Merge branch '23341-fix-viewing-mr-from-deleted-project' into 'master'

Fix a 500 error viewing an MR with a deleted source project

## What does this MR do?

Allows merged MRs to be shown without any 500 errors if the source project is removed

## Are there points in the code the reviewer needs to double check?

https://gitlab.com/gitlab-org/gitlab-ce/commit/31c37c6c38258684fc92e0d91119c33872e39034 fixed this for closed MRs only. I had trouble understanding the introduced helper and logic, so reverted it and keyed everything on the existence of the source project or branch directly.

commits.json returns a 500 error for a closed or merged MR; the approach taken in the above MR was to hide the commits... tab, so I've run with that.

For merged MRs, the commits (but not the pipeline data) are in the target project, so we *could* do better, but it's a fairly nasty intervention to make it happen.

## Why was this MR needed?

Viewing merged MRs should work even if the fork they came from has been deleted or unlinked.

## Screenshots (if relevant)

![Screen_Shot_2016-10-19_at_17.56.37](/uploads/1aeadd5147b9a4ad29b946b1c7ea52cb/Screen_Shot_2016-10-19_at_17.56.37.png)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG.md) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [x] API support added
- Tests
  - [x] Added for this feature/bug
  - [ ] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?

Closes #23341

See merge request !6991

2 files changed, 18 insertions, 36 deletions

diff --git a/spec/features/merge_requests/created_from_fork_spec.rb b/spec/features/merge_requests/created_from_fork_spec.rb
index a506624b30d..cfc1244429f 100644
--- a/spec/features/merge_requests/created_from_fork_spec.rb
+++ b/spec/features/merge_requests/created_from_fork_spec.rb
@@ -25,6 +25,20 @@ feature 'Merge request created from fork' do
     expect(page).to have_content 'Test merge request'
   end
 
+  context 'source project is deleted' do
+    background do
+      MergeRequests::MergeService.new(project, user).execute(merge_request)
+      fork_project.destroy!
+    end
+
+    scenario 'user can access merge request' do
+      visit_merge_request(merge_request)
+
+      expect(page).to have_content 'Test merge request'
+      expect(page).to have_content "(removed):#{merge_request.source_branch}"
+    end
+  end
+
   context 'pipeline present in source project' do
     include WaitForAjax
 
diff --git a/spec/models/merge_request_spec.rb b/spec/models/merge_request_spec.rb
index 6db5e7f7d80..6e5137602aa 100644
--- a/spec/models/merge_request_spec.rb
+++ b/spec/models/merge_request_spec.rb
@@ -1198,7 +1198,7 @@ describe MergeRequest, models: true do
     end
   end
 
-  describe "#forked_source_project_missing?" do
+  describe "#source_project_missing?" do
     let(:project)      { create(:project) }
     let(:fork_project) { create(:project, forked_from_project: project) }
     let(:user)         { create(:user) }
@@ -1211,13 +1211,13 @@ describe MergeRequest, models: true do
           target_project: project)
       end
 
-      it { expect(merge_request.forked_source_project_missing?).to be_falsey }
+      it { expect(merge_request.source_project_missing?).to be_falsey }
     end
 
     context "when the source project is the same as the target project" do
       let(:merge_request) { create(:merge_request, source_project: project) }
 
-      it { expect(merge_request.forked_source_project_missing?).to be_falsey }
+      it { expect(merge_request.source_project_missing?).to be_falsey }
     end
 
     context "when the fork does not exist" do
@@ -1231,7 +1231,7 @@ describe MergeRequest, models: true do
         unlink_project.execute
         merge_request.reload
 
-        expect(merge_request.forked_source_project_missing?).to be_truthy
+        expect(merge_request.source_project_missing?).to be_truthy
       end
     end
   end
@@ -1274,38 +1274,6 @@ describe MergeRequest, models: true do
     end
   end
 
-  describe '#closed_without_source_project?' do
-    let(:project)      { create(:project) }
-    let(:user)         { create(:user) }
-    let(:fork_project) { create(:project, forked_from_project: project, namespace: user.namespace) }
-    let(:destroy_service) { Projects::DestroyService.new(fork_project, user) }
-
-    context 'when the merge request is closed' do
-      let(:closed_merge_request) do
-        create(:closed_merge_request,
-          source_project: fork_project,
-          target_project: project)
-      end
-
-      it 'returns false if the source project exists' do
-        expect(closed_merge_request.closed_without_source_project?).to be_falsey
-      end
-
-      it 'returns true if the source project does not exist' do
-        destroy_service.execute
-        closed_merge_request.reload
-
-        expect(closed_merge_request.closed_without_source_project?).to be_truthy
-      end
-    end
-
-    context 'when the merge request is open' do
-      it 'returns false' do
-        expect(subject.closed_without_source_project?).to be_falsey
-      end
-    end
-  end
-
   describe '#reopenable?' do
     context 'when the merge request is closed' do
       it 'returns true' do