Invalidate branches cache on PostReceive

Whenever `PostReceive` is enqueued, `UpdateMergeRequestsWorker`
is enqueued and `MergeRequests::RefreshService` is called, it'll
check if the source branch of each MR asssociated to the push exists
or not via `MergeRequest#source_branch_exists?`. The said method will
call `Repository#branch_exists?` which is cached in `Rails.cache`.

When the cache contains outdated data and the source branch actually
exists, the `MergeRequests#RefreshService` job will close associated
MRs which is not correct.

The fix is to expire the branches cache of the project so we have
updated data during the post receive hook which will help in the
accuracy of the check if we need to close associated MRs or not.

3 files changed, 83 insertions, 6 deletions

diff --git a/spec/lib/gitlab/git_post_receive_spec.rb b/spec/lib/gitlab/git_post_receive_spec.rb
new file mode 100644
index 00000000000..f4a10d8d984
--- /dev/null
+++ b/spec/lib/gitlab/git_post_receive_spec.rb
@@ -0,0 +1,52 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe ::Gitlab::GitPostReceive do
+  let(:project) { create(:project) }
+
+  subject { described_class.new(project, "project-#{project.id}", changes.dup, {}) }
+
+  describe '#branches_exist?' do
+    context 'with no branches' do
+      let(:changes) do
+        <<~EOF
+          654321 210987 refs/nobranches/tag1
+          654322 210986 refs/tags/test1
+          654323 210985 refs/merge-requests/mr1
+        EOF
+      end
+
+      it 'returns false' do
+        expect(subject.branches_exist?).to be_falsey
+      end
+    end
+
+    context 'with branches' do
+      let(:changes) do
+        <<~EOF
+          654322 210986 refs/heads/test1
+          654321 210987 refs/tags/tag1
+          654323 210985 refs/merge-requests/mr1
+        EOF
+      end
+
+      it 'returns true' do
+        expect(subject.branches_exist?).to be_truthy
+      end
+    end
+
+    context 'with malformed changes' do
+      let(:changes) do
+        <<~EOF
+          ref/heads/1 a
+          somebranch refs/heads/2
+        EOF
+      end
+
+      it 'returns false' do
+        expect(subject.branches_exist?).to be_falsey
+      end
+    end
+  end
+end
diff --git a/spec/models/repository_spec.rb b/spec/models/repository_spec.rb
index 12dff440ce2..fa243876632 100644
--- a/spec/models/repository_spec.rb
+++ b/spec/models/repository_spec.rb
@@ -1781,6 +1781,12 @@ describe Repository do
 
       repository.after_create_branch
     end
+
+    it 'does not expire the branch caches when specified' do
+      expect(repository).not_to receive(:expire_branches_cache)
+
+      repository.after_create_branch(expire_cache: false)
+    end
   end
 
   describe '#after_remove_branch' do
@@ -1789,6 +1795,12 @@ describe Repository do
 
       repository.after_remove_branch
     end
+
+    it 'does not expire the branch caches when specified' do
+      expect(repository).not_to receive(:expire_branches_cache)
+
+      repository.after_remove_branch(expire_cache: false)
+    end
   end
 
   describe '#after_create' do
diff --git a/spec/workers/post_receive_spec.rb b/spec/workers/post_receive_spec.rb
index 39f1beb4efa..01ccae194fb 100644
--- a/spec/workers/post_receive_spec.rb
+++ b/spec/workers/post_receive_spec.rb
@@ -57,12 +57,19 @@ describe PostReceive do
     context 'with changes' do
       before do
         allow_any_instance_of(Gitlab::GitPostReceive).to receive(:identify).and_return(project.owner)
+        allow(Gitlab::GlRepository).to receive(:parse).and_return([project, Gitlab::GlRepository::PROJECT])
       end
 
       context "branches" do
-        let(:changes) { "123456 789012 refs/heads/tést" }
+        let(:changes) { '123456 789012 refs/heads/tést' }
+
+        it 'expires the branches cache' do
+          expect(project.repository).to receive(:expire_branches_cache)
+
+          described_class.new.perform(gl_repository, key_id, base64_changes)
+        end
 
-        it "calls Git::BranchPushService" do
+        it 'calls Git::BranchPushService' do
           expect_next_instance_of(Git::BranchPushService) do |service|
             expect(service).to receive(:execute).and_return(true)
           end
@@ -73,16 +80,22 @@ describe PostReceive do
         end
       end
 
-      context "tags" do
-        let(:changes) { "123456 789012 refs/tags/tag" }
+      context 'tags' do
+        let(:changes) { '123456 789012 refs/tags/tag' }
 
-        it "calls Git::TagPushService" do
-          expect(Git::BranchPushService).not_to receive(:execute)
+        it 'does not expire branches cache' do
+          expect(project.repository).not_to receive(:expire_branches_cache)
 
+          described_class.new.perform(gl_repository, key_id, base64_changes)
+        end
+
+        it 'calls Git::TagPushService' do
           expect_next_instance_of(Git::TagPushService) do |service|
             expect(service).to receive(:execute).and_return(true)
           end
 
+          expect(Git::BranchPushService).not_to receive(:new)
+
           described_class.new.perform(gl_repository, key_id, base64_changes)
         end
       end