Enforce "developers can merge" during `pre-receive`.

1. When a merge request is being merged, save the merge commit SHA in
   the `in_progress_merge_commit_sha` database column.

2. The `pre-receive` hook looks for any locked (in progress) merge
   request with `in_progress_merge_commit_sha` matching the `newrev` it
   is passed.

3. If it finds a matching MR, the merge is legitimate.

4. Update `git_access_spec` to test the behaviour we added here. Also
   refactored this spec a bit to make it easier to add more contexts / conditions.

app/models/repository.rb

@@ -769,9 +769,9 @@ class Repository
     end
   end
 
-  def merge(user, source_sha, target_branch, options = {})
-    our_commit = rugged.branches[target_branch].target
-    their_commit = rugged.lookup(source_sha)
+  def merge(user, merge_request, options = {})
+    our_commit = rugged.branches[merge_request.target_branch].target
+    their_commit = rugged.lookup(merge_request.diff_head_sha)
 
     raise "Invalid merge target" if our_commit.nil?
     raise "Invalid merge source" if their_commit.nil?
@@ -779,14 +779,16 @@ class Repository
     merge_index = rugged.merge_commits(our_commit, their_commit)
     return false if merge_index.conflicts?
 
-    commit_with_hooks(user, target_branch) do |ref|
+    commit_with_hooks(user, merge_request.target_branch) do |tmp_ref|
       actual_options = options.merge(
         parents: [our_commit, their_commit],
         tree: merge_index.write_tree(rugged),
-        update_ref: ref
+        update_ref: tmp_ref
       )
 
-      Rugged::Commit.create(rugged, actual_options)
+      commit_id = Rugged::Commit.create(rugged, actual_options)
+      merge_request.update(in_progress_merge_commit_sha: commit_id)
+      commit_id
     end
   end
 

app/services/merge_requests/merge_service.rb

@@ -34,7 +34,7 @@ module MergeRequests
         committer: committer
       }
 
-      commit_id = repository.merge(current_user, merge_request.diff_head_sha, merge_request.target_branch, options)
+      commit_id = repository.merge(current_user, merge_request, options)
       merge_request.update(merge_commit_sha: commit_id)
     rescue GitHooksService::PreReceiveError => e
       merge_request.update(merge_error: e.message)
@@ -43,6 +43,8 @@ module MergeRequests
       merge_request.update(merge_error: "Something went wrong during merge")
       Rails.logger.error(e.message)
       false
+    ensure
+      merge_request.update(in_progress_merge_commit_sha: nil)
     end
 
     def after_merge

db/migrate/20160629025435_add_column_in_progress_merge_commit_sha_to_merge_requests.rb

+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class AddColumnInProgressMergeCommitShaToMergeRequests < ActiveRecord::Migration
+  def change
+    add_column :merge_requests, :in_progress_merge_commit_sha, :string
+  end
+end

db/schema.rb

@@ -626,6 +626,7 @@ ActiveRecord::Schema.define(version: 20160712171823) do
     t.string   "merge_commit_sha"
     t.datetime "deleted_at"
     t.integer  "lock_version",              default: 0,     null: false
+    t.string   "in_progress_merge_commit_sha"
   end
 
   add_index "merge_requests", ["assignee_id"], name: "index_merge_requests_on_assignee_id", using: :btree

lib/gitlab/checks/matching_merge_request.rb

+module Gitlab
+  module Checks
+    class MatchingMergeRequest
+      def initialize(newrev, branch_name, project)
+        @newrev = newrev
+        @branch_name = branch_name
+        @project = project
+      end
+
+      def match?
+        @project.merge_requests
+          .with_state(:locked)
+          .where(in_progress_merge_commit_sha: @newrev, target_branch: @branch_name)
+          .exists?
+      end
+    end
+  end
+end

lib/gitlab/git_access.rb

@@ -177,10 +177,15 @@ module Gitlab
       Gitlab::ForcePushCheck.force_push?(project, oldrev, newrev)
     end
 
+
     def protocol_allowed?
       Gitlab::ProtocolAccess.allowed?(protocol)
     end
 
+    def matching_merge_request?(newrev, branch_name)
+      Checks::MatchingMergeRequest.new(newrev, branch_name, project).match?
+    end
+
     private
 
     def protected_branch_action(oldrev, newrev, branch_name)
@@ -190,6 +195,8 @@ module Gitlab
       elsif Gitlab::Git.blank_ref?(newrev)
         # and we dont allow remove of protected branch
         :remove_protected_branches
+      elsif matching_merge_request?(newrev, branch_name) && project.developers_can_merge_to_protected_branch?(branch_name)
+        :push_code
       elsif project.developers_can_push_to_protected_branch?(branch_name)
         :push_code
       else

spec/lib/gitlab/diff/position_tracer_spec.rb

@@ -1639,7 +1639,8 @@ describe Gitlab::Diff::PositionTracer, lib: true do
           committer: committer
         }
 
