Add latest changes from gitlab-org/gitlab@master

2 files changed, 59 insertions, 30 deletions

diff --git a/lib/gitlab/git/cross_repo_comparer.rb b/lib/gitlab/git/cross_repo_comparer.rb
new file mode 100644
index 00000000000..3958373f7cb
--- /dev/null
+++ b/lib/gitlab/git/cross_repo_comparer.rb
@@ -0,0 +1,56 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Git
+    class CrossRepoComparer
+      attr_reader :source_repo, :target_repo
+
+      def initialize(source_repo, target_repo)
+        @source_repo = source_repo
+        @target_repo = target_repo
+      end
+
+      def compare(source_ref, target_ref, straight:)
+        ensuring_ref_in_source(target_ref) do |target_commit_id|
+          Gitlab::Git::Compare.new(
+            source_repo,
+            target_commit_id,
+            source_ref,
+            straight: straight
+          )
+        end
+      end
+
+      private
+
+      def ensuring_ref_in_source(ref, &blk)
+        return yield ref if source_repo == target_repo
+
+        # If the commit doesn't exist in the target, there's nothing we can do
+        commit_id = target_repo.commit(ref)&.sha
+        return unless commit_id
+
+        # The commit pointed to by ref may exist in the source even when they
+        # are different repositories. This is particularly true of close forks,
+        # but may also be the case if a temporary ref for this comparison has
+        # already been created in the past, and the result hasn't been GC'd yet.
+        return yield commit_id if source_repo.commit(commit_id)
+
+        # Worst case: the commit is not in the source repo so we need to fetch
+        # it. Use a temporary ref and clean up afterwards
+        with_commit_in_source_tmp(commit_id, &blk)
+      end
+
+      # Fetch the ref into source_repo from target_repo, using a temporary ref
+      # name that will be deleted once the method completes. This is a no-op if
+      # fetching the source branch fails
+      def with_commit_in_source_tmp(commit_id, &blk)
+        tmp_ref = "refs/tmp/#{SecureRandom.hex}"
+
+        yield commit_id if source_repo.fetch_source_branch!(target_repo, commit_id, tmp_ref)
+      ensure
+        source_repo.delete_refs(tmp_ref) # best-effort
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/git/repository.rb b/lib/gitlab/git/repository.rb
index ed3e7a1e39c..0120e3be14c 100644
--- a/lib/gitlab/git/repository.rb
+++ b/lib/gitlab/git/repository.rb
@@ -746,29 +746,9 @@ module Gitlab
       end
 
       def compare_source_branch(target_branch_name, source_repository, source_branch_name, straight:)
-        reachable_ref =
-          if source_repository == self
-            source_branch_name
-          else
-            # If a tmp ref was created before for a separate repo comparison (forks),
-            # we're able to short-circuit the tmp ref re-creation:
-            # 1. Take the SHA from the source repo
-            # 2. Read that in the current "target" repo
-            # 3. If that SHA is still known (readable), it means GC hasn't
-            # cleaned it up yet, so we can use it instead re-writing the tmp ref.
-            source_commit_id = source_repository.commit(source_branch_name)&.sha
-            commit(source_commit_id)&.sha if source_commit_id
-          end
-
-        return compare(target_branch_name, reachable_ref, straight: straight) if reachable_ref
-
-        tmp_ref = "refs/tmp/#{SecureRandom.hex}"
-
-        return unless fetch_source_branch!(source_repository, source_branch_name, tmp_ref)
-
-        compare(target_branch_name, tmp_ref, straight: straight)
-      ensure
-        delete_refs(tmp_ref) if tmp_ref
+        CrossRepoComparer
+          .new(source_repository, self)
+          .compare(source_branch_name, target_branch_name, straight: straight)
       end
 
       def write_ref(ref_path, ref, old_ref: nil)
@@ -1046,13 +1026,6 @@ module Gitlab
 
       private
 
-      def compare(base_ref, head_ref, straight:)
-        Gitlab::Git::Compare.new(self,
-                                 base_ref,
-                                 head_ref,
-                                 straight: straight)
-      end
-
       def empty_diff_stats
         Gitlab::Git::DiffStatsCollection.new([])
       end