dotnet
C# Extension Crashes When Saving New File Created via ".NET New File" in VS Code
Type: Bug
Issue Description
Whenever I create a new file in Visual Studio Code using the ".NET New File" command and attempt to save it, the C# extension crashes. The output window shows repeated errors such as "Failed to get language for textDocument/diagnostic" and "Document pull failed for text document untitled:Untitled-1". This issue occurs consistently and prevents saving new files created through the ".NET New File" workflow.
Steps to Reproduce
- Create a new file in VS Code using the ".NET New File" command
- Try to save the file
- Observe that C# crashes with the error above
Expected Behavior
The file should be saved without crashing the C# extension.
Actual Behavior
C# crashes with the error message above when saving a new file created via ".NET New File".
Extension version: 2.90.60 VS Code version: Code 1.104.2 (e3a5acfb517a443235981655413d566533107e92, 2025-09-24T11:21:37.073Z) OS version: Darwin arm64 24.6.0 Modes:
Logs
C# log
2025-10-02 11:37:36.318 [info] Locating .NET runtime version 9.0.1
2025-10-02 11:37:36.377 [info] Dotnet path: /usr/local/share/dotnet/dotnet
2025-10-02 11:37:36.377 [info] Activating C# + C# Dev Kit...
2025-10-02 11:37:36.454 [info] [stdout] info: Program[0]
Server started with process ID 3563
2025-10-02 11:37:36.708 [info] [stdout] {"pipeName":"/var/folders/lc/nf0p2stx0rld6r95vd22s28h0000gn/T/7403409d.sock"}
2025-10-02 11:37:36.708 [info] received named pipe information from server
2025-10-02 11:37:36.709 [info] client has connected to server
2025-10-02 11:37:36.762 [info] [Program] Language server initialized
2025-10-02 11:37:39.764 [info] [textDocument/diagnostic] [Microsoft.CodeAnalysis.LanguageServer.DotnetCliHelper] Using dotnet executable configured on the PATH
2025-10-02 11:37:39.769 [info] [textDocument/diagnostic] [Microsoft.CodeAnalysis.LanguageServer.FileBasedPrograms.FileBasedProgramsProjectSystem] Failed to obtain virtual project for '/Users/florestankorp/Documents/Coding/WEBDEV/dotnet/Webshop/src/WebShop.Api/Contracts/Products/test.cs' using dotnet run-api. Falling back to directly creating the virtual project.
2025-10-02 11:37:39.788 [warning] [textDocument/diagnostic] [LanguageServerProjectLoader] Project /Users/florestankorp/Documents/Coding/WEBDEV/dotnet/Webshop/src/WebShop.Api/Contracts/Products/test.csproj has unresolved dependencies
2025-10-02 11:37:39.793 [info] [textDocument/diagnostic] [LanguageServerProjectLoader] Successfully completed load of /Users/florestankorp/Documents/Coding/WEBDEV/dotnet/Webshop/src/WebShop.Api/Contracts/Products/test.cs
2025-10-02 11:37:40.134 [error] [workspace/_roslyn_restore] [Microsoft.CodeAnalysis.LanguageServer.Handler.RestoreHandler] Restore completed with errors.
2025-10-02 11:37:40.146 [info] [textDocument/diagnostic] [LanguageServerProjectLoader] Completed (re)load of all projects in 00:00:01.1999756
2025-10-02 11:37:41.971 [info] [serviceBroker/connect] [WorkspaceProjectFactoryService] Project /Users/florestankorp/Documents/Coding/WEBDEV/dotnet/Webshop/src/WebShop.Infrastructure/WebShop.Infrastructure.csproj loaded by C# Dev Kit
2025-10-02 11:37:41.978 [info] [serviceBroker/connect] [WorkspaceProjectFactoryService] Project /Users/florestankorp/Documents/Coding/WEBDEV/dotnet/Webshop/tests/WebShop.Api.Tests/WebShop.Api.Tests.csproj loaded by C# Dev Kit
2025-10-02 11:37:41.982 [info] [serviceBroker/connect] [WorkspaceProjectFactoryService] Project /Users/florestankorp/Documents/Coding/WEBDEV/dotnet/Webshop/tests/WebShop.Integration.Tests/WebShop.Integration.Tests.csproj loaded by C# Dev Kit
2025-10-02 11:37:41.982 [info] [serviceBroker/connect] [WorkspaceProjectFactoryService] Project /Users/florestankorp/Documents/Coding/WEBDEV/dotnet/Webshop/src/WebShop.Api/WebShop.Api.csproj loaded by C# Dev Kit
2025-10-02 11:37:41.984 [info] [serviceBroker/connect] [WorkspaceProjectFactoryService] Project /Users/florestankorp/Documents/Coding/WEBDEV/dotnet/Webshop/src/WebShop.Domain/WebShop.Domain.csproj loaded by C# Dev Kit
2025-10-02 11:37:41.984 [info] [serviceBroker/connect] [WorkspaceProjectFactoryService] Project /Users/florestankorp/Documents/Coding/WEBDEV/dotnet/Webshop/src/WebShop.Application/WebShop.Application.csproj loaded by C# Dev Kit
2025-10-02 11:37:41.985 [info] [serviceBroker/connect] [WorkspaceProjectFactoryService] Project /Users/florestankorp/Documents/Coding/WEBDEV/dotnet/Webshop/tests/WebShop.Unit.Tests/WebShop.Unit.Tests.csproj loaded by C# Dev Kit
2025-10-02 11:38:50.885 [error] [textDocument/diagnostic] [LSP] Failed to get language for untitled:Untitled-1 with language
2025-10-02 11:38:50.887 [error] [textDocument/diagnostic] [LSP] System.Exception: Failed to get language for textDocument/diagnostic
2025-10-02 11:38:50.891 [error] Request textDocument/diagnostic failed.
