Port semi-linear merge strategy to CE (mostly FE)

6 files changed, 26 insertions, 1 deletions

diff --git a/app/assets/javascripts/vue_merge_request_widget/components/states/mr_widget_conflicts.js b/app/assets/javascripts/vue_merge_request_widget/components/states/mr_widget_conflicts.js
index e745de89b8d..dc252f8a9b7 100644
--- a/app/assets/javascripts/vue_merge_request_widget/components/states/mr_widget_conflicts.js
+++ b/app/assets/javascripts/vue_merge_request_widget/components/states/mr_widget_conflicts.js
@@ -15,7 +15,7 @@ export default {
         showDisabledButton />
       <div class="media-body space-children">
         <span
-          v-if="mr.ffOnlyEnabled"
+          v-if="mr.shouldBeRebased"
           class="bold">
           Fast-forward merge is not possible.
           To merge this request, first rebase locally.
diff --git a/app/assets/javascripts/vue_merge_request_widget/stores/mr_widget_store.js b/app/assets/javascripts/vue_merge_request_widget/stores/mr_widget_store.js
index 03969e33e97..8255fd3e792 100644
--- a/app/assets/javascripts/vue_merge_request_widget/stores/mr_widget_store.js
+++ b/app/assets/javascripts/vue_merge_request_widget/stores/mr_widget_store.js
@@ -58,6 +58,7 @@ export default class MergeRequestStore {
     this.mergeWhenPipelineSucceeds = data.merge_when_pipeline_succeeds || false;
     this.mergePath = data.merge_path;
     this.ffOnlyEnabled = data.ff_only_enabled;
+    this.shouldBeRebased = !!data.should_be_rebased;
     this.statusPath = data.status_path;
     this.emailPatchesPath = data.email_patches_path;
     this.plainDiffPath = data.plain_diff_path;
diff --git a/app/models/merge_request.rb b/app/models/merge_request.rb
index 8d9a30397a9..e85b83daf9e 100644
--- a/app/models/merge_request.rb
+++ b/app/models/merge_request.rb
@@ -524,6 +524,14 @@ class MergeRequest < ActiveRecord::Base
     true
   end
 
+  def ff_merge_possible?
+    project.repository.ancestor?(target_branch_sha, diff_head_sha)
+  end
+
+  def should_be_rebased?
+    project.ff_merge_must_be_possible? && !ff_merge_possible?
+  end
+
   def can_cancel_merge_when_pipeline_succeeds?(current_user)
     can_be_merged_by?(current_user) || self.author == current_user
   end
diff --git a/app/serializers/merge_request_entity.rb b/app/serializers/merge_request_entity.rb
index 5f2700df692..7d3c752b8e6 100644
--- a/app/serializers/merge_request_entity.rb
+++ b/app/serializers/merge_request_entity.rb
@@ -13,6 +13,7 @@ class MergeRequestEntity < IssuableEntity
   expose :target_branch
   expose :target_project_id
 
+  expose :should_be_rebased?, as: :should_be_rebased
   expose :ff_only_enabled do |merge_request|
     merge_request.project.merge_requests_ff_only_enabled
   end
diff --git a/app/views/projects/_merge_request_rebase_settings.html.haml b/app/views/projects/_merge_request_rebase_settings.html.haml
new file mode 100644
index 00000000000..c52e09573a6
--- /dev/null
+++ b/app/views/projects/_merge_request_rebase_settings.html.haml
@@ -0,0 +1,13 @@
+- form = local_assigns.fetch(:form)
+
+.radio
+  = label_tag :project_merge_method_rebase_merge do
+    = form.radio_button :merge_method, :rebase_merge, class: "js-merge-method-radio"
+    %strong Merge commit with semi-linear history
+    %br
+    %span.descr
+      A merge commit is created for every merge, but merging is only allowed if fast-forward merge is possible.
+      This way you could make sure that if this merge request would build, after merging to target branch it would also build.
+    %br
+    %span.descr
+      When fast-forward merge is not possible, the user must first rebase locally.
diff --git a/app/views/projects/_merge_request_settings.html.haml b/app/views/projects/_merge_request_settings.html.haml
index 939750ed1e5..fd0c419cdac 100644
--- a/app/views/projects/_merge_request_settings.html.haml
+++ b/app/views/projects/_merge_request_settings.html.haml
@@ -11,6 +11,8 @@
       %span.descr
         A merge commit is created for every merge, and merging is allowed as long as there are no conflicts.
 
+  = render 'merge_request_rebase_settings', form: form
+
   = render 'merge_request_fast_forward_settings', project: @project, form: form
 
 = render 'projects/merge_request_merge_settings', form: form