Revert "[libc++][CMake] Removes LIBCXX_ENABLE_CLANG_TIDY. (#85262)"

This reverts commit 4109b18.

It looks like the automatic detection has false positives. This broke
the following build llvm/llvm-project#85262

libcxx/CMakeLists.txt

@@ -123,6 +123,7 @@ option(LIBCXX_ENABLE_VENDOR_AVAILABILITY_ANNOTATIONS
    to provide compile-time errors when using features unavailable on some version of
    the shared library they shipped should turn this on and see `include/__availability`
    for more details." OFF)
+option(LIBCXX_ENABLE_CLANG_TIDY "Whether to compile and run clang-tidy checks" OFF)
 
 if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
   set(LIBCXX_DEFAULT_TEST_CONFIG "llvm-libc++-shared-gcc.cfg.in")
@@ -862,6 +863,10 @@ add_subdirectory(modules)
 
 set(LIBCXX_TEST_DEPS "cxx_experimental")
 
+if (LIBCXX_ENABLE_CLANG_TIDY)
+  list(APPEND LIBCXX_TEST_DEPS cxx-tidy)
+endif()
+
 list(APPEND LIBCXX_TEST_DEPS generate-cxx-modules)
 
 if (LIBCXX_INCLUDE_BENCHMARKS)

libcxx/docs/ReleaseNotes/19.rst

@@ -82,6 +82,7 @@ Deprecations and Removals
   libatomic is not available. If you are one such user, please reach out to the libc++ developers so we can collaborate
   on a path for supporting atomics properly on freestanding platforms.
 
+
 Upcoming Deprecations and Removals
 ----------------------------------
 
@@ -106,6 +107,3 @@ Build System Changes
 
 - The ``LIBCXX_EXECUTOR`` and ``LIBCXXABI_EXECUTOR`` CMake variables have been removed. Please
   set ``LIBCXX_TEST_PARAMS`` to ``executor=<...>`` instead.
-
-- The Cmake variable ``LIBCXX_ENABLE_CLANG_TIDY`` has been removed. The build system has been changed
-  to automatically detect the presence of ``clang-tidy`` and the required ``Clang`` libraries.

libcxx/test/tools/CMakeLists.txt

@@ -1,8 +1,12 @@
 
 set(LIBCXX_TEST_TOOLS_PATH ${CMAKE_CURRENT_BINARY_DIR} PARENT_SCOPE)
 
-if(NOT CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
-  message(STATUS "Clang-tidy tests are disabled due to non-clang based compiler.")
-  return()
+# TODO: Remove LIBCXX_ENABLE_CLANG_TIDY
+if(LIBCXX_ENABLE_CLANG_TIDY)
+  if(NOT CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
+    message(STATUS "Clang-tidy can only be used when building libc++ with "
+                   "a clang compiler.")
+    return()
+  endif()
+  add_subdirectory(clang_tidy_checks)
 endif()
-add_subdirectory(clang_tidy_checks)

libcxx/test/tools/clang_tidy_checks/CMakeLists.txt

@@ -9,17 +9,6 @@ set(Clang_DIR_SAVE ${Clang_DIR})
 # versions must match. Otherwise there likely will be ODR-violations. This had
 # led to crashes and incorrect output of the clang-tidy based checks.
 find_package(Clang ${CMAKE_CXX_COMPILER_VERSION})
-if(NOT Clang_FOUND)
-  message(STATUS "Clang-tidy tests are disabled since the "
-                 "Clang development package is unavailable.")
-  return()
-endif()
-if(NOT TARGET clangTidy)
-  message(STATUS "Clang-tidy tests are disabled since the "
-                 "Clang development package has no clangTidy target.")
-  return()
-endif()
-message(STATUS "Clang-tidy tests are enabled.")
 
 set(SOURCES
     abi_tag_on_virtual.cpp
@@ -33,7 +22,11 @@ set(SOURCES
     libcpp_module.cpp
    )
 
-list(APPEND LIBCXX_TEST_DEPS cxx-tidy)
+if(NOT Clang_FOUND)
+  message(STATUS "Could not find a suitable version of the Clang development package;
+                  custom libc++ clang-tidy checks will not be available.")
+  return()
+endif()
 
 set(LLVM_DIR "${LLVM_DIR_SAVE}" CACHE PATH "The directory containing a CMake configuration file for LLVM." FORCE)
 set(Clang_DIR "${Clang_DIR_SAVE}" CACHE PATH "The directory containing a CMake configuration file for Clang." FORCE)

libcxx/utils/ci/buildkite-pipeline.yml

@@ -43,6 +43,7 @@ definitions:
 
 environment_definitions:
   _common_env: &common_env
+      ENABLE_CLANG_TIDY: "On"
       LLVM_SYMBOLIZER_PATH: "/usr/bin/llvm-symbolizer-${LLVM_HEAD_VERSION}"
       CLANG_CRASH_DIAGNOSTICS_DIR: "crash_diagnostics"
       CC: clang-${LLVM_HEAD_VERSION}

libcxx/utils/ci/run-buildbot

@@ -44,6 +44,9 @@ CMAKE               The CMake binary to use. This variable is optional.
 CLANG_FORMAT        The clang-format binary to use when generating the format
                     ignore list.
 
+ENABLE_CLANG_TIDY   Whether to compile and run clang-tidy checks. This variable
+                    is optional.
+
 EOF
 }
 
@@ -108,6 +111,10 @@ function clean() {
     rm -rf "${BUILD_DIR}"
 }
 
+if [ -z "${ENABLE_CLANG_TIDY}" ]; then
+    ENABLE_CLANG_TIDY=Off
+fi
+
 function generate-cmake-base() {
     echo "--- Generating CMake"
     ${CMAKE} \
@@ -119,6 +126,7 @@ function generate-cmake-base() {
           -DLIBCXX_ENABLE_WERROR=YES \
           -DLIBCXXABI_ENABLE_WERROR=YES \
           -DLIBUNWIND_ENABLE_WERROR=YES \
+          -DLIBCXX_ENABLE_CLANG_TIDY=${ENABLE_CLANG_TIDY} \
           -DLLVM_LIT_ARGS="-sv --xunit-xml-output test-results.xml --timeout=1500 --time-tests" \
           "${@}"
 }