Backport 'Rebase' feature from EE to CEjprovazn-rebase

When a project uses fast-forward merging strategy user has
to rebase MRs to target branch before it can be merged.
Now user can do rebase in UI by clicking 'Rebase' button
instead of doing rebase locally.

This feature was already present in EE, this is only backport
of the feature to CE. Couple of changes:
* removed rebase license check
* renamed migration (changed timestamp)

Closes #40301

11 files changed, 480 insertions, 7 deletions

diff --git a/spec/controllers/projects/merge_requests_controller_spec.rb b/spec/controllers/projects/merge_requests_controller_spec.rb
index 45c424af8c4..c8cc6b374f6 100644
--- a/spec/controllers/projects/merge_requests_controller_spec.rb
+++ b/spec/controllers/projects/merge_requests_controller_spec.rb
@@ -684,4 +684,62 @@ describe Projects::MergeRequestsController do
                             format: :json
     end
   end
+
+  describe 'POST #rebase' do
+    let(:viewer)        { user }
+
+    def post_rebase
+      post :rebase, namespace_id: project.namespace, project_id: project, id: merge_request
+    end
+
+    def expect_rebase_worker_for(user)
+      expect(RebaseWorker).to receive(:perform_async).with(merge_request.id, user.id)
+    end
+
+    context 'successfully' do
+      it 'enqeues a RebaseWorker' do
+        expect_rebase_worker_for(viewer)
+
+        post_rebase
+
+        expect(response.status).to eq(200)
+      end
+    end
+
+    context 'with a forked project' do
+      let(:fork_project) { create(:project, :repository, forked_from_project: project) }
+      let(:fork_owner) { fork_project.owner }
+
+      before do
+        merge_request.update!(source_project: fork_project)
+        fork_project.add_reporter(user)
+      end
+
+      context 'user cannot push to source branch' do
+        it 'returns 404' do
+          expect_rebase_worker_for(viewer).never
+
+          post_rebase
+
+          expect(response.status).to eq(404)
+        end
+      end
+
+      context 'user can push to source branch' do
+        before do
+          project.add_reporter(fork_owner)
+
+          sign_in(fork_owner)
+        end
+
+        it 'returns 200' do
+          expect_rebase_worker_for(fork_owner)
+
+          post_rebase
+
+          expect(response.status).to eq(200)
+        end
+      end
+    end
+  end
 end
diff --git a/spec/fixtures/api/schemas/entities/merge_request_basic.json b/spec/fixtures/api/schemas/entities/merge_request_basic.json
index 995f13381ad..f1199468d53 100644
--- a/spec/fixtures/api/schemas/entities/merge_request_basic.json
+++ b/spec/fixtures/api/schemas/entities/merge_request_basic.json
@@ -9,6 +9,7 @@
     "human_time_estimate": { "type": ["string", "null"] },
     "human_total_time_spent": { "type": ["string", "null"] },
     "merge_error": { "type": ["string", "null"] },
+    "rebase_in_progress": { "type": "boolean" },
     "assignee_id": { "type": ["integer", "null"] },
     "subscribed": { "type": ["boolean", "null"] },
     "participants": { "type": "array" }
diff --git a/spec/fixtures/api/schemas/entities/merge_request_widget.json b/spec/fixtures/api/schemas/entities/merge_request_widget.json
index 9de27bee751..7f662098216 100644
--- a/spec/fixtures/api/schemas/entities/merge_request_widget.json
+++ b/spec/fixtures/api/schemas/entities/merge_request_widget.json
@@ -103,7 +103,11 @@
     "remove_source_branch": { "type": ["boolean", "null"] },
     "merge_ongoing": { "type": "boolean" },
     "ff_only_enabled": { "type": ["boolean", false] },
-    "should_be_rebased": { "type": "boolean" }
+    "should_be_rebased": { "type": "boolean" },
+    "rebase_commit_sha": { "type": ["string", "null"] },
+    "rebase_in_progress": { "type": "boolean" },
+    "can_push_to_source_branch": { "type": "boolean" },
+    "rebase_path": { "type": ["string", "null"] }
   },
   "additionalProperties": false
 }
diff --git a/spec/javascripts/vue_mr_widget/components/mr_widget_rebase_spec.js b/spec/javascripts/vue_mr_widget/components/mr_widget_rebase_spec.js
new file mode 100644
index 00000000000..66ecaa316c8
--- /dev/null
+++ b/spec/javascripts/vue_mr_widget/components/mr_widget_rebase_spec.js
@@ -0,0 +1,115 @@
+import Vue from 'vue';
+import eventHub from '~/vue_merge_request_widget/event_hub';
+import component from '~/vue_merge_request_widget/components/states/mr_widget_rebase.vue';
+import mountComponent from '../../helpers/vue_mount_component_helper';
+
+describe('Merge request widget rebase component', () => {
+  let Component;
+  let vm;
+  beforeEach(() => {
+    Component = Vue.extend(component);
+  });
+
+  afterEach(() => {
+    vm.$destroy();
+  });
+
+  describe('While rebasing', () => {
+    it('should show progress message', () => {
+      vm = mountComponent(Component, {
+        mr: { rebaseInProgress: true },
+        service: {},
+      });
+
+      expect(
