chore: Optionally run clang-tidy via pre-commit (#6680)

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Ayaz Salikhov <mathbunnyru@users.noreply.github.com>
Co-authored-by: Bart <bthomee@users.noreply.github.com>

.pre-commit-config.yaml

@@ -67,6 +67,14 @@ repos:
 
   - repo: local
     hooks:
+      - id: clang-tidy
+        name: "clang-tidy (enable with: TIDY=1)"
+        entry: ./bin/pre-commit/clang_tidy_check.py
+        language: python
+        types_or: [c++, c]
+        exclude: ^include/xrpl/protocol_autogen
+        pass_filenames: false # script determines the staged files itself
+
       - id: nix-fmt
         name: Format Nix files
         entry: |

CONTRIBUTING.md

@@ -267,6 +267,26 @@ See the [environment setup guide](./docs/build/environment.md#clang-tidy) for pl
 
 Before running clang-tidy, you must build the project to generate required files (particularly protobuf headers). Refer to [`BUILD.md`](./BUILD.md) for build instructions.
 
+#### Via pre-commit (recommended)
+
+If you have already installed the pre-commit hooks (see above), you can run clang-tidy on your staged files using:
+
+```
+TIDY=1 pre-commit run clang-tidy
+```
+
+This runs clang-tidy locally with the same configuration/flags as CI, scoped to your staged C++ files. The `TIDY=1` environment variable is required to opt in — without it the hook is skipped.
+
+You can also have clang-tidy run automatically on every `git commit` by setting `TIDY=1` in your shell environment:
+
+```
+export TIDY=1
+```
+
+With this set, the hook will run as part of `git commit` alongside the other pre-commit checks.
+
+#### Manually
+
 Then run clang-tidy on your local changes:
 
 ```

bin/pre-commit/clang_tidy_check.py

@@ -0,0 +1,206 @@
+#!/usr/bin/env python3
+"""Pre-commit hook that runs clang-tidy on changed files using run-clang-tidy."""
+
+from __future__ import annotations
+
+import json
+import os
+import re
+import shutil
+import subprocess
+import sys
+from collections import defaultdict
+from pathlib import Path
+
+HEADER_EXTENSIONS = {".h", ".hpp", ".ipp"}
+SOURCE_EXTENSIONS = {".cpp"}
+INCLUDE_RE = re.compile(r"^\s*#\s*include\s*[<\"]([^>\"]+)[>\"]")
+
+
+def find_run_clang_tidy() -> str | None:
+    for candidate in ("run-clang-tidy-21", "run-clang-tidy"):
+        if path := shutil.which(candidate):
+            return path
+    return None
+
+
+def find_build_dir(repo_root: Path) -> Path | None:
+    for name in (".build", "build"):
+        candidate = repo_root / name
+        if (candidate / "compile_commands.json").exists():
+            return candidate
+    return None
+
+
+def build_include_graph(build_dir: Path, repo_root: Path) -> tuple[dict, set]:
+    """
+    Scan all files reachable from compile_commands.json and build an inverted include graph.
+
+    Returns:
+        inverted: header_path -> set of files that include it
+        source_files: set of all TU paths from compile_commands.json
+    """
+    with open(build_dir / "compile_commands.json") as f:
+        db = json.load(f)
+
+    source_files = {Path(e["file"]).resolve() for e in db}
+    include_roots = [repo_root / "include", repo_root / "src"]
+    inverted: dict[Path, set[Path]] = defaultdict(set)
+
+    to_scan: set[Path] = set(source_files)
+    scanned: set[Path] = set()
+
+    while to_scan:
+        file = to_scan.pop()
+        if file in scanned or not file.exists():
+            continue
+        scanned.add(file)
+
+        content = file.read_text()
+
+        for line in content.splitlines():
+            m = INCLUDE_RE.match(line)
+            if not m:
+                continue
+            for root in include_roots:
+                candidate = (root / m.group(1)).resolve()
+                if candidate.exists():
+                    inverted[candidate].add(file)
+                    if candidate not in scanned:
+                        to_scan.add(candidate)
+                    break
+
+    return inverted, source_files
