Hmbown/CodeWhale · error · RuntimeContractError

measurement emitted invalid JSON

Error message

measurement emitted invalid JSON: {error}

What it means

After the measurement subprocess succeeds, run_measurement parses its stdout as JSON to obtain the receipt. If json.loads raises JSONDecodeError — the measurement printed warnings, logs, or partial output mixed with the JSON — the checker raises RuntimeContractError chaining the parse error. This isolates the contract so a malformed receipt never reaches validation.

Solutions

1. Inspect the raw stdout shown in the JSONDecodeError context; remove stray non-JSON output (debug prints) from the measurement script.
2. Re-run the measurement to rule out truncation or interruption.
3. In measure-runtime-contract.py, send diagnostics to stderr and reserve stdout exclusively for the JSON document.
4. Validate the script's output manually: `python3 scripts/measure-runtime-contract.py | python3 -m json.tool`.

Example fix

# before (measure script)
print("measuring...")
print(json.dumps(receipt))
# after
print("measuring...", file=sys.stderr)
print(json.dumps(receipt))

import json
raw = subprocess.run(["python3", "scripts/measure-runtime-contract.py"], capture_output=True, text=True).stdout
json.loads(raw)  # fails fast with position info before the checker runs

def is_parseable_json(text: str) -> bool:
    import json
    try:
        json.loads(text)
        return True
    except json.JSONDecodeError:
        return False

try:
    receipt = json.loads(proc.stdout)
except json.JSONDecodeError as e:
    print(f"non-JSON stdout at line {e.lineno} col {e.colno}: {e.msg}", file=sys.stderr)
    print(proc.stdout[:500], file=sys.stderr)

When it happens

Trigger: measure-runtime-contract.py writes anything other than pure JSON to stdout (progress prints, cargo warnings captured into stdout, a panic message after exit 0 is impossible but partial writes on crash paths), producing unparseable stdout.

Common situations: A modified measure script added a print() for debugging; some environment hook or wrapper emitted banner text; the JSON was truncated by an interrupted run or pipe buffering issue.

Understand the failure class

Background: JSON parse error: "Unexpected token" / "not valid JSON" / "failed to parse" — what JSON parsers are really complaining about — this error's family across 45 libraries.

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

Related errors

• Cannot parse portable data; use JSON for OpenCode or plain…
• <dynamic: wrapped serde_json parse error>
• measurement emitted invalid JSON
• measurement top level must be an object
• runtime-contract measurement failed with exit code

AI-assisted analysis of Hmbown/CodeWhale@433685b202 (2026-09-15). Data as JSON: /api/errors/d5811f5eafd4ea60. Report an issue: GitHub.

Appendix: source

Thrown at scripts/check-runtime-contract-budget.py:418

    env["CARGO_NET_OFFLINE"] = "true"
    proc = subprocess.run(
        [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

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