Enable clang-tidy tooling

.clang-tidy

@@ -0,0 +1,36 @@
+# Shared clang-tidy baseline for dd-trace-cpp, httpd-datadog, and nginx-datadog.
+# Keep this file in sync across those repositories.
+Checks: >
+  -*,
+  bugprone-assert-side-effect,
+  bugprone-bool-pointer-implicit-conversion,
+  bugprone-copy-constructor-init,
+  bugprone-dangling-handle,
+  bugprone-forwarding-reference-overload,
+  bugprone-inaccurate-erase,
+  bugprone-infinite-loop,
+  bugprone-macro-repeated-side-effects,
+  bugprone-move-forwarding-reference,
+  bugprone-parent-virtual-call,
+  bugprone-posix-return,
+  bugprone-string-constructor,
+  bugprone-undelegated-constructor,
+  bugprone-unused-raii,
+  bugprone-virtual-near-miss,
+  misc-unused-using-decls,
+  readability-delete-null-pointer,
+  readability-redundant-control-flow,
+  readability-redundant-string-cstr
+# Deferred until existing findings are cleaned up:
+# bugprone-argument-comment
+# bugprone-use-after-move
+# misc-redundant-expression
+# misc-static-assert
+# modernize-redundant-void-arg
+# performance-move-const-arg
+# performance-noexcept-move-constructor
+# readability-redundant-member-init
+# readability-simplify-boolean-expr
+WarningsAsErrors: '*'
+HeaderFilterRegex: 'mod_datadog/src/'
+FormatStyle: file

.devcontainer/Dockerfile

@@ -20,7 +20,7 @@ ENV SYSROOT=/sysroot/${ARCH}-none-linux-musl
 COPY deps/nginx-datadog/build_env/CHECKSUMS /CHECKSUMS
 
 RUN apk --no-cache add alpine-sdk coreutils sudo bash samurai python3 linux-headers \
-	compiler-rt clang llvm lld wget cmake make binutils musl-dev git patchelf xz lit
+	compiler-rt clang clang-extra-tools llvm lld wget cmake make binutils musl-dev git patchelf xz lit
 RUN wget https://github.com/llvm/llvm-project/releases/download/llvmorg-${LLVM_VERSION}/llvm-project-${LLVM_VERSION}.src.tar.xz && \
     grep -F llvm-project-${LLVM_VERSION}.src.tar.xz /CHECKSUMS | sha512sum --check && \
     tar -xvf llvm-project-${LLVM_VERSION}.src.tar.xz

.github/workflows/dev.yml

@@ -1,5 +1,6 @@
 name: Development
 on:
+  pull_request:
   push:
   workflow_dispatch:
   schedule:
@@ -19,6 +20,18 @@ jobs:
       - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4.3.1
       - run: ./scripts/codestyle.sh lint
 
+  clang-tidy:
+    runs-on: ubuntu-22.04
+    container:
+      image: ghcr.io/datadog/httpd-datadog/devcontainer:main
+      credentials:
+        username: ${{ github.actor }}
+        password: ${{ secrets.GITHUB_TOKEN }}
+    steps:
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4.3.1
+      - name: clang-tidy
+        run: ./scripts/clang-tidy.sh
+
   build:
     needs: format
     runs-on: ubuntu-22.04

.gitignore

@@ -25,6 +25,7 @@ compile_commands.json
 __pycache__/
 build-container/
 build-rum/
+.clang-tidy-build/
 build/
 dist-container/
 httpd-*/