+        vm.$el.querySelector('.rebase-state-find-class-convention span').textContent.trim(),
+      ).toContain('Rebase in progress');
+    });
+  });
+
+  describe('With permissions', () => {
+    beforeEach(() => {
+      vm = mountComponent(Component, {
+        mr: {
+          rebaseInProgress: false,
+          canPushToSourceBranch: true,
+        },
+        service: {},
+      });
+    });
+
+    it('it should render rebase button and warning message', () => {
+      const text = vm.$el.querySelector('.rebase-state-find-class-convention span').textContent.trim();
+      expect(text).toContain('Fast-forward merge is not possible.');
+      expect(text).toContain('Rebase the source branch onto the target branch or merge target');
+      expect(text).toContain('branch into source branch to allow this merge request to be merged.');
+    });
+
+    it('it should render error message when it fails', (done) => {
+      vm.rebasingError = 'Something went wrong!';
+
+      Vue.nextTick(() => {
+        expect(
+          vm.$el.querySelector('.rebase-state-find-class-convention span').textContent.trim(),
+        ).toContain('Something went wrong!');
+        done();
+      });
+    });
+  });
+
+  describe('Without permissions', () => {
+    it('should render a message explaining user does not have permissions', () => {
+      vm = mountComponent(Component, {
+        mr: {
+          rebaseInProgress: false,
+          canPushToSourceBranch: false,
+          targetBranch: 'foo',
+        },
+        service: {},
+      });
+
+      const text = vm.$el.querySelector('.rebase-state-find-class-convention span').textContent.trim();
+
+      expect(text).toContain('Fast-forward merge is not possible.');
+      expect(text).toContain('Rebase the source branch onto');
+      expect(text).toContain('foo');
+      expect(text).toContain('to allow this merge request to be merged.');
+    });
+  });
+
+  describe('methods', () => {
+    it('checkRebaseStatus', (done) => {
+      spyOn(eventHub, '$emit');
+      vm = mountComponent(Component, {
+        mr: {},
+        service: {
+          rebase() {
+            return Promise.resolve();
+          },
+          poll() {
+            return Promise.resolve({
+              data: {
+                rebase_in_progress: false,
+                merge_error: null,
+              },
+            });
+          },
+        },
+      });
+
+      vm.rebase();
+
+      // Wait for the rebase request
+      vm.$nextTick()
+        // Wait for the polling request
+        .then(vm.$nextTick())
+        // Wait for the eventHub to be called
+        .then(vm.$nextTick())
+        .then(() => {
+          expect(eventHub.$emit).toHaveBeenCalledWith('MRWidgetUpdateRequested');
+        })
+        .then(done)
+        .catch(done.fail);
+    });
+  });
+});
diff --git a/spec/models/merge_request_spec.rb b/spec/models/merge_request_spec.rb
index d8ebd46faab..07b3e1c1758 100644
--- a/spec/models/merge_request_spec.rb
+++ b/spec/models/merge_request_spec.rb
@@ -1903,4 +1903,50 @@ describe MergeRequest do
       end
     end
   end
+
+  describe '#should_be_rebased?' do
+    let(:project) { create(:project, :repository) }
+
+    it 'returns false for the same source and target branches' do
+      merge_request = create(:merge_request, source_project: project, target_project: project)
+
+      expect(merge_request.should_be_rebased?).to be_falsey
+    end
+  end
+
+  describe '#rebase_in_progress?' do
+    # Create merge request and project before we stub file calls
+    before do
+      subject
+    end
+
+    it 'returns true when there is a current rebase directory' do
+      allow(File).to receive(:exist?).and_return(true)
+      allow(File).to receive(:mtime).and_return(Time.now)
+
+      expect(subject.rebase_in_progress?).to be_truthy
+    end
+
+    it 'returns false when there is no rebase directory' do
+      allow(File).to receive(:exist?).and_return(false)
+
+      expect(subject.rebase_in_progress?).to be_falsey
+    end
+
+    it 'returns false when the rebase directory has expired' do
+      allow(File).to receive(:exist?).and_return(true)
+      allow(File).to receive(:mtime).and_return(20.minutes.ago)
+
+      expect(subject.rebase_in_progress?).to be_falsey
+    end
+
+    it 'returns false when the source project has been removed' do
+      allow(subject).to receive(:source_project).and_return(nil)
+      allow(File).to receive(:exist?).and_return(true)
+      allow(File).to receive(:mtime).and_return(Time.now)
+
+      expect(File).not_to have_received(:exist?)
+      expect(subject.rebase_in_progress?).to be_falsey
+    end
+  end
 end
diff --git a/spec/models/project_spec.rb b/spec/models/project_spec.rb
index 3c2ed043b82..13e5345ee4c 100644
--- a/spec/models/project_spec.rb
+++ b/spec/models/project_spec.rb
@@ -418,14 +418,21 @@ describe Project do
   end
 
