Smarter flushing of branch statistics caches

Instead of flushing the behind/ahead counts for all branches upon every
push we now only flush the cache of branches that actually need to have
these statistics recalculated. There are now basically 2 scenarios and
their effects:

1. A user pushes a commit to the default branch, this results in the
   cache being flushed for all branches.
2. A user pushes to a non default branch, this results in _only_ the
   cache for that branch being flushed.

The existing code (Repository#expire_cache) remains backwards compatible
with the previous behaviour, the new behaviour is only applied when a
branch name is passed as an argument. This ensures that when for example
a project is deleted the cache for all branches is flushed.

2 files changed, 37 insertions, 3 deletions

diff --git a/spec/models/repository_spec.rb b/spec/models/repository_spec.rb
index 753012be578..72b4ac6d660 100644
--- a/spec/models/repository_spec.rb
+++ b/spec/models/repository_spec.rb
@@ -291,6 +291,12 @@ describe Repository, models: true do
 
       repository.expire_cache
     end
+
+    it 'expires the caches for a specific branch' do
+      expect(repository).to receive(:expire_branch_cache).with('master')
+
+      repository.expire_cache('master')
+    end
   end
 
   describe '#expire_root_ref_cache' do
@@ -320,4 +326,32 @@ describe Repository, models: true do
       expect(repository.has_visible_content?).to eq(false)
     end
   end
+
+  describe '#expire_branch_ache' do
+    # This method is private but we need it for testing purposes. Sadly there's
+    # no other proper way of testing caching operations.
+    let(:cache) { repository.send(:cache) }
+
+    it 'expires the cache for all branches' do
+      expect(cache).to receive(:expire).
+        at_least(repository.branches.length).
+        times
+
+      repository.expire_branch_cache
+    end
+
+    it 'expires the cache for all branches when the root branch is given' do
+      expect(cache).to receive(:expire).
+        at_least(repository.branches.length).
+        times
+
+      repository.expire_branch_cache(repository.root_ref)
+    end
+
+    it 'expires the cache for a specific branch' do
+      expect(cache).to receive(:expire).once
+
+      repository.expire_branch_cache('foo')
+    end
+  end
 end
diff --git a/spec/services/git_push_service_spec.rb b/spec/services/git_push_service_spec.rb
index 349809743c7..eb3a5fe43f5 100644
--- a/spec/services/git_push_service_spec.rb
+++ b/spec/services/git_push_service_spec.rb
@@ -23,7 +23,7 @@ describe GitPushService, services: true do
       it { is_expected.to be_truthy }
 
       it 'flushes general cached data' do
-        expect(project.repository).to receive(:expire_cache)
+        expect(project.repository).to receive(:expire_cache).with('master')
 
         subject
       end
@@ -43,7 +43,7 @@ describe GitPushService, services: true do
       it { is_expected.to be_truthy }
 
       it 'flushes general cached data' do
-        expect(project.repository).to receive(:expire_cache)
+        expect(project.repository).to receive(:expire_cache).with('master')
 
         subject
       end
@@ -63,7 +63,7 @@ describe GitPushService, services: true do
       end
 
       it 'flushes general cached data' do
-        expect(project.repository).to receive(:expire_cache)
+        expect(project.repository).to receive(:expire_cache).with('master')
 
         subject
       end