feat: integrate ctcache for clang-tidy result caching in CI

.github/workflows/build-src.yml

@@ -113,14 +113,36 @@ jobs:
             /cache/ccache
           key: ccache-${{ hashFiles('contrib/containers/ci/ci.Dockerfile', 'depends/packages/*') }}-${{ inputs.build-target }}-${{ github.sha }}
 
+      - name: Restore ctcache cache
+        if: inputs.build-target == 'linux64_multiprocess'
+        uses: actions/cache/restore@v4
+        with:
+          path: |
+            /cache/ctcache
+          key: ctcache-${{ hashFiles('contrib/containers/ci/ci.Dockerfile', 'depends/packages/*') }}-${{ inputs.build-target }}-${{ github.sha }}
+          restore-keys: |
+            ctcache-${{ hashFiles('contrib/containers/ci/ci.Dockerfile', 'depends/packages/*') }}-${{ inputs.build-target }}-
+
       - name: Run linters
         if: inputs.build-target == 'linux64_multiprocess'
         run: |
+          CACHE_DIR="/cache"
           export BUILD_TARGET="${{ inputs.build-target }}"
           source ./ci/dash/matrix.sh
           ./ci/dash/lint-tidy.sh
         shell: bash
 
+      - name: Save ctcache cache
+        if: |
+          inputs.build-target == 'linux64_multiprocess' &&
+          github.event_name == 'push' &&
+          github.ref_name == github.event.repository.default_branch
+        uses: actions/cache/save@v4
+        with:
+          path: |
+            /cache/ctcache
+          key: ctcache-${{ hashFiles('contrib/containers/ci/ci.Dockerfile', 'depends/packages/*') }}-${{ inputs.build-target }}-${{ github.sha }}
+
       - name: Run unit tests
         run: |
           BUILD_TARGET="${{ inputs.build-target }}"

ci/dash/lint-tidy.sh

@@ -11,13 +11,76 @@ set -eo pipefail
 #          only on nor do they set the requisite build parameters. Make sure you do
 #          that *before* running this script.
 
+# Cleanup old ctcache entries to keep cache size under limit
+cleanup_ctcache() {
+  local cache_dir=$1
+  local max_size_mb=$2
+  local cache_size_mb
+
+  cache_size_mb=$(du -sm "${cache_dir}" 2>/dev/null | cut -f1)
+  if [ "${cache_size_mb}" -gt "${max_size_mb}" ]; then
+    echo "Cache size ${cache_size_mb}MB exceeds limit ${max_size_mb}MB, cleaning old entries..."
+    # Remove files older than 7 days, or if still too large, oldest 20% of files
+    find "${cache_dir}" -type f -mtime +7 -delete 2>/dev/null || true
+    cache_size_mb=$(du -sm "${cache_dir}" 2>/dev/null | cut -f1)
+    if [ "${cache_size_mb}" -gt "${max_size_mb}" ]; then
+      local file_count remove_count
+      file_count=$(find "${cache_dir}" -type f | wc -l)
+      remove_count=$((file_count / 5))
+      find "${cache_dir}" -type f -printf '%T+ %p\0' | sort -z | head -z -n "${remove_count}" | cut -z -d' ' -f2- | xargs -0 rm -f 2>/dev/null || true
+      echo "Attempted to remove ${remove_count} oldest cache entries"
+    fi
+    echo "Cache size after cleanup: $(du -sh "${cache_dir}" 2>/dev/null | cut -f1)"
+  fi
+}
+
+# Verify clang-tidy is available
+CLANG_TIDY_BIN=$(command -v clang-tidy)
+if [ -z "${CLANG_TIDY_BIN}" ]; then
+  echo "Error: clang-tidy not found in PATH"
+  exit 1
+fi
+
+# Setup ctcache for clang-tidy result caching
+export CTCACHE_SAVE_OUTPUT=1
+export CTCACHE_CLANG_TIDY="${CLANG_TIDY_BIN}"
+mkdir -p "${CTCACHE_DIR}"
+
+CLANG_TIDY_CACHE=$(command -v clang-tidy-cache)
+
+# Verify ctcache is installed
+if [ -z "${CLANG_TIDY_CACHE}" ]; then
+  echo "Error: clang-tidy-cache not found in PATH"
+  exit 1
+fi
+
+# Derive Python script path from wrapper location (matches wrapper's own logic)
+CLANG_TIDY_CACHE_PY="$(dirname "${CLANG_TIDY_CACHE}")/src/ctcache/clang_tidy_cache.py"
+if [ ! -f "${CLANG_TIDY_CACHE_PY}" ]; then
+  echo "Error: ctcache Python script not found at ${CLANG_TIDY_CACHE_PY}"
+  exit 1
+fi
+
+# Zero stats before run to get accurate statistics for this run only
+python3 "${CLANG_TIDY_CACHE_PY}" --zero-stats 2>&1 || true
+
 cd "${BASE_ROOT_DIR}/build-ci/dashcore-${BUILD_TARGET}/src"
-if ! ( run-clang-tidy -quiet "${MAKEJOBS}" | tee tmp.tidy-out.txt ); then
+
+if ! ( run-clang-tidy -clang-tidy-binary="${CLANG_TIDY_CACHE}" -quiet "${MAKEJOBS}" | tee tmp.tidy-out.txt ); then
   grep -C5 "error: " tmp.tidy-out.txt
   echo "^^^ ⚠️ Failure generated from clang-tidy"
   false
 fi
 