Message: Failed to get language for textDocument/diagnostic
Code: -32000
[object Object]
2025-10-02 11:38:50.891 [error] Document pull failed for text document untitled:Untitled-1
Message: Failed to get language for textDocument/diagnostic
Code: -32000
[object Object]
C# LSP Trace Logs log
Environment Information
VSCode version: 1.104.2 C# Extension: 2.90.60 Using OmniSharp: false
Dotnet Information
.NET SDK: Version: 9.0.301 Commit: a596cd22e2 Workload version: 9.0.300-manifests.9bcbba73 MSBuild version: 17.14.5+edd3bbf37Runtime Environment: OS Name: Mac OS X OS Version: 15.6 OS Platform: Darwin RID: osx-arm64 Base Path: /usr/local/share/dotnet/sdk/9.0.301/
.NET workloads installed: There are no installed workloads to display. Configured to use loose manifests when installing new manifests.
Host: Version: 9.0.6 Architecture: arm64 Commit: 3875b54e7b
.NET SDKs installed: 9.0.301 [/usr/local/share/dotnet/sdk]
.NET runtimes installed: Microsoft.AspNetCore.App 9.0.6 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App] Microsoft.NETCore.App 9.0.6 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Other architectures found: None
Environment variables: Not set
global.json file: Not found
Learn more: https://aka.ms/dotnet/info
Download .NET: https://aka.ms/dotnet/download
Visual Studio Code Extensions
| Extension | Author | Version | Folder Name |
|---|---|---|---|
| angular-console | nrwl | 18.70.0 | nrwl.angular-console-18.70.0 |
| angular-essentials | johnpapa | 18.0.0 | johnpapa.angular-essentials-18.0.0 |
| Angular2 | johnpapa | 18.0.2 | johnpapa.angular2-18.0.2 |
| astro-vscode | astro-build | 2.15.4 | astro-build.astro-vscode-2.15.4-darwin-arm64 |
| auto-close-tag | formulahendry | 0.5.15 | formulahendry.auto-close-tag-0.5.15 |
| auto-complete-tag | formulahendry | 0.1.0 | formulahendry.auto-complete-tag-0.1.0 |
| code-spell-checker | streetsidesoftware | 4.2.6 | streetsidesoftware.code-spell-checker-4.2.6 |
| code-spell-checker-dutch | streetsidesoftware | 0.5.4 | streetsidesoftware.code-spell-checker-dutch-0.5.4 |
| copilot | GitHub | 1.372.0 | github.copilot-1.372.0 |
| copilot-chat | GitHub | 0.31.3 | github.copilot-chat-0.31.3 |
| cpptools | ms-vscode | 1.27.7 | ms-vscode.cpptools-1.27.7-darwin-arm64 |
| csdevkit | ms-dotnettools | 1.50.51 | ms-dotnettools.csdevkit-1.50.51-darwin-arm64 |
| csharp | ms-dotnettools | 2.90.60 | ms-dotnettools.csharp-2.90.60-darwin-arm64 |
| data-workspace-vscode | ms-mssql | 0.6.3 | ms-mssql.data-workspace-vscode-0.6.3 |
| docker | docker | 0.17.0 | docker.docker-0.17.0-darwin-arm64 |
| dupchecker | jianbingfang | 0.1.7 | jianbingfang.dupchecker-0.1.7 |
| EditorConfig | EditorConfig | 0.17.4 | editorconfig.editorconfig-0.17.4 |
| errorlens | usernamehw | 3.26.0 | usernamehw.errorlens-3.26.0 |
| explorer | vitest | 1.30.0 | vitest.explorer-1.30.0 |
| gc-excelviewer | GrapeCity | 4.2.64 | grapecity.gc-excelviewer-4.2.64 |
| gitlens | eamodio | 17.5.1 | eamodio.gitlens-17.5.1 |
| go | golang | 0.50.0 | golang.go-0.50.0 |
| grafana-alloy | Grafana | 0.2.0 | grafana.grafana-alloy-0.2.0 |
| hexeditor | ms-vscode | 1.11.1 | ms-vscode.hexeditor-1.11.1 |
| html-css-class-completion | Zignd | 1.20.0 | zignd.html-css-class-completion-1.20.0 |
| LiveServer | ritwickdey | 5.7.9 | ritwickdey.liveserver-5.7.9 |
