C# extension doesn't work under devcontainer

Environment data

`dotnet --info` output:

b09f71e2c0a6:/_workspace# dotnet --info
.NET SDK (reflecting any global.json):
 Version:   5.0.400
 Commit:    d61950f9bf

Runtime Environment:
 OS Name:     alpine
 OS Version:  3.13
 OS Platform: Linux
 RID:         linux-musl-x64
 Base Path:   /usr/share/dotnet/sdk/5.0.400/

Host (useful for support):
  Version: 5.0.9
  Commit:  208e377a53

.NET SDKs installed:
  5.0.400 [/usr/share/dotnet/sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 5.0.9 [/usr/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 5.0.9 [/usr/share/dotnet/shared/Microsoft.NETCore.App]

To install additional .NET runtimes or SDKs:
  https://aka.ms/dotnet-download  

VS Code version: 1.59.1 C# Extension version: v1.23.15

OmniSharp log

`"omnisharp.loggingLevel": "debug",`

Starting OmniSharp server at 9/3/2021, 11:20:48 AM
    Target: /_workspace/_dumps.sln

OmniSharp server started.
    Path: /root/.vscode-server/extensions/ms-dotnettools.csharp-1.23.15/.omnisharp/1.37.15/run
    PID: 13284

[ERROR] Error: OmniSharp server load timed out. Use the 'omnisharp.projectLoadTimeout' setting to override the default delay (one minute).

Steps to reproduce

1. dotnet new console
2. Create dev container (I tried 5.0.400-alpine3.13 and 5.0.400-buster-slim dotnet sdk images)
3. Open dev container environment
4. Install C# extension there

Expected behavior

Omnisharp is started under a dev container

Actual behavior

Omnisharp doesn’t start.

Additional error output

ps -a
PID   USER     TIME  COMMAND
    1 root      0:00 /bin/sh -c echo Container started trap "exit 0" 15  while sleep 1 & wait $!; do :; done
   92 root      0:00 /root/.vscode-server/bin/3866c3553be8b268c8a7f8c0482c0c0177aa8bfa/node /tmp/vscode-remote-containers-server-21929b26aee4891be33964a51c53d19882a636df.js
  109 root      0:00 sh /root/.vscode-server/bin/3866c3553be8b268c8a7f8c0482c0c0177aa8bfa/server.sh --log debug --force-disable-user-env --use-host-proxy --disable-telemetry --port 0 --extensions-download-dir /root/.vscode-server/extensionsCache --start-server --disable-websocket-compression
  111 root      0:06 /root/.vscode-server/bin/3866c3553be8b268c8a7f8c0482c0c0177aa8bfa/node /root/.vscode-server/bin/3866c3553be8b268c8a7f8c0482c0c0177aa8bfa/out/vs/server/main.js --log debug --force-disable-user-env --use-host-proxy --disable-telemetry --port 0 --extensions-download-dir /root/.vscode-server/e
  143 root      0:02 /vscode/vscode-server/bin/alpine/3866c3553be8b268c8a7f8c0482c0c0177aa8bfa/node /vscode/vscode-server/bin/alpine/3866c3553be8b268c8a7f8c0482c0c0177aa8bfa/out/bootstrap-fork --type=ptyHost
 9401 root      0:00 /root/.vscode-server/bin/3866c3553be8b268c8a7f8c0482c0c0177aa8bfa/node /tmp/vscode-remote-containers-server-1bd12ce1f85f8aeebaf5402d837160af3889198b.js
 9646 root      0:00 /bin/sh
12857 root      0:00 /bin/sh
12878 root      0:00 /bin/sh
13100 root      0:00 /root/.vscode-server/bin/3866c3553be8b268c8a7f8c0482c0c0177aa8bfa/node /tmp/vscode-remote-containers-server-9d32d59ba578629e8bb99396c91218d9a591fb35.js
13142 root      0:00 /root/.vscode-server/bin/3866c3553be8b268c8a7f8c0482c0c0177aa8bfa/node -e      const net = require('net');     process.stdin.pause();     const client = net.createConnection({ port: 41955 }, () => {      client.pipe(process.stdout);      process.stdin.pipe(client);     });     client.on('c
13162 root      0:00 /vscode/vscode-server/bin/alpine/3866c3553be8b268c8a7f8c0482c0c0177aa8bfa/node /vscode/vscode-server/bin/alpine/3866c3553be8b268c8a7f8c0482c0c0177aa8bfa/out/bootstrap-fork --type=watcherService
13173 root      0:00 /root/.vscode-server/bin/3866c3553be8b268c8a7f8c0482c0c0177aa8bfa/node -e      const net = require('net');     process.stdin.pause();     const client = net.createConnection({ port: 41955 }, () => {      client.pipe(process.stdout);      process.stdin.pipe(client);     });     client.on('c
13190 root      0:01 /vscode/vscode-server/bin/alpine/3866c3553be8b268c8a7f8c0482c0c0177aa8bfa/node /vscode/vscode-server/bin/alpine/3866c3553be8b268c8a7f8c0482c0c0177aa8bfa/out/bootstrap-fork --type=extensionHost --uriTransformerPath=/vscode/vscode-server/bin/alpine/3866c3553be8b268c8a7f8c0482c0c0177aa8bfa/ou
13305 root      0:00 /vscode/vscode-server/bin/alpine/3866c3553be8b268c8a7f8c0482c0c0177aa8bfa/node /vscode/vscode-server/bin/alpine/3866c3553be8b268c8a7f8c0482c0c0177aa8bfa/extensions/json-language-features/server/dist/node/jsonServerMain --node-ipc --clientProcessId=13190
13346 root      0:00 /bin/ash
13356 root      0:00 sleep 1
13357 root      0:00 ps -a

[nohwnd]

Perfect, thanks for letting me know. We looked at this in our triage yesterday, and were surprised by this error: Unknown language in contributes.csharp.language. Provided value: csharp because that looks like something that should not happen.

/fyi @JoeRobich

[vchirikov]

@nohwnd, now I use official bootstrap scripts microsoft/vscode-dev-containers and C# extension loads correctly (you still need to install gcompat on Alpine though).

For history, the solution is here: https://github.com/vchirikov/dotnet-dumps-devcontainer