More fixes.

libcxx/modules/std/ranges.inc

@@ -138,9 +138,6 @@ export namespace std {
     }
 #endif // _LIBCPP_HAS_NO_LOCALIZATION
 
-#if _LIBCPP_STD_VER >= 23
-    // [range.adaptor.object], range adaptor objects
-    using std::ranges::range_adaptor_closure;
     // Note: This declaration not in the synopsis or explicitly in the wording.
     // However it is needed for the range adaptors.
     // [range.adaptor.object]/3
@@ -151,7 +148,11 @@ export namespace std {
     //   involving an object of type cv D as an operand to the | operator is
     //   undefined if overload resolution selects a program-defined operator|
     //   function.
+    // This is used internally in C++20 mode.
     using std::ranges::operator|;
+#if _LIBCPP_STD_VER >= 23
+    // [range.adaptor.object], range adaptor objects
+    using std::ranges::range_adaptor_closure;
 #endif
 
     // [range.all], all view

libcxx/test/tools/clang_tidy_checks/CMakeLists.txt

@@ -64,6 +64,25 @@ if(NOT HAS_CLANG_TIDY_HEADERS)
                  "clang-tidy headers are not present.")
   return()
 endif()
+
+# The clangTidy plugin uses C++20, when using stdlibc++ verify the version is correct.
+# Note it has not been tested whether version 11 works.
+file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/test.cpp" "
+#if defined(_GLIBCXX_RELEASE) && _GLIBCXX_RELEASE < 12
+  # error The stdlibc++ version is too old.
+#endif
+int main(){}
+")
+try_compile(HAS_NEWER_STANDARD_LIBRARY
+  "${CMAKE_CURRENT_BINARY_DIR}"
+  "${CMAKE_CURRENT_BINARY_DIR}/test.cpp"
+   LINK_LIBRARIES clangTidy)
+
+if(NOT HAS_NEWER_STANDARD_LIBRARY)
+  message(STATUS "Clang-tidy tests are disabled due to using "
+                 "stdlibc++ older than version 12")
+  return()
+endif()
 message(STATUS "Clang-tidy tests are enabled.")
 
 set(SOURCES