Add GCC's noexcept-type alias for c++1z-compat-mangling

[teemperor]

Summary

GCC has named this -Wnoexcept-type, so let's add an alias to stay compatible with the GCC flags.

[ahatanak]

I didn't know gcc had its own option. This change seems reasonable to me.

Since c++1z-compat-mangling was added just a few days ago, should we just rename it instead of adding an alias?

[teemperor]

@ahatanak I think we can leave the more expressive clang name for this warning and just add the bit cryptic GCC name for compability. But I don't have a strong opinion on this.

[karies]

For the record, here's what GCC does (from https://gcc.gnu.org/onlinedocs/gcc/C_002b_002b-Dialect-Options.html#C_002b_002b-Dialect-Options which probably has a typo, the second -Wnoexcept is likely meant to be -Wnoexcept-type): "Enabled by -Wabi and -Wc++1z-compat." -Wc++1z-compat is probably meant to enable a group out of which -Wnoexcept-type is just one (currently the only one as far as I can see). FWIW, we notice the missing -Wno-noexcept-type but not -Wc++1z-compat.

[teemperor]

ping. Any objections to adding this GCC alias?

[dexonsmith]

LGTM.

include/clang/Basic/DiagnosticGroups.td

 def ExtraSemi : DiagGroup<"extra-semi", [CXX11ExtraSemi]>;
 
 def GNUFlexibleArrayInitializer : DiagGroup<"gnu-flexible-array-initializer">;
 def GNUFlexibleArrayUnionMember : DiagGroup<"gnu-flexible-array-union-member">;
 def GNUFoldingConstant : DiagGroup<"gnu-folding-constant">;
 def FormatExtraArgs : DiagGroup<"format-extra-args">;
 def FormatZeroLength : DiagGroup<"format-zero-length">;
 def CXX1zCompatMangling : DiagGroup<"c++1z-compat-mangling">;
+// Name of this warning in GCC.
+def NoexceptType : DiagGroup<"noexcept-type", [CXX1zCompatMangling]>;
 
 // Warnings for C++1y code which is not compatible with prior C++ standards.
 def CXXPre14Compat : DiagGroup<"c++98-c++11-compat">;
 def CXXPre14CompatPedantic : DiagGroup<"c++98-c++11-compat-pedantic",
                                        [CXXPre14Compat]>;
 def CXXPre1zCompat : DiagGroup<"c++98-c++11-c++14-compat">;
 def CXXPre1zCompatPedantic : DiagGroup<"c++98-c++11-c++14-compat-pedantic",
                                        [CXXPre1zCompat]>;

test/SemaCXX/cxx1z-noexcept-function-type.cpp

 // RUN: %clang_cc1 -std=c++14 -verify -fexceptions -fcxx-exceptions %s
 // RUN: %clang_cc1 -std=c++1z -verify -fexceptions -fcxx-exceptions %s -Wno-dynamic-exception-spec
 // RUN: %clang_cc1 -std=c++14 -verify -fexceptions -fcxx-exceptions -Wno-c++1z-compat-mangling -DNO_COMPAT_MANGLING %s
+// RUN: %clang_cc1 -std=c++14 -verify -fexceptions -fcxx-exceptions -Wno-noexcept-type -DNO_COMPAT_MANGLING %s
 
 #if __cplusplus > 201402L
 
 template<typename T> void redecl1() noexcept(noexcept(T())) {} // expected-note {{previous}}
 template<typename T> void redecl1() noexcept(noexcept(T())); // ok, same type
 template<typename T> void redecl1() noexcept(noexcept(T())) {} // expected-error {{redefinition}}
 
 template<bool A, bool B> void redecl2() noexcept(A); // expected-note {{previous}}