-        repository.merge(current_user, second_create_file_commit.sha, branch_name, options)
+        merge_request = create(:merge_request, source_branch: second_create_file_commit.sha, target_branch: branch_name, source_project: project)
+        repository.merge(current_user, merge_request, options)
         project.commit(branch_name)
       end
 

spec/lib/gitlab/git_access_spec.rb

@@ -181,96 +181,47 @@ describe Gitlab::GitAccess, lib: true do
   end
 
   describe 'push_access_check' do
-    def protect_feature_branch
-      create(:protected_branch, name: 'feature', project: project)
-    end
+    before { merge_into_protected_branch }
+    let(:unprotected_branch) { FFaker::Internet.user_name }
 
-    def changes
-      {
-        push_new_branch: "#{Gitlab::Git::BLANK_SHA} 570e7b2ab refs/heads/wow",
+    let(:changes) do
+      { push_new_branch: "#{Gitlab::Git::BLANK_SHA} 570e7b2ab refs/heads/wow",
         push_master: '6f6d7e7ed 570e7b2ab refs/heads/master',
         push_protected_branch: '6f6d7e7ed 570e7b2ab refs/heads/feature',
         push_remove_protected_branch: "570e7b2ab #{Gitlab::Git::BLANK_SHA} "\
                                       'refs/heads/feature',
         push_tag: '6f6d7e7ed 570e7b2ab refs/tags/v1.0.0',
         push_new_tag: "#{Gitlab::Git::BLANK_SHA} 570e7b2ab refs/tags/v7.8.9",
-        push_all: ['6f6d7e7ed 570e7b2ab refs/heads/master', '6f6d7e7ed 570e7b2ab refs/heads/feature']
-      }
-    end
-
-    def self.permissions_matrix
-      {
-        master: {
-          push_new_branch: true,
-          push_master: true,
-          push_protected_branch: true,
-          push_remove_protected_branch: false,
-          push_tag: true,
-          push_new_tag: true,
-          push_all: true,
-        },
-
-        developer: {
-          push_new_branch: true,
-          push_master: true,
-          push_protected_branch: false,
-          push_remove_protected_branch: false,
-          push_tag: false,
-          push_new_tag: true,
-          push_all: false,
-        },
-
-        reporter: {
-          push_new_branch: false,
-          push_master: false,
-          push_protected_branch: false,
-          push_remove_protected_branch: false,
-          push_tag: false,
-          push_new_tag: false,
-          push_all: false,
-        },
-
-        guest: {
-          push_new_branch: false,
-          push_master: false,
-          push_protected_branch: false,
-          push_remove_protected_branch: false,
-          push_tag: false,
-          push_new_tag: false,
-          push_all: false,
-        }
-      }
+        push_all: ['6f6d7e7ed 570e7b2ab refs/heads/master', '6f6d7e7ed 570e7b2ab refs/heads/feature'],
+        merge_into_protected_branch: "0b4bc9a #{merge_into_protected_branch} refs/heads/feature" }
     end
 
-    def self.updated_permissions_matrix
-      updated_permissions_matrix = permissions_matrix.dup
-      updated_permissions_matrix[:developer][:push_protected_branch] = true
-      updated_permissions_matrix[:developer][:push_all] = true
-      updated_permissions_matrix
+    def stub_git_hooks
+      # Running the `pre-receive` hook is expensive, and not necessary for this test.
+      allow_any_instance_of(GitHooksService).to receive(:execute).and_yield
     end
 
-    permissions_matrix.keys.each do |role|
-      describe "#{role} access" do
-        before { protect_feature_branch }
-        before { project.team << [user, role] }
+    def merge_into_protected_branch
+      @protected_branch_merge_commit ||= begin
+        stub_git_hooks
+        project.repository.add_branch(user, unprotected_branch, 'feature')
+        target_branch = project.repository.lookup('feature')
+        source_branch = project.repository.commit_file(user, FFaker::InternetSE.login_user_name, FFaker::HipsterIpsum.paragraph, FFaker::HipsterIpsum.sentence, unprotected_branch, false)
+        rugged = project.repository.rugged
+        author = { email: "email@example.com", time: Time.now, name: "Example Git User" }
 
-        permissions_matrix[role].each do |action, allowed|
-          context action do
-            subject { access.push_access_check(changes[action]) }
 
-            it { expect(subject.allowed?).to allowed ? be_truthy : be_falsey }
-          end
-        end
+        merge_index = rugged.merge_commits(target_branch, source_branch)
+        Rugged::Commit.create(rugged, author: author, committer: author, message: "commit message", parents: [target_branch, source_branch], tree: merge_index.write_tree(rugged))
       end
     end
 
-    context "with enabled developers push to protected branches " do
-      updated_permissions_matrix.keys.each do |role|
+    def self.run_permission_checks(permissions_matrix)
+      permissions_matrix.keys.each do |role|
         describe "#{role} access" do
-          before { create(:protected_branch, name: 'feature', developers_can_push: true, project: project) }
           before { project.team << [user, role] }
 
-          updated_permissions_matrix[role].each do |action, allowed|
+          permissions_matrix[role].each do |action, allowed|
             context action do
               subject { access.push_access_check(changes[action]) }
 
