Generated code can contain unused variables

[PIG208]

Describe the bug

The generated validateIntegrity method can contain a final data = instance.toColumns(true);
statement that defines an unused local variable.

This can be reproduced by having a table that contains only columns with a type converter.

For example:

enum Fruit {
  apple,
  pear,
}
class Foo extends Table {
  Column<String> get fruit => textEnum<Fruit>()
    .withDefault(const Variable('apple'))();
}

  @override
  VerificationContext validateIntegrity(Insertable<FooData> instance,
      {bool isInserting = false}) {
    final context = VerificationContext();
    final data = instance.toColumns(true); // The value of the local variable 'data' isn't used
    context.handle(_fruitMeta, const VerificationResult.success());
    return context;
  }

We don't necessarily need to avoid generating code like this. Adding the lint rule to ignore_for_file should fix this issue.

[simolus3]

Hm, there should be an //ignore_for_file: type=lint comment at the top of the file, but I guess that doesn't catch dead code warnings?

Still, good catch! It's not hard to just not generate that effectively empty method in that case.

[gnprice]

Thanks for the swift fix!

I believe type=lint covers the rules that appear here:
https://dart.dev/tools/linter-rules

I'm not sure what specific warning was appearing in this issue, but on a quick search for "unused" it doesn't look like that list includes one about unused variables. So it may be a Dart analyzer warning that isn't one of the "linter" rules, and therefore isn't covered by type=lint.

[PIG208]

Generated file contains unused variable when the table contains only a textEnum. Maybe we should reopen this issue? @simolus3

class GlobalSettings extends Table {
  Column<String> get themeSetting => textEnum<ThemeSetting>()();
}

class $GlobalSettingsTable extends GlobalSettings
    with TableInfo<$GlobalSettingsTable, GlobalSetting> {
  @override
  final GeneratedDatabase attachedDatabase;
  final String? _alias;
  $GlobalSettingsTable(this.attachedDatabase, [this._alias]);
  // Warning: The value of the field '_themeSettingMeta' isn't used.
  static const VerificationMeta _themeSettingMeta = const VerificationMeta(
    'themeSetting',
  );
  @override
  late final GeneratedColumnWithTypeConverter<ThemeSetting, String>
  themeSetting = GeneratedColumn<String>(
    'theme_setting',
    aliasedName,
    false,
    type: DriftSqlType.string,
    requiredDuringInsert: true,
  ).withConverter<ThemeSetting>($GlobalSettingsTable.$converterthemeSetting);
  @override
  List<GeneratedColumn> get $columns => [themeSetting];
  @override
  String get aliasedName => _alias ?? actualTableName;
  @override
  String get actualTableName => $name;
  static const String $name = 'global_settings';
  @override
  Set<GeneratedColumn> get $primaryKey => const {};
  @override
  GlobalSetting map(Map<String, dynamic> data, {String? tablePrefix}) {
    final effectivePrefix = tablePrefix != null ? '$tablePrefix.' : '';
    return GlobalSetting(
      themeSetting: $GlobalSettingsTable.$converterthemeSetting.fromSql(
        attachedDatabase.typeMapping.read(
          DriftSqlType.string,
          data['${effectivePrefix}theme_setting'],
        )!,
      ),
    );
  }

If another column is added to the table, or the column builder is changed to other things like text or integer, there is no longer this issue.

It seems like the fix #3384 (comment) needs to further drop VerificationMeta for fields like this when validateIntegrity is not generated.

Reproduced on 2.25.1.

[simolus3]

Thanks for the report, I've fixed this in 8b8aacb.

[PIG208]

Hi @simolus3. Thanks a lot for the prompt fix!

Do you have an estimate of when the next release will come out?

(It's not necessarily blocking us as we can pin a Git revision containing the fix for now)

[simolus3]

I'll try to do a release this weekend, there are some other minor patches I want to look at too in the meantime.