Run clang tidy on diff with CI

Added a script for CI execution. This script is not intended for local
user execution due to the following reasons:

1. `clang-tidy-diff` supports exit with a failure code when there are
   errors from version 17 or 18 onward. (The exact version is uncertain.
   For more details, please refer to
   llvm/llvm-project#65000.)
2. `bear` has different command line interfaces between version <= 2.4.x
    and onward. (For more details, please refer to
    https://github.com/rizsotto/Bear?tab=readme-ov-file#how-to-use.)

The script may not function properly if any of these issues arise. In
the CI environment, we ensure that the versions of these dependencies
are up-to-date. Specifically, the version of `clang-tidy-diff` is
specified as `18`, and the version of `Bear` on Ubuntu 22.04 is 3.0.x.

.github/workflows/ci.yml

@@ -13,10 +13,26 @@ jobs:
     runs-on: ubuntu-22.04
     steps:
       - uses: actions/checkout@v3
+        with:
+          # Fetch all history for proper diffing.
+          fetch-depth: 0
       - name: coding convention
         run: |
           sudo apt-get install -q -y clang-format
           scripts/check-format.sh
+      - name: Install cxxopts
+        run: scripts/install-cxxopts.sh
+      - name: Install fmt
+        run: scripts/install-fmt.sh
+      - name: static checks
+        run: |
+          sudo add-apt-repository -y 'deb http://apt.llvm.org/jammy/ llvm-toolchain-jammy-18 main'
+          wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | sudo apt-key add -
+          sudo apt-get update
+          sudo apt-get install -q -y bear clang-tidy-18
+          export CLANG_TIDY_DIFF=clang-tidy-diff-18.py
+          scripts/check-tidy.sh
+
   test:
     runs-on: ubuntu-22.04
     strategy:

.gitignore

@@ -58,3 +58,6 @@ venv.bak/
 
 # VS Code configs
 .vscode
+
+# Compilation database
+compile_commands.json

scripts/check-tidy.sh

@@ -0,0 +1,26 @@
+#!/usr/bin/env sh
+
+#
+# Runs clang-tidy on the diff between main and HEAD.
+# Note: This script is intended to be run in CI.
+#
+
+set -eu
+
+if [ -z "${GITHUB_ACTIONS+x}" ]; then
+  echo "error: this script is intended to be run in CI"
+  exit 1
+fi
+
+CLANG_TIDY_DIFF=${CLANG_TIDY_DIFF:-clang-tidy-diff.py}
+
+command -v bear >/dev/null 2>&1 || (
+  echo "error: bear is required to generate compile_commands.json; see https://github.com/rizsotto/Bear"
+  exit 1
+)
+
+# Run a clean build to generate compile_commands.json.
+make clean
+bear -- make
+git fetch origin main:refs/remotes/origin/main
+git diff -U0 "origin/${GITHUB_BASE_REF}" | ${CLANG_TIDY_DIFF} -p1