API for "reviving" DartObject

[matanlurey]

One of the hardest and most brittle parts of the AngularDart compiler...

Basically, we need to go from a computed DartObject to some sort of model class that enables code generation of an identical object. Here are some simple (trivial) examples that are solvable with ConstantReader today:

• String
• int / double
• bool
• null
• List<...> or Map<...> of these types, recursively

However, it's much harder with classes and enums. Consider these:

• const Duration(seconds: 5)
• const SomeClass._privateConstructor()
• Enum.someValue

---

We could do this with ConstantReader, if we add a few more methods:

abstract class ConstantReader {
  bool get isEnum;
  RevivableEnum get enumValue;

  bool get isInstance;
  RevivableInstance get instanceValue;
}

abstract class RevivableEnum implements ConstantReader {
  Uri get uri;
  String get name;
  int get index;
}

abstract class RevivableInstance implements ConstantReader {
  Uri get uri;
  String get name;
  String get constructor;
  List<ConstantReader> get positionalArguments;
  Map<String, ConstantReader> get namedArguments;
}

We could also do error handling, i.e., a flag for checking if it is revivable (visible):

abstract class RevivableInstance implements ConstantReader {
  ...
  bool get isVisible;
}

This isn't a perfect API, but it is probably better for some of this to live in source_gen (and have closer watch by the ecosystem team and analysis team) than buried in the AngularDart compiler.

/cc @jakemac53 @alorenzen @kevmoo

[jakemac53]

I am not 100% sure about the Revivable* names but generally this SGTM.

We probably also want to probably add a base class, something similar to this:

abstract RevivableBase<T> {
  String toCodeString();
  T toInstance();
}

[matanlurey]

I mostly agree - except the toCodeString - this seems too difficult to get right for all users, and then we are sort of duplicating logic for from code_builder. I'd be OK with doing this in toString() mostly for debugging though.

[matanlurey]

I'm OK with the progress here so far.

[bitsydarel]

Hi guys, so what's the current api to get the value of a enum using constantReader ?

[bitsydarel]

is their a toInstance ?

[natebosch]

what's the current api to get the value of a enum using constantReader ?

I don't think we have one. We could review a contribution adding an API to ConstantReader for this.

is their a toInstance ?

No, it's not feasible to implement since it depends on statically importing the class that needs to be constructed. Most likely the best we can do is something like T enumValue<T>(Iterable<T> selectFrom) with usage like reader.enumValue(SomeEnum.values);

One concern is we can't statically know that T is an enum, so it would be easy to misuse with "enum like" classes that might not fit our assumptions...

[bitsydarel]

Can dart allow us to bound generic type?

[bitsydarel]

Currently I'm doing this like that :

        .firstAnnotationOfExact(field, throwOnUnresolved: false);

    if (annotation == null) {
      return null;
    } else {
      final columnTypeValue = ColumnType.values.firstWhere(
        (columnType) =>
            annotation
                .getField("type")
                .getField(columnType.toString().split('.')[1]) !=
            null,
        orElse: () => null,
      );```

[lukepighetti]

Hey all, I'm trying to take @MyAnnotation("") and get the String r'""', or @MyAnnotation(["Foo"]) and get the string r'["Foo"]'. Basically I'm trying to recreate the value.

I tried this with no luck final nullValue = annotation.read("nullValue").revive().toString();, does this issue cover this use case or am I misunderstanding this issue?

[kevmoo]

You can write code to handle this.

See

https://github.com/dart-lang/json_serializable/blob/3ea5351cb73f1e1131a252533276e1887bb883c8/json_serializable/lib/src/json_key_utils.dart#L52-L112

[lukepighetti]

@kevmoo any reason why this hasn't been contributed to source_gen or whichever package would typically contain this type of utility method?

[kevmoo]

@lukepighetti – time/priority

Doing it for simple things is easy, but you fall off a cliff pretty quick.

PR welcome!

[lukepighetti]

@kevmoo I don't feel qualified to contribute your source to a package like source_gen. I don't even know if that's the appropriate location for that utility method.