# C# — LSP setup (Hermes / LitHermes)

- **Recommended server:** `csharp-ls`
- **Extensions:** `.cs`
- **Install hint:** `dotnet tool install -g csharp-ls`

## Install

Requires the **.NET SDK**. Install the tool globally:

- **macOS:** `dotnet tool install -g csharp-ls`
- **Linux:** `dotnet tool install -g csharp-ls`
- **Windows:** `dotnet tool install -g csharp-ls`

Global .NET tools land in `~/.dotnet/tools` — ensure that directory is on PATH (Windows: `%USERPROFILE%\.dotnet\tools`).

Confirm it resolves:

```bash
command -v csharp-ls
```

## Configure

Add a `csharp` entry to the Hermes LSP config under `lsp.<language>`:

```json
{
  "lsp": {
    "csharp": {
      "command": [
        "csharp-ls"
      ],
      "extensions": [
        ".cs"
      ]
    }
  }
}
```

Hermes routes `.cs` edits to `csharp-ls` via the `extensions` list. `csharp-ls` picks up
the nearest `.sln` or `.csproj`; keep the solution restorable (`dotnet restore`).

## Razor / Blazor

Razor and Blazor files use a separate server. Add a second entry:

```json
{
  "lsp": {
    "razor": {
      "command": [
        "roslyn-language-server",
        "--stdio"
      ],
      "extensions": [
        ".razor",
        ".cshtml"
      ]
    }
  }
}
```

Install it (requires **v5.8.0+**; see [dotnet/razor](https://github.com/dotnet/razor)):

```bash
dotnet tool install -g roslyn-language-server --prerelease
command -v roslyn-language-server
```

## Alternatives

**OmniSharp** — legacy C# language server. Still works but is being superseded by
the Roslyn-based servers; prefer `csharp-ls` / `roslyn-language-server`.

## Troubleshooting

- **PATH:** `csharp-ls` / `roslyn-language-server` on PATH (`~/.dotnet/tools`); reopen shell after install.
- **No .NET SDK:** install the SDK (not just the runtime) before installing the tool.
- **No symbols:** run `dotnet restore`; an unrestored solution yields empty results.
- **Razor needs v5.8.0+:** older `roslyn-language-server` builds lack the `--stdio` Razor support — install with `--prerelease`.

## Verify

```bash
node --experimental-strip-types ../../scripts/verify-lsp.ts path/to/File.cs
# or: bun ../../scripts/verify-lsp.ts path/to/File.cs
```