oraios/serena · error · ValueError

ls_specific_settings.nix.config_path must be absolute: {conf

Error message

ls_specific_settings.nix.config_path must be absolute: {config_path_value!r}

What it means

_load_nixd_settings requires config_path to be absolute (after expanduser). Relative paths are rejected with ValueError because the working directory of the language-server process is not guaranteed, making relative config paths ambiguous.

Source

Thrown at src/solidlsp/language_servers/nixd_ls.py:253

    @classmethod
    def _load_nixd_settings(cls, custom_settings: SolidLSPSettings.CustomLSSettings) -> dict[str, Any]:
        """Load nixd settings from ``config_path`` or return the built-in defaults.

        :param custom_settings: Nix-specific language-server settings.
        :return: The value of the nixd configuration section.
        :raises ValueError: If ``config_path`` or its JSON document has an invalid shape.
        :raises RuntimeError: If the configuration file cannot be read.
        """
        config_path_value = custom_settings.get("config_path")
        if config_path_value is None:
            return cls._create_default_nixd_settings()
        if not isinstance(config_path_value, str) or not config_path_value.strip():
            raise ValueError("ls_specific_settings.nix.config_path must be a non-empty absolute path")

        config_path = Path(config_path_value).expanduser()
        if not config_path.is_absolute():
            raise ValueError(f"ls_specific_settings.nix.config_path must be absolute: {config_path_value!r}")

        try:
            with config_path.open(encoding="utf-8") as config_file:
                settings = json.load(config_file)
        except json.JSONDecodeError as exc:
            raise ValueError(
                f"Invalid JSON in nixd configuration file '{config_path}': {exc.msg} (line {exc.lineno}, column {exc.colno})"
            ) from exc
        except OSError as exc:
            raise RuntimeError(f"Failed to read nixd configuration file '{config_path}': {exc}") from exc

        if not isinstance(settings, dict):
            raise ValueError(
                f"Invalid nixd configuration file '{config_path}': expected a JSON object containing the value of the 'nixd' section"
            )
        return settings

    @staticmethod

View on GitHub (pinned to 7fcbca7e62)

Solutions

Use an absolute path, e.g. /home/user/.config/nixd/nixd.json.
A leading ~ is allowed: ~/.config/nixd/nixd.json expands before the absolute check.
In generated configs, resolve the path programmatically (e.g. Path('nixd.json').resolve()) before assigning.

Example fix

// before
ls_specific_settings.nix.config_path = "./nixd.json"
// after
ls_specific_settings.nix.config_path = "/home/user/.config/nixd/nixd.json"

Defensive patterns

Strategy: validation

Validate before calling

from pathlib import Path
p = Path(config_path).expanduser()
assert p.is_absolute(), f"config_path must be absolute: {config_path}"

Try / catch

try:
    server = NixdLanguageServer(...)
except ValueError as e:
    if "must be absolute" in str(e):
        settings["ls_specific_settings"]["nix"]["config_path"] = str(Path(old_value).expanduser().resolve())
        server = NixdLanguageServer(...)
    else:
        raise

Prevention

Always store absolute paths (or ~/...) in config_path.
Resolve relative paths programmatically with Path(...).resolve() before assignment.
Remember ~ is expanded, ./ and ../ are not accepted.

When it happens

Trigger: Setting ls_specific_settings.nix.config_path to a relative path such as "nixd.json" or "./config/nixd.json" and initializing the server.

Common situations: Users copying settings between machines/projects where cwd differs; assuming the config resolves relative to the project root; tilde paths are fine (~ expands) but ./ paths are not.

Understand the failure class

Background: Config validation failed: what "invalid value for {key}" and settings-rejection errors mean across 19 open-source libraries — this error's family across 19 libraries.

Related errors

AI-assisted analysis of oraios/serena@7fcbca7e62 (2026-08-29). Data as JSON: /api/errors/1332744384a6d65c. Report an issue: GitHub.