[RFC][libc++] Reworks clang-tidy selection.

The current selection is done in the test scipts which gives the user
no control where to find clang-tidy. The version selection itself is
hard-coded and not based on the version of clang used.

This moves the selection to configuration time and tries to find a better
match.
- Mixing the version of clang-tidy and the clang libraries causes ODR
  violations. This results in practice in crashes or incorrect results.
- Mixing the version of clang-tidy and the clang binaray sometimes causes
  issues with supported diagnotic flags. For example, flags tested against
  clang 17 may not be available in clang-tidy 16.

Currently clang-tidy 18.1 can be used, it tests against the clang
libraries version 18. This is a caused by the new LLVM version numbering
scheme.

The new selection tries to match the clang version or the version of the
HEAD and the last 3 releases. (During the release period libc++ supports 4
versions instead of the typical 3 versions.)

Author: mordante

cmake/Modules/LLVMVersion.cmake

@@ -0,0 +1,15 @@
+# The LLVM Version number information
+
+if(NOT DEFINED LLVM_VERSION_MAJOR)
+  set(LLVM_VERSION_MAJOR 19)
+endif()
+if(NOT DEFINED LLVM_VERSION_MINOR)
+  set(LLVM_VERSION_MINOR 0)
+endif()
+if(NOT DEFINED LLVM_VERSION_PATCH)
+  set(LLVM_VERSION_PATCH 0)
+endif()
+if(NOT DEFINED LLVM_VERSION_SUFFIX)
+  set(LLVM_VERSION_SUFFIX git)
+endif()
+

libcxx/test/tools/CMakeLists.txt

@@ -3,5 +3,10 @@ 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.")
+    return()
+  endif()
   add_subdirectory(clang_tidy_checks)
 endif()

libcxx/test/tools/clang_tidy_checks/CMakeLists.txt

@@ -5,10 +5,10 @@
 set(LLVM_DIR_SAVE ${LLVM_DIR})
 set(Clang_DIR_SAVE ${Clang_DIR})
 
-find_package(Clang 18)
-if (NOT Clang_FOUND)
-  find_package(Clang 17)
-endif()
+# Since the Clang C++ ABI is not stable the Clang libraries and clang-tidy
+# 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

libcxx/utils/libcxx/test/features.py

@@ -23,30 +23,6 @@
 _isMSVC = lambda cfg: "_MSC_VER" in compilerMacros(cfg)
 _msvcVersion = lambda cfg: (int(compilerMacros(cfg)["_MSC_VER"]) // 100, int(compilerMacros(cfg)["_MSC_VER"]) % 100)
 
-
-def _getSuitableClangTidy(cfg):
-    try:
-        # If we didn't build the libcxx-tidy plugin via CMake, we can't run the clang-tidy tests.
-        if runScriptExitCode(cfg, ["stat %{test-tools-dir}/clang_tidy_checks/libcxx-tidy.plugin"]) != 0:
-            return None
-
-        # TODO MODULES require ToT due module specific fixes.
-        if runScriptExitCode(cfg, ['clang-tidy-18 --version']) == 0:
-          return 'clang-tidy-18'
-
-        # TODO This should be the last stable release.
-        # LLVM RELEASE bump to latest stable version
-        if runScriptExitCode(cfg, ["clang-tidy-16 --version"]) == 0:
-            return "clang-tidy-16"
-
-        # LLVM RELEASE bump version
-        if int(re.search("[0-9]+", commandOutput(cfg, ["clang-tidy --version"])).group()) >= 16:
-            return "clang-tidy"
-
-    except ConfigurationRuntimeError:
-        return None
-
-
 def _getAndroidDeviceApi(cfg):
     return int(
         programOutput(
@@ -297,13 +273,6 @@ def _getAndroidDeviceApi(cfg):
         name="executor-has-no-bash",
         when=lambda cfg: runScriptExitCode(cfg, ["%{exec} bash -c 'bash --version'"]) != 0,
     ),
-    Feature(
-        name="has-clang-tidy",
-        when=lambda cfg: _getSuitableClangTidy(cfg) is not None,
-        actions=[
-            AddSubstitution("%{clang-tidy}", lambda cfg: _getSuitableClangTidy(cfg))
-        ],
-    ),
     # Whether module support for the platform is available.
     Feature(
         name="has-no-cxx-module-support",

libcxx/utils/libcxx/test/params.py

@@ -110,6 +110,37 @@ def getSizeOptimizationFlag(cfg):
         )
 
