Add a new driver option to disable warning about c++17's non-throwing exception specification in function signature

[ahatanak]

Summary

The option allows disabling just the warning about non-throwing exception specification in function signature instead of disabling all c++1z compatibility warnings with -Wno-c++1z-compat.

I'm not sure "-Wc++1z-compat-exception-spec" sounds right.

Maybe -Wc++1z-compat-mangling, -Wc++1z-mangling, or -Wc++1z-compat-exception-spec-function is better?

rdar://problem/32628743

[dexonsmith]

I think -Wc++1z-mangling is best. IMO, with C++1z in the name, it's already clear that this is about compatibility. I also don't think we need to get as specific as -Wc++1z-compat-exception-spec.

LGTM with that name, but you might wait a day or two in case someone has a strong opinion to the contrary.

[rsmith]

We use the -Wc++NN-compat- prefix on all the other subwarnings of -Wc++NN-compat warnings (examples: -Wc++98-compat-bind-to-temporary-copy, -Wc++11-compat-reserved-user-defined-literal, ...). I'd prefer to include the -compat in the name for consistency; I also find it less clear what the warning flag would mean without it (I would expect -Wc++1z-mangling to only fire in C++1z mode, whereas this warning never fires in C++1z mode).

-Wc++1z-compat-mangling seems fine to me.

Just curious, though: what is the motivation for enabling the rest of -Wc++1z-compat but not this part? This seems a lot more serious than the other warnings in the group. (Regardless, I think this patch is useful for the opposite: enabling just this one warning without the rest...)

[dexonsmith]

We use the -Wc++NN-compat- prefix on all the other subwarnings of -Wc++NN-compat warnings

Interesting; I thought I saw a counter-example recently, and took that as the rule (although I can't for the life of me remember what it was). -Wc++NN-compat-mangling SGTM though.

Just curious, though: what is the motivation for enabling the rest of -Wc++1z-compat but not this part? This seems a lot more serious than the other warnings in the group. (Regardless, I think this patch is useful for the opposite: enabling just this one warning without the rest...)

A user is recompiling the codebase as a unit so binary compatibility doesn't matter, but language semantics do.

cfe/trunk/include/clang/Basic/DiagnosticGroups.td

 def CXX11ExtraSemi : DiagGroup<"c++11-extra-semi">;
 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">;
 
 // 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]>;
def CXX11CompatPedantic : DiagGroup<"c++11-compat-pedantic",
                                     [CXXPre14CompatPedantic,
                                      CXXPre1zCompatPedantic]>;
 
 def CXX14Compat : DiagGroup<"c++14-compat", [CXXPre1zCompat]>;
 def CXX14CompatPedantic : DiagGroup<"c++14-compat-pedantic",
                                     [CXXPre1zCompatPedantic]>;
 
 def CXX1zCompat : DiagGroup<"c++1z-compat", [DeprecatedRegister,
-                                             DeprecatedIncrementBool]>;
+                                             DeprecatedIncrementBool,
+                                             CXX1zCompatMangling]>;
 
 def ExitTimeDestructors : DiagGroup<"exit-time-destructors">;
 def FlexibleArrayExtensions : DiagGroup<"flexible-array-extensions">;
 def FourByteMultiChar : DiagGroup<"four-char-constants">;
 def GlobalConstructors : DiagGroup<"global-constructors">;
 def BitwiseOpParentheses: DiagGroup<"bitwise-op-parentheses">;
 def LogicalOpParentheses: DiagGroup<"logical-op-parentheses">;
 def LogicalNotParentheses: DiagGroup<"logical-not-parentheses">;

cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td

 def note_exception_spec_deprecated : Note<"use '%0' instead">;
 def warn_deprecated_copy_operation : Warning<
   "definition of implicit copy %select{constructor|assignment operator}1 "
   "for %0 is deprecated because it has a user-declared "
   "%select{copy %select{assignment operator|constructor}1|destructor}2">,
   InGroup<Deprecated>, DefaultIgnore;
 def warn_cxx1z_compat_exception_spec_in_signature : Warning<
   "mangled name of %0 will change in C++17 due to non-throwing exception "
-  "specification in function signature">, InGroup<CXX1zCompat>;
+  "specification in function signature">, InGroup<CXX1zCompatMangling>;
 
 def warn_global_constructor : Warning<
   "declaration requires a global constructor">,
   InGroup<GlobalConstructors>, DefaultIgnore;
 def warn_global_destructor : Warning<
   "declaration requires a global destructor">,
    InGroup<GlobalConstructors>, DefaultIgnore;
 def warn_exit_time_destructor : Warning<

cfe/trunk/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
 
 #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}}
namespace CompatWarning {
   // These cases take an ABI break in C++17 because their parameter / return types change.
   void f1(void p() noexcept);
   void f2(void (*p)() noexcept(true));
   void f3(void (&p)() throw());
   void f4(void (X::*p)() throw());
   auto f5() -> void (*)() throw();
   auto f6() -> void (&)() throw();
   auto f7() -> void (X::*)() throw();
-#if __cplusplus <= 201402L
+#if __cplusplus <= 201402L && !defined(NO_COMPAT_MANGLING)
   // expected-warning@-8 {{mangled name of 'f1' will change in C++17 due to non-throwing exception specification in function signature}}
   // expected-warning@-8 {{mangled name of 'f2' will change in C++17 due to non-throwing exception specification in function signature}}
   // expected-warning@-8 {{mangled name of 'f3' will change in C++17 due to non-throwing exception specification in function signature}}
   // expected-warning@-8 {{mangled name of 'f4' will change in C++17 due to non-throwing exception specification in function signature}}
   // expected-warning@-8 {{mangled name of 'f5' will change in C++17 due to non-throwing exception specification in function signature}}
   // expected-warning@-8 {{mangled name of 'f6' will change in C++17 due to non-throwing exception specification in function signature}}
   // expected-warning@-8 {{mangled name of 'f7' will change in C++17 due to non-throwing exception specification in function signature}}
 #endif