Types declared by a macro are not visible outside the library where the macro was applied

[alexeyinkin]

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When a macro is applied in a library application.dart and generates a class there, this class can only be used inside that library. When importing application.dart in another library, the generated class can't be used there.

macro.dart:

import 'package:macros/macros.dart';

macro class MyMacro implements ClassTypesMacro {
  const MyMacro();

  @override
  Future<void> buildTypesForClass(ClassDeclaration clazz, ClassTypeBuilder builder) async {
    builder.declareType('GeneratedClass', DeclarationCode.fromString('class GeneratedClass {}'));
  }
}

application.dart:

import 'macro.dart';

@MyMacro()
class MyClass {}

final generatedInstanceSameLibrary = GeneratedClass(); // OK.

main.dart:

import 'application.dart';

final generatedInstanceDifferentLibrary = GeneratedClass(); // Error.

void main() {
  print(generatedInstanceSameLibrary);
}

pubspec.yaml

name: temp1

environment:
  sdk: ^3.5.0-180

dependencies:
  macros: ^0.1.0-main.5 # For 3.5.0-180

% dart run --enable-experiment=macros lib/main.dart
lib/main.dart:3:43: Error: Method not found: 'GeneratedClass'.
final generatedInstanceDifferentLibrary = GeneratedClass();
                                          ^^^^^^^^^^^^^^

The expected behavior is that GeneratedClass is available everywhere application.dart is imported. Quoting the augmentation feature specification:

• Like a part file, all of the top-level declarations it produces end up in the top-level scope of the augmented library.

If the erroneous line in main.dart is commented out, the program runs as expected.

dart info

#### General info

- Dart 3.5.0-180.3.beta (beta) (Wed Jun 5 15:06:15 2024 +0000) on "macos_arm64"
- on macos / Version 13.6 (Build 22G120)
- locale is en-GE

#### Project info

- sdk constraint: '^3.5.0-180'
- dependencies: macros
- dev_dependencies: 

#### Process info

| Memory |  CPU | Elapsed time | Command line                                                                               |
| -----: | ---: | -----------: | ------------------------------------------------------------------------------------------ |
| 124 MB | 0.0% |     05:57:34 | dart language-server --client-id=Android-Studio --client-version=AI-223.8836.35 --protocol=analyzer |
| 110 MB | 0.0% |     12:14:41 | dart language-server --client-id=Android-Studio --client-version=AI-223.8836.35 --protocol=analyzer |
|  88 MB | 0.0% |  01-10:36:02 | dart language-server --client-id=Android-Studio --client-version=AI-223.8836.35 --protocol=analyzer |
| 112 MB | 0.0% |     04:56:23 | dart language-server --client-id=Android-Studio --client-version=AI-223.8836.35 --protocol=analyzer |
| 101 MB | 0.0% |     04:41:48 | dart language-server --client-id=Android-Studio --client-version=AI-223.8836.35 --protocol=analyzer |
| 107 MB | 0.0% |  01-08:01:56 | dart language-server --client-id=Android-Studio --client-version=AI-223.8836.35 --protocol=analyzer |
|  89 MB | 0.0% |     04:31:30 | dart language-server --client-id=Android-Studio --client-version=AI-223.8836.35 --protocol=analyzer |
|  73 MB | 0.0% |     04:30:53 | dart language-server --client-id=Android-Studio --client-version=AI-223.8836.35 --protocol=analyzer |
| 111 MB | 0.0% |        04:58 | dart language-server --client-id=Android-Studio --client-version=AI-223.8836.35 --protocol=analyzer |
| 240 MB | 0.0% |     07:40:44 | dart language-server --client-id=Android-Studio --client-version=AI-223.8836.35 --protocol=analyzer |
|  57 MB | 0.0% |  04-11:59:25 | dart language-server --protocol=lsp --client-id=VS-Code --client-version=3.90.0            |
|  27 MB | 0.0% |  04-11:59:25 | dart tooling-daemon --machine                                                              |
|  49 MB | 0.0% |     05:57:34 | flutter_tools.snapshot daemon                                                              |
|  41 MB | 0.0% |     12:14:40 | flutter_tools.snapshot daemon                                                              |
|  47 MB | 0.0% |     04:56:23 | flutter_tools.snapshot daemon                                                              |
|  48 MB | 0.0% |     04:41:48 | flutter_tools.snapshot daemon                                                              |
|  41 MB | 0.0% |  01-08:01:56 | flutter_tools.snapshot daemon                                                              |
|  47 MB | 0.0% |     07:40:44 | flutter_tools.snapshot daemon                                                              |

[dart-github-bot]

Labels: area-language, type-bug Summary: Types generated by a macro within a library are not visible outside that library, even when the library is imported. This contradicts the expected behavior where generated types should be accessible in the augmented library's top-level scope.

[alexeyinkin]

No, that one concerned using macros from a different package. This one is within the same project. By library I mean just a .dart file.

Also, with this issue a macro works (this is seen by application.dart having no errors) but what it declares on the top level is not merged into the augmented library's top-level scope from the standpoint of anyone importing it.

And there's no workaround for this I could find. I just have to declare empty classes and let a macro fill them instead of fully creating them. It's OK for playing around but I can't release my betas with this.

[jakemac53]

@alexeyinkin Does the analyzer give an error, or do you only see the error when running dart run?

[alexeyinkin]

@jakemac53 as of 3.5.0-292 the analyzer is showing no issues, just dart run.

[jakemac53]

Sounds like a CFE issue then (already categorized as such).