oraios/serena · error · FileNotFoundError

elm-language-server executable not found at {elm_ls_executab

Error message

elm-language-server executable not found at {elm_ls_executable_path}, something went wrong with the installation.

What it means

Serena manages the elm-language-server binary under a managed-dependencies directory. After attempting to install the language server (and Elm compiler if missing), _setup_runtime_dependencies checks the executable exists; if not, installation failed silently and it raises FileNotFoundError indicating the install went wrong.

Source

Thrown at src/solidlsp/language_servers/elm_language_server.py:126

        )

        # legacy unversioned dir reserved for INITIAL pair; any other version combination goes into a versioned subdir
        is_initial = (
            elm_language_server_version == INITIAL_ELM_LANGUAGE_SERVER_VERSION and elm_compiler_version == INITIAL_ELM_COMPILER_VERSION
        )
        ls_dirname = "elm-lsp" if is_initial else f"elm-lsp-{elm_language_server_version}-{elm_compiler_version}"
        elm_ls_dir = os.path.join(cls.ls_resources_dir(solidlsp_settings), ls_dirname)
        elm_ls_executable_path = os.path.join(elm_ls_dir, "node_modules", ".bin", "elm-language-server")
        if not os.path.exists(elm_ls_executable_path):
            log.info(f"Elm Language Server executable not found at {elm_ls_executable_path}. Installing...")
            with LogTime("Installation of Elm language server dependencies", logger=log):
                deps.install(elm_ls_dir)
        elif not system_elm:
            log.info("Elm compiler not found on PATH. Installing a managed Elm compiler...")
            with LogTime("Installation of Elm compiler dependency", logger=log):
                deps.install(elm_ls_dir)

        if not os.path.exists(elm_ls_executable_path):
            raise FileNotFoundError(
                f"elm-language-server executable not found at {elm_ls_executable_path}, something went wrong with the installation."
            )
        return [elm_ls_executable_path, "--stdio"]

    def _create_base_initialize_params(self) -> dict:
        """
        Returns the initialize params for the Elm Language Server.
        """
        initialize_params = {
            "locale": "en",
            "capabilities": {
                "textDocument": {
                    "synchronization": {"didSave": True, "dynamicRegistration": True},
                    "completion": {"dynamicRegistration": True, "completionItem": {"snippetSupport": True}},
                    "definition": {"dynamicRegistration": True},
                    "references": {"dynamicRegistration": True},
                    "documentSymbol": {

View on GitHub (pinned to 7fcbca7e62)

Solutions

Delete Serena's managed elm-language-server directory (the elm_ls_dir under the managed dependencies cache) and retry so a fresh install runs
Ensure Node.js and npm are installed and on PATH (node --version, npm --version), then restart Serena
Check network/proxy settings if the download failed (set HTTPS_PROXY etc.)
Verify file permissions on the managed dependencies directory allow writing

Example fix

// before
$ rm -rf ~/.serena/language_servers/static/elm-language-server   # partially installed
// after
$ rm -rf ~/.serena/language_servers/static/elm-language-server   # force clean reinstall
$ # restart Serena; it re-downloads and validates the executable

Defensive patterns

Strategy: try-catch

Validate before calling

import os
def elm_ls_installed(managed_dir: str) -> bool:
    exe = os.path.join(managed_dir, "node_modules", ".bin", "elm-language-server")
    return os.path.exists(exe) and os.access(exe, os.X_OK)

Type guard

def executable_exists(path: str) -> bool:
    import os
    return os.path.isfile(path) and os.access(path, os.X_OK)

Try / catch

try:
    server = LanguageServer.create(LanguageServerId.ELM, ...)
except FileNotFoundError as e:
    logger.error("Elm LS install broken: %s", e)
    clear_managed_deps_dir_and_retry()  # wipe cache and let Serena reinstall

Prevention

Ensure Node.js and npm are on PATH before starting Serena
Allow network access to npm registries (configure proxies)
Never partially delete the managed language-server cache; remove whole dirs
Verify disk space and write permissions in the managed dependencies directory

When it happens

Trigger: Starting the Elm language server when the managed elm-language-server executable is absent at the expected path after deps.install(elm_ls_dir) ran — download failure, wrong Node/npm setup, partial install, or corrupted dependency directory.

Common situations: Offline/proxied environments where the npm download fails; global npm misconfiguration; deleting or wiping Serena's managed language-server cache directory mid-install; running as a user without write permission to the install directory.

Related errors

AI-assisted analysis of oraios/serena@7fcbca7e62 (2026-08-29). Data as JSON: /api/errors/3dea237b50ef7753. Report an issue: GitHub.