Expression eval fails with "Error: Module dart_sdk not loaded in the browser."

[DanTup]

When debugging (non-Flutter) web apps in VS Code, expression eval fails on some expressions with "Module dart_sdk not loaded in the browser".

I think this only started recently, as Dart-Code integration tests start failing which (as far as I can tell) were passing previously.

I'm not sure whether the issue is in webdev, dwds, or the SDK. Although I don't seem to be able to repro in Flutter web apps.

==> {
	"id": "20",
	"jsonrpc": "2.0",
	"method": "evaluateInFrame",
	"params": {
		"disableBreakpoints": true,
		"expression": "DateTime.now().year",
		"frameIndex": 0,
		"isolateId": "193"
	}
}
<== {
	"jsonrpc": "2.0",
	"result": {
		"type": "@Instance",
		"id": "#StringInstanceRef#Error: Module dart_sdk not loaded in the browser.",
		"kind": "String",
		"identityHashCode": 154905552,
		"class": {
			"type": "@Class",
			"id": "classes|dart:core|String",
			"name": "String",
			"library": {
				"type": "@Library",
				"id": "dart:core",
				"name": "dart:core",
				"uri": "dart:core"
			}
		},
		"valueAsString": "Error: Module dart_sdk not loaded in the browser.",
		"length": 49
	},
	"id": "20"
}

To repro, I:

• created a new project using the basic web template from dart create (and VS Code's Dart: Create New Project command)
• created a .vscode/launch.json setting program to web/ for the web debugger
  {
  "name": "dart_web_application_1",
  "request": "launch",
  "type": "dart",
  "program": "web/"
  }
• added a breakpoint into the main function in main.dart
• launched with F5
• when the app loaded, hit the Restart icon (since due to a race, breakpoints in startup code don't currently work for non-Flutter web debugging)
• when the debugger paused, tried to evaluate DateTime.now().year in the Debug Console

[nshahan]

@Markzipan
I can reproduce this with the provided instructions. Furthermore, it seems that other evaluations are broken as well. I tried adding a top level field in main.dart

var foo = 99;

void main() {
  final now = DateTime.now();
  ...
}

and evaluating it when stopped at the breakpoint and that also fails:

"Error: Module web/main.dart not loaded in the browser."

and even when stopped at lines of code in other library imports:

"Error: Module packages/web_create/foo.dart not loaded in the browser."

[nshahan]

@Markzipan
I tried to downgrade various packages and my SDK but could not find a working version solve. Do we have a known set of packages (webdev, dwds, build_xxx...) that we know worked with the Dart SDK v3.12? I can get a working version solve but I keep getting version skew errors from build_daemon even though I tried pinning versions that don't include the version skew check.

[nshahan]

I investigated the output from the expression compiler and I think I found the route cause. The format of the expression doesn't match the compiled application. Based on what what the output looks like it seems:

Application Compiler

• module format: ddc
• canary features: true

Expression Compiler

• module format: ddc
• canary features: false

I'm still looking for where the canary flag isn't getting plumbed correctly.