oraios/serena · error · SolidLSPException

Failed to initialize F# language server for {self.repository

Error message

Failed to initialize F# language server for {self.repository_root_path}: {e}

What it means

SolidLSPException raised when the LSP 'initialize' request sent to the F# language server (fsautocomplete) fails or times out. The library wraps any exception from self.server.send.initialize() to add context about which repository root failed. It indicates the F# server process started but never completed the LSP handshake.

Source

Thrown at src/solidlsp/language_servers/fsharp_language_server.py:422

        self.server.on_request("window/workDoneProgress/create", handle_work_done_progress_create)

        log.info("Starting FsAutoComplete F# language server process")

        try:
            self.server.start()
        except Exception as e:
            log.error(f"Failed to start F# language server process: {e}")
            raise SolidLSPException(f"Failed to start F# language server: {e}")

        # Send initialization
        initialize_params = self._create_initialize_params()

        log.info("Sending initialize request to F# language server")
        try:
            self.server.send.initialize(initialize_params)
            log.debug("Received initialize response from F# language server")
        except Exception as e:
            raise SolidLSPException(f"Failed to initialize F# language server for {self.repository_root_path}: {e}") from e

        # Complete initialization
        self.server.notify.initialized({})

        log.info("F# language server initialized successfully")

    @override
    def _get_wait_time_for_cross_file_referencing(self) -> float:
        """
        F# projects can be large and may need more time for cross-file analysis.
        """
        return 15.0  # 15 seconds should be sufficient for most F# projects

View on GitHub (pinned to 7fcbca7e62)

Solutions

1. Run `dotnet tool list -g` / reinstall fsautocomplete (`dotnet tool install --global fsautocomplete`) and verify `fsautocomplete --version` works
2. Verify the target F# project builds (`dotnet build`) — broken fsproj/sln files crash the server during initialize
3. Increase the LSP startup timeout in the environment to rule out slow first-run .NET JIT/restore
4. Reproduce manually by launching fsautocomplete and sending an initialize request; inspect stderr for the underlying exception

Example fix

// before (no version pin, broken tool)
dotnet tool install --global fsautocomplete
// after (reinstall clean and verify)
dotnet tool uninstall --global fsautocomplete
dotnet tool install --global fsautocomplete
fsautocomplete --version

import shutil, subprocess
def ensure_fsautocomplete_ready():
    if not shutil.which('fsautocomplete'):
        raise FileNotFoundError('fsautocomplete not on PATH')
    subprocess.run(['dotnet', '--version'], check=True, capture_output=True)

def is_fsharp_project(root: str) -> bool:
    import os
    return os.path.isdir(root) and any(f.endswith(('.fsproj', '.sln')) for f in os.listdir(root))

from solidlsp import SolidLSPException
try:
    ls = FsharpLanguageServer(repo_root, ...)
    ls.start()
except SolidLSPException as e:
    log.error(f'F# LS init failed: {e}')  # inspect underlying Exception via e.__cause__

When it happens

Trigger: Calling _start_server for an F# project when the fsautocomplete process crashes during startup, the initialize request times out, or the server writes an invalid JSON-RPC response.

Common situations: Broken .NET/F# toolchain installation, incompatible fsautocomplete version, corrupted project files (fsproj) that crash the compiler service on startup, or resource exhaustion killing the server process mid-initialize.

Related errors

• Unhandled document change kind: {change}; Please report to S
• Failed to start {len(exceptions)} language server(s): {failu
• The language server manager is not initialized, indicating a
• Language server is missing required capabilities: {', '.join
• Failed to start F# language server: {e}

AI-assisted analysis of oraios/serena@7fcbca7e62 (2026-08-29). Data as JSON: /api/errors/e8af0e1b739013d6. Report an issue: GitHub.