CMakeLists.txt

@@ -13,6 +13,9 @@ set(ZLIB_USE_STATIC_LIBS ON)
 option(HTTPD_DATADOG_ENABLE_RUM "Enable RUM product" OFF)
 option(HTTPD_DATADOG_ENABLE_COVERAGE "Enable code coverage instrumentation" OFF)
 option(HTTPD_DATADOG_PATCH_AWAY_LIBC "Patch away libc dependency" OFF)
+option(HTTPD_DATADOG_ENABLE_CLANG_TIDY "Run clang-tidy on first-party sources during build" OFF)
+set(HTTPD_DATADOG_CLANG_TIDY "clang-tidy-17" CACHE STRING
+    "clang-tidy executable when HTTPD_DATADOG_ENABLE_CLANG_TIDY is ON")
 
 if (NOT CMAKE_BUILD_TYPE)
   set(CMAKE_BUILD_TYPE ReleaseWithDeb)

CONTRIBUTING.md

@@ -4,6 +4,34 @@
 
 Follow [docs/conventions.md](doc/conventions.md).
 
+## Format
+
+C++ is formatted with `clang-format-14` and `.clang-format`.
+
+```sh
+./scripts/codestyle.sh lint     # check; fails on drift
+./scripts/codestyle.sh format   # rewrite files
+```
+
+## Static Analysis
+
+C++ is analyzed with **clang-tidy-17** (pinned to the LLVM 17 toolchain in the
+devcontainer) using the shared `.clang-tidy` baseline. Warnings are errors.
+
+Do not run clang-tidy on the host. Tidy must use the same compiler, flags, and
+sysroot as the real build (`ci-dev`). Locally:
+
+```sh
+make lint-tidy
+```
+
+That builds/pulls the devcontainer, configures CMake inside it (`ci-dev`, RUM
+off, `HTTPD_DATADOG_ENABLE_CLANG_TIDY`), and builds `mod_datadog` so CMake
+invokes clang-tidy-17 with the exact compile line. `rum/`, `deps/`, and tests
+are not on that target. `./scripts/clang-tidy.sh` re-execs through
+`make lint-tidy` when run on the host. CI runs the same script in
+`ghcr.io/datadog/httpd-datadog/devcontainer:main`.
+
 ## Clone
 
 When cloning the repo, initialize the submodules you need. For a standard build:

Makefile

@@ -18,6 +18,11 @@ test-integration: dev-image
 
 # GitHub build entrypoint. RUM is off, so inject-browser-sdk is unnecessary.
 PRESET ?= ci-dev
+
+.PHONY: lint-tidy
+lint-tidy: dev-image
+	$(IN_DEVCONTAINER) env HTTPD_DATADOG_TIDY_IN_CONTAINER=1 ./scripts/clang-tidy.sh
+
 .PHONY: ci-build
 ci-build:
 	git config --global --add safe.directory "$(CURDIR)"

mod_datadog/CMakeLists.txt

@@ -27,6 +27,10 @@ add_library(
 )
 
 set_property(TARGET mod_datadog PROPERTY POSITION_INDEPENDENT_CODE ON)
+if(HTTPD_DATADOG_ENABLE_CLANG_TIDY)
+  set_property(TARGET mod_datadog PROPERTY CXX_CLANG_TIDY
+    "${HTTPD_DATADOG_CLANG_TIDY};--quiet;--use-color")
+endif()
 