@@ -280,5 +231,97 @@ describe Gitlab::GitAccess, lib: true do
         end
       end
     end
+
+    permissions_matrix = {
+      master: {
+        push_new_branch: true,
+        push_master: true,
+        push_protected_branch: true,
+        push_remove_protected_branch: false,
+        push_tag: true,
+        push_new_tag: true,
+        push_all: true,
+        merge_into_protected_branch: true
+      },
+
+      developer: {
+        push_new_branch: true,
+        push_master: true,
+        push_protected_branch: false,
+        push_remove_protected_branch: false,
+        push_tag: false,
+        push_new_tag: true,
+        push_all: false,
+        merge_into_protected_branch: false
+      },
+
+      reporter: {
+        push_new_branch: false,
+        push_master: false,
+        push_protected_branch: false,
+        push_remove_protected_branch: false,
+        push_tag: false,
+        push_new_tag: false,
+        push_all: false,
+        merge_into_protected_branch: false
+      },
+
+      guest: {
+        push_new_branch: false,
+        push_master: false,
+        push_protected_branch: false,
+        push_remove_protected_branch: false,
+        push_tag: false,
+        push_new_tag: false,
+        push_all: false,
+        merge_into_protected_branch: false
+      }
+    }
+
+    [['feature', 'exact'], ['feat*', 'wildcard']].each do |protected_branch_name, protected_branch_type|
+      context do
+        before { create(:protected_branch, name: protected_branch_name, project: project) }
+
+        run_permission_checks(permissions_matrix)
+      end
+
+      context "when 'developers can push' is turned on for the #{protected_branch_type} protected branch" do
+        before { create(:protected_branch, name: protected_branch_name, developers_can_push: true, project: project) }
+
+        run_permission_checks(permissions_matrix.deep_merge(developer: { push_protected_branch: true, push_all: true, merge_into_protected_branch: true }))
+      end
+
+      context "when 'developers can merge' is turned on for the #{protected_branch_type} protected branch" do
+        before { create(:protected_branch, name: protected_branch_name, developers_can_merge: true, project: project) }
+
+        context "when a merge request exists for the given source/target branch" do
+          context "when the merge request is in progress" do
+            before do
+              create(:merge_request, source_project: project, source_branch: unprotected_branch, target_branch: 'feature', state: 'locked', in_progress_merge_commit_sha: merge_into_protected_branch)
+            end
+
+            run_permission_checks(permissions_matrix.deep_merge(developer: { merge_into_protected_branch: true }))
+          end
+
+          context "when the merge request is not in progress" do
+            before do
+              create(:merge_request, source_project: project, source_branch: unprotected_branch, target_branch: 'feature', in_progress_merge_commit_sha: nil)
+            end
+
+            run_permission_checks(permissions_matrix.deep_merge(developer: { merge_into_protected_branch: false }))
+          end
+        end
+
+        context "when a merge request does not exist for the given source/target branch" do
+          run_permission_checks(permissions_matrix.deep_merge(developer: { merge_into_protected_branch: false }))
+        end
+      end
+
+      context "when 'developers can merge' and 'developers can push' are turned on for the #{protected_branch_type} protected branch" do
+        before { create(:protected_branch, name: protected_branch_name, developers_can_merge: true, developers_can_push: true, project: project) }
+
+        run_permission_checks(permissions_matrix.deep_merge(developer: { push_protected_branch: true, push_all: true, merge_into_protected_branch: true }))
+      end
+    end
   end
 end

spec/models/repository_spec.rb

@@ -4,16 +4,17 @@ describe Repository, models: true do
   include RepoHelpers
   TestBlob = Struct.new(:name)
 
-  let(:repository) { create(:project).repository }
+  let(:project) { create(:project) }
+  let(:repository) { project.repository }
   let(:user) { create(:user) }
   let(:commit_options) do
     author = repository.user_to_committer(user)
     { message: 'Test message', committer: author, author: author }
   end
   let(:merge_commit) do
-    source_sha = repository.find_branch('feature').target
-    merge_commit_sha = repository.merge(user, source_sha, 'master', commit_options)
-    repository.commit(merge_commit_sha)
+    merge_request = create(:merge_request, source_branch: 'feature', target_branch: 'master', source_project: project)
+    merge_commit_id = repository.merge(user, merge_request, commit_options)
+    repository.commit(merge_commit_id)
   end
 
   describe '#branch_names_contains' do

spec/services/merge_requests/refresh_service_spec.rb

@@ -88,8 +88,7 @@ describe MergeRequests::RefreshService, services: true do
         # Merge master -> feature branch
         author = { email: 'test@gitlab.com', time: Time.now, name: "Me" }
         commit_options = { message: 'Test message', committer: author, author: author }
-        master_commit = @project.repository.commit('master')
-        @project.repository.merge(@user, master_commit.id, 'feature', commit_options)
+        @project.repository.merge(@user, @merge_request, commit_options)
         commit = @project.repository.commit('feature')
         service.new(@project, @user).execute(@oldrev, commit.id, 'refs/heads/feature')
         reload_mrs