Show merge request for squashed and merge commits

Contributes to https://gitlab.com/gitlab-org/gitlab/-/issues/21686

* Add database indices for `squash_commit_sha` field
* Add new scope `by_related_commit_sha` to MergeRequest model
* Update MergeRequestFinder logic to use `by_related_commit_sha` scope
for filtering

app/finders/merge_requests_finder.rb

@@ -84,7 +84,7 @@ class MergeRequestsFinder < IssuableFinder
   def by_commit(items)
     return items unless params[:commit_sha].presence
 
-    items.by_commit_sha(params[:commit_sha])
+    items.by_related_commit_sha(params[:commit_sha])
   end
 
   def source_branch

app/models/merge_request.rb

@@ -261,6 +261,19 @@ class MergeRequest < ApplicationRecord
   scope :by_merge_commit_sha, -> (sha) do
     where(merge_commit_sha: sha)
   end
+  scope :by_squash_commit_sha, -> (sha) do
+    where(squash_commit_sha: sha)
+  end
+  scope :by_related_commit_sha, -> (sha) do
+    from_union(
+      [
+        by_commit_sha(sha),
+        by_squash_commit_sha(sha),
+        by_merge_commit_sha(sha)
+      ],
+      remove_duplicates: false
+    )
+  end
   scope :by_cherry_pick_sha, -> (sha) do
     joins(:notes).where(notes: { commit_id: sha })
   end

changelogs/unreleased/21686_show_merge_request_for_squashed_commits.yml

+---
+title: Extend MergeRequestFinder to search by squash and merge commits
+merge_request: 49968
+author:
+type: added

db/migrate/20201216151616_add_squash_commit_sha_index.rb

+# frozen_string_literal: true
+
+class AddSquashCommitShaIndex < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+  INDEX_NAME = "index_merge_requests_on_target_project_id_and_squash_commit_sha"
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_index :merge_requests,
+      [:target_project_id, :squash_commit_sha],
+      name: INDEX_NAME
+  end
+
+  def down
+    remove_concurrent_index :merge_requests,
+      [:target_project_id, :squash_commit_sha],
+      name: INDEX_NAME
+  end
+end

db/schema_migrations/20201216151616

+f1c6927431895c6ce03fe7e0be30fcd0a1f4ccfeac8277ee0662d7434b97d257
\ No newline at end of file

db/structure.sql

@@ -21982,6 +21982,8 @@ CREATE INDEX index_merge_requests_on_target_project_id_and_iid_and_state_id ON m
 
 CREATE INDEX index_merge_requests_on_target_project_id_and_iid_jira_title ON merge_requests USING btree (target_project_id, iid) WHERE ((title)::text ~ '[A-Z][A-Z_0-9]+-\d+'::text);
 
+CREATE INDEX index_merge_requests_on_target_project_id_and_squash_commit_sha ON merge_requests USING btree (target_project_id, squash_commit_sha);
+
 CREATE INDEX index_merge_requests_on_target_project_id_and_target_branch ON merge_requests USING btree (target_project_id, target_branch) WHERE ((state_id = 1) AND (merge_when_pipeline_succeeds = true));
 
 CREATE INDEX index_merge_requests_on_target_project_id_iid_jira_description ON merge_requests USING btree (target_project_id, iid) WHERE (description ~ '[A-Z][A-Z_0-9]+-\d+'::text);

spec/finders/merge_requests_finder_spec.rb

@@ -76,13 +76,40 @@ RSpec.describe MergeRequestsFinder do
         expect(merge_requests).to contain_exactly(merge_request3, merge_request4)
       end
 
-      it 'filters by commit sha' do
-        merge_requests = described_class.new(
-          user,
-          commit_sha: merge_request5.merge_request_diff.last_commit_sha
-        ).execute
+      context 'filters by commit sha' do
+        subject(:merge_requests) { described_class.new(user, commit_sha: commit_sha).execute }
+
+        context 'when commit belongs to the merge request' do
+          let(:commit_sha) { merge_request5.merge_request_diff.last_commit_sha }
+
+          it 'filters by commit sha' do
+            is_expected.to contain_exactly(merge_request5)
+          end
+        end
+
+        context 'when commit is a squash commit' do
+          before do
+            merge_request4.update!(squash_commit_sha: commit_sha)
+          end
+
+          let(:commit_sha) { '1234abcd' }
 
-        expect(merge_requests).to contain_exactly(merge_request5)
+          it 'filters by commit sha' do
+            is_expected.to contain_exactly(merge_request4)
+          end
+        end
+
+        context 'when commit is a merge commit' do
+          before do
+            merge_request4.update!(merge_commit_sha: commit_sha)
+          end
+
+          let(:commit_sha) { '1234dcba' }
+
+          it 'filters by commit sha' do
+            is_expected.to contain_exactly(merge_request4)
+          end
+        end
       end
 
       context 'filters by merged_at date' do

spec/models/merge_request_spec.rb

@@ -411,6 +411,48 @@ RSpec.describe MergeRequest, factory_default: :keep do
     end
   end
 
+  describe '.by_squash_commit_sha' do
+    subject { described_class.by_squash_commit_sha(sha) }
+
+    let(:sha) { '123abc' }
+    let(:merge_request) { create(:merge_request, :merged, squash_commit_sha: sha) }
+
+    it 'returns merge requests that match the given squash commit' do
+      is_expected.to eq([merge_request])
+    end
+  end
+
+  describe '.by_related_commit_sha' do
+    subject { described_class.by_related_commit_sha(sha) }
+
+    context 'when commit is a squash commit' do
+      let!(:merge_request) { create(:merge_request, :merged, squash_commit_sha: sha) }
+      let(:sha) { '123abc' }
+
+      it { is_expected.to eq([merge_request]) }
+    end
+
+    context 'when commit is a part of the merge request' do
+      let!(:merge_request) { create(:merge_request, :with_diffs) }
+      let(:sha) { 'b83d6e391c22777fca1ed3012fce84f633d7fed0' }
+
+      it { is_expected.to eq([merge_request]) }
+    end
+
+    context 'when commit is a merge commit' do
+      let!(:merge_request) { create(:merge_request, :merged, merge_commit_sha: sha) }
+      let(:sha) { '123abc' }
+
+      it { is_expected.to eq([merge_request]) }
+    end
+
+    context 'when commit is not found' do
+      let(:sha) { '0000' }
+
+      it { is_expected.to be_empty }
+    end
+  end
+
   describe '.by_cherry_pick_sha' do
     it 'returns merge requests that match the given merge commit' do
       note = create(:track_mr_picking_note, commit_id: '456abc')