Merge branch 'bvl-fork-network-schema' into 'master'

Create merge requests across a fork network

Closes #20097

See merge request gitlab-org/gitlab-ce!14422

13 files changed, 117 insertions, 20 deletions

diff --git a/app/controllers/projects/merge_requests/creations_controller.rb b/app/controllers/projects/merge_requests/creations_controller.rb
index 1096afbb798..99dc3dda9e7 100644
--- a/app/controllers/projects/merge_requests/creations_controller.rb
+++ b/app/controllers/projects/merge_requests/creations_controller.rb
@@ -120,10 +120,13 @@ class Projects::MergeRequests::CreationsController < Projects::MergeRequests::Ap
   end
 
   def selected_target_project
-    if @project.id.to_s == params[:target_project_id] || @project.forked_project_link.nil?
+    if @project.id.to_s == params[:target_project_id] || !@project.forked?
       @project
+    elsif params[:target_project_id].present?
+      MergeRequestTargetProjectFinder.new(current_user: current_user, source_project: @project)
+        .execute.find(params[:target_project_id])
     else
-      @project.forked_project_link.forked_from_project
+      @project.forked_from_project
     end
   end
 end
diff --git a/app/finders/merge_request_target_project_finder.rb b/app/finders/merge_request_target_project_finder.rb
new file mode 100644
index 00000000000..189eb3847eb
--- /dev/null
+++ b/app/finders/merge_request_target_project_finder.rb
@@ -0,0 +1,18 @@
+class MergeRequestTargetProjectFinder
+  attr_reader :current_user, :source_project
+
+  def initialize(current_user: nil, source_project:)
+    @current_user = current_user
+    @source_project = source_project
+  end
+
+  def execute
+    if @source_project.fork_network
+      @source_project.fork_network.projects
+        .public_or_visible_to_user(current_user)
+        .with_feature_available_for_user(:merge_requests, current_user)
+    else
+      Project.where(id: source_project)
+    end
+  end
+end
diff --git a/app/helpers/merge_requests_helper.rb b/app/helpers/merge_requests_helper.rb
index c31023f2d9a..5b2c58d193d 100644
--- a/app/helpers/merge_requests_helper.rb
+++ b/app/helpers/merge_requests_helper.rb
@@ -73,7 +73,8 @@ module MergeRequestsHelper
   end
 
   def target_projects(project)
-    [project, project.default_merge_request_target].uniq
+    MergeRequestTargetProjectFinder.new(current_user: current_user, source_project: project)
+      .execute
   end
 
   def merge_request_button_visibility(merge_request, closed)
diff --git a/app/models/fork_network.rb b/app/models/fork_network.rb
new file mode 100644
index 00000000000..218e37a5312
--- /dev/null
+++ b/app/models/fork_network.rb
@@ -0,0 +1,15 @@
+class ForkNetwork < ActiveRecord::Base
+  belongs_to :root_project, class_name: 'Project'
+  has_many :fork_network_members
+  has_many :projects, through: :fork_network_members
+
+  after_create :add_root_as_member, if: :root_project
+
+  def add_root_as_member
+    projects << root_project
+  end
+
+  def find_forks_in(other_projects)
+    projects.where(id: other_projects)
+  end
+end
diff --git a/app/models/fork_network_member.rb b/app/models/fork_network_member.rb
new file mode 100644
index 00000000000..6a9b52a1ef8
--- /dev/null
+++ b/app/models/fork_network_member.rb
@@ -0,0 +1,7 @@
+class ForkNetworkMember < ActiveRecord::Base
+  belongs_to :fork_network
+  belongs_to :project
+  belongs_to :forked_from_project, class_name: 'Project'
+
+  validates :fork_network, :project, presence: true
+end
diff --git a/app/models/merge_request.rb b/app/models/merge_request.rb
index 086226618e6..9b312f7db6c 100644
--- a/app/models/merge_request.rb
+++ b/app/models/merge_request.rb
@@ -403,7 +403,7 @@ class MergeRequest < ActiveRecord::Base
     return false unless for_fork?
     return true unless source_project
 
-    !source_project.forked_from?(target_project)
+    !source_project.in_fork_network_of?(target_project)
   end
 
   def reopenable?
diff --git a/app/models/namespace.rb b/app/models/namespace.rb
index e279d8dd8c5..4672881e220 100644
--- a/app/models/namespace.rb
+++ b/app/models/namespace.rb
@@ -139,7 +139,9 @@ class Namespace < ActiveRecord::Base
   end
 
   def find_fork_of(project)
-    projects.joins(:forked_project_link).find_by('forked_project_links.forked_from_project_id = ?', project.id)
+    return nil unless project.fork_network
+
+    project.fork_network.find_forks_in(projects).first
   end
 
   def lfs_enabled?
diff --git a/app/models/project.rb b/app/models/project.rb
index 608b545f99f..ad1c339ae78 100644
--- a/app/models/project.rb
+++ b/app/models/project.rb
@@ -118,11 +118,20 @@ class Project < ActiveRecord::Base
   has_one :mock_monitoring_service
   has_one :microsoft_teams_service
 
+  # TODO: replace these relations with the fork network versions
   has_one  :forked_project_link,  foreign_key: "forked_to_project_id"
   has_one  :forked_from_project,  through:   :forked_project_link
 
   has_many :forked_project_links, foreign_key: "forked_from_project_id"
   has_many :forks,                through:     :forked_project_links, source: :forked_to_project
+  # TODO: replace these relations with the fork network versions
+
+  has_one :root_of_fork_network,
+          foreign_key: 'root_project_id',
+          inverse_of: :root_project,
+          class_name: 'ForkNetwork'
+  has_one :fork_network_member
+  has_one :fork_network, through: :fork_network_member
 
