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[tool_crash] flutter widget-preview start crashes with RpcException - Unknown method "Lsp.dart/workspace/getFlutterWidgetPreviews" #187367
Description
Command
flutter widget-preview startSteps to Reproduce
- Create a Flutter package project
- Run
flutter widget-preview startin the project root - Wait for "Connected to DTD" message
- Flutter crashes immediately after connecting
Expected Behavior
Widget Preview should start successfully and open in Chrome browser.
Actual Behavior
Crashes with:
JSON-RPC error -32601 (method not found):
Unknown method "Lsp.dart/workspace/getFlutterWidgetPreviews"
Environment
Flutter version: 3.44.0 (stable)
Dart version: 3.12.0
OS: Windows 11 (24H2)
IDE: Android Studio
Project type: Flutter Package (not a full app)
Logs
RpcException
package:json_rpc_2/src/client.dart 134:62 Client.sendRequest
package:json_rpc_2/src/peer.dart 116:15 Peer.sendRequest
package:dtd/src/dart_tooling_daemon.dart 218:36 DartToolingDaemon.call
package:flutter_tools/src/widget_preview/dtd_services.dart 176:48 WidgetPreviewDtdServices.getFlutterWidgetPreviewsFlutter Application Metadata
Type: malformed
Version: 0.0.1
Material: true
Activity
mbcorona commentedon Jun 2, 2026
Thanks for the report. I couldn't reproduce this on macOS (Flutter 3.44.0) — flutter widget-preview start on a clean flutter create --template=package project starts fine, with the analysis server registering the LSP service and reaching "Done loading previews". The -32601 Unknown method "…getFlutterWidgetPreviews" means the analysis server on your machine isn't exposing that LSP method, which usually points to a Dart SDK / analysis-server version mismatch rather than the project itself.
To narrow it down, could you share:
Your full flutter doctor -v
The verbose log: flutter widget-preview start -v (this shows whether the analysis server registers the LSP service and which SDK versions are in play)
Whether you have a separate Dart SDK on your PATH (vs. the one bundled with this Flutter)
Also, does it reproduce on a brand-new flutter create --template=package project? That'll help confirm whether it's Windows-specific or an SDK-state issue on your machine.
Alimmzdev commentedon Jun 2, 2026
Hi @mbcorona ,
Thanks for the quick follow-up!
Just to clarify, I didn't write this issue manually. Flutter itself suggested filing it in the terminal after the command failed. I simply confirmed and submitted it.
The issue reproduces on my Windows machine in a corporate environment. I'll add the requested information (
flutter doctor -voutput and the verbose log) tomorrow.Thanks for your patience!
Alimmzdev commentedon Jun 3, 2026
@mbcorona
flutter doctor -v
flutter widget-preview start -v
The verbose log is attached above (the original report). Key observations from it:
Connected to DTD and registered services)$/progressANALYZING → endevent, meaning it does start upJSON-RPC error -32601 (method not found): Unknown method "Lsp.dart/workspace/getFlutterWidgetPreviews"77cd65d419280f17)Dart SDK situation
I do not have a separate Dart SDK on my PATH — I'm using only the Dart SDK bundled with this Flutter install.
flutter doctor -v
Reproduction on a clean project
After further testing, this does not reproduce on a brand-new
flutter create --template=packageproject — the command works fine there.Alimmzdev commentedon Jun 3, 2026
Update — Root cause found
After more testing, the command actually works correctly on a clean
flutter create --template=packageproject. So this isn't a Windows-specific bug or an SDK version mismatch.The real issue was my own mistake: I was running
flutter widget-preview startfrom the package root (E:\Projects\Flutter Packages\BCM— a Flutter package, not a full app), instead of from theexample/directory where the actual app lives.The tool connects to DTD successfully, then calls
Lsp.dart/workspace/getFlutterWidgetPreviewson a workspace that isn't set up as a widget-preview app — so it crashes with-32601 method not found. Running the same command fromexample/works fine.Fix:
That said — while this was my mistake, it does seem like
flutter widget-preview startshould detect that it's being run from an invalid project context and show a clear, actionable error message (e.g. "This directory is not a Flutter app. Did you mean to run this from your example/ folder?") rather than crashing with a raw JSON-RPC error and sending a crash report to Google. The current failure mode is pretty opaque for something that could be caught early. Might be worth a separate issue or UX improvement request.Alimmzdev commentedon Jun 3, 2026
Sorry, I accidentally closed this issue. I'm available if you need any further information or logs to investigate.
puneetkukreja98 commentedon Jun 3, 2026
@Nullexdev Thanks for reporting the issue. I tested this on the latest master channel, and I was able to reproduce it.
Findings:
The error occurs specifically when running the flutter widget-preview start command directly from PowerShell. However, when opening the folder in VS Code and running the exact same command from there, everything works perfectly fine.
LOGS:
Steps to repro:
@Nullexdev could you please confirm if I followed any steps incorrectly?
2 remaining items
puneetkukreja98 commentedon Jun 3, 2026
similar issue #185657
Alimmzdev commentedon Jun 3, 2026
@puneetkukreja98
Yes, I can confirm your steps are correct and the issue reproduces.
However, I also found the root cause in my case: I was running
flutter widget-preview startfrom the package root (which is a Flutter package, not a full app). Running it from theexample/directory works correctly.So in my situation, the crash happens when running the command from a directory that isn't a Flutter app. It seems the tool doesn't validate the project type before attempting to connect — it just crashes with a raw JSON-RPC error instead of giving a helpful message like "This directory is not a Flutter app."
I tested from Git Bash, PowerShell, and the VS Code terminal, running the command from the
example/directory — the same error occurs regardless of where I run it from.ThomasDuffinMears commentedon Jun 18, 2026
Feels related to the limitation mentioned here (linked in the docs): #173550.
We have a monorepo setup like so 👇
. └── workspaceRoot ├── apps │ ├── app1 │ │ └── lib/main.dart │ └── ... ├── packages │ └── ... └── scripts └── ...Which explains why running
flutter widget-preview startfails with the same error.Notably, running
cd ~/workspaceRoot/apps/app1 && flutter widget-preview startalso fails. I wonder if that's because the IDE's context is set to~/workspaceRootregardless of the context of the terminal?EDIT: Even setting up a new workspace for the app on its own doesn't fix it. Even tried running flutter clean etc and killing the processes.
[Tool] Fix widget-preview crash by waiting for analysis server (flutt…
[Tool] Fix widget-preview crash by waiting for analysis server (flutt…
github-actions commentedon Jul 14, 2026
This thread has been automatically locked since there has not been any recent activity after it was closed. If you are still experiencing a similar issue, please open a new bug, including the output of
flutter doctor -vand a minimal reproduction of the issue.