MEF composition errors during C# extension startup #8695
Description
Issue Description
The latest C# extension (12.93.22`) is logging several MEF composition errors at startup for me (and at least one of my colleagues).
Downgrading to 2.90.60 fixes it.
2025-10-13 09:15:37.003 [info] [stdout] fail: Microsoft.CodeAnalysis.Remote.ExportProviderBuilder[0]
Encountered errors in the MEF composition:
----- CompositionError level 1 ------
Microsoft.CodeAnalysis.ExternalAccess.Copilot.Internal.CodeMapper.CSharpMapCodeService.ctor(service): expected exactly 1 export matching constraints:
Contract name: Microsoft.CodeAnalysis.ExternalAccess.Copilot.CodeMapper.ICSharpCopilotMapCodeService
TypeIdentityName: Microsoft.CodeAnalysis.ExternalAccess.Copilot.CodeMapper.ICSharpCopilotMapCodeService
but found 0.
part definition Microsoft.CodeAnalysis.ExternalAccess.Copilot.Internal.CodeMapper.CSharpMapCodeService
Microsoft.CodeAnalysis.ExternalAccess.Copilot.Internal.SemanticSearch.CopilotSemanticSearchQueryExecutor.ctor(workspaceProvider): expected exactly 1 export matching constraints:
Contract name: Microsoft.CodeAnalysis.Host.IHostWorkspaceProvider
TypeIdentityName: Microsoft.CodeAnalysis.Host.IHostWorkspaceProvider
but found 0.
part definition Microsoft.CodeAnalysis.ExternalAccess.Copilot.Internal.SemanticSearch.CopilotSemanticSearchQueryExecutor
Microsoft.CodeAnalysis.ExternalAccess.Pythia.PythiaSignatureHelpProvider.ctor(implementation): expected exactly 1 export matching constraints:
Contract name: Microsoft.CodeAnalysis.ExternalAccess.Pythia.Api.IPythiaSignatureHelpProviderImplementation
TypeIdentityName: Microsoft.CodeAnalysis.ExternalAccess.Pythia.Api.IPythiaSignatureHelpProviderImplementation
but found 0.
part definition Microsoft.CodeAnalysis.ExternalAccess.Pythia.PythiaSignatureHelpProvider
Microsoft.VisualStudio.Copilot.Roslyn.Completion.CSharpReferencedSymbolDefinitionSnippetProvider.ctor(joinableTaskContext): expected exactly 1 export matching constraints:
Contract name: Microsoft.VisualStudio.Threading.JoinableTaskContext
TypeIdentityName: Microsoft.VisualStudio.Threading.JoinableTaskContext
but found 0.
part definition Microsoft.VisualStudio.Copilot.Roslyn.Completion.CSharpReferencedSymbolDefinitionSnippetProvider
Microsoft.VisualStudio.Copilot.Roslyn.Completion.CSharpMethodCallerBlueprintProvider.ctor(joinableTaskContext): expected exactly 1 export matching constraints:
Contract name: Microsoft.VisualStudio.Threading.JoinableTaskContext
TypeIdentityName: Microsoft.VisualStudio.Threading.JoinableTaskContext
but found 0.
part definition Microsoft.VisualStudio.Copilot.Roslyn.Completion.CSharpMethodCallerBlueprintProvider
Microsoft.VisualStudio.Copilot.Roslyn.Completion.CSharpMemberAccessSymbolBlueprintProvider.ctor(joinableTaskContext): expected exactly 1 export matching constraints:
Contract name: Microsoft.VisualStudio.Threading.JoinableTaskContext
TypeIdentityName: Microsoft.VisualStudio.Threading.JoinableTaskContext
but found 0.
part definition Microsoft.VisualStudio.Copilot.Roslyn.Completion.CSharpMemberAccessSymbolBlueprintProvider
Microsoft.VisualStudio.Composition.CompositionFailedException: Errors exist in the composition.
