Hmbown/CodeWhale · error · RuntimeContractError

measurement top level must be an object

Error message

measurement top level must be an object

What it means

The measurement stdout parsed as valid JSON, but the top-level value is not an object (dict) - for example an array, a bare string, or a number. run_measurement() requires a top-level object because validate_receipt() navigates keys like document_kind and tool_catalog. Distinct from error 211, which covers stdout that is not JSON at all.

Source

Thrown at scripts/check-runtime-contract-budget.py:413

        [sys.executable, str(MEASURE_SCRIPT)],
        cwd=REPO_ROOT,
        env=env,
        capture_output=True,
        text=True,
        check=False,
    )
    sys.stderr.write(proc.stderr)
    if proc.returncode != 0:
        sys.stdout.write(proc.stdout)
        raise RuntimeContractError(
            f"runtime-contract measurement failed with exit code {proc.returncode}"
        )
    try:
        receipt = json.loads(proc.stdout)
    except json.JSONDecodeError as error:
        raise RuntimeContractError(f"measurement emitted invalid JSON: {error}") from error
    if not isinstance(receipt, dict):
        raise RuntimeContractError("measurement top level must be an object")
    validate_receipt(receipt)
    return receipt


def update_command(receipt_path: Path | None, budget_path: Path) -> str:
    parts = ["python3", "scripts/check-runtime-contract-budget.py"]
    if receipt_path is not None:
        parts.extend(["--receipt", str(receipt_path)])
    if budget_path != BUDGET_PATH:
        parts.extend(["--budget", str(budget_path)])
    parts.append("--update")
    return shlex.join(parts)


FRAGMENT_MODULE = REPO_ROOT / "crates" / "core" / "src" / "fragments.rs"
FRAGMENT_MAX_TOKENS_CEILING = 10_000
FRAGMENT_MAX_BYTES_CEILING = FRAGMENT_MAX_TOKENS_CEILING * 4
FRAGMENT_DEFAULT_MAX_BYTES_CEILING = 4 * 1024

View on GitHub (pinned to 8880682c63)

Solutions

1. Make the measure script print exactly one top-level JSON object and nothing else on stdout
2. If you need multiple documents, wrap them in an object keyed by purpose rather than a top-level array
3. Check the emitted shape first: python3 -c "import json,sys;print(type(json.load(sys.stdin)))" < out.json

Example fix

# before (scripts/measure-runtime-contract.py)
print(json.dumps([receipt]))

# after
print(json.dumps(receipt))

import json


def measurement_emits_object() -> bool:
    proc = subprocess.run(
        [sys.executable, "scripts/measure-runtime-contract.py"],
        capture_output=True,
        text=True,
    )
    if proc.returncode != 0:
        return False
    try:
        return isinstance(json.loads(proc.stdout), dict)
    except json.JSONDecodeError:
        return False

import json

def parses_to_json_object(stdout: str) -> bool:
    try:
        return isinstance(json.loads(stdout), dict)
    except json.JSONDecodeError:
        return False

When it happens

Trigger: A measure script change that emits a list of receipts or a JSON scalar; a wrapper that outputs a JSON array of log lines; hand-fabricated measurement output for testing the checker.

Common situations: Refactoring measure-runtime-contract.py's serialization and accidentally wrapping the receipt in a list; piping through jq without the leading '.' selection; test harnesses that emit NDJSON (one object per line), which parses as error 211 unless wrapped in [...], and then fails here.

Related errors

• measurement emitted invalid JSON: {error}
• measurement receipt must be an object
• {kind} metric `{dotted}` must be a non-negative integer
• measurement emitted invalid JSON: {error}
• rss_during_delta_bytes is inconsistent

AI-assisted analysis of Hmbown/CodeWhale@8880682c63 (2026-08-16). Data as JSON: /api/errors/74abeca03f99212a. Report an issue: GitHub.