langflow-ai/langflow · error · SystemExit

error: invalid JSON in {source}: {exc}

Error message

error: invalid JSON in {source}: {exc}

What it means

Printed and raised (exit code 2) by _parse in check_migration_append_only.py when json.loads fails on the migration-table JSON — either the current working-tree file or the baseline blob fetched via `git show`. The message includes the source label and the JSONDecodeError so you can tell which side is malformed.

Source

Thrown at scripts/migrate/check_migration_append_only.py:93

        raise SystemExit(msg) from None
    if completed.returncode != 0:
        # Most likely: file not present at base ref.  We treat that as
        # "no baseline" and return None.
        return None
    return completed.stdout


def _parse(raw: str, *, source: str) -> tuple[list[dict], list[dict]]:
    """Return ``(entries, ambiguous_bare_names)`` from a migration-table JSON.

    Both lists default to empty when the field is absent so this script can
    compare across baselines that pre-date a given field.
    """
    try:
        data = json.loads(raw)
    except json.JSONDecodeError as exc:
        print(f"error: invalid JSON in {source}: {exc}", file=sys.stderr)
        raise SystemExit(2) from exc
    if not isinstance(data, dict):
        print(f"error: {source} top-level value must be an object", file=sys.stderr)
        raise SystemExit(2)
    entries = data.get("entries", [])
    if not isinstance(entries, list):
        print(f"error: {source} entries field must be a list", file=sys.stderr)
        raise SystemExit(2)
    ambig = data.get("ambiguous_bare_names", [])
    if not isinstance(ambig, list):
        print(f"error: {source} ambiguous_bare_names field must be a list", file=sys.stderr)
        raise SystemExit(2)
    return entries, ambig


def _compare(baseline: list[dict], current: list[dict]) -> list[str]:
    """Return human-readable violations; empty list means clean."""
    violations: list[str] = []
    current_by_key: dict[tuple[str, str], dict] = {}

View on GitHub (pinned to 976ec789d2)

Solutions

1. Identify which source is bad from the message's {source} label, then run it through a JSON validator or `python -m json.tool <file>`
2. Fix syntax issues: trailing commas, unquoted keys, smart quotes, unclosed brackets
3. If the baseline (git ref) is corrupt, compare against an earlier known-good ref or fix the file and amend the commit
4. Re-run the script to confirm it parses both sides before trusting the append-only comparison

Example fix

# before
python -m json.tool migrations.json  # reveals: Expecting ',' delimiter
# fix the reported line, e.g. remove trailing comma:
{"entries": [{"name": "0001"},]},

# after
{"entries": [{"name": "0001"}]}

import json
json.loads(open("path/to/migration_table.json").read())  # raises before the script if malformed
# CI gate: python -m json.tool migrations/*.json

# shell: validate before running the checker
python -m json.tool migrations/migration_table.json > /dev/null \
  && python scripts/migrate/check_migration_append_only.py

When it happens

Trigger: Hand-editing the migration-table JSON and leaving a trailing comma / stray character; or the baseline version at the compared git ref being corrupt (e.g. a merge artifact), causing `git show` to return invalid JSON.

Common situations: Manual edits to migration tables without running a JSON validator; CRLF or BOM introduced by Windows editors; conflict resolution that leaves duplicate keys or fragments in the 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

• error: {source} top-level value must be an object
• git is not available; cannot check append-only invariant.
• Invalid flow data
• Invalid JSON format.
• No valid MCP server found in the input.

AI-assisted analysis of langflow-ai/langflow@976ec789d2 (2026-08-14). Data as JSON: /api/errors/de049307204965be. Report an issue: GitHub.