at Microsoft.VisualStudio.Composition.CompositionConfiguration.ThrowOnErrors()
at Microsoft.CodeAnalysis.Remote.ExportProviderBuilder.CheckForAndReportCompositionErrors(CompositionConfiguration configuration, ComposableCatalog catalog) in /_/src/Workspaces/Remote/Core/ExportProviderBuilder.cs:line 208
Environment data
dotnet --info output:
.NET SDK:
Version: 9.0.110
Commit: 999243871a
Workload version: 9.0.100-manifests.3277c30b
MSBuild version: 17.12.44+999243871
Runtime Environment:
OS Name: ubuntu
OS Version: 24.04
OS Platform: Linux
RID: ubuntu.24.04-x64
Base Path: /usr/lib/dotnet/sdk/9.0.110/
.NET workloads installed:
There are no installed workloads to display.
Configured to use loose manifests when installing new manifests.
Host:
Version: 9.0.9
Architecture: x64
Commit: 999243871a
.NET SDKs installed:
8.0.119 [/usr/lib/dotnet/sdk]
9.0.110 [/usr/lib/dotnet/sdk]
.NET runtimes installed:
Microsoft.AspNetCore.App 8.0.19 [/usr/lib/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 9.0.9 [/usr/lib/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.NETCore.App 8.0.19 [/usr/lib/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 9.0.9 [/usr/lib/dotnet/shared/Microsoft.NETCore.App]
Other architectures found:
None
Environment variables:
DOTNET_ROOT [/usr/share/dotnet]
global.json file:
Not found
Learn more:
https://aka.ms/dotnet/info
Download .NET:
https://aka.ms/dotnet/download
VS Code version: 1.104.1
C# Extension version: 2.93.22
C# logs
C# output window contents:
2025-10-13 09:15:33.931 [info] Locating .NET runtime version 9.0.1
2025-10-13 09:15:34.077 [info] Dotnet path: /usr/lib/dotnet/dotnet
2025-10-13 09:15:34.077 [info] Activating C# + C# Dev Kit...
2025-10-13 09:15:34.533 [info] [stdout] info: Program[0]
Server started with process ID 707470
2025-10-13 09:15:37.003 [info] [stdout] fail: Microsoft.CodeAnalysis.Remote.ExportProviderBuilder[0]
Encountered errors in the MEF composition:
----- CompositionError level 1 ------
Microsoft.CodeAnalysis.ExternalAccess.Copilot.Internal.CodeMapper.CSharpMapCodeService.ctor(service): expected exactly 1 export matching constraints:
Contract name: Microsoft.CodeAnalysis.ExternalAccess.Copilot.CodeMapper.ICSharpCopilotMapCodeService
TypeIdentityName: Microsoft.CodeAnalysis.ExternalAccess.Copilot.CodeMapper.ICSharpCopilotMapCodeService
but found 0.
part definition Microsoft.CodeAnalysis.ExternalAccess.Copilot.Internal.CodeMapper.CSharpMapCodeService
Microsoft.CodeAnalysis.ExternalAccess.Copilot.Internal.SemanticSearch.CopilotSemanticSearchQueryExecutor.ctor(workspaceProvider): expected exactly 1 export matching constraints:
Contract name: Microsoft.CodeAnalysis.Host.IHostWorkspaceProvider
TypeIdentityName: Microsoft.CodeAnalysis.Host.IHostWorkspaceProvider
but found 0.
part definition Microsoft.CodeAnalysis.ExternalAccess.Copilot.Internal.SemanticSearch.CopilotSemanticSearchQueryExecutor
Microsoft.CodeAnalysis.ExternalAccess.Pythia.PythiaSignatureHelpProvider.ctor(implementation): expected exactly 1 export matching constraints:
Contract name: Microsoft.CodeAnalysis.ExternalAccess.Pythia.Api.IPythiaSignatureHelpProviderImplementation
TypeIdentityName: Microsoft.CodeAnalysis.ExternalAccess.Pythia.Api.IPythiaSignatureHelpProviderImplementation
but found 0.
