Ignore missing source project when editing MR

Also hide the branch chooser if the branch has been merged, not only
when the MR was closed.

Closes https://gitlab.com/gitlab-org/gitlab/-/issues/218228

app/helpers/merge_requests_helper.rb

@@ -83,7 +83,7 @@ module MergeRequestsHelper
   end
 
   def merge_request_button_hidden?(merge_request, closed)
-    merge_request.closed? == closed || (merge_request.merged? == closed && !merge_request.closed?) || merge_request.closed_without_fork?
+    merge_request.closed? == closed || (merge_request.merged? == closed && !merge_request.closed?) || merge_request.closed_or_merged_without_fork?
   end
 
   def merge_request_version_path(project, merge_request, merge_request_diff, start_sha = nil)

app/models/merge_request.rb

@@ -233,13 +233,13 @@ class MergeRequest < ApplicationRecord
     cannot_be_merged_rechecking? ? 'checking' : merge_status
   end
 
-  validates :source_project, presence: true, unless: [:allow_broken, :importing?, :closed_without_fork?]
+  validates :source_project, presence: true, unless: [:allow_broken, :importing?, :closed_or_merged_without_fork?]
   validates :source_branch, presence: true
   validates :target_project, presence: true
   validates :target_branch, presence: true
   validates :merge_user, presence: true, if: :auto_merge_enabled?, unless: :importing?
-  validate :validate_branches, unless: [:allow_broken, :importing?, :closed_without_fork?]
-  validate :validate_fork, unless: :closed_without_fork?
+  validate :validate_branches, unless: [:allow_broken, :importing?, :closed_or_merged_without_fork?]
+  validate :validate_fork, unless: :closed_or_merged_without_fork?
   validate :validate_target_project, on: :create
 
   scope :by_source_or_target_branch, ->(branch_name) do
@@ -883,8 +883,8 @@ class MergeRequest < ApplicationRecord
     !!merge_jid && !merged? && Gitlab::SidekiqStatus.running?(merge_jid)
   end
 
-  def closed_without_fork?
-    closed? && source_project_missing?
+  def closed_or_merged_without_fork?
+    (closed? || merged?) && source_project_missing?
   end
 
   def source_project_missing?

app/services/merge_requests/update_service.rb

@@ -11,7 +11,7 @@ module MergeRequests
       params.delete(:target_project_id)
       params.delete(:source_branch)
 
-      if merge_request.closed_without_fork?
+      if merge_request.closed_or_merged_without_fork?
         params.delete(:target_branch)
         params.delete(:force_remove_source_branch)
       end

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

@@ -4,7 +4,7 @@
 - state_human_name, state_icon_name = state_name_with_icon(@merge_request)
 - are_close_and_open_buttons_hidden = merge_request_button_hidden?(@merge_request, true) && merge_request_button_hidden?(@merge_request, false)
 
-- if @merge_request.closed_without_fork?
+- if @merge_request.closed_or_merged_without_fork?
   .gl-alert.gl-alert-danger.gl-mb-5
     = sprite_icon('error', size: 16, css_class: 'gl-icon gl-alert-icon gl-alert-icon-no-title')
     .gl-alert-body

app/views/shared/issuable/form/_branch_chooser.html.haml

@@ -2,7 +2,7 @@
 - form = local_assigns.fetch(:form)
 
 - return unless issuable.is_a?(MergeRequest)
-- return if issuable.closed_without_fork?
+- return if issuable.closed_or_merged_without_fork?
 
 - source_title, target_title = format_mr_branch_names(@merge_request)
 

app/views/shared/issuable/form/_merge_params.html.haml

@@ -2,7 +2,7 @@
 - project = local_assigns.fetch(:project)
 
 - return unless issuable.is_a?(MergeRequest)
-- return if issuable.closed_without_fork?
+- return if issuable.closed_or_merged_without_fork?
 
 .form-group.row
   .col-sm-2.col-form-label.pt-sm-0

spec/models/merge_request_spec.rb

@@ -3370,7 +3370,7 @@ RSpec.describe MergeRequest, factory_default: :keep do
     end
   end
 
-  describe "#closed_without_fork?" do
+  describe "#closed_or_merged_without_fork?" do
     let(:project) { create(:project) }
     let(:forked_project) { fork_project(project) }
     let(:user) { create(:user) }
@@ -3384,14 +3384,33 @@ RSpec.describe MergeRequest, factory_default: :keep do
       end
 
       it "returns false if the fork exist" do
-        expect(closed_merge_request.closed_without_fork?).to be_falsey
+        expect(closed_merge_request.closed_or_merged_without_fork?).to be_falsey
       end
 
       it "returns true if the fork does not exist" do
         unlink_project.execute
         closed_merge_request.reload
 
-        expect(closed_merge_request.closed_without_fork?).to be_truthy
+        expect(closed_merge_request.closed_or_merged_without_fork?).to be_truthy
+      end
+    end
+
+    context "when the merge request was merged" do
+      let(:merged_merge_request) do
+        create(:merged_merge_request,
+          source_project: forked_project,
+          target_project: project)
+      end
+
+      it "returns false if the fork exist" do
+        expect(merged_merge_request.closed_or_merged_without_fork?).to be_falsey
+      end
+
+      it "returns true if the fork does not exist" do
+        unlink_project.execute
+        merged_merge_request.reload
+
+        expect(merged_merge_request.closed_or_merged_without_fork?).to be_truthy
       end
     end
 
@@ -3403,7 +3422,7 @@ RSpec.describe MergeRequest, factory_default: :keep do
       end
 
       it "returns false" do
-        expect(open_merge_request.closed_without_fork?).to be_falsey
+        expect(open_merge_request.closed_or_merged_without_fork?).to be_falsey
       end
     end
   end