 if (HTTPD_DATADOG_ENABLE_RUM)
   target_compile_definitions(

scripts/clang-tidy.sh

@@ -0,0 +1,89 @@
+#!/usr/bin/env bash
+# Run the pinned clang-tidy through CMake in the httpd-datadog devcontainer.
+#
+# clang-tidy must use the same compiler, flags, and sysroot as the real
+# build (ci-dev). CMake's CXX_CLANG_TIDY on mod_datadog does that: it
+# invokes tidy with the exact compile line after `--`. Do not run tidy
+# against a host compilation database.
+#
+# Usage:
+#   make lint-tidy
+#   ./scripts/clang-tidy.sh
+
+set -euo pipefail
+
+SCRIPT_DIR=$(cd "$(dirname "$0")" && pwd)
+REPO_ROOT=$(cd "$SCRIPT_DIR/.." && pwd)
+cd "$REPO_ROOT"
+
+# Must match LLVM_VERSION in .devcontainer/Dockerfile (major).
+CLANG_TIDY_VERSION=17
+
+in_container() {
+    [[ -f /.dockerenv ]] || [[ -n "${KUBERNETES_SERVICE_HOST:-}" ]] || \
+        [[ "${HTTPD_DATADOG_TIDY_IN_CONTAINER:-}" == "1" ]]
+}
+
+if ! in_container; then
+    if ! command -v docker >/dev/null 2>&1; then
+        >&2 echo "docker is required to run clang-tidy-${CLANG_TIDY_VERSION}."
+        exit 1
+    fi
+    exec make -C "$REPO_ROOT" lint-tidy
+fi
+
+build_dir=${BUILD_DIR:-.clang-tidy-build}
+tidy="clang-tidy-${CLANG_TIDY_VERSION}"
+
+if ! command -v "$tidy" >/dev/null 2>&1 && command -v clang-tidy >/dev/null 2>&1; then
+    found_major=$(clang-tidy --version | sed -n 's/.*version \([0-9][0-9]*\).*/\1/p' | head -n 1)
+    if [[ "$found_major" == "$CLANG_TIDY_VERSION" ]]; then
+        tidy=clang-tidy
+    fi
+fi
+
+if ! command -v "$tidy" >/dev/null 2>&1; then
+    apk add --no-cache clang-extra-tools
+    if command -v clang-tidy >/dev/null 2>&1; then
+        found_major=$(clang-tidy --version | sed -n 's/.*version \([0-9][0-9]*\).*/\1/p' | head -n 1)
+        if [[ "$found_major" != "$CLANG_TIDY_VERSION" ]]; then
+            >&2 echo "clang-tidy ${found_major} is installed, but ${CLANG_TIDY_VERSION} is pinned."
+            exit 1
+        fi
+        tidy=clang-tidy
+    fi
+fi
+
+if ! command -v "$tidy" >/dev/null 2>&1; then
+    >&2 echo "clang-tidy-${CLANG_TIDY_VERSION} is required (pinned)."
+    exit 1
+fi
+
+compiler=${CXX:-clang++}
+if ! command -v "$compiler" >/dev/null 2>&1; then
+    >&2 echo "$compiler is required (same toolchain as CMake)."
+    exit 1
+fi
+
+compiler_major=$("$compiler" -dumpversion | cut -d. -f1)
+tidy_major=$("$tidy" --version | sed -n 's/.*version \([0-9][0-9]*\).*/\1/p' | head -n 1)
+if [[ "$compiler_major" != "$CLANG_TIDY_VERSION" || "$tidy_major" != "$CLANG_TIDY_VERSION" ]]; then
+    >&2 echo "clang-tidy and the CMake compiler must both be LLVM ${CLANG_TIDY_VERSION}."
+    >&2 echo "  ${compiler}: ${compiler_major}"
+    >&2 echo "  ${tidy}: ${tidy_major}"
+    exit 1
+fi
+
+git config --global --add safe.directory "$REPO_ROOT" >/dev/null 2>&1 || true
+if [[ ! -f deps/dd-trace-cpp/CMakeLists.txt ]] || [[ ! -f deps/nginx-datadog/CMakeLists.txt ]]; then
+    git submodule update --init --depth=1 deps/dd-trace-cpp deps/nginx-datadog
+fi
+
+# Reconfigure so CXX_CLANG_TIDY is attached to mod_datadog, then compile
+# that target. CMake passes the exact ci-dev compile line to tidy.
+# RUM is off in ci-dev, so rum/ is not a source of mod_datadog.
+cmake --preset=ci-dev -B "$build_dir" . \
+    -DHTTPD_DATADOG_ENABLE_CLANG_TIDY=ON \
+    -DHTTPD_DATADOG_CLANG_TIDY="$tidy"
+
+cmake --build "$build_dir" --target mod_datadog