coverage_diff.py

import json
import os
import sys

def load(path):
    if not os.path.exists(path):
        raise RuntimeError(f"Missing coverage export: {path}")
    if os.path.getsize(path) == 0:
        raise RuntimeError(f"Coverage export is empty: {path}")

    try:
        with open(path, "r", encoding="utf-8") as handle:
            data = json.load(handle)
    except json.JSONDecodeError as err:
        raise RuntimeError(f"Invalid JSON in {path}: {err}") from err

    try:
        files = data["data"][0]["files"]
    except (KeyError, IndexError, TypeError) as err:
        raise RuntimeError(f"Unexpected llvm-cov export shape in {path}") from err

    result = {}

    for f in files:
        summary = f["summary"]["lines"]
        percent = summary["percent"]
        covered = summary["covered"]
        total = summary["count"]

        result[f["filename"]] = {
            "percent": percent,
            "covered": covered,
            "total": total,
            "missing": total - covered
        }

    return result

try:
    macros = load("data/macros.json")
    borrow = load("data/borrow.json")
except RuntimeError as err:
    print(f"Error: {err}")
    print("Hint: run ./run_coverage.sh, ./merge_profiles.sh, and ./export_coverage.sh first")
    sys.exit(1)

print("\n=== Coverage Differences ===\n")

# Files only in macros
only_macros = set(macros.keys()) - set(borrow.keys())
if only_macros:
    print("Files only covered by macro tests:")
    for f in only_macros:
        print(f"  {f}")

# Files only in borrow
only_borrow = set(borrow.keys()) - set(macros.keys())
if only_borrow:
    print("Files only covered by borrow tests:")
    for f in only_borrow:
        print(f"  {f}")

# Common files with big differences
common = set(macros.keys()) & set(borrow.keys())
big_diffs = []
for f in common:
    diff = abs(macros[f]["percent"] - borrow[f]["percent"])
    if diff > 10:  # arbitrary threshold
        big_diffs.append((f, diff, macros[f]["percent"], borrow[f]["percent"]))

big_diffs.sort(key=lambda x: x[1], reverse=True)

if big_diffs:
    print("Files with significant coverage differences (>10%):")
    for f, diff, m_pct, b_pct in big_diffs[:10]:
        print(f"  {f}: macro {m_pct:.2f}%, borrow {b_pct:.2f}% (diff {diff:.2f}%)")