[libc++][CMake] Removes LIBCXX_ENABLE_CLANG_TIDY. (#85794)

The clang-tidy selection in CMake was refactored in
https://github.com/llvm/llvm-project/pull/81362. During review it was
suggested to remove this CMake option.

libcxx/CMakeLists.txt

@@ -123,7 +123,6 @@ 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")
@@ -863,10 +862,6 @@ 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

@@ -132,3 +132,6 @@ 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

@@ -1,12 +1,8 @@
 
 set(LIBCXX_TEST_TOOLS_PATH ${CMAKE_CURRENT_BINARY_DIR} PARENT_SCOPE)
 
-# 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.")
+  message(STATUS "Clang-tidy tests are disabled due to non-clang based compiler.")
   return()
 endif()
 add_subdirectory(clang_tidy_checks)
-endif()

libcxx/test/tools/clang_tidy_checks/CMakeLists.txt

@@ -9,22 +9,14 @@ 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})
-
-set(SOURCES
-    abi_tag_on_virtual.cpp
-    header_exportable_declarations.cpp
-    hide_from_abi.cpp
-    proper_version_checks.cpp
-    qualify_declval.cpp
-    robust_against_adl.cpp
-    uglify_attributes.cpp
-
-    libcpp_module.cpp
-   )
-
 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.")
+  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()
 
@@ -54,6 +46,38 @@ if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
                         )
 endif()
 
+# In some cases even with the clangTidy target present the headers appear not to
+# be on the system. Run a short test to see whether the header is present.
+file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/test.cpp" "
+#if !__has_include(\"clang-tidy/ClangTidyCheck.h\")
+  # error No clang-tidy headers
+#endif
+int main(){}
+")
+try_compile(HAS_CLANG_TIDY_HEADERS
+  "${CMAKE_CURRENT_BINARY_DIR}"
+  "${CMAKE_CURRENT_BINARY_DIR}/test.cpp"
+   LINK_LIBRARIES clangTidy)
+
+if(NOT HAS_CLANG_TIDY_HEADERS)
+  message(STATUS "Clang-tidy tests are disabled since the "
+                 "clang-tidy headers are not present.")
+  return()
+endif()
+message(STATUS "Clang-tidy tests are enabled.")
+
+set(SOURCES
+    abi_tag_on_virtual.cpp
+    header_exportable_declarations.cpp
+    hide_from_abi.cpp
+    proper_version_checks.cpp
+    qualify_declval.cpp
+    robust_against_adl.cpp
+    uglify_attributes.cpp
+
+    libcpp_module.cpp
+   )
+
 add_library(cxx-tidy MODULE ${SOURCES})
 target_link_libraries(cxx-tidy clangTidy)
 
@@ -64,3 +88,5 @@ set_target_properties(cxx-tidy PROPERTIES
 
 set_target_properties(cxx-tidy PROPERTIES LIBRARY_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})
 set(CMAKE_SHARED_MODULE_SUFFIX_CXX .plugin) # Use a portable suffix to simplify how we can find it from Lit
+
+list(APPEND LIBCXX_TEST_DEPS cxx-tidy)

libcxx/utils/ci/buildkite-pipeline.yml

@@ -43,7 +43,6 @@ 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

@@ -44,9 +44,6 @@ 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
 }
 
@@ -111,10 +108,6 @@ function clean() {
     rm -rf "${BUILD_DIR}"
 }
 
-if [ -z "${ENABLE_CLANG_TIDY}" ]; then
-    ENABLE_CLANG_TIDY=Off
-fi
-
 function generate-cmake-base() {
     echo "--- Generating CMake"
     ${CMAKE} \
@@ -126,7 +119,6 @@ function generate-cmake-base() {
           -DLIBCXX_ENABLE_WERROR=YES \
           -DLIBCXXABI_ENABLE_WERROR=YES \
           -DLIBUNWIND_ENABLE_WERROR=YES \
-          -DLIBCXX_ENABLE_CLANG_TIDY=${ENABLE_CLANG_TIDY} \
           -DLLVM_LIT_ARGS="-sv --xunit-xml-output test-results.xml --timeout=1500 --time-tests" \
           "${@}"
 }