sifr lsp: Language Server Protocol Support for Sifr

Sifr includes a native Language Server Protocol (LSP) server that gives your editor real-time feedback as you write code. Once configured, your editor gets type-checking diagnostics, completions, hover documentation, go-to-definition, formatting, and more — all powered by the same compiler that runs sifr check and sifr build.

Starting the language server

Launch the language server over stdio:

sifr lsp --stdio

The --stdio flag is required. The server reads JSON-RPC messages from stdin and writes responses to stdout. Your editor’s LSP client is responsible for launching and managing the process. An optional --parent-pid flag tells the server to exit when the specified process is no longer alive:

sifr lsp --stdio --parent-pid 12345

Most editor integrations pass this automatically.

sifr lsp --stdio is the only supported transport in the current release. Socket and pipe transports are not yet available.

What the language server provides

Capability	Description
Diagnostics	Hard compiler errors and policy-rule warnings, pushed to the editor as you type.
Completions	Context-aware identifier and keyword completions.
Hover	Type information and documentation for the symbol under the cursor.
Go-to-definition	Jump to the definition of any symbol in your project.
Formatting	Document and range formatting backed by the Sifr formatter.
Code actions	Safe-fix application and inline suppression for policy diagnostics.
Inlay hints	Inline type annotations and parameter labels shown in the editor gutter.
Semantic tokens	Rich syntax highlighting based on the compiler’s understanding of your code.
Folding ranges	Code folding regions for functions, classes, and other block-level constructs.
Selection range	Expand and shrink selection by syntax node boundaries.
Type hierarchy	Navigate supertypes and subtypes for any named type in your project.

Diagnostics

The language server publishes two kinds of diagnostics:

Hard diagnostics — compiler errors from parsing and type-checking. These cannot be suppressed with inline comments and are marked as hard in the diagnostic metadata.
Policy diagnostics — lint-rule violations from sifr lint. These are marked as policy and include the Sifr rule ID. Editors may offer suppression and safe-fix code actions for policy diagnostics only.

Fix-all is policy-only, safe by default, and deferred through codeAction/resolve. The server rejects a fix if the document version changed between the time the action was offered and the time it is resolved.

Formatting

The language server advertises formatting support when sifr.format.enable is true in your editor configuration. Editors should request formatting through standard LSP methods (textDocument/formatting and textDocument/rangeFormatting) rather than invoking sifr fmt as a shell command.

Editor integrations must not call sifr fmt as their primary document-formatting provider. LSP-based formatting through sifr lsp --stdio is the correct integration point. Calling sifr fmt directly from an editor bypasses the server’s document-version tracking and can conflict with in-flight edits.

Configuring your editor

VS Code

The protected stable activation publishes and verifies the exact qualified sifr.sifr-vscode version 0.2.0 in the VS Code Marketplace without rebuilding it. After activation, install that governed package by its Marketplace identifier:

code --install-extension sifr.sifr-vscode

The extension automatically locates sifr on your PATH and launches sifr lsp --stdio when you open a .sifr file. To point the extension at a custom binary:

{
  "sifr.lsp.path": "/path/to/sifr"
}

Neovim

Use nvim-lspconfig with a manual server definition. Add the following to your Neovim configuration:

local lspconfig = require('lspconfig')
local configs = require('lspconfig.configs')

if not configs.sifr then
  configs.sifr = {
    default_config = {
      cmd = { 'sifr', 'lsp', '--stdio' },
      filetypes = { 'sifr' },
      root_dir = lspconfig.util.root_pattern('sifr.toml', '.git'),
      settings = {},
    },
  }
end

lspconfig.sifr.setup {}

Add a filetype detection autocmd if your editor does not recognise .sifr files automatically:

vim.filetype.add({ extension = { sifr = 'sifr' } })

Helix

Add a language entry to your languages.toml:

[[language]]
name = "sifr"
scope = "source.sifr"
file-types = ["sifr"]
roots = ["sifr.toml"]
language-servers = ["sifr"]

[language-server.sifr]
command = "sifr"
args = ["lsp", "--stdio"]

Zed

Add a language server entry in your Zed settings:

{
  "languages": {
    "Sifr": {
      "language_servers": ["sifr"]
    }
  },
  "lsp": {
    "sifr": {
      "binary": {
        "path": "sifr",
        "arguments": ["lsp", "--stdio"]
      }
    }
  }
}

Emacs

Use eglot (built into Emacs 29+) or lsp-mode. With eglot:

(add-to-list 'eglot-server-programs
             '(sifr-mode . ("sifr" "lsp" "--stdio")))

(add-hook 'sifr-mode-hook #'eglot-ensure)

Keeping `sifr` on your PATH

Every editor integration listed above discovers sifr by searching your PATH. If you installed Sifr with the official installer, ~/.sifr/bin is added to your shell profile automatically. Verify that the binary is reachable:

which sifr
sifr --version

If your editor cannot find sifr, configure the full binary path explicitly with sifr.lsp.path in VS Code or the command/path option shown in the other editor examples above.

Run sifr lsp --stdio manually in a terminal and confirm it starts without error before troubleshooting editor connectivity. A clean startup means the binary is working; the issue is likely a path or editor configuration problem.

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sifr lsp: Language Server Protocol Support for Sifr

Starting the language server

What the language server provides

Diagnostics

Formatting

Configuring your editor

VS Code

Neovim

Helix

Zed

Emacs

Keeping `sifr` on your PATH

​Starting the language server

​What the language server provides

​Diagnostics

​Formatting

​Configuring your editor

​VS Code

​Neovim

​Helix

​Zed

​Emacs

​Keeping sifr on your PATH

Starting the language server

What the language server provides

Diagnostics

Formatting

Configuring your editor

VS Code

Neovim

Helix

Zed

Emacs

Keeping `sifr` on your PATH