`augment` keyword analyzes fine but is not recognized and produces error during compile

[timmaffett]

This simple example passes analysis fine but produces errors on attempting to run/compile.

// @dart = 3.7

class Person {
  Person(this.name);

  final String name;
}

augment class Person {
  @override
  String toString() {
    return 'Person(name: $name)';
  }
}

void main() {
  var person =  Person('John Doe');

  print(person);
}

Output results:

dart --version

C:\src\superbasic>dart --version
Dart SDK version: 3.8.0-24.0.dev (dev) (Wed Jan 22 12:05:43 2025 -0800) on "windows_x64"

dart analyze basic_test3.dart

C:\src\superbasic>dart analyze basic_test3.dart
Analyzing basic_test3.dart...
No issues found!

dart run basic_test3.dart

C:\src\superbasic>dart run basic_test3.dart
basic_test3.dart:9:1: Error: Variables must be declared using the keywords 'const', 'final', 'var' or a type name.
Try adding the name of the type of the variable or the keyword 'var'.
augment class Person {
^^^^^^^
basic_test3.dart:9:1: Error: Expected ';' after this.
augment class Person {
^^^^^^^
basic_test3.dart:9:15: Error: 'Person' is already declared in this scope.
augment class Person {
              ^^^^^^
basic_test3.dart:3:7: Context: Previous declaration of 'Person'.
class Person {
      ^^^^^^
basic_test3.dart:12:27: Error: The getter 'name' isn't defined for the class 'Person#1#0'.
 - 'Person#1#0' is from 'basic_test3.dart'.
Try correcting the name to the name of an existing getter, or defining a getter or field named 'name'.
    return 'Person(name: $name)';
                          ^^^^
basic_test3.dart:17:17: Error: Can't use 'Person' because it is declared more than once.
  var person =  Person('John Doe');
                ^

Executing dart --enable-experiment=augmentations run basic_test3.dart produces the same results (on the off chance it was somehow not enabling augmentations by version.

[lrhn]

That's a bug in the analyzer. Augmentations are not released, so you need the experiment flag enabeld for the syntax to be valid.

[jakemac53]

@timmaffett are you enabling the experiment in an analysis_options.yaml file? That only applies to the analyzer and not the compiler.

[sma]

But he's running dart --enable-experiment=augmentations run basic_test3.dart (see the last paragraph) and I can reproduce that both with augmentations and with macros as experiment, using the same Dart version. Currently, there seems to be no way to run (or format) code with the augment keyword.

[timmaffett]

and I am/was attempting to compile/run with flag to force augmentations on:
dart --enable-experiment=augmentations run basic_test3.dart

and I mistook the documentation to say that the experiment would be enabled for any version from 3.6.0, but I also tried passing the --enable-experiment=augmentations flag explicitly with no change in behavior.

My analysis_options.yaml file:

include: package:lints/recommended.yaml

analyzer:
  enable-experiment:
    - macros
    - augmentations

(My .vscode launch.json also included these (before I created isolated example for creating issue)

{
    // Use IntelliSense to learn about possible attributes.
    // Hover to view descriptions of existing attributes.
    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
    "version": "0.2.0",
    "configurations": [
        {
            "name": "codable",
            "request": "launch",
            "type": "dart",
            "toolArgs": [
                "--enable-experiment=augmentations,enhanced-parts,macros,inference-update-4,num-shorthands,variance"
            ]
        }
    ]
}

[timmaffett]

@timmaffett are you enabling the experiment in an analysis_options.yaml file? That only applies to the analyzer and not the compiler.

yes and I am compiling with --enable-experiment=augmentations,macros

(I tried adding other experiments also)

[lrhn]

Ack. I took the last paragraph to mean that he ran without the flag first, and the flag made no difference.

If the flag is enabled in the analysis options file, then that would explain it working for analyzer, but not for compilers.

The bug is still that the analyser enables the experiment for language version 3.7 in a 3.8 SDK.
Experiments are only available on the latest language version of a dev-build.
They're not available for code that runs an earlier, released version of the language where the future was known to not be included.

[sma]

But how can the above code be executed?

Like the OP, I've

% dart --version
Dart SDK version: 3.8.0-24.0.dev (dev) (Wed Jan 22 12:05:43 2025 -0800) on "macos_arm64"

and

environment:
  sdk: ^3.8.0-24.0.dev

in my pubspec.yaml and

analyzer:
  enable-experiment:
    - macros
    - augmentations

in my analysis_options.yaml file.

The IDE is happy and I can jump between "Augmentation" and "Augmented", for example.

However, there seems to be no way to run that code successfully.

% dart --enable-experiment=macros,augmentations run lib/test.dart 
lib/test.dart:9:1: Error: Variables must be declared using the keywords 'const', 'final', 'var' or a type name.
Try adding the name of the type of the variable or the keyword 'var'.
augment class Person {
^^^^^^^
lib/test.dart:9:1: Error: Expected ';' after this.

I tried to add // @dart = 3.8 or remove the // @dart = 3.7 comment.

I tried to run it with and without the experimental flags.

Note that is works:

% dart analyze lib/test.dart 
Analyzing test.dart...                  0.2s
No issues found!

[timmaffett]

@irhn Before reporting this I had attempted many things to try and get the compiler to compiler, run or format this code. Using the --enable-experiments=macros initially but then adding in augmentations then adding in the // @dart = 3.7 (and 3.8) and going over the SDK code to see if I could find any explanations..
I am always using the current master channel/dev sdk here,

The bug seems to be that the compiler currently does not recognize the augment keyword no matter what you do.

I would LOVE to hear that I am doing something wrong and that you found a way to compile/run that code!
I can't seem to find a way with the current version.

Using master channel pulled just now: (also tested on macos_arm64 , exactly same result)

dart --version

Dart SDK version: 3.8.0-67.0.dev (dev) (Mon Feb 3 04:02:25 2025 -0800) on "windows_x64"

dart --enable-experiment=augmentations,macros run basic_test3.dart

basic_test3.dart:9:1: Error: Variables must be declared using the keywords 'const', 'final', 'var' or a type name.
Try adding the name of the type of the variable or the keyword 'var'.
augment class Person {
^^^^^^^
basic_test3.dart:9:1: Error: Expected ';' after this.
augment class Person {
^^^^^^^
basic_test3.dart:9:15: Error: 'Person' is already declared in this scope.
augment class Person {
              ^^^^^^
basic_test3.dart:3:7: Context: Previous declaration of 'Person'.
class Person {
      ^^^^^^
basic_test3.dart:12:27: Error: The getter 'name' isn't defined for the class 'Person#1#0'.
 - 'Person#1#0' is from 'basic_test3.dart'.
Try correcting the name to the name of an existing getter, or defining a getter or field named 'name'.
    return 'Person(name: $name)';
                          ^^^^
basic_test3.dart:17:17: Error: Can't use 'Person' because it is declared more than once.
  var person =  Person('John Doe');