Disable -Wnoexcept-type wholesale

[kimgr]

Summary

-Wnoexcept-type under GCC triggers false positives if a nothrow function is called through a template argument.
See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80985 for details.

Several low-level constructs in LLVM take predicates by template-arg and the warning appears to be triggered by
all GNU libc character classification functions, for example.

The LLVM libraries have no stable C++ API, so the warning is not useful.

[kimgr]

Thanks! Could you also commit this for me?

Might be worth mentioning https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80985 in the commit message -- seems to capture exactly this usage.

[kimgr]

@thakis I updated the Title/Summary to what I think is a reasonable commit message. Could you commit this for me? Thanks!

[kimgr]

This appears ready to go, here's a weekly commit ping.

[aaron.ballman]

I've commit in r341361, thank you for the patch!

cmake/modules/HandleLLVMOptions.cmake

if (LLVM_ENABLE_WARNINGS AND (LLVM_COMPILER_IS_GCC_COMPATIBLE OR CLANG_CL))
   append_if(USE_NO_UNINITIALIZED "-Wno-uninitialized" CMAKE_CXX_FLAGS)
   append_if(USE_NO_MAYBE_UNINITIALIZED "-Wno-maybe-uninitialized" CMAKE_CXX_FLAGS)
 
   # Disable -Wclass-memaccess, a C++-only warning from GCC 8 that fires on
   # LLVM's ADT classes.
   check_cxx_compiler_flag("-Wclass-memaccess" CXX_SUPPORTS_CLASS_MEMACCESS_FLAG)
   append_if(CXX_SUPPORTS_CLASS_MEMACCESS_FLAG "-Wno-class-memaccess" CMAKE_CXX_FLAGS)
 
+  # The LLVM libraries have no stable C++ API, so -Wnoexcept-type is not useful.
+  check_cxx_compiler_flag("-Wnoexcept-type" CXX_SUPPORTS_NOEXCEPT_TYPE_FLAG)
+  append_if(CXX_SUPPORTS_NOEXCEPT_TYPE_FLAG "-Wno-noexcept-type" CMAKE_CXX_FLAGS)
+
   # Check if -Wnon-virtual-dtor warns even though the class is marked final.
   # If it does, don't add it. So it won't be added on clang 3.4 and older.
   # This also catches cases when -Wnon-virtual-dtor isn't supported by
   # the compiler at all.  This flag is not activated for gcc since it will
   # incorrectly identify a protected non-virtual base when there is a friend
   # declaration. Don't activate this in general on Windows as this warning has
   # too many false positives on COM-style classes, which are destroyed with
   # Release() (PR32286).