Drop invalid index in safe_add_index

lib/strong_migrations/adapters/postgresql_adapter.rb

@@ -169,6 +169,22 @@ def default_volatile?(default)
         rows.empty? || rows.any? { |r| r["provolatile"] == "v" }
       end
 
+      def invalid_index?(index_name)
+        query = <<~SQL
+          SELECT
+            pg_class.relname
+          FROM
+            pg_class
+          INNER JOIN
+            pg_index ON pg_index.indexrelid = pg_class.oid
+          WHERE
+            pg_index.indisvalid = false AND
+            pg_class.relname = #{connection.quote(index_name)}
+        SQL
+
+        select_all(query.squish).any?
+      end
+
       private
 
       def set_timeout(setting, timeout)

lib/strong_migrations/safe_methods.rb

@@ -4,10 +4,15 @@ def safe_by_default_method?(method)
       StrongMigrations.safe_by_default && [:add_index, :add_belongs_to, :add_reference, :remove_index, :add_foreign_key, :add_check_constraint, :change_column_null].include?(method)
     end
 
-    # TODO check if invalid index with expected name exists and remove if needed
-    def safe_add_index(*args, **options)
+    def safe_add_index(table, columns, **options)
+      index_name = options.fetch(:name, connection.index_name(table, columns))
+      if postgresql? && adapter.invalid_index?(index_name)
+        safe_remove_index(table, columns, **options)
+      end
+
       disable_transaction
-      @migration.add_index(*args, **options.merge(algorithm: :concurrently))
+
+      @migration.add_index(table, columns, **options.merge(algorithm: :concurrently))
     end
 
     def safe_remove_index(*args, **options)
@@ -124,5 +129,11 @@ def disable_transaction
     def in_transaction?
       @migration.connection.open_transactions > 0
     end
+
+    private
+
+    def postgresql?
+      adapter.instance_of?(Adapters::PostgreSQLAdapter)
+    end
   end
 end

test/migrations/add_index.rb

@@ -59,6 +59,12 @@ def change
   end
 end
 
+class SafeAddIndexColumnsUnique < TestMigration
+  def change
+    add_index :users, :name, unique: true
+  end
+end
+
 class AddIndexName < TestMigration
   def change
     add_index :users, :name, name: "my_index"

test/safe_by_default_test.rb

@@ -152,4 +152,21 @@ def test_change_column_null_default
   ensure
     User.delete_all
   end
+
+  def test_add_index_with_invalid_present
+    skip unless postgresql?
+
+    User.create(name: 'same')
+    duplicate = User.create(name: 'same')
+
+    assert_raises(ActiveRecord::RecordNotUnique) do
+      migrate SafeAddIndexColumnsUnique
+    end
+
+    duplicate.delete
+
+    assert_safe SafeAddIndexColumnsUnique
+  ensure
+    User.delete_all
+  end
 end