   describe '#merge_method' do
-    it 'returns "ff" merge_method when ff is enabled' do
-      project = build(:project, merge_requests_ff_only_enabled: true)
-      expect(project.merge_method).to be :ff
+    using RSpec::Parameterized::TableSyntax
+
+    where(:ff, :rebase, :method) do
+      true  | true  | :ff
+      true  | false | :ff
+      false | true  | :rebase_merge
+      false | false | :merge
     end
 
-    it 'returns "merge" merge_method when ff is disabled' do
-      project = build(:project, merge_requests_ff_only_enabled: false)
-      expect(project.merge_method).to be :merge
+    with_them do
+      let(:project) { build(:project, merge_requests_rebase_enabled: rebase, merge_requests_ff_only_enabled: ff) }
+
+      subject { project.merge_method }
+
+      it { is_expected.to eq(method) }
     end
   end
 
diff --git a/spec/presenters/merge_request_presenter_spec.rb b/spec/presenters/merge_request_presenter_spec.rb
index 969c4753f33..e3b37739e8e 100644
--- a/spec/presenters/merge_request_presenter_spec.rb
+++ b/spec/presenters/merge_request_presenter_spec.rb
@@ -404,4 +404,67 @@ describe MergeRequestPresenter do
         .to eq("<a href=\"/#{resource.source_project.full_path}/tree/#{resource.source_branch}\">#{resource.source_branch}</a>")
     end
   end
+
+  describe '#rebase_path' do
+    before do
+      allow(resource).to receive(:rebase_in_progress?) { rebase_in_progress }
+      allow(resource).to receive(:should_be_rebased?) { should_be_rebased }
+
+      allow_any_instance_of(Gitlab::UserAccess::RequestCacheExtension)
+        .to receive(:can_push_to_branch?)
+        .with(resource.source_branch)
+        .and_return(can_push_to_branch)
+    end
+
+    subject do
+      described_class.new(resource, current_user: user).rebase_path
+    end
+
+    context 'when can rebase' do
+      let(:rebase_in_progress) { false }
+      let(:can_push_to_branch) { true }
+      let(:should_be_rebased) { true }
+
+      before do
+        allow(resource).to receive(:source_branch_exists?) { true }
+      end
+
+      it 'returns path' do
+        is_expected
+          .to eq("/#{project.full_path}/merge_requests/#{resource.iid}/rebase")
+      end
+    end
+
+    context 'when cannot rebase' do
+      context 'when rebase in progress' do
+        let(:rebase_in_progress) { true }
+        let(:can_push_to_branch) { true }
+        let(:should_be_rebased) { true }
+
+        it 'returns nil' do
+          is_expected.to be_nil
+        end
+      end
+
+      context 'when user cannot merge' do
+        let(:rebase_in_progress) { false }
+        let(:can_push_to_branch) { false }
+        let(:should_be_rebased) { true }
+
+        it 'returns nil' do
+          is_expected.to be_nil
+        end
+      end
+
+      context 'should not be rebased' do
+        let(:rebase_in_progress) { false }
+        let(:can_push_to_branch) { true }
+        let(:should_be_rebased) { false }
+
+        it 'returns nil' do
+          is_expected.to be_nil
+        end
+      end
+    end
+  end
 end
diff --git a/spec/serializers/merge_request_widget_entity_spec.rb b/spec/serializers/merge_request_widget_entity_spec.rb
index e25552eb0d8..80a271ba7fb 100644
--- a/spec/serializers/merge_request_widget_entity_spec.rb
+++ b/spec/serializers/merge_request_widget_entity_spec.rb
@@ -190,4 +190,20 @@ describe MergeRequestWidgetEntity do
       end
     end
   end
+
+  describe 'when source project is deleted' do
+    let(:project) { create(:project, :repository) }
+    let(:fork_project) { create(:project, :repository, forked_from_project: project) }
