Disable warnings related to anonymous types in the ObjC plugin

[vsk]

Summary

This part of lldb make use of anonymous structs and unions. The usage is
idiomatic and doesn't deserve a warning. Logic in the NSDictionary and NSSet
plugins use anonymous structs in a manner consistent with the relevant Apple
frameworks.

[davide]

LGTM, I stumbled upon the same issue :)
An alternative would be that of naming (as you suggested), but if this is consistent, no worries.

[labath]

If the "excuse" for not following llvm here is that these structs mirror apple headers, should we restrict these warnings only to the relevant files (e.g. everything in source/Plugins/Language/ObjC)?

I don't particularly care about whether we do, but I wanted to throw the idea out there, as this is the reason why I haven't done something similar yet (although the warnings are quite annoying).

[vsk]

In D40757#943483, @labath wrote:

If the "excuse" for not following llvm here is that these structs mirror apple headers, should we restrict these warnings only to the relevant files (e.g. everything in source/Plugins/Language/ObjC)?

I don't particularly care about whether we do, but I wanted to throw the idea out there, as this is the reason why I haven't done something similar yet (although the warnings are quite annoying).

I'd like to make this a narrower change as well, but unfortunately, I haven't found a way to add in extra CXX flags through the add_library or llvm_add_library utilities. Somebody tried to do this once in AddLLDB.cmake (see "set(CMAKE_CXX_FLAGS ...)"), but it's busted, and does not do anything, AFAICT.

In this case, I think it should be safe to disable these warnings project-wide, because they're not often (ever?) immediate indicators of correctness issues / undefined behavior. Given all of that, @labath are you OK with the patch as-is?

cmake/modules/LLDBConfig.cmake

241

I should point out that there's a typo here -- I've fixed this so it's spelled CXX_SUPPORTS_NO_NESTED_ANON_TYPES locally.

[labath]

In D40757#944293, @vsk wrote:

I'd like to make this a narrower change as well, but unfortunately, I haven't found a way to add in extra CXX flags through the add_library or llvm_add_library utilities. Somebody tried to do this once in AddLLDB.cmake (see "set(CMAKE_CXX_FLAGS ...)"), but it's busted, and does not do anything, AFAICT.

Yeah, I believe the correct cmake incantation in this case should be:

target_compile_options(lldbPluginObjCLanguage PRIVATE -Wno-nested-anon-types -Wno-gnu-anonymous-struct)

(placed just after add_lldb_library)

In this case, I think it should be safe to disable these warnings project-wide, because they're not often (ever?) immediate indicators of correctness issues / undefined behavior. Given all of that, @labath are you OK with the patch as-is?

I'm fine with this as well, but since we both agree that a narrower scope would be better, maybe you could try the above snippet instead.

[vsk]

• Thanks @labath! I've disabled the GNU warnings in a narrower way. PTAL.

[labath]

Cool. Thanks.

[davide]

LGTM (again)

cmake/modules/LLDBConfig.cmake

 endif ()
 
 check_cxx_compiler_flag("-Wno-vla-extension"
                         CXX_SUPPORTS_NO_VLA_EXTENSION)
 if (CXX_SUPPORTS_NO_VLA_EXTENSION)
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-vla-extension")
 endif ()
 
+check_cxx_compiler_flag("-Wno-gnu-anonymous-struct"
+                        CXX_SUPPORTS_NO_GNU_ANONYMOUS_STRUCT)
+if (CXX_SUPPORTS_NO_GNU_ANONYMOUS_STRUCT)
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-gnu-anonymous-struct")
+endif ()
+
+check_cxx_compiler_flag("-Wno-nested-anon-types"
+                        CXX_SUPPORTS_NO_GNU_ANONYMOUS_STRUCT)
+if (CXX_SUPPORTS_NO_GNU_ANONYMOUS_STRUCT)
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-nested-anon-types")
+endif ()
+
 # Disable MSVC warnings
 if( MSVC )
   add_definitions(
     -wd4018 # Suppress 'warning C4018: '>=' : signed/unsigned mismatch'
     -wd4068 # Suppress 'warning C4068: unknown pragma'
     -wd4150 # Suppress 'warning C4150: deletion of pointer to incomplete type'
     -wd4251 # Suppress 'warning C4251: T must have dll-interface to be used by clients of class U.'
     -wd4521 # Suppress 'warning C4521: 'type' : multiple copy constructors specified'