Scope clang-tidy to C++ targets (#355)

## Summary
- Scope `make clang-tidy` to exact `cc_library` / `cc_test` labels for
touched `envpool` packages instead of building `//...`.
- Skip clang-tidy entirely when a change has no C++-relevant files,
while global Bazel / third-party edits still fall back to all C++
targets.

## Test Plan
- `ruff check scripts/clang_tidy_targets.py`
- `ruff format --check scripts/clang_tidy_targets.py`
- `python3 -m compileall scripts/clang_tidy_targets.py`
- `brix ssh dev-0 -C -- "bash -lc "cd /root/code/envpool && make lint""`
- On `dev-0`, combined clang-tidy over all 38 exact C++ targets
completed without hanging.

Author: Trinkle23897

Makefile

@@ -19,6 +19,7 @@ CLANG_TIDY_MAJOR = 18
 CLANG_TIDY_BIN = clang-tidy-$(CLANG_TIDY_MAJOR)
 CLANG_TIDY_WRAPPER_DIR = $(HOME)/.cache/$(PROJECT_NAME)/bin
 PATH           := $(CLANG_TIDY_WRAPPER_DIR):$(HOME)/go/bin:$(PATH)
+CLANG_TIDY_TARGET_RESOLVER = python3 scripts/clang_tidy_targets.py
 
 # installation
 
@@ -124,7 +125,13 @@ bazel-pip-requirement-release:
 	cd third_party/pip_requirements && (cmp requirements.txt requirements-release-lock.txt || ln -sf requirements-release-lock.txt requirements.txt)
 
 clang-tidy: clang-tidy-install bazel-pip-requirement-dev
-	$(BAZEL) build $(BAZELOPT) //... --config=clang-tidy --config=test
+	targets="$${CLANG_TIDY_TARGETS:-$$($(CLANG_TIDY_TARGET_RESOLVER) | tr '\n' ' ')}"; \
+	if [ -z "$$targets" ]; then \
+		echo "No clang-tidy-relevant C++ changes detected; skipping."; \
+		exit 0; \
+	fi; \
+	echo "Running clang-tidy on: $$targets"; \
+	$(BAZEL) build $(BAZELOPT) $$targets --config=clang-tidy --config=test
 
 bazel-debug: bazel-install bazel-pip-requirement-dev
 	$(BAZEL) run $(BAZELOPT) //:setup --config=debug -- bdist_wheel

scripts/clang_tidy_targets.py

@@ -0,0 +1,119 @@
+#!/usr/bin/env python3
+"""Resolve the smallest safe Bazel target set for clang-tidy."""
+
+from __future__ import annotations
+
+import os
+import pathlib
+import subprocess
+import sys
+
+REPO_ROOT = pathlib.Path(__file__).resolve().parents[1]
+FULL_RUN_FILES = {
+    ".bazelrc",
+    ".clang-tidy",
+    "BUILD",
+    "WORKSPACE",
+    "envpool/BUILD",
+    "envpool/pip.bzl",
+    "envpool/requirements.bzl",
+    "envpool/workspace0.bzl",
+    "envpool/workspace1.bzl",
+}
+FULL_RUN_PREFIXES = ("third_party/",)
+CPP_SUFFIXES = (".cc", ".h")
+CC_RULE_KIND = "cc_(library|test)"
+
+
+def _git(*args: str) -> str:
+    return subprocess.check_output(
+        ["git", *args],
+        cwd=REPO_ROOT,
+        text=True,
+    ).strip()
+
+
+def _bazel(*args: str) -> str:
+    env = os.environ.copy()
+    env.setdefault("USE_BAZEL_VERSION", "8.6.0")
+    return subprocess.check_output(
+        ["bazelisk", *args],
+        cwd=REPO_ROOT,
+        env=env,
+        text=True,
+    ).strip()
+
+
+def _is_valid_commit(rev: str) -> bool:
+    if not rev or set(rev) == {"0"}:
+        return False
+    return (
+        subprocess.run(
+            ["git", "rev-parse", "--verify", f"{rev}^{{commit}}"],
+            cwd=REPO_ROOT,
+            stdout=subprocess.DEVNULL,
+            stderr=subprocess.DEVNULL,
+            text=True,
+            check=False,
+        ).returncode
+        == 0
+    )
+
+
+def _infer_changed_files() -> list[str]:
+    base_sha = os.environ.get("CLANG_TIDY_BASE_SHA", "").strip()
+    head_sha = os.environ.get("CLANG_TIDY_HEAD_SHA", "").strip() or "HEAD"
+    if not _is_valid_commit(base_sha):
+        try:
+            base_sha = _git("merge-base", "HEAD", "origin/main")
+        except subprocess.CalledProcessError:
+            base_sha = _git("rev-parse", "HEAD^")
+    committed = _git("diff", "--name-only", base_sha, head_sha)
+    working_tree = _git("diff", "--name-only", "HEAD")
+    changed_files = {
+        line
+        for diff in (committed, working_tree)
+        for line in diff.splitlines()
+        if line
+    }
+    return sorted(changed_files)
+
+
+def _resolve_targets(changed_files: list[str]) -> list[str]:
+    if not changed_files:
+        return []
+
+    for path in changed_files:
+        if path in FULL_RUN_FILES or path.startswith(FULL_RUN_PREFIXES):
+            query = _bazel("query", f'kind("{CC_RULE_KIND}", //...)')
+            return [line for line in query.splitlines() if line]
+
+    package_patterns: set[str] = set()
+    for path in changed_files:
+        parts = pathlib.PurePosixPath(path).parts
+        if len(parts) < 2 or parts[0] != "envpool":
+            continue
+        if parts[1] == "python":
+            continue
+        if (
+            path.endswith(CPP_SUFFIXES)
+            or pathlib.PurePosixPath(path).name == "BUILD"
+        ):
+            package_patterns.add(f"//envpool/{parts[1]}:*")
+
+    targets: set[str] = set()
+    for pattern in sorted(package_patterns):
+        query = _bazel("query", f'kind("{CC_RULE_KIND}", {pattern})')
+        targets.update(line for line in query.splitlines() if line)
+    return sorted(targets)
+
+
+def _main() -> int:
+    changed_files = sys.argv[1:] or _infer_changed_files()
+    for target in _resolve_targets(changed_files):
+        print(target)
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(_main())