feat(doc-freshness): add checker to flag stale documentation references (Closes #104)

This adds scripts/doc_freshness.py — a tool that scans markdown documentation
for function call references (`foo()`) and PascalCase class names (`Bar`), then
verifies that each referenced symbol exists in the Python codebase (via AST
symbol collection).

- Parses docs for function/class references (backticked identifiers that are
  either function calls ending with () or PascalCase class names)
- Checks if referenced items still exist in the code
- Reports stale doc references with file paths and line numbers
- Suitable for weekly cron execution; exit code 1 when stale refs found

Includes tests in tests/test_doc_freshness.py covering:
- symbol collection from Python AST
- doc reference extraction heuristics
- missing detection integration

Smallest concrete implementation satisfying all acceptance criteria.

scripts/doc_freshness.py

@@ -0,0 +1,176 @@
+#!/usr/bin/env python3
+"""
+Doc Freshness Checker — Issue #104
+
+Compare docs to code. Flag docs that reference removed functions or outdated APIs.
+
+Usage:
+    python3 scripts/doc_freshness.py [--root .] [--docs-dir .] [--json]
+
+Outputs:
+    Human-readable report by default listing missing references.
+    JSON output with --json for machine consumption.
+
+"""
+
+import argparse
+import ast
+import json
+import os
+import re
+import sys
+from datetime import datetime, timezone
+from pathlib import Path
+from typing import Set, List, Tuple, Dict, Any
+
+
+def collect_python_symbols(repo_root: str) -> Set[str]:
+    """Collect all top-level function and class names from Python files."""
+    symbols: Set[str] = set()
+    for root, dirs, files in os.walk(repo_root):
+        # Skip irrelevant dirs
+        dirs[:] = [d for d in dirs if d not in ['.git', '__pycache__', '.venv', 'venv', 'node_modules']]
+        for fname in files:
+            if fname.endswith('.py'):
+                path = os.path.join(root, fname)
+                try:
+                    with open(path, 'r', encoding='utf-8') as f:
+                        tree = ast.parse(f.read())
+                    for node in ast.walk(tree):
+                        if isinstance(node, (ast.FunctionDef, ast.AsyncFunctionDef, ast.ClassDef)):
+                            symbols.add(node.name)
+                except Exception:
+                    # Skip unparsable files
+                    pass
+    return symbols
+
+
+def extract_doc_references(docs_dir: str) -> List[Tuple[str, str, int]]:
+    """
+    Walk markdown files and extract function/class references.
+
+    Only considers backticked content that is clearly a function call (ending
+    with ()) or a PascalCase class name. This filters out filenames, paths,
+    URLs, JSON fields, and other non-API references.
+    """
+    refs: List[Tuple[str, str, int]] = []
+    backtick_pat = re.compile(r'`([^`]+)`')
+    func_pat = re.compile(r'^[a-zA-Z_][a-zA-Z0-9_]*$')
+    class_pat = re.compile(r'^[A-Z][a-zA-Z0-9_]*$')
+
+    for root, dirs, files in os.walk(docs_dir):
+        dirs[:] = [d for d in dirs if d != '.git']
+        for fname in files:
+            if not fname.endswith('.md'):
+                continue
+            path = os.path.join(root, fname)
+            rel_path = os.path.relpath(path, docs_dir)
+            try:
+                with open(path, 'r', encoding='utf-8') as fh:
+                    for lineno, line in enumerate(fh, 1):
+                        for m in backtick_pat.finditer(line):
+                            raw = m.group(1).strip()
+                            # Function call: ends with ()
+                            if raw.endswith('()'):
+                                name = raw[:-2].strip()
+                                if func_pat.fullmatch(name):
+                                    refs.append((name, rel_path, lineno))
+                                    continue
+                            # Class reference: PascalCase
+                            if class_pat.fullmatch(raw):
+                                refs.append((raw, rel_path, lineno))
+            except Exception:
+                pass
+
+    return refs
+
+
+def check_doc_freshness(repo_root: str, docs_dir: str) -> Dict[str, Any]:
+    """Run the full check and return structured results."""
+    symbols = collect_python_symbols(repo_root)
+    refs = extract_doc_references(docs_dir)
+
+    missing: List[Dict[str, Any]] = []
+    found: List[Dict[str, Any]] = []
+
+    for ref, file, lineno in refs:
+        if ref in symbols:
+            found.append({"reference": ref, "file": file, "line": lineno})
+        else:
+            missing.append({"reference": ref, "file": file, "line": lineno})
+
+    # Deduplicate missing by (reference, file)
+    missing_keys = set()
+    for item in missing:
+        missing_keys.add((item["reference"], item["file"]))
+
+    total_unique_refs = len({(r, f) for r, f, _ in refs})
+
+    return {
+        "timestamp": "..",  # filled by main
+        "repo_root": repo_root,
+        "docs_dir": docs_dir,
+        "total_unique_references": total_unique_refs,
+        "defined_symbols": len(symbols),
+        "missing": missing,
+        "found": found,
+        "missing_count": len(missing_keys),
+        "found_count": total_unique_refs - len(missing_keys),
+    }
+
+
+def format_report(result: Dict[str, Any]) -> str:
+    """Format check results as a human-readable report."""
+    lines = [
+        "Doc Freshness Report",
+        "=" * 50,
+        f"Repo: {result['repo_root']}",
+        f"Docs: {result['docs_dir']}",
+        f"Defined Python symbols: {result['defined_symbols']}",
+        f"References found: {result['total_unique_references']}",
+        f"Stale references: {result['missing_count']}",
+        "",
+    ]
+
+    if result["missing"]:
+        lines.append("Stale references:")
+        by_file: Dict[str, List] = {}
+        for item in result["missing"]:
+            by_file.setdefault(item["file"], []).append(item)
+        for fname in sorted(by_file):
+            lines.append(f"\n  {fname}:")
+            for item in by_file[fname]:
+                lines.append(f"    line {item['line']}: {item['reference']}")
+    else:
+        lines.append("All references are current.")
+
+    lines.append("")
+    lines.append("Note: Only backticked function calls () and PascalCase class names are checked.")
+    return "\n".join(lines)
+
+
+def main() -> None:
+    parser = argparse.ArgumentParser(
+        description="Doc Freshness Checker — compare docs to code")
+    parser.add_argument("--root", default=".", help="Repository root (code location)")
+    parser.add_argument("--docs-dir", default=None,
+                        help="Docs directory (default: same as --root)")
+    parser.add_argument("--json", action="store_true", help="Machine-readable output")
+    args = parser.parse_args()
+
+    docs_dir = args.docs_dir or args.root
+
+    result = check_doc_freshness(args.root, docs_dir)
+    result["timestamp"] = datetime.now(timezone.utc).isoformat()
+
+    if args.json:
+        print(json.dumps(result, indent=2))
+    else:
+        print(format_report(result))
+
+    # Exit non-zero if stale references found
+    sys.exit(1 if result["missing_count"] > 0 else 0)
+
+
+if __name__ == "__main__":
+    main()

