oraios/serena · error · ValueError

Invalid JSON in nixd configuration file '{config_path}': {ex

Error message

Invalid JSON in nixd configuration file '{config_path}': {exc.msg} (line {exc.lineno}, column {exc.colno})

What it means

When the config_path file exists but is not valid JSON, json.load raises JSONDecodeError, which _load_nixd_settings converts into a ValueError that includes the file path, the parse message, and the line/column of the syntax error.

Source

Thrown at src/solidlsp/language_servers/nixd_ls.py:259

        :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
    def _resolve_nixd_configuration_section(settings: dict[str, Any], section: object) -> Any:
        """Resolve a ``nixd`` configuration section from the effective settings."""
        if section == "nixd":
            return deepcopy(settings)
        if not isinstance(section, str) or not section.startswith("nixd."):
            return {}

View on GitHub (pinned to 7fcbca7e62)

Solutions

Fix the JSON at the reported line/column (remove trailing commas, comments, or stray characters).
Validate the file with `python -m json.tool <config_path>` before restarting.
Regenerate the file if truncated, or point config_path at a known-good nixd settings file.

Example fix

// before (nixd.json)
{ "nixd": { "formatting": { "command": ["nixfmt"], }, } }
// after
{ "nixd": { "formatting": { "command": ["nixfmt"] } } }

Defensive patterns

Strategy: validation

Validate before calling

import json
from pathlib import Path
p = Path(config_path).expanduser()
json.loads(p.read_text(encoding="utf-8"))  # raises with line/col before server start

Try / catch

try:
    server = NixdLanguageServer(...)
except ValueError as e:
    if "Invalid JSON in nixd configuration file" in str(e):
        restore_valid_config()  # e.g. regenerate or fix the reported line/column
    else:
        raise

Prevention

Validate JSON with `python -m json.tool` after every manual edit.
Never put JSONC comments or trailing commas in nixd config files.
Keep nixd config files under version control to catch truncation/corruption.

When it happens

Trigger: The file at ls_specific_settings.nix.config_path contains a JSON syntax error (trailing comma, comments, single quotes, truncation) and the nixd language server is constructed.

Common situations: Hand-edited nixd config with a trailing comma; writing JSONC-style comments into a .json file; a crashed editor leaving a truncated file; copying YAML into a .json file.

Understand the failure class

Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

AI-assisted analysis of oraios/serena@7fcbca7e62 (2026-08-29). Data as JSON: /api/errors/b9a8a4f1b6384f6a. Report an issue: GitHub.