What causes "start_line must be non-negative, got {start_line}" in oraios/serena?

Pass a 0-based, non-negative start_line (first line is 0)

oraios/serena · error · ValueError

start_line must be non-negative, got {start_line}

Error message

start_line must be non-negative, got {start_line}

What it means

Before querying diagnostics, SolidLSP validates arguments in _validate_text_document_diagnostics_request. A negative start_line is invalid because LSP positions are 0-based line numbers, so a ValueError('start_line must be non-negative, ...') is raised.

Source

Thrown at src/solidlsp/ls.py:818

        end_line: int,
        min_severity: int,
    ) -> list[ls_types.Diagnostic]:
        diagnostics = [d for d in diagnostics if cls._diagnostic_matches_range(d, start_line, end_line)]
        diagnostics = [d for d in diagnostics if cls._diagnostic_matches_min_severity(d, min_severity)]
        return diagnostics

    def _validate_text_document_diagnostics_request(
        self,
        relative_file_path: str,
        start_line: int,
        end_line: int,
        min_severity: int,
    ) -> str:
        if not self.server_started:
            log.error("request_text_document_diagnostics called before Language Server started")
            raise SolidLSPException("Language Server not started")
        if start_line < 0:
            raise ValueError(f"start_line must be non-negative, got {start_line}")
        if end_line != -1 and end_line < start_line:
            raise ValueError(f"end_line must be -1 or >= start_line, got {end_line} < {start_line}")
        if min_severity not in {1, 2, 3, 4}:
            raise ValueError(f"min_severity must be one of 1, 2, 3, 4, got {min_severity}")
        return pathlib.Path(str(PurePath(self.repository_root_path, relative_file_path))).as_uri()

    def get_published_diagnostics_generation(self, relative_file_path: str) -> int:
        """
        Get the generation number for the latest published diagnostics of a file.

        :param relative_file_path: The relative path of the file.
        :return: the generation number, or ``-1`` if none were published yet.
        """
        uri = pathlib.Path(str(PurePath(self.repository_root_path, relative_file_path))).as_uri()
        return self._get_published_diagnostics_generation(uri)

    def get_cached_published_text_document_diagnostics(
        self,

View on GitHub (pinned to 7fcbca7e62)

Solutions

Pass a 0-based, non-negative start_line (first line is 0)
Use end_line=-1 to indicate 'to end of file' instead of a negative start_line
Validate/clamp user- or computed-provided line numbers before calling

Example fix

// before
ls.request_text_document_diagnostics("src/a.py", -1, -1, 3)
// after
ls.request_text_document_diagnostics("src/a.py", 0, -1, 3)

Defensive patterns

Strategy: validation

Validate before calling

assert isinstance(start_line, int) and start_line >= 0, f"start_line must be >= 0, got {start_line}"

Prevention

Remember LSP lines are 0-based; first line is 0
Use end_line=-1 (not negative start_line) for 'whole file'
Clamp computed positions: start_line = max(0, start_line)

When it happens

Trigger: Calling request_text_document_diagnostics / request_published_text_document_diagnostics / get_cached_published_text_document_diagnostics with start_line < 0 (e.g. -1 used as a sentinel, or an unsigned conversion bug).

Common situations: Passing -1 to mean 'whole file' (the sentinel is end_line, not start_line); converting unsigned LSP positions with signed overflow; uninitialized/default-initialized position variables.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

AI-assisted analysis of oraios/serena@7fcbca7e62 (2026-08-29). Data as JSON: /api/errors/db44c9f928fa4231. Report an issue: GitHub.