| material-icon-theme | PKief | 5.27.0 | pkief.material-icon-theme-5.27.0 |
| ng-template | Angular | 20.2.2 | angular.ng-template-20.2.2 |
| output-colorizer | IBM | 0.1.2 | ibm.output-colorizer-0.1.2 |
| playwright | ms-playwright | 1.1.15 | ms-playwright.playwright-1.1.15 |
| prettier-vscode | esbenp | 11.0.0 | esbenp.prettier-vscode-11.0.0 |
| pretty-ts-errors | YoavBls | 0.6.1 | yoavbls.pretty-ts-errors-0.6.1 |
| properties-validator | vivek-kasture | 0.0.6 | vivek-kasture.properties-validator-0.0.6 |
| rainbow-csv | mechatroner | 3.22.0 | mechatroner.rainbow-csv-3.22.0 |
| remote-containers | ms-vscode-remote | 0.429.0 | ms-vscode-remote.remote-containers-0.429.0 |
| remote-explorer | ms-vscode | 0.5.0 | ms-vscode.remote-explorer-0.5.0 |
| remote-server | ms-vscode | 1.5.3 | ms-vscode.remote-server-1.5.3 |
| remote-ssh | ms-vscode-remote | 0.120.0 | ms-vscode-remote.remote-ssh-0.120.0 |
| remote-ssh-edit | ms-vscode-remote | 0.87.0 | ms-vscode-remote.remote-ssh-edit-0.87.0 |
| remote-wsl | ms-vscode-remote | 0.104.3 | ms-vscode-remote.remote-wsl-0.104.3 |
| sonarlint-vscode | SonarSource | 4.31.0 | sonarsource.sonarlint-vscode-4.31.0-darwin-arm64 |
| svelte-vscode | svelte | 109.11.1 | svelte.svelte-vscode-109.11.1 |
| terraform | hashicorp | 2.37.2 | hashicorp.terraform-2.37.2-darwin-arm64 |
| vscode-azureappservice | ms-azuretools | 0.26.4 | ms-azuretools.vscode-azureappservice-0.26.4 |
| vscode-azureresourcegroups | ms-azuretools | 0.11.4 | ms-azuretools.vscode-azureresourcegroups-0.11.4 |
| vscode-containers | ms-azuretools | 2.2.0 | ms-azuretools.vscode-containers-2.2.0 |
| vscode-counter | uctakeoff | 3.7.2 | uctakeoff.vscode-counter-3.7.2 |
| vscode-css-formatter | aeschli | 1.0.2 | aeschli.vscode-css-formatter-1.0.2 |
| vscode-diff | fabiospampinato | 2.1.2 | fabiospampinato.vscode-diff-2.1.2 |
| vscode-docker | ms-azuretools | 2.0.0 | ms-azuretools.vscode-docker-2.0.0 |
| vscode-dotnet-runtime | ms-dotnettools | 2.3.7 | ms-dotnettools.vscode-dotnet-runtime-2.3.7 |
| vscode-eslint | dbaeumer | 3.0.16 | dbaeumer.vscode-eslint-3.0.16 |
| vscode-github-actions | github | 0.27.2 | github.vscode-github-actions-0.27.2 |
| vscode-icons | vscode-icons-team | 12.14.0 | vscode-icons-team.vscode-icons-12.14.0 |
| vscode-jest | Orta | 6.4.4 | orta.vscode-jest-6.4.4 |
| vscode-jest-runner | firsttris | 0.4.84 | firsttris.vscode-jest-runner-0.4.84 |
| vscode-pylance | ms-python | 2025.8.3 | ms-python.vscode-pylance-2025.8.3 |
| vscode-remote-extensionpack | ms-vscode-remote | 0.26.0 | ms-vscode-remote.vscode-remote-extensionpack-0.26.0 |
| vscode-speech | ms-vscode | 0.16.0 | ms-vscode.vscode-speech-0.16.0-darwin-arm64 |
| vscode-sqlite | alexcvzz | 0.14.1 | alexcvzz.vscode-sqlite-0.14.1 |
| vscode-stylelint | stylelint | 1.5.3 | stylelint.vscode-stylelint-1.5.3 |
| vscode-svgviewer | cssho | 2.0.0 | cssho.vscode-svgviewer-2.0.0 |
| vscode-tailwindcss | bradlc | 0.14.26 | bradlc.vscode-tailwindcss-0.14.26 |
| vscode-xml | redhat | 0.29.0 | redhat.vscode-xml-0.29.0-darwin-arm64 |
| vscode-yaml | redhat | 1.19.0 | redhat.vscode-yaml-1.19.0 |
C# Settings
| Setting | Value |
|---|---|
| preferCSharpExtension | false |
| compilerDiagnosticScope | openFiles |
| analyzerDiagnosticScope | openFiles |
| enableXamlTools | true |
| useServerGC | true |
System Info
| Item | Value |
|---|---|
| CPUs | Apple M2 Pro (10 x 2400) |
