# Ruby — LSP setup (Hermes / LitHermes)

- **Recommended server:** `rubocop --lsp`
- **Extensions:** `.rb .rake .gemspec .ru`
- **Install hint:** `gem install rubocop`

> **Note:** the executable invoked is **`rubocop`** (`rubocop --lsp`). RuboCop must be installed: `gem install rubocop`.

## Install

- **macOS:** `gem install rubocop`
- **Linux:** `gem install rubocop`
- **Windows:** `gem install rubocop`

In a Bundler project, prefer adding `rubocop` to the `Gemfile` and running via `bundle exec`.

Confirm it resolves (check `rubocop`, since that is what runs):

```bash
command -v rubocop
```

## Configure

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

```json
{
  "lsp": {
    "ruby": {
      "command": [
        "rubocop",
        "--lsp"
      ],
      "extensions": [
        ".rb",
        ".rake",
        ".gemspec",
        ".ru"
      ]
    }
  }
}
```

Hermes routes these extensions to `rubocop --lsp` via the `extensions` list. Behavior is
driven by your `.rubocop.yml`; the server surfaces RuboCop diagnostics,
formatting, and code actions over LSP.

## Alternatives

- **Shopify `ruby-lsp`** — the standalone `ruby-lsp` executable, richer navigation than RuboCop alone. Set the `command` to `["ruby-lsp"]`.
- **`solargraph`** — older completion/type server; install with `gem install solargraph`, set the `command` to `["solargraph", "stdio"]`.

## Troubleshooting

- **PATH:** `rubocop` on PATH (that is the invoked binary); reopen shell after install.
- **`rubocop` not found:** install RuboCop with `gem install rubocop`.
- **Bundler mismatch:** if the project pins RuboCop in its `Gemfile`, run inside the bundle so versions match.
- **No diagnostics:** check `.rubocop.yml` is valid and not disabling everything.

## Verify

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