Merge branch 'empty-mrs' into 'master'

Allows empty merge requests for a workflow described in gitlab-org/gitlab-ce#14606

Closes gitlab-org/gitlab-ce#14606

See merge request !6384

7 files changed, 71 insertions, 49 deletions

diff --git a/CHANGELOG b/CHANGELOG
index 22a96d8cbd5..56c3ee90541 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -85,6 +85,7 @@ v 8.13.0 (unreleased)
   - Changed Slack service user referencing from full name to username (Sebastian Poxhofer)
   - Retouch environments list and deployments list
   - Add Container Registry on/off status to Admin Area !6638 (the-undefined)
+  - Allow empty merge requests !6384 (Artem Sidorenko)
   - Grouped pipeline dropdown is a scrollable container
   - Cleanup Ci::ApplicationController. !6757 (Takuya Noguchi)
   - Fix a typo in doc/api/labels.md
diff --git a/app/assets/stylesheets/pages/merge_requests.scss b/app/assets/stylesheets/pages/merge_requests.scss
index 043f3f3afe1..1006b3e62e8 100644
--- a/app/assets/stylesheets/pages/merge_requests.scss
+++ b/app/assets/stylesheets/pages/merge_requests.scss
@@ -204,6 +204,18 @@
   word-break: break-all;
 }
 
+.commits-empty {
+  text-align: center;
+
+  h4 {
+    padding-top: 20px;
+    padding-bottom: 10px;
+  }
+  svg {
+    width: 230px;
+  }
+}
+
 .mr-list {
   .merge-request {
     padding: 10px 15px;
diff --git a/app/services/merge_requests/build_service.rb b/app/services/merge_requests/build_service.rb
index e57791f6818..404f75616b5 100644
--- a/app/services/merge_requests/build_service.rb
+++ b/app/services/merge_requests/build_service.rb
@@ -4,7 +4,7 @@ module MergeRequests
       merge_request = MergeRequest.new(params)
 
       # Set MR attributes
-      merge_request.can_be_created = false
+      merge_request.can_be_created = true
       merge_request.compare_commits = []
       merge_request.source_project = project unless merge_request.source_project
 
@@ -22,6 +22,12 @@ module MergeRequests
         return build_failed(merge_request, message)
       end
 
+      if merge_request.source_project == merge_request.target_project &&
+         merge_request.target_branch == merge_request.source_branch
+
+        return build_failed(merge_request, 'You must select different branches')
+      end
+
       compare = CompareService.new.execute(
         merge_request.source_project,
         merge_request.source_branch,
@@ -29,17 +35,8 @@ module MergeRequests
         merge_request.target_branch,
       )
 
-      commits = compare.commits
-
-      # At this point we decide if merge request can be created
-      # If we have at least one commit to merge -> creation allowed
-      if commits.present?
-        merge_request.compare_commits = commits
-        merge_request.can_be_created = true
-        merge_request.compare = compare
-      else
-        merge_request.can_be_created = false
-      end
+      merge_request.compare_commits = compare.commits
+      merge_request.compare = compare
 
       set_title_and_description(merge_request)
     end
@@ -89,6 +86,8 @@ module MergeRequests
         end
       end
 
+      merge_request.title = merge_request.wip_title if commits.empty?
+
       merge_request
     end
 
diff --git a/app/views/projects/merge_requests/_new_compare.html.haml b/app/views/projects/merge_requests/_new_compare.html.haml
index de39964fca8..466ec1475d8 100644
--- a/app/views/projects/merge_requests/_new_compare.html.haml
+++ b/app/views/projects/merge_requests/_new_compare.html.haml
@@ -65,19 +65,6 @@
 
   - if @merge_request.errors.any?
     = form_errors(@merge_request)
-  - elsif @merge_request.source_branch.present? && @merge_request.target_branch.present?
-    .light-well.append-bottom-default
-      .center
-        %h4
-          There isn't anything to merge.
-        %p.slead
-          - if @merge_request.source_branch == @merge_request.target_branch
-            You'll need to use different branch names to get a valid comparison.
-          - else
-            %span.label-branch #{@merge_request.source_branch}
-            and
-            %span.label-branch #{@merge_request.target_branch}
-            are the same.
   = f.submit 'Compare branches and continue', class: "btn btn-new mr-compare-btn"
 