+# Show ctcache statistics and manage cache size
+echo "=== ctcache statistics ==="
+du -sh "${CTCACHE_DIR}" 2>/dev/null || echo "Cache directory not found"
+python3 "${CLANG_TIDY_CACHE_PY}" --show-stats 2>&1 || true
+
+# Limit cache size (ctcache has no built-in size management)
+cleanup_ctcache "${CTCACHE_DIR}" "${CTCACHE_MAXSIZE_MB}"
+echo "=========================="
+
 cd "${BASE_ROOT_DIR}/build-ci/dashcore-${BUILD_TARGET}"
 iwyu_tool.py \
   "src/compat" \

ci/test/00_setup_env.sh

@@ -61,6 +61,9 @@ export CCACHE_COMPRESS=${CCACHE_COMPRESS:-1}
 # The cache dir.
 # This folder exists on the ci host and ci guest. Changes are propagated back and forth.
 export CCACHE_DIR=${CCACHE_DIR:-$CACHE_DIR/ccache}
+# ctcache (clang-tidy cache) configuration
+export CTCACHE_DIR=${CTCACHE_DIR:-$CACHE_DIR/ctcache}
+export CTCACHE_MAXSIZE_MB=${CTCACHE_MAXSIZE_MB:-50}
 # The depends dir.
 # This folder exists on the ci host and ci guest. Changes are propagated back and forth.
 export DEPENDS_DIR=${DEPENDS_DIR:-$BASE_ROOT_DIR/depends}

contrib/containers/ci/ci.Dockerfile

@@ -65,8 +65,20 @@ RUN set -ex; \
     make install -j "$(( $(nproc) - 1 ))"; \
     cd /opt && rm -rf /opt/iwyu;
 
+# Install ctcache for clang-tidy result caching
+# Pin to specific commit to ensure patch applies correctly
+ARG CTCACHE_COMMIT=e393144d5c49b060a1dbc7ae15b9c6973efb967d
+RUN set -ex; \
+    mkdir -p /usr/local/bin/src/ctcache; \
+    curl -fsSL "https://raw.githubusercontent.com/matus-chochlik/ctcache/${CTCACHE_COMMIT}/src/ctcache/clang_tidy_cache.py" \
+        -o /usr/local/bin/src/ctcache/clang_tidy_cache.py; \
+    curl -fsSL "https://raw.githubusercontent.com/matus-chochlik/ctcache/${CTCACHE_COMMIT}/clang-tidy" \
+        -o /usr/local/bin/clang-tidy-cache; \
+    chmod +x /usr/local/bin/clang-tidy-cache;
+
 RUN \
   mkdir -p /cache/ccache && \
+  mkdir /cache/ctcache && \
   mkdir /cache/depends && \
   mkdir /cache/sdk-sources && \
   chown ${USER_ID}:${GROUP_ID} /cache && \