      compare = CompareService.new.execute(project, after_sha, project, before_sha)
       diff_refs = compare.diff_refs
 
       return false if compare.same
 
       if compare.commits.empty?
-        compare = CompareService.new.execute(project, after_sha, project, before_sha)
+        compare = CompareService.new.execute(project, before_sha, project, after_sha)
         diff_refs = compare.diff_refs
 
         reverse_compare = true

spec/workers/emails_on_push_worker_spec.rb

@@ -2,19 +2,19 @@ require 'spec_helper'
 
 describe EmailsOnPushWorker do
   include RepoHelpers
+  include EmailSpec::Matchers
 
   let(:project) { create(:project) }
   let(:user) { create(:user) }
   let(:data) { Gitlab::DataBuilder::Push.build_sample(project, user) }
   let(:recipients) { user.email }
   let(:perform) { subject.perform(project.id, recipients, data.stringify_keys) }
+  let(:email) { ActionMailer::Base.deliveries.last }
 
   subject { EmailsOnPushWorker.new }
 
   describe "#perform" do
     context "when push is a new branch" do
-      let(:email) { ActionMailer::Base.deliveries.last }
-
       before do
         data_new_branch = data.stringify_keys.merge("before" => Gitlab::Git::BLANK_SHA)
 
@@ -31,8 +31,6 @@ describe EmailsOnPushWorker do
     end
 
     context "when push is a deleted branch" do
-      let(:email) { ActionMailer::Base.deliveries.last }
-
       before do
         data_deleted_branch = data.stringify_keys.merge("after" => Gitlab::Git::BLANK_SHA)
 
@@ -48,15 +46,40 @@ describe EmailsOnPushWorker do
       end
     end
 
-    context "when there are no errors in sending" do
-      let(:email) { ActionMailer::Base.deliveries.last }
+    context "when push is a force push to delete commits" do
+      before do
+        data_force_push = data.stringify_keys.merge(
+          "after"  => data[:before],
+          "before" => data[:after]
+        )
+
+        subject.perform(project.id, recipients, data_force_push)
+      end
+
+      it "sends a mail with the correct subject" do
+        expect(email.subject).to include('Change some files')
+      end
+
+      it "mentions force pushing in the body" do
+        expect(email).to have_body_text("force push")
+      end
+
+      it "sends the mail to the correct recipient" do
+        expect(email.to).to eq([user.email])
+      end
+    end
 
+    context "when there are no errors in sending" do
       before { perform }
 
       it "sends a mail with the correct subject" do
         expect(email.subject).to include('Change some files')
       end
 
+      it "does not mention force pushing in the body" do
+        expect(email).not_to have_body_text("force push")
+      end
+
       it "sends the mail to the correct recipient" do
         expect(email.to).to eq([user.email])
       end