Show proper message for new MR when satellite fails

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/controllers/projects/merge_requests_controller.rb

@@ -74,9 +74,17 @@ class Projects::MergeRequestsController < Projects::ApplicationController
         @merge_request.source_branch
       )
 
+      @compare_failed = false
       @commits = compare_action.commits
-      @commits.map! { |commit| Commit.new(commit) }
-      @commit = @commits.first
+
+      if @commits
+        @commits.map! { |commit| Commit.new(commit) }
+        @commit = @commits.first
+      else
+        # false value because failed to get commits from satellite
+        @commits = []
+        @compare_failed = true
+      end
 
       @diffs = compare_action.diffs
       @merge_request.title = @merge_request.source_branch.titleize.humanize

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

@@ -33,18 +33,23 @@
         %div= msg
 
   - if @merge_request.source_branch.present? && @merge_request.target_branch.present?
-    .light-well
-      %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.
+    - if @compare_failed
+      .alert.alert-danger
+        %h4 Compare failed
+        %p We can't compare selected branches. It may be because of huge diff or satellite timeout. Please try again or select different branches.
+    - else
+      .light-well
+        %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.
 
 
   %hr