oraios/serena · error · ValueError

Invalid language server identifier: {request_remove_language

Error message

Invalid language server identifier: {request_remove_language.language}

What it means

The remove-language endpoint parses `request_remove_language.language` into a `LanguageServerId` enum. An unknown or misspelled identifier makes the enum constructor raise ValueError, which `_remove_language` re-raises as ValueError('Invalid language server identifier: ...'). The language server is not touched.

Source

Thrown at src/serena/dashboard.py:793

        return {}

    def _add_language(self, request_add_language: RequestAddLanguage) -> None:
        from solidlsp.ls_config import LanguageServerId

        try:
            language = LanguageServerId(request_add_language.language)
        except ValueError:
            raise ValueError(f"Invalid language server identifier: {request_add_language.language}")
        # add_language is already thread-safe
        self._agent.add_language_server(language)

    def _remove_language(self, request_remove_language: RequestRemoveLanguage) -> None:
        from solidlsp.ls_config import LanguageServerId

        try:
            language = LanguageServerId(request_remove_language.language)
        except ValueError:
            raise ValueError(f"Invalid language server identifier: {request_remove_language.language}")
        # remove_language is already thread-safe
        self._agent.remove_language_server(language)

    @staticmethod
    def _find_first_free_port(start_port: int, host: str) -> int:
        port = start_port
        while port <= 65535:
            try:
                with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:
                    sock.bind((host, port))
                    return port
            except OSError:
                port += 1

        raise RuntimeError(f"No free ports found starting from {start_port}")

    def run(self, port: int) -> int:
        """

View on GitHub (pinned to 7fcbca7e62)

Solutions

Pass the exact LanguageServerId enum name as it was accepted by /add_language (list members from solidlsp/ls_config.py to confirm).
Correct casing/spelling in the request body.
Upgrade solidlsp if the identifier is only defined in newer versions.
Echo back the valid identifier list in the error handler so callers self-correct.

Example fix

// before
await fetch(`${dashboard}/remove_language`, {method: "POST", body: JSON.stringify({language: "Python"})});
// after
await fetch(`${dashboard}/remove_language`, {method: "POST", body: JSON.stringify({language: "python"})});

Defensive patterns

Strategy: try-catch

Validate before calling

from solidlsp.ls_config import LanguageServerId
valid = {m.value for m in LanguageServerId}
if lang not in valid:
    raise ValueError(f"Cannot remove {lang!r}; valid: {sorted(valid)}")

Type guard

def is_valid_language(name: str) -> bool:
    try:
        LanguageServerId(name)
        return True
    except ValueError:
        return False

Try / catch

try:
    requests.post(f"{dashboard}/remove_language", json={"language": lang})
except ValueError:
    logger.error("Invalid language identifier %r; use an exact LanguageServerId value", lang)

Prevention

Use the exact same identifier string that add_language accepted.
List LanguageServerId members before writing remove calls.
Keep add/remove language identifiers in a shared constant in automation code.
Check casing and avoid abbreviations ('js', 'ts') — use full enum names.

When it happens

Trigger: Calling the dashboard /remove_language endpoint with a language string not in the LanguageServerId enum — wrong casing ('Python'), abbreviations ('js' instead of 'javascript'), unsupported languages, or a name from a different solidlsp version.

Common situations: Cleanup scripts removing servers added earlier with a different spelling; config drift between the identifier used at add-time and remove-time; users guessing identifier names instead of reading the enum.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

AI-assisted analysis of oraios/serena@7fcbca7e62 (2026-08-29). Data as JSON: /api/errors/7ed520d8ada54bab. Report an issue: GitHub.