part definition Microsoft.CodeAnalysis.ExternalAccess.Pythia.PythiaSignatureHelpProvider
Microsoft.VisualStudio.Copilot.Roslyn.Completion.CSharpReferencedSymbolDefinitionSnippetProvider.ctor(joinableTaskContext): expected exactly 1 export matching constraints:
Contract name: Microsoft.VisualStudio.Threading.JoinableTaskContext
TypeIdentityName: Microsoft.VisualStudio.Threading.JoinableTaskContext
but found 0.
part definition Microsoft.VisualStudio.Copilot.Roslyn.Completion.CSharpReferencedSymbolDefinitionSnippetProvider
Microsoft.VisualStudio.Copilot.Roslyn.Completion.CSharpMethodCallerBlueprintProvider.ctor(joinableTaskContext): expected exactly 1 export matching constraints:
Contract name: Microsoft.VisualStudio.Threading.JoinableTaskContext
TypeIdentityName: Microsoft.VisualStudio.Threading.JoinableTaskContext
but found 0.
part definition Microsoft.VisualStudio.Copilot.Roslyn.Completion.CSharpMethodCallerBlueprintProvider
Microsoft.VisualStudio.Copilot.Roslyn.Completion.CSharpMemberAccessSymbolBlueprintProvider.ctor(joinableTaskContext): expected exactly 1 export matching constraints:
Contract name: Microsoft.VisualStudio.Threading.JoinableTaskContext
TypeIdentityName: Microsoft.VisualStudio.Threading.JoinableTaskContext
but found 0.
part definition Microsoft.VisualStudio.Copilot.Roslyn.Completion.CSharpMemberAccessSymbolBlueprintProvider
Microsoft.VisualStudio.Composition.CompositionFailedException: Errors exist in the composition.
at Microsoft.VisualStudio.Composition.CompositionConfiguration.ThrowOnErrors()
at Microsoft.CodeAnalysis.Remote.ExportProviderBuilder.CheckForAndReportCompositionErrors(CompositionConfiguration configuration, ComposableCatalog catalog) in /_/src/Workspaces/Remote/Core/ExportProviderBuilder.cs:line 208
2025-10-13 09:15:37.896 [info] [stdout] {"pipeName":"/tmp/4de08c8e.sock"}
2025-10-13 09:15:37.896 [info] received named pipe information from server
2025-10-13 09:15:37.897 [info] client has connected to server
2025-10-13 09:15:38.317 [info] [Program] Language server initialized
2025-10-13 09:15:42.312 [info] [serviceBroker/connect] [WorkspaceProjectFactoryService] Project /persist/code/OpenTsdb-ReadProxy/src/TsdbQueryParser/TsdbQueryParser.csproj loaded by C# Dev Kit
2025-10-13 09:15:42.888 [info] [serviceBroker/connect] [WorkspaceProjectFactoryService] Project /persist/code/OpenTsdb-ReadProxy/src/TsdbReadProxy/TsdbReadProxy.csproj loaded by C# Dev Kit
2025-10-13 09:15:42.896 [info] [serviceBroker/connect] [WorkspaceProjectFactoryService] Project /persist/code/OpenTsdb-ReadProxy/tests/TsdbQueryParser.Test/TsdbQueryParser.Test.csproj loaded by C# Dev Kit
See this page for collecting more detailed logs
Steps to reproduce
- Update C# and C# Dev Kit to latest
- Open a .NET solution
- See error in C# extension logs
Expected behavior
The extension should start cleanly.
Actual behavior
I get the following errors shown above.
Additional context
- I'm using VS Code in Remote (SSH) mode.
- Neither the remote or local side has internet access (apart from a constrained set of URLs for browsing/downloading extensions).