   # Merge Requests for target project should be removed with it
   has_many :merge_requests, foreign_key: 'target_project_id'
@@ -1000,6 +1009,11 @@ class Project < ActiveRecord::Base
   end
 
   def forked?
+    return true if fork_network && fork_network.root_project != self
+
+    # TODO: Use only the above conditional using the `fork_network`
+    # This is the old conditional that looks at the `forked_project_link`, we
+    # fall back to this while we're migrating the new models
     !(forked_project_link.nil? || forked_project_link.forked_from_project.nil?)
   end
 
@@ -1119,8 +1133,19 @@ class Project < ActiveRecord::Base
     end
   end
 
-  def forked_from?(project)
-    forked? && project == forked_from_project
+  def forked_from?(other_project)
+    forked? && forked_from_project == other_project
+  end
+
+  def in_fork_network_of?(other_project)
+    # TODO: Remove this in a next release when all fork_networks are populated
+    # This makes sure all MergeRequests remain valid while the projects don't
+    # have a fork_network yet.
+    return true if forked_from?(other_project)
+
+    return false if fork_network.nil? || other_project.fork_network.nil?
+
+    fork_network == other_project.fork_network
   end
 
   def origin_merge_requests
diff --git a/app/models/user.rb b/app/models/user.rb
index 959738ba608..c3f115ca074 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -697,15 +697,7 @@ class User < ActiveRecord::Base
   end
 
   def fork_of(project)
-    links = ForkedProjectLink.where(
-      forked_from_project_id: project,
-      forked_to_project_id: personal_projects.unscope(:order)
-    )
-    if links.any?
-      links.first.forked_to_project
-    else
-      nil
-    end
+    namespace.find_fork_of(project)
   end
 
   def ldap_user?
diff --git a/app/services/projects/destroy_service.rb b/app/services/projects/destroy_service.rb
index 54eb75ab9bf..19d75ff2efa 100644
--- a/app/services/projects/destroy_service.rb
+++ b/app/services/projects/destroy_service.rb
@@ -22,6 +22,13 @@ module Projects
 
       Projects::UnlinkForkService.new(project, current_user).execute
 
+      # The project is not necessarily a fork, so update the fork network originating
+      # from this project
+      if fork_network = project.root_of_fork_network
+        fork_network.update(root_project: nil,
+                            deleted_root_project_name: project.full_name)
+      end
+
       attempt_destroy_transaction(project)
 
       system_hook_service.execute_hooks_for(project, :destroy)
diff --git a/app/services/projects/fork_service.rb b/app/services/projects/fork_service.rb
index ad67e68a86a..eb5cce5ab98 100644
--- a/app/services/projects/fork_service.rb
+++ b/app/services/projects/fork_service.rb
@@ -23,11 +23,31 @@ module Projects
 
       refresh_forks_count
 
+      link_fork_network(new_project)
+
       new_project
     end
 
     private
 
+    def fork_network
+      if @project.fork_network
+        @project.fork_network
+      elsif forked_from_project = @project.forked_from_project
+        # TODO: remove this case when all background migrations have completed
+        # this only happens when a project had a `forked_project_link` that was
+        # not migrated to the `fork_network` relation
+        forked_from_project.fork_network || forked_from_project.create_root_of_fork_network
+      else
+        @project.create_root_of_fork_network
+      end
+    end
+
+    def link_fork_network(new_project)
+      fork_network.fork_network_members.create(project: new_project,
+                                               forked_from_project: @project)
+    end
+
     def refresh_forks_count
       Projects::ForksCountService.new(@project).refresh_cache
     end
diff --git a/app/services/projects/unlink_fork_service.rb b/app/services/projects/unlink_fork_service.rb
index f30b40423c8..abe414d0c05 100644
--- a/app/services/projects/unlink_fork_service.rb
+++ b/app/services/projects/unlink_fork_service.rb
@@ -16,6 +16,7 @@ module Projects
       refresh_forks_count(@project.forked_from_project)
 
       @project.forked_project_link.destroy
+      @project.fork_network_member.destroy
     end
 
     def refresh_forks_count(project)
diff --git a/app/views/projects/_home_panel.html.haml b/app/views/projects/_home_panel.html.haml
index 873b3045ea9..619b632918e 100644
--- a/app/views/projects/_home_panel.html.haml
+++ b/app/views/projects/_home_panel.html.haml
@@ -1,4 +1,6 @@
 - empty_repo = @project.empty_repo?
+- fork_network = @project.fork_network
+- forked_from_project = @project.forked_from_project || fork_network&.root_project
 .project-home-panel.text-center{ class: ("empty-project" if empty_repo) }
   .limit-container-width{ class: container_class }
     .avatar-container.s70.project-avatar
@@ -12,11 +14,15 @@
       - if @project.description.present?
         = markdown_field(@project, :description)
 
-      - if forked_from_project = @project.forked_from_project
+      - if @project.forked?
         %p
-          #{ s_('ForkedFromProjectPath|Forked from') }
-          = link_to project_path(forked_from_project) do
-            = forked_from_project.namespace.try(:name)
+          - if forked_from_project
+            #{ s_('ForkedFromProjectPath|Forked from') }
+            = link_to project_path(forked_from_project) do
+              = forked_from_project.full_name
+          - else
+            - deleted_message = s_('ForkedFromProjectPath|Forked from %{project_name} (deleted)')
+            = deleted_message % { project_name: fork_network.deleted_root_project_name }
 
     .project-repo-buttons
       .count-buttons