 :javascript
diff --git a/app/views/projects/merge_requests/_new_submit.html.haml b/app/views/projects/merge_requests/_new_submit.html.haml
index 88d8013a0d1..da6927879a4 100644
--- a/app/views/projects/merge_requests/_new_submit.html.haml
+++ b/app/views/projects/merge_requests/_new_submit.html.haml
@@ -18,29 +18,35 @@
   = f.hidden_field :target_branch
 
 .mr-compare.merge-request
-  %ul.merge-request-tabs.nav-links.no-top.no-bottom
-    %li.commits-tab.active
-      = link_to url_for(params), data: {target: 'div#commits', action: 'new', toggle: 'tab'} do
-        Commits
-        %span.badge= @commits.size
-    - if @pipeline
-      %li.builds-tab
-        = link_to url_for(params), data: {target: 'div#builds', action: 'builds', toggle: 'tab'} do
-          Builds
-          %span.badge= @statuses.size
-    %li.diffs-tab
-      = link_to url_for(params.merge(action: 'new_diffs')), data: {target: 'div#diffs', action: 'new/diffs', toggle: 'tab'} do
-        Changes
-        %span.badge= @merge_request.diff_size
+  - if @commits.empty?
+    .commits-empty
+      %h4
+        There are no commits yet.
+      = custom_icon ('illustration_no_commits')
+  - else
+    %ul.merge-request-tabs.nav-links.no-top.no-bottom
+      %li.commits-tab.active
+        = link_to url_for(params), data: {target: 'div#commits', action: 'new', toggle: 'tab'} do
+          Commits
+          %span.badge= @commits.size
+      - if @pipeline
+        %li.builds-tab
+          = link_to url_for(params), data: {target: 'div#builds', action: 'builds', toggle: 'tab'} do
+            Builds
+            %span.badge= @statuses.size
+      %li.diffs-tab
+        = link_to url_for(params.merge(action: 'new_diffs')), data: {target: 'div#diffs', action: 'new/diffs', toggle: 'tab'} do
+          Changes
+          %span.badge= @merge_request.diff_size
 
-  .tab-content
-    #commits.commits.tab-pane.active
-      = render "projects/merge_requests/show/commits"
-    #diffs.diffs.tab-pane
-      - # This tab is always loaded via AJAX
-    - if @pipeline
-      #builds.builds.tab-pane
-        = render "projects/merge_requests/show/builds"
+    .tab-content
+      #commits.commits.tab-pane.active
+        = render "projects/merge_requests/show/commits"
+      #diffs.diffs.tab-pane
+        - # This tab is always loaded via AJAX
+      - if @pipeline
+        #builds.builds.tab-pane
+          = render "projects/merge_requests/show/builds"
 
   .mr-loading-status
     = spinner
diff --git a/app/views/shared/icons/_illustration_no_commits.svg b/app/views/shared/icons/_illustration_no_commits.svg
new file mode 100644
index 00000000000..4f9d9add60d
--- /dev/null
+++ b/app/views/shared/icons/_illustration_no_commits.svg
@@ -0,0 +1 @@
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\ No newline at end of file
diff --git a/spec/services/merge_requests/build_service_spec.rb b/spec/services/merge_requests/build_service_spec.rb
index 0d586e2216b..3a3f07ddcb9 100644
--- a/spec/services/merge_requests/build_service_spec.rb
+++ b/spec/services/merge_requests/build_service_spec.rb
@@ -52,12 +52,28 @@ describe MergeRequests::BuildService, services: true do
       end
     end
 
-    context 'no commits in the diff' do
-      let(:commits) { [] }
+    context 'same source and target branch' do
+      let(:source_branch) { 'master' }
 
       it 'forbids the merge request from being created' do
         expect(merge_request.can_be_created).to eq(false)
       end
+
+      it 'adds an error message to the merge request' do
+        expect(merge_request.errors).to contain_exactly('You must select different branches')
+      end
+    end
+
+    context 'no commits in the diff' do
+      let(:commits) { [] }
+
+      it 'allows the merge request to be created' do
+        expect(merge_request.can_be_created).to eq(true)
+      end
+
+      it 'adds a WIP prefix to the merge request title' do
+        expect(merge_request.title).to eq('WIP: Feature branch')
+      end
     end
 
     context 'one commit in the diff' do