Fix the merge request view when source projects or branches are removed

app/controllers/projects/merge_requests_controller.rb

@@ -554,7 +554,7 @@ class Projects::MergeRequestsController < Projects::ApplicationController
   def define_pipelines_vars
     @pipelines = @merge_request.all_pipelines
 
-    if @pipelines.any?
+    if @pipelines.present?
       @pipeline = @pipelines.first
       @statuses = @pipeline.statuses.relevant
     end

app/helpers/merge_requests_helper.rb

@@ -86,11 +86,15 @@ module MergeRequestsHelper
   end
 
   def source_branch_with_namespace(merge_request)
-    branch = link_to(merge_request.source_branch, namespace_project_commits_path(merge_request.source_project.namespace, merge_request.source_project, merge_request.source_branch))
+    namespace = merge_request.source_project_namespace
+    branch = merge_request.source_branch
+
+    if merge_request.source_branch_exists?
+      namespace = link_to(namespace, project_path(merge_request.source_project))
+      branch = link_to(branch, namespace_project_commits_path(merge_request.source_project.namespace, merge_request.source_project, merge_request.source_branch))
+    end
 
     if merge_request.for_fork?
-      namespace = link_to(merge_request.source_project_namespace,
-        project_path(merge_request.source_project))
       namespace + ":" + branch
     else
       branch

app/models/merge_request.rb

@@ -333,7 +333,7 @@ class MergeRequest < ActiveRecord::Base
   end
 
   def closed_without_fork?
-    closed? && (forked_source_project_missing? || !source_project)
+    closed? && forked_source_project_missing?
   end
 
   def forked_source_project_missing?
@@ -344,7 +344,7 @@ class MergeRequest < ActiveRecord::Base
   end
 
   def reopenable?
-    source_branch_exists? && closed?
+    closed? && !source_project_missing? && source_branch_exists?
   end
 
   def ensure_merge_request_diff
@@ -656,7 +656,7 @@ class MergeRequest < ActiveRecord::Base
   end
 
   def has_ci?
-    source_project.ci_service && commits.any?
+    source_project.try(:ci_service) && commits.any?
   end
 
   def branch_missing?
@@ -688,12 +688,9 @@ class MergeRequest < ActiveRecord::Base
 
     @environments ||=
       begin
-        environments = source_project.environments_for(
-          source_branch, diff_head_commit)
-        environments += target_project.environments_for(
-          target_branch, diff_head_commit, with_tags: true)
-
-        environments.uniq
+        envs = target_project.environments_for(target_branch, diff_head_commit, with_tags: true)
+        envs.concat(source_project.environments_for(source_branch, diff_head_commit)) if source_project
+        envs.uniq
       end
   end
 

app/views/projects/merge_requests/_show.html.haml

@@ -35,7 +35,9 @@
         - if @merge_request.open? && @merge_request.diverged_from_target_branch?
           %span (#{pluralize(@merge_request.diverged_commits_count, 'commit')} behind)
 
-    = render "projects/merge_requests/show/how_to_merge"
+    - if @merge_request.source_branch_exists?
+      = render "projects/merge_requests/show/how_to_merge"
+
     = render "projects/merge_requests/widget/show.html.haml"
 
     - if @merge_request.source_branch_exists? && @merge_request.mergeable? && @merge_request.can_be_merged_by?(current_user)
@@ -50,10 +52,11 @@
           = link_to namespace_project_merge_request_path(@project.namespace, @project, @merge_request), data: { target: 'div#notes', action: 'notes', toggle: 'tab' } do
             Discussion
             %span.badge= @merge_request.mr_and_commit_notes.user.count
-        %li.commits-tab
-          = link_to commits_namespace_project_merge_request_path(@project.namespace, @project, @merge_request), data: { target: 'div#commits', action: 'commits', toggle: 'tab' } do
-            Commits
-            %span.badge= @commits_count
+        - if @merge_request.source_project
+          %li.commits-tab
+            = link_to commits_namespace_project_merge_request_path(@project.namespace, @project, @merge_request), data: { target: 'div#commits', action: 'commits', toggle: 'tab' } do
+              Commits
+              %span.badge= @commits_count
         - if @pipeline
           %li.pipelines-tab
             = link_to pipelines_namespace_project_merge_request_path(@project.namespace, @project, @merge_request), data: { target: '#pipelines', action: 'pipelines', toggle: 'tab' } do

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