| GPU Status | 2d_canvas: enabled direct_rendering_display_compositor: disabled_off_ok gpu_compositing: enabled multiple_raster_threads: enabled_on opengl: enabled_on rasterization: enabled raw_draw: disabled_off_ok skia_graphite: enabled_on trees_in_viz: disabled_off video_decode: enabled video_encode: enabled webgl: enabled webgl2: enabled webgpu: enabled webnn: disabled_off |
| Load (avg) | 3, 6, 6 |
| Memory (System) | 16.00GB (0.31GB free) |
| Process Argv | |
| Screen Reader | no |
| VM | 0% |
From the C# log: 2025-10-02 11:38:50.885 [error] [textDocument/diagnostic] [LSP] Failed to get language for untitled:Untitled-1 with language
Since the new file is unsaved and has no extension, the CDK tells VS Code in advance that the file should be treated as a C# file. However, this could potentially be overridden by Auto-Detect. I was able to reproduce this issue by manually switching from C# to Plain Text.
@florestankorp What language is shown in the status bar for the new file?
@JoeRobich Once I open the output and the IDE "settles down", I get C#:
I was also only able to reproduce the error when manually changing the file type to something else. This is what happens
- File type manually changed to something other than c#
- Client sends
didClosenotification to the server for the prior language - we clear out the state information (including the language) since the document no longer exists from the server's perspective. - Client sends
textDocument/diagnosticfor the now closed document - believe this is triggered for the closing of any file. Server throws here because we no longer have any information for the closed document.
Can look into potential improvements there, but I'm not 100% sure that scenario is exactly the same as described in the original issue - I cannot reproduce this on saving a file created by .net new file. Note that this error should not cause any further issues (just a single failed diagnostics request).
Apologies for the delay here, but @florestankorp if you could collect the C# LSP Trace logs as described here - https://github.com/dotnet/vscode-csharp/blob/main/SUPPORT.md#c-lsp-trace-logs it'll help confirm what is going on.
@dibarbet Here are the C# LSP Trace logs after the crash:
2025-10-23 11:51:33.526 [error] [textDocument/diagnostic] [LSP] Failed to get language for untitled:Untitled-1 with language
2025-10-23 11:51:33.526 [error] [textDocument/diagnostic] [LSP] System.Exception: Failed to get language for textDocument/diagnostic
2025-10-23 11:51:33.528 [error] Request textDocument/diagnostic failed.
Message: Failed to get language for textDocument/diagnostic
Code: -32000
[object Object]
2025-10-23 11:51:33.529 [error] Document pull failed for text document untitled:Untitled-1
Message: Failed to get language for textDocument/diagnostic
Code: -32000
[object Object]
Note that this error should not cause any further issues (just a single failed diagnostics request).
Unfortunately this is not the case, instead the LSP crashes, ending my coding session and I have to restart VS Code for the LSP to come back online. If fixing the issue is not possible, then might I suggest a "Restart C# Language Server" feature from the command palette? Although this would not be ideal, at least that way I could quickly get back into coding again :)