Fix copy_indexes helper when an index has opclass

Fix the Fix copy_indexes migration helper failing to
properly set the opclass of the new index when the old
index has opclasses like gin_trgm_ops defined for it

changelogs/unreleased/256094-fix-copy-indexes-migration-helper-opclass-replication.yml

+---
+title: Fix copy_indexes migration helper skipping the opclass for indexes
+  with operator classes defined for them
+merge_request: 43471
+author:
+type: fixed

lib/gitlab/database/migration_helpers.rb

@@ -882,7 +882,7 @@ module Gitlab
             # column.
             opclasses[new] = opclasses.delete(old) if opclasses[old]
 
-            options[:opclasses] = opclasses
+            options[:opclass] = opclasses
           end
 
           add_concurrent_index(table, new_columns, options)

spec/lib/gitlab/database/migration_helpers_spec.rb

@@ -1128,7 +1128,65 @@ RSpec.describe Gitlab::Database::MigrationHelpers do
                name: 'index_on_issues_gl_project_id',
                length: [],
                order: [],
-               opclasses: { 'gl_project_id' => 'bar' })
+               opclass: { 'gl_project_id' => 'bar' })
+
+        model.copy_indexes(:issues, :project_id, :gl_project_id)
+      end
+    end
+
+    context 'using an index with multiple columns and custom operator classes' do
+      it 'copies the index' do
+        index = double(:index,
+                       columns: %w(project_id foobar),
+                       name: 'index_on_issues_project_id_foobar',
+                       using: :gin,
+                       where: nil,
+                       opclasses: { 'project_id' => 'bar', 'foobar' => :gin_trgm_ops },
+                       unique: false,
+                       lengths: [],
+                       orders: [])
+
+        allow(model).to receive(:indexes_for).with(:issues, 'project_id')
+          .and_return([index])
+
+        expect(model).to receive(:add_concurrent_index)
+          .with(:issues,
+               %w(gl_project_id foobar),
+               unique: false,
+               name: 'index_on_issues_gl_project_id_foobar',
+               length: [],
+               order: [],
+               opclass: { 'gl_project_id' => 'bar', 'foobar' => :gin_trgm_ops },
+               using: :gin)
+
+        model.copy_indexes(:issues, :project_id, :gl_project_id)
+      end
+    end
+
+    context 'using an index with multiple columns and a custom operator class on the non affected column' do
+      it 'copies the index' do
+        index = double(:index,
+                       columns: %w(project_id foobar),
+                       name: 'index_on_issues_project_id_foobar',
+                       using: :gin,
+                       where: nil,
+                       opclasses: { 'foobar' => :gin_trgm_ops },
+                       unique: false,
+                       lengths: [],
+                       orders: [])
+
+        allow(model).to receive(:indexes_for).with(:issues, 'project_id')
+          .and_return([index])
+
+        expect(model).to receive(:add_concurrent_index)
+          .with(:issues,
+               %w(gl_project_id foobar),
+               unique: false,
+               name: 'index_on_issues_gl_project_id_foobar',
+               length: [],
+               order: [],
+               opclass: { 'foobar' => :gin_trgm_ops },
+               using: :gin)
 
         model.copy_indexes(:issues, :project_id, :gl_project_id)
       end