Fixed ordering in Project.find_with_namespace

This ensures that Project.find_with_namespace returns a row matching
literally as the first value, instead of returning a random value.

The ordering here is _only_ applied to Project.find_with_namespace and
_not_ Project.where_paths_in as currently there's no code that requires
Project.where_paths_in to return rows in a certain order. Since this
method also returns all rows that match there's no real harm in not
setting a specific order either. Another reason is that generating all
the "WHEN" arms for multiple values in Project.where_paths_in becomes
really messy.

On MySQL we have to use the "BINARY" operator to turn a "WHERE" into a
case-sensitive WHERE as otherwise MySQL may still end up returning rows
in an unpredictable order.

Fixes gitlab-org/gitlab-ce#18603

app/models/project.rb

@@ -262,7 +262,23 @@ class Project < ActiveRecord::Base
     #
     # Returns a Project, or nil if no project could be found.
     def find_with_namespace(path)
-      where_paths_in([path]).reorder(nil).take
+      namespace_path, project_path = path.split('/', 2)
+
+      return unless namespace_path && project_path
+
+      namespace_path = connection.quote(namespace_path)
+      project_path = connection.quote(project_path)
+
+      # On MySQL we want to ensure the ORDER BY uses a case-sensitive match so
+      # any literal matches come first, for this we have to use "BINARY".
+      # Without this there's still no guarantee in what order MySQL will return
+      # rows.
+      binary = Gitlab::Database.mysql? ? 'BINARY' : ''
+
+      order_sql = "(CASE WHEN #{binary} namespaces.path = #{namespace_path} " \
+        "AND #{binary} projects.path = #{project_path} THEN 0 ELSE 1 END)"
+
+      where_paths_in([path]).reorder(order_sql).take
     end
 
     # Builds a relation to find multiple projects by their full paths.

spec/models/project_spec.rb

@@ -220,7 +220,7 @@ describe Project, models: true do
     end
   end
 
-  describe :find_with_namespace do
+  describe '.find_with_namespace' do
     context 'with namespace' do
       before do
         @group = create :group, name: 'gitlab'
@@ -231,6 +231,22 @@ describe Project, models: true do
       it { expect(Project.find_with_namespace('GitLab/GitlabHQ')).to eq(@project) }
       it { expect(Project.find_with_namespace('gitlab-ci')).to be_nil }
     end
+
+    context 'when multiple projects using a similar name exist' do
+      let(:group) { create(:group, name: 'gitlab') }
+
+      let!(:project1) do
+        create(:empty_project, name: 'gitlab1', path: 'gitlab', namespace: group)
+      end
+
+      let!(:project2) do
+        create(:empty_project, name: 'gitlab2', path: 'GITLAB', namespace: group)
+      end
+
+      it 'returns the row where the path matches literally' do
+        expect(Project.find_with_namespace('gitlab/GITLAB')).to eq(project2)
+      end
+    end
   end
 
   describe :to_param do