+    let(:merge_request) { create(:merge_request, source_project: fork_project, target_project: project) }
+
+    it 'returns a blank rebase_path' do
+      allow(merge_request).to receive(:should_be_rebased?).and_return(true)
+      fork_project.destroy
+      merge_request.reload
+
+      entity = described_class.new(merge_request, request: request).as_json
+
+      expect(entity[:rebase_path]).to be_nil
+    end
+  end
 end
diff --git a/spec/services/merge_requests/rebase_service_spec.rb b/spec/services/merge_requests/rebase_service_spec.rb
new file mode 100644
index 00000000000..d1b37cdd073
--- /dev/null
+++ b/spec/services/merge_requests/rebase_service_spec.rb
@@ -0,0 +1,134 @@
+require 'spec_helper'
+
+describe MergeRequests::RebaseService do
+  include ProjectForksHelper
+
+  let(:user) { create(:user) }
+  let(:merge_request) do
+    create(:merge_request,
+           source_branch: 'feature_conflict',
+           target_branch: 'master')
+  end
+  let(:project) { merge_request.project }
+  let(:repository) { project.repository.raw }
+
+  subject(:service) { described_class.new(project, user, {}) }
+
+  before do
+    project.add_master(user)
+  end
+
+  describe '#execute' do
+    context 'when another rebase is already in progress' do
+      before do
+        allow(merge_request).to receive(:rebase_in_progress?).and_return(true)
+      end
+
+      it 'saves the error message' do
+        subject.execute(merge_request)
+
+        expect(merge_request.reload.merge_error).to eq 'Rebase task canceled: Another rebase is already in progress'
+      end
+
+      it 'returns an error' do
+        expect(service.execute(merge_request)).to match(status: :error,
+                                                        message: 'Failed to rebase. Should be done manually')
+      end
+    end
+
+    context 'when unexpected error occurs' do
+      before do
+        allow(repository).to receive(:run_git!).and_raise('Something went wrong')
+      end
+
+      it 'saves the error message' do
+        subject.execute(merge_request)
+
+        expect(merge_request.reload.merge_error).to eq 'Something went wrong'
+      end
+
+      it 'returns an error' do
+        expect(service.execute(merge_request)).to match(status: :error,
+                                                        message: 'Failed to rebase. Should be done manually')
+      end
+    end
+
+    context 'with git command failure' do
+      before do
+        allow(repository).to receive(:run_git!).and_raise(Gitlab::Git::Repository::GitError, 'Something went wrong')
+      end
+
+      it 'saves the error message' do
+        subject.execute(merge_request)
+
+        expect(merge_request.reload.merge_error).to eq 'Something went wrong'
+      end
+
+      it 'returns an error' do
+        expect(service.execute(merge_request)).to match(status: :error,
+                                                        message: 'Failed to rebase. Should be done manually')
+      end
+    end
+
+    context 'valid params' do
+      before do
+        service.execute(merge_request)
+      end
+
+      it 'rebases source branch' do
+        parent_sha = merge_request.source_project.repository.commit(merge_request.source_branch).parents.first.sha
+        target_branch_sha = merge_request.target_project.repository.commit(merge_request.target_branch).sha
+        expect(parent_sha).to eq(target_branch_sha)
+      end
+
+      it 'records the new SHA on the merge request' do
+        head_sha = merge_request.source_project.repository.commit(merge_request.source_branch).sha
