C# LSP

C# code intelligence via csharp-ls — a lightweight Roslyn-based language server.

Capabilities

• Go-to-definition: Jump to symbol definitions across solution
• Find references: Locate all usages of a symbol
• Hover info: Type signatures, XML docs, parameter info
• Diagnostics: Real-time compiler errors and warnings
• Document symbols: List classes, methods, properties in a file
• Workspace symbol search: Find symbols across the entire solution

Supported extensions: .cs, .csx

Prerequisites

• .NET SDK (9.0+): https://dot.net/download
• Python 3: Required to run the lsp-query daemon
• .sln or .csproj: Project file is required (loose .cs files give limited results)

Setup

Run the one-time setup script (idempotent — safe to re-run):

bash {baseDir}/scripts/setup.sh           # setup only
bash {baseDir}/scripts/setup.sh --verify  # setup + verification test

What it does:

1. Checks for .NET SDK
2. Installs csharp-ls via dotnet tool install --global
3. Registers ~/.dotnet/tools in PATH
4. Creates lsp-query symlink
5. Creates cache directory

Usage

# Set workspace to the directory containing .sln/.csproj
export LSP_WORKSPACE=/path/to/project

# Go to definition
lsp-query definition src/Program.cs 15 8

# Find all references
lsp-query references src/Models/User.cs 42 10

# Type info / hover
lsp-query hover src/Services/AuthService.cs 30 22

# List symbols in a file
lsp-query symbols src/Program.cs

# Search symbols across workspace
lsp-query workspace-symbols "UserService"

# Compiler diagnostics
lsp-query diagnostics src/Program.cs

# Check running servers
lsp-query servers

# Shut down daemon
lsp-query shutdown

Line/column numbers are 1-indexed.

Architecture

lsp-query CLI → Unix Socket → lsp-query daemon (Python)
                                   ↓
                              csharp-ls (subprocess, stdin/stdout JSON-RPC)
                                   ↓
                              Roslyn (.sln → full type system)

• Daemon: Auto-forks on first call. Shuts down after 5 min idle.
• csharp-ls: Starts on first C# query. Shuts down after 5 min idle.
• Cold start: Solution loading takes 30–60s for large projects. Subsequent queries ~200ms.

Project Detection

1. Solution file (.sln) — best: enables cross-project references
2. Project file (.csproj) — good: single project analysis
3. Loose .cs files — limited: basic syntax only

What's Included

{baseDir}/
├── SKILL.md              # This file
└── scripts/
    ├── setup.sh          # One-time setup (idempotent)
    └── lsp-query.py      # LSP daemon + CLI (self-contained)

Troubleshooting

• Install fails (DotnetToolSettings.xml): Pin version with dotnet tool install --global csharp-ls --version 0.20.0
• Empty results: Check that LSP_WORKSPACE points to a directory with .sln or .csproj
• Slow first query: Normal — Roslyn project loading takes 30–60s for large solutions
• PATH issues: Add export PATH="$PATH:$HOME/.dotnet/tools" to your shell profile
• Stale daemon: Run lsp-query shutdown and retry

Links

• csharp-ls on GitHub
• .NET SDK Downloads
• LSP Specification