How to get full display type name from DartType?

[ductranit]

I have a property like:

Map<MyEnum, Map<String, String>> animations = {};

Before I can read its type when running analyzer with this code:

class MyGenerator extends Generator {
 @override
 String generate(LibraryReader library, BuildStep buildStep) {
     ClassElement clazzElement;   // get class Element from LibraryReader
     for (var field in clazzElement.fields) {
          var type = field.type.getDisplayString(withNullability: false); // it returns "Map<MyEnum, Map<String, String>>"
     }
 }
}

But now the field type result is Map<dynamic, Map<dynamic, dynamic>**>
The doc says that I shouldn't depend on getDisplayString(), but I can't find any way to do this.
How can I get the full type Map<MyEnum, Map<String, String>> from my property?

Flutter doctor:

Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel master, 2.5.0-6.0.pre.30, on Mac OS X 10.15.7 19H1323 darwin-x64, locale en-US)
[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.3)
[✓] Xcode - develop for iOS and macOS
[✓] Chrome - develop for the web
[✓] Android Studio (version 4.2)
[✓] VS Code (version 1.58.2)
[✓] VS Code (version 1.60.0-insider)
[✓] Connected device (2 available)

• No issues found!

[jakemac53]

Can you provide more info, and ideally a reproduction case? It sounds like you said this used to work and no longer does. When did it stop working? Was there an SDK or analyzer update that changed the behavior?

[ductranit]

@jakemac53 This issue just happen recently on latest SDK (I upgraded flutter few times). I can't tell you which version that worked before because it was few months ago. The source_gen version was 1.0.2 (but the same issue on 1.0.5).
To reproduce, you can use the source_gen example and add this class:

class Test {
    Map<MyEnum, Map<String, String>> animations = {};
}

Then use this generator to read it:

class MyGenerator extends Generator {
 @override
 String generate(LibraryReader library, BuildStep buildStep) {
    library.allElements.forEach((element) {
      final classElement = cast<ClassElement>(element);
      final annotations = library.annotatedWith(typeChecker);
      if (classElement != null && !classElement.isEnum) {
        for (var field in classElement.fields) {
          var type = field.type.getDisplayString(withNullability: false);
           // I expect the type is "Map<MyEnum, Map<String, String>>" but it returns "Map<dynamic, Map<dynamic, dynamic>**>"
          print(type);
        }
      }
    });
 }
}

The problem is that the sdk changed behavior of getDisplayString

[natebosch]

I'm not sure if this is something we want to try to support directly.

Mockito has a utility to help get a TypeReference since it uses code_builder. I'm not sure if we could generalize this in some way that it's not tied to code_builder.
https://github.com/dart-lang/mockito/blob/15ca5ad2132abfddad54677e29025b2b7a9a0ab1/lib/src/builder.dart#L1420-L1473

@srawlins - do you think there is an opportunity to share any of this logic in source_gen or is this better left to individual builders?

[srawlins]

I've lightly pondered this for a while, but my use case always comes down to a necessary dependency on code_builder since I definitely want _i1.Map<_i2.MyEnum, ... if the types are provided via import prefixes (as they are in mockito, using code_builder.

So the utility necessarily depends on code_builder and source_gen. One possible solution is a new package, "source_gen code_builder utilities". Right off the bat, it could be used by mockito and angular, perhaps more.

What are the downsides to a new package? Maintenance..., not much else. (Not to minimize "maintenance," this is huge during language version bump cycles, like Null Safety, or a major version bump to dependencies...)

[natebosch]

What do you think about creating a class in source_gen that holds the same symbol, url, and types information as TypeReference. It would take a small amount of shim code in each usage to translate from the new class to TypeReference.