Fix IDE detecting MR from fork branch

**Why?**
Currently the IDE loads a merge request based on only the
`source_branch` name. This means it loads MR's from
forks that have the same branch name (not good).

- This required updating the BE API to accept `source_project_id`

1 files changed, 12 insertions, 1 deletions

diff --git a/app/finders/merge_requests_finder.rb b/app/finders/merge_requests_finder.rb
index 84689ff5dc7..29947bc94d5 100644
--- a/app/finders/merge_requests_finder.rb
+++ b/app/finders/merge_requests_finder.rb
@@ -40,7 +40,8 @@ class MergeRequestsFinder < IssuableFinder
     items = by_commit(super)
     items = by_source_branch(items)
     items = by_wip(items)
-    by_target_branch(items)
+    items = by_target_branch(items)
+    by_source_project_id(items)
   end
 
   private
@@ -74,6 +75,16 @@ class MergeRequestsFinder < IssuableFinder
     items.where(target_branch: target_branch)
   end
 
+  def source_project_id
+    @source_project_id ||= params[:source_project_id].presence
+  end
+
+  def by_source_project_id(items)
+    return items unless source_project_id
+
+    items.where(source_project_id: source_project_id)
+  end
+
   def by_wip(items)
     if params[:wip] == 'yes'
       items.where(wip_match(items.arel_table))