Link squashed commits using the changelog API

When generating changelogs using the API, we now link to merge requests
for squashed commits. Prior to this commit, when a merge request was
squashed into a target branch, we weren't able to link back to that
merge request in a generated changelog.

See https://gitlab.com/gitlab-com/gl-infra/delivery/-/issues/1551 for
more information.

app/finders/merge_requests/oldest_per_commit_finder.rb

@@ -18,8 +18,8 @@ module MergeRequests
       mapping = {}
       shas = commits.map(&:id)
 
-      # To include merge requests by the commit SHA, we don't need to go through
-      # any diff rows.
+      # To include merge requests by the merge/squash SHA, we don't need to go
+      # through any diff rows.
       #
       # We can't squeeze all this into a single query, as the diff based data
       # relies on a GROUP BY. On the other hand, retrieving MRs by their merge
@@ -27,12 +27,17 @@ module MergeRequests
       @project
         .merge_requests
         .preload_target_project
-        .by_merge_commit_sha(shas)
+        .by_merge_or_squash_commit_sha(shas)
         .each do |mr|
-          # Merge SHAs can't be in the merge request itself. It _is_ possible a
-          # newer merge request includes the merge commit, but in that case we
-          # still want the oldest merge request.
-          mapping[mr.merge_commit_sha] = mr
+          # Merge/squash SHAs can't be in the merge request itself. It _is_
+          # possible a newer merge request includes the commit, but in that case
+          # we still want the oldest merge request.
+          #
+          # It's also possible that a merge request produces both a squashed
+          # commit and a merge commit. In that case we want to store the mapping
+          # for both the SHAs.
+          mapping[mr.squash_commit_sha] = mr if mr.squash_commit_sha
+          mapping[mr.merge_commit_sha] = mr if mr.merge_commit_sha
         end
 
       remaining = shas - mapping.keys

app/models/merge_request.rb

@@ -276,6 +276,9 @@ class MergeRequest < ApplicationRecord
   scope :by_squash_commit_sha, -> (sha) do
     where(squash_commit_sha: sha)
   end
+  scope :by_merge_or_squash_commit_sha, -> (sha) do
+    from_union([by_squash_commit_sha(sha), by_merge_commit_sha(sha)])
+  end
   scope :by_related_commit_sha, -> (sha) do
     from_union(
       [

changelogs/unreleased/include-squash-commits-in-changelogs.yml

+---
+title: Link squashed commits using the changelog API
+merge_request: 56985
+author:
+type: added

spec/finders/merge_requests/oldest_per_commit_finder_spec.rb

@@ -77,6 +77,45 @@ RSpec.describe MergeRequests::OldestPerCommitFinder do
       expect(described_class.new(project).execute(commits)).to eq(sha => mr)
     end
 
+    it 'includes a merge request that was squashed into the target branch' do
+      project = create(:project)
+      sha = Digest::SHA1.hexdigest('foo')
+      mr = create(
+        :merge_request,
+        :merged,
+        target_project: project,
+        squash_commit_sha: sha
+      )
+
+      commits = [double(:commit, id: sha)]
+
+      expect(MergeRequestDiffCommit)
+        .not_to receive(:oldest_merge_request_id_per_commit)
+
+      expect(described_class.new(project).execute(commits)).to eq(sha => mr)
+    end
+
+    it 'includes a merge request for both a squash and merge commit' do
+      project = create(:project)
+      sha1 = Digest::SHA1.hexdigest('foo')
+      sha2 = Digest::SHA1.hexdigest('bar')
+      mr = create(
+        :merge_request,
+        :merged,
+        target_project: project,
+        squash_commit_sha: sha1,
+        merge_commit_sha: sha2
+      )
+
+      commits = [double(:commit1, id: sha1), double(:commit2, id: sha2)]
+
+      expect(MergeRequestDiffCommit)
+        .not_to receive(:oldest_merge_request_id_per_commit)
+
+      expect(described_class.new(project).execute(commits))
+        .to eq(sha1 => mr, sha2 => mr)
+    end
+
     it 'includes the oldest merge request when a merge commit is present in a newer merge request' do
       project = create(:project)
       sha = Digest::SHA1.hexdigest('foo')

spec/models/merge_request_spec.rb

@@ -420,6 +420,19 @@ RSpec.describe MergeRequest, factory_default: :keep do
     end
   end
 
+  describe '.by_merge_or_squash_commit_sha' do
+    subject { described_class.by_merge_or_squash_commit_sha([sha1, sha2]) }
+
+    let(:sha1) { '123abc' }
+    let(:sha2) { '456abc' }
+    let(:mr1) { create(:merge_request, :merged, squash_commit_sha: sha1) }
+    let(:mr2) { create(:merge_request, :merged, merge_commit_sha: sha2) }
+
+    it 'returns merge requests that match the given squash and merge commits' do
+      is_expected.to include(mr1, mr2)
+    end
+  end
+
   describe '.by_related_commit_sha' do
     subject { described_class.by_related_commit_sha(sha) }