+
+
+def find_tus_for_headers(
+    headers: list[Path],
+    inverted: dict[Path, set[Path]],
+    source_files: set[Path],
+) -> set[Path]:
+    """
+    For each header, pick one TU that transitively includes it.
+    Prefers a TU whose stem matches the header's stem, otherwise picks the first found.
+    """
+    result: set[Path] = set()
+
+    for header in headers:
+        preferred: Path | None = None
+        visited: set[Path] = {header}
+        stack: list[Path] = [header]
+
+        while stack:
+            h = stack.pop()
+            for inc in inverted.get(h, ()):
+                if inc in source_files:
+                    if inc.stem == header.stem:
+                        preferred = inc
+                        break
+                    if preferred is None:
+                        preferred = inc
+                if inc not in visited:
+                    visited.add(inc)
+                    stack.append(inc)
+            if preferred is not None and preferred.stem == header.stem:
+                break
+
+        if preferred is not None:
+            result.add(preferred)
+
+    return result
+
+
+def resolve_files(
+    input_files: list[str], build_dir: Path, repo_root: Path
+) -> list[str]:
+    """
+    Split input into source files and headers. Source files are passed through;
+    headers are resolved to the TUs that transitively include them.
+    """
+    sources: list[Path] = []
+    headers: list[Path] = []
+
+    for f in input_files:
+        p = Path(f).resolve()
+        if p.suffix in SOURCE_EXTENSIONS:
+            sources.append(p)
+        elif p.suffix in HEADER_EXTENSIONS:
+            headers.append(p)
+
+    if not headers:
+        return [str(p) for p in sources]
+
+    print(
+        f"Resolving {len(headers)} header(s) to compilation units...", file=sys.stderr
+    )
+    inverted, source_files = build_include_graph(build_dir, repo_root)
+    tus = find_tus_for_headers(headers, inverted, source_files)
+
+    if not tus:
+        print(
+            "Warning: no compilation units found that include the modified headers; "
+            "skipping clang-tidy for headers.",
+            file=sys.stderr,
+        )
+
+    return sorted({str(p) for p in (*sources, *tus)})
+
+
+def staged_files(repo_root: Path) -> list[str]:
+    result = subprocess.run(
+        ["git", "diff", "--staged", "--name-only", "--diff-filter=d"],
+        capture_output=True,
+        text=True,
+        cwd=repo_root,
+    )
+    if result.returncode != 0:
+        print(
+            "clang-tidy check failed: 'git diff --staged' command failed.",
+            file=sys.stderr,
+        )
+        if result.stderr:
+            print(result.stderr, file=sys.stderr)
+        sys.exit(result.returncode or 1)
+    return [str(repo_root / p) for p in result.stdout.splitlines() if p]
+
+
+def main():
+    if not os.environ.get("TIDY"):
+        return 0
+
+    repo_root = Path(__file__).parent.parent
+    files = staged_files(repo_root)
+    if not files:
+        return 0
+
+    run_clang_tidy = find_run_clang_tidy()
+    if not run_clang_tidy:
+        print(
+            "clang-tidy check failed: TIDY is enabled but neither "
+            "'run-clang-tidy-21' nor 'run-clang-tidy' was found in PATH.",
+            file=sys.stderr,
+        )
+        return 1
+
+    build_dir = find_build_dir(repo_root)
+    if not build_dir:
+        print(
+            "clang-tidy check failed: no build directory with compile_commands.json found "
+            "(looked for .build/ and build/)",
+            file=sys.stderr,
+        )
+        return 1
+
+    tidy_files = resolve_files(files, build_dir, repo_root)
+    if not tidy_files:
+        return 0
+
+    result = subprocess.run(
+        [run_clang_tidy, "-quiet", "-p", str(build_dir), "-fix", "-allow-no-checks"]
+        + tidy_files
+    )
+    return result.returncode
+
+
+if __name__ == "__main__":
+    sys.exit(main())