dap-debug: Dart library 'dart:ui' is not available on this platform

[shenso]

Describe the bug
Upon starting a debug session from my configuration in .vscode/launch.json, I get spammed with endless errors, all ultimately explained by the first few lines of the debug output:

../../.local/opt/flutter/packages/flutter/lib/src/widgets/app.dart:45:1: Error: Dart library 'dart:ui' is not available on this platform.
export 'dart:ui' show Locale;
^

To Reproduce

My emacs configuration on MacOS:

(use-package dart-mode
  :if (member system-name dart-systems)
  :ensure t
  :config
  (use-package flutter
    :ensure t
    :init
    (setq flutter-sdk-path (expand-file-name "~/.local/opt/flutter")))

  (use-package lsp-dart
    :if (member system-name lsp-systems)
    :requires lsp-mode
    :after flutter
    :ensure t
    :hook (dart-mode . lsp)
    :init
    (setq lsp-dart-sdk-dir (expand-file-name "~/.local/opt/flutter/bin/cache/dart-sdk")
          lsp-dart-flutter-sdk-dir (expand-file-name "~/.local/opt/flutter")
          lsp-dart-dap-use-sdk-debugger t)
    (dap-register-debug-template "Flutter :: Custom debug"
                                 (list :type "flutter"
                                       :program "lib/main_development.dart"
                                       :args '("--web-browser-flag"
                                               "--disable-web-security"
                                               "--flavor"
                                               "development"
                                               "--target"
                                               "lib/main_development.dart"
                                               "--web-port"
                                               "5555")))
    :config
    (setq gc-cons-threshold (* 100 1024 1024)
          read-process-output-max (* 1024 1024))))

I've tried keeping the sdk dirs as relative paths, keeping them unset, I've tried switching between which debugger is used and the result is the same. You can see I also created a custom debug template working off the guidelines in the README, but due to #226 / #222 this has just caused different problems.

My launch.json:

        {
            "name": "Launch development",
            "request": "launch",
            "type": "dart",
            "program": "lib/main_development.dart",
            "args": [
                "--web-browser-flag",
                "--disable-web-security",
                "--flavor",
                "development",
                "--target",
                "lib/main_development.dart",
                "--web-port",
                "5555"
            ]
        },

I've tried changing the type to "flutter" but that seems to have no effect.

Expected behavior

I would expect things to just work when selecting the configuration after invoking dap-debug just as they do on vscode.

Version

LSP Dart: 1.24.3
Dart SDK: 3.6.1

[maavelar5]

I faced the same issue, here's what I was able to figure out a bit from reading the source code, you should also pass :flutterPlatform "web" to the debug template, in my case the error went away but DAP didn't do anything after that, not even tried to run chrome or something else, I figured that it was because of a silent error that wasn't even getting reported. I was eventually able to get the setup to work properly by overriding the flutter provider. Also, it seems to be using :toolArgs instead of :args

(dap-register-debug-provider
 "flutter"
 (lambda (conf)
   (-> conf
       (dap--put-if-absent :type "flutter")
       (dap--put-if-absent :name "Flutter Direct Debug")
       (dap--put-if-absent :request "launch")
       (dap--put-if-absent :cwd "/maeproject/")
       (dap--put-if-absent :program "/lib/main.dart")
       (dap--put-if-absent :toolArgs '("-d" "chrome" "--web-port" "9000"))
       (dap--put-if-absent :flutterPlatform "web")
       (dap--put-if-absent :flutterMode "debug")
       (dap--put-if-absent :deviceId "chrome")
       (dap--put-if-absent :dap-server-path lsp-dart-dap-flutter-debugger-program)
       lsp-dart-dap--base-debugger-args)))

Hope it helps

[ericdallo]

Sorry folks, I'm not finding time to check lsp-dart, but is you have a way to fix it, feel free to open a PR and I can take a look!