tests/test_doc_freshness.py

@@ -0,0 +1,89 @@
+#!/usr/bin/env python3
+"""Tests for scripts/doc_freshness.py — Issue #104."""
+
+import os
+import sys
+import tempfile
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).parent.parent / "scripts"))
+
+import doc_freshness as df
+
+
+def test_collect_python_symbols():
+    """Should collect function and class names from Python files."""
+    with tempfile.TemporaryDirectory() as tmpdir:
+        # Create a simple Python file
+        py_path = os.path.join(tmpdir, "sample.py")
+        with open(py_path, "w") as f:
+            f.write('''
+def my_func():
+    pass
+
+class MyClass:
+    def method(self):
+        pass
+
+async def my_async():
+    pass
+''')
+        symbols = df.collect_python_symbols(tmpdir)
+        assert "my_func" in symbols
+        assert "MyClass" in symbols
+        assert "my_async" in symbols
+        # method (inside class) is also collected and should be considered valid
+        assert "method" in symbols
+    print("PASS: test_collect_python_symbols")
+
+
+def test_extract_doc_references_function_and_class():
+    """Should extract only function calls () and PascalCase class refs."""
+    with tempfile.TemporaryDirectory() as tmpdir:
+        docs = os.path.join(tmpdir, "docs")
+        os.makedirs(docs)
+        md_path = os.path.join(docs, "test.md")
+        with open(md_path, "w") as f:
+            f.write('''
+# Test
+
+`call_this()` is a function.
+`SomeClass` is a class.
+`not_a_function` (lowercase, no parens) should be ignored.
+`filename.py` should be ignored.
+`https://example.com` ignored.
+''')
+        refs = df.extract_doc_references(docs)
+        names = [r[0] for r in refs]
+        assert "call_this" in names
+        assert "SomeClass" in names
+        assert "not_a_function" not in names
+        assert "filename" not in names  # filename.py filtered
+        assert "https" not in names
+    print("PASS: test_extract_doc_references_function_and_class")
+
+
+def test_check_doc_freshness_missing_detection():
+    """Should detect missing symbols."""
+    with tempfile.TemporaryDirectory() as tmpdir:
+        # Code with one function
+        code_dir = os.path.join(tmpdir, "code")
+        os.makedirs(code_dir)
+        with open(os.path.join(code_dir, "a.py"), "w") as f:
+            f.write("def existing_func(): pass\n")
+        # Docs reference existing_func and missing_func
+        docs_dir = os.path.join(tmpdir, "docs")
+        os.makedirs(docs_dir)
+        with open(os.path.join(docs_dir, "readme.md"), "w") as f:
+            f.write("`existing_func()` and `missing_func()` are mentioned.")
+        result = df.check_doc_freshness(code_dir, docs_dir)
+        assert result["missing_count"] == 1
+        assert result["found_count"] == 1
+    print("PASS: test_check_doc_freshness_missing_detection")
+
+
+if __name__ == "__main__":
+    test_collect_python_symbols()
+    test_extract_doc_references_function_and_class()
+    test_check_doc_freshness_missing_detection()
+    print("All tests passed!")