Merge branch '19315-can-edit-merge-request-with-deleted-fork' into 'master'

User can edit closed MR with deleted fork

## What does this MR do?
User can edit closed MR with deleted fork (can't change "Target branch"). When fork is deleted "Reopen" button is hidden.

## What are the relevant issue numbers?
Closes #19315 

## Screenshots (if relevant)
* hidden Reopen button and information about deleted fork
![Zrzut_ekranu_2016-08-12_o_13.19.24](/uploads/d288c5625e788382e31b2979acb601df/Zrzut_ekranu_2016-08-12_o_13.19.24.png)

* editable fields for closed MR without fork
![Zrzut_ekranu_2016-08-05_o_12.24.38](/uploads/1549e54d4bc2a9939ef296ce66139706/Zrzut_ekranu_2016-08-05_o_12.24.38.png)


## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

cc @ubudzisz @yorickpeterse @grzesiek @tmaczukin

See merge request !5496

5 files changed, 29 insertions, 18 deletions

diff --git a/app/helpers/merge_requests_helper.rb b/app/helpers/merge_requests_helper.rb
index db6e731c744..a9e175c3f5c 100644
--- a/app/helpers/merge_requests_helper.rb
+++ b/app/helpers/merge_requests_helper.rb
@@ -98,6 +98,6 @@ module MergeRequestsHelper
   end
 
   def merge_request_button_visibility(merge_request, closed)
-    return 'hidden' if merge_request.closed? == closed || (merge_request.merged? == closed && !merge_request.closed?)
+    return 'hidden' if merge_request.closed? == closed || (merge_request.merged? == closed && !merge_request.closed?) || merge_request.closed_without_fork?
   end
 end
diff --git a/app/models/merge_request.rb b/app/models/merge_request.rb
index 1d05e4a85d1..a8dd4a306cf 100644
--- a/app/models/merge_request.rb
+++ b/app/models/merge_request.rb
@@ -91,13 +91,13 @@ class MergeRequest < ActiveRecord::Base
     end
   end
 
-  validates :source_project, presence: true, unless: [:allow_broken, :importing?]
+  validates :source_project, presence: true, unless: [:allow_broken, :importing?, :closed_without_fork?]
   validates :source_branch, presence: true
   validates :target_project, presence: true
   validates :target_branch, presence: true
   validates :merge_user, presence: true, if: :merge_when_build_succeeds?
-  validate :validate_branches, unless: [:allow_broken, :importing?]
-  validate :validate_fork
+  validate :validate_branches, unless: [:allow_broken, :importing?, :closed_without_fork?]
+  validate :validate_fork, unless: :closed_without_fork?
 
   scope :by_branch, ->(branch_name) { where("(source_branch LIKE :branch) OR (target_branch LIKE :branch)", branch: branch_name) }
   scope :cared, ->(user) { where('assignee_id = :user OR author_id = :user', user: user.id) }
@@ -305,19 +305,22 @@ class MergeRequest < ActiveRecord::Base
 
   def validate_fork
     return true unless target_project && source_project
+    return true if target_project == source_project
+    return true unless forked_source_project_missing?
 
-    if target_project == source_project
-      true
-    else
-      # If source and target projects are different
-      # we should check if source project is actually a fork of target project
-      if source_project.forked_from?(target_project)
-        true
-      else
-        errors.add :validate_fork,
-                   'Source project is not a fork of target project'
-      end
-    end
+    errors.add :validate_fork,
+               'Source project is not a fork of the target project'
+  end
+
+  def closed_without_fork?
+    closed? && forked_source_project_missing?
+  end
+
+  def forked_source_project_missing?
+    return false unless for_fork?
+    return true unless source_project
+
+    !source_project.forked_from?(target_project)
   end
 
   def ensure_merge_request_diff
diff --git a/app/services/merge_requests/update_service.rb b/app/services/merge_requests/update_service.rb
index 30c5f24988c..398ec47f0ea 100644
--- a/app/services/merge_requests/update_service.rb
+++ b/app/services/merge_requests/update_service.rb
@@ -11,6 +11,10 @@ module MergeRequests
       params.except!(:target_project_id)
       params.except!(:source_branch)
 
+      if merge_request.closed_without_fork?
+        params.except!(:target_branch, :force_remove_source_branch)
+      end
+
       merge_request.merge_params['force_remove_source_branch'] = params.delete(:force_remove_source_branch)
 
       update(merge_request)
diff --git a/app/views/projects/merge_requests/show/_mr_title.html.haml b/app/views/projects/merge_requests/show/_mr_title.html.haml
index 098ce19da21..e35291dff7d 100644
--- a/app/views/projects/merge_requests/show/_mr_title.html.haml
+++ b/app/views/projects/merge_requests/show/_mr_title.html.haml
@@ -1,3 +1,7 @@
+- if @merge_request.closed_without_fork?
+  .alert.alert-danger
+    %p The source project of this merge request has been removed.
+
 .clearfix.detail-page-header
   .issuable-header
     .issuable-status-box.status-box{ class: status_box_class(@merge_request) }
diff --git a/app/views/shared/issuable/_form.html.haml b/app/views/shared/issuable/_form.html.haml
index 22594b46443..3856a4917b4 100644
--- a/app/views/shared/issuable/_form.html.haml
+++ b/app/views/shared/issuable/_form.html.haml
@@ -134,7 +134,7 @@
       title: 'Moving an issue will copy the discussion to a different project and close it here. All participants will be notified of the new location.' }
         = icon('question-circle')
 
-- if issuable.is_a?(MergeRequest)
+- if issuable.is_a?(MergeRequest) && !issuable.closed_without_fork?
   %hr
   - if @merge_request.new_record?
     .form-group
@@ -175,7 +175,7 @@
     = link_to 'Cancel', polymorphic_path([@project.namespace.becomes(Namespace), @project, issuable.class]), class: 'btn btn-cancel'
   - else
     .pull-right
-      - if current_user.can?(:"destroy_#{issuable.to_ability_name}", @project)
+      - if can?(current_user, :"destroy_#{issuable.to_ability_name}", @project)
         = link_to 'Delete', polymorphic_path([@project.namespace.becomes(Namespace), @project, issuable]), data: { confirm: "#{issuable.class.name.titleize} will be removed! Are you sure?" },
                                                                                                   method: :delete, class: 'btn btn-danger btn-grouped'
       = link_to 'Cancel', polymorphic_path([@project.namespace.becomes(Namespace), @project, issuable]), class: 'btn btn-grouped btn-cancel'