 
+def testClangTidy(cfg, version, executable):
+    try:
+        if version in commandOutput(cfg, [f"{executable} --version"]):
+            return executable
+    except ConfigurationRuntimeError:
+        return None
+
+
+def getSuitableClangTidy(cfg):
+    # If we didn't build the libcxx-tidy plugin via CMake, we can't run the clang-tidy tests.
+    if (
+        runScriptExitCode(
+            cfg, ["stat %{test-tools-dir}/clang_tidy_checks/libcxx-tidy.plugin"]
+        )
+        != 0
+    ):
+        return None
+
+    version = "{__clang_major__}.{__clang_minor__}.{__clang_patchlevel__}".format(
+        **compilerMacros(cfg)
+    )
+    exe = testClangTidy(
+        cfg, version, "clang-tidy-{__clang_major__}".format(**compilerMacros(cfg))
+    )
+
+    if not exe:
+        exe = testClangTidy(cfg, version, "clang-tidy")
+
+    return exe
+
+
 # fmt: off
 DEFAULT_PARAMETERS = [
     Parameter(
@@ -366,6 +397,16 @@ def getSizeOptimizationFlag(cfg):
         default=f"{shlex.quote(sys.executable)} {shlex.quote(str(Path(__file__).resolve().parent.parent.parent / 'run.py'))}",
         help="Custom executor to use instead of the configured default.",
         actions=lambda executor: [AddSubstitution("%{executor}", executor)],
-    )
+    ),
+    Parameter(
+        name='clang-tidy-executable',
+        type=str,
+        default=lambda cfg: getSuitableClangTidy(cfg),
+        help="Selects the clang-tidy executable to use.",
+        actions=lambda exe: [] if exe is None else [
+            AddFeature('has-clang-tidy'),
+            AddSubstitution('%{clang-tidy}', exe),
+        ]
+     ),
 ]
 # fmt: on

llvm/CMakeLists.txt

@@ -15,18 +15,7 @@ if(NOT LLVM_NO_INSTALL_NAME_DIR_FOR_BUILD_TREE)
   set(CMAKE_BUILD_WITH_INSTALL_NAME_DIR ON)
 endif()
 
-if(NOT DEFINED LLVM_VERSION_MAJOR)
-  set(LLVM_VERSION_MAJOR 19)
-endif()
-if(NOT DEFINED LLVM_VERSION_MINOR)
-  set(LLVM_VERSION_MINOR 0)
-endif()
-if(NOT DEFINED LLVM_VERSION_PATCH)
-  set(LLVM_VERSION_PATCH 0)
-endif()
-if(NOT DEFINED LLVM_VERSION_SUFFIX)
-  set(LLVM_VERSION_SUFFIX git)
-endif()
+include(${LLVM_COMMON_CMAKE_UTILS}/Modules/LLVMVersion.cmake)
 
 set_directory_properties(PROPERTIES LLVM_VERSION_MAJOR "${LLVM_VERSION_MAJOR}")
 

runtimes/CMakeLists.txt

@@ -6,6 +6,8 @@ set(LLVM_COMMON_CMAKE_UTILS "${CMAKE_CURRENT_SOURCE_DIR}/../cmake")
 include(${LLVM_COMMON_CMAKE_UTILS}/Modules/CMakePolicy.cmake
   NO_POLICY_SCOPE)
 
+include(${LLVM_COMMON_CMAKE_UTILS}/Modules/LLVMVersion.cmake)
+
 project(Runtimes C CXX ASM)
 
 list(INSERT CMAKE_MODULE_PATH 0