+        expect(merge_request.reload.rebase_commit_sha).to eq(head_sha)
+      end
+
+      it 'logs correct author and commiter' do
+        head_commit = merge_request.source_project.repository.commit(merge_request.source_branch)
+
+        expect(head_commit.author_email).to eq('dmitriy.zaporozhets@gmail.com')
+        expect(head_commit.author_name).to eq('Dmitriy Zaporozhets')
+        expect(head_commit.committer_email).to eq(user.email)
+        expect(head_commit.committer_name).to eq(user.name)
+      end
+
+      context 'git commands' do
+        it 'sets GL_REPOSITORY env variable when calling git commands' do
+          expect(repository).to receive(:popen).exactly(3)
+            .with(anything, anything, hash_including('GL_REPOSITORY'))
+            .and_return(['', 0])
+
+          service.execute(merge_request)
+        end
+      end
+
+      context 'fork' do
+        let(:forked_project) do
+          fork_project(project, user, repository: true)
+        end
+
+        let(:merge_request_from_fork) do
+          forked_project.repository.create_file(
+            user,
+            'new-file-to-target',
+            '',
+            message: 'Add new file to target',
+            branch_name: 'master')
+
+          create(:merge_request,
+                 source_branch: 'master', source_project: forked_project,
+                 target_branch: 'master', target_project: project)
+        end
+
+        it 'rebases source branch' do
+          parent_sha = forked_project.repository.commit(merge_request_from_fork.source_branch).parents.first.sha
+          target_branch_sha = project.repository.commit(merge_request_from_fork.target_branch).sha
+          expect(parent_sha).to eq(target_branch_sha)
+        end
+      end
+    end
+  end
+end
diff --git a/spec/views/projects/merge_requests/show.html.haml_spec.rb b/spec/views/projects/merge_requests/show.html.haml_spec.rb
index 28d54c2fb77..264e0ce0b40 100644
--- a/spec/views/projects/merge_requests/show.html.haml_spec.rb
+++ b/spec/views/projects/merge_requests/show.html.haml_spec.rb
@@ -54,6 +54,8 @@ describe 'projects/merge_requests/show.html.haml' do
     it 'closes the merge request if the source project does not exist' do
       closed_merge_request.update_attributes(state: 'open')
       forked_project.destroy
+      # Reload merge request so MergeRequest#source_project turns to `nil`
+      closed_merge_request.reload
 
       render
 
diff --git a/spec/workers/rebase_worker_spec.rb b/spec/workers/rebase_worker_spec.rb
new file mode 100644
index 00000000000..20aff020dbb
--- /dev/null
+++ b/spec/workers/rebase_worker_spec.rb
@@ -0,0 +1,27 @@
+require 'spec_helper'
+
+describe RebaseWorker, '#perform' do
+  context 'when rebasing an MR from a fork where upstream has protected branches' do
+    let(:upstream_project) { create(:project, :repository) }
+    let(:fork_project) { create(:project, :repository) }
+
+    let(:merge_request) do
+      create(:merge_request,
+             source_project: fork_project,
+             source_branch: 'feature_conflict',
+             target_project: upstream_project,
+             target_branch: 'master')
+    end
+
+    before do
+      create(:forked_project_link, forked_to_project: fork_project, forked_from_project: upstream_project)
+    end
+
+    it 'sets the correct project for running hooks' do
+      expect(MergeRequests::RebaseService)
+        .to receive(:new).with(fork_project, merge_request.author).and_call_original
+
+      subject.perform(merge_request, merge_request.author)
+    end
+  end
+end