[C++] Patch Snappy config to avoid disabling RTTI

[pitrou]

Describe the enhancement requested

Snappy's CMakeLists.txt unconditionally disables RTTI. This is incompatible with some other options, such as activating UBSAN for a fuzzing build:
google/snappy#189

We should probably patch Snappy's CMakeLists.txt in our bundled build of Snappy.

Component(s)

C++, Continuous Integration

[pitrou]

@kou Does this sound reasonable to you?

[kou]

I don't want to require patch as much as possible because it's difficult that preparing patch on some environments as you noticed: #43689 (comment)

How about using CMAKE_CXX_FLAGS_<CONFIG> to override -fno-rtti instead of using patch?

diff --git a/cpp/cmake_modules/ThirdpartyToolchain.cmake b/cpp/cmake_modules/ThirdpartyToolchain.cmake
index 495aa70483..263f9d91ea 100644
--- a/cpp/cmake_modules/ThirdpartyToolchain.cmake
+++ b/cpp/cmake_modules/ThirdpartyToolchain.cmake
@@ -1365,6 +1365,13 @@ macro(build_snappy)
     endforeach()
   endif()
 
+  foreach(CONFIG DEBUG MINSIZEREL RELEASE RELWITHDEBINFO)
+    list(APPEND
+         SNAPPY_CMAKE_ARGS
+         "-DCMAKE_CXX_FLAGS_${UPPERCASE_BUILD_TYPE}=${EP_CXX_FLAGS_${CONFIG}} -frtti"
+    )
+  endforeach()
+
   if(APPLE AND CMAKE_HOST_SYSTEM_VERSION VERSION_LESS 20)
     # On macOS 10.13 we need to explicitly add <functional> to avoid a missing include error
     # This can be removed once CRAN no longer checks on macOS 10.13

Or how about using patched Snappy in system? For example, Debian's Snappy enables RTTI ( https://sources.debian.org/patches/snappy/1.2.1-1/add_option_to_enable_rtti.patch/ ) and Conda's Snappy enables RTTI ( conda-forge/snappy-feedstock#32 ).

[pitrou]

How about using CMAKE_CXX_FLAGS_<CONFIG> to override -fno-rtti instead of using patch?

I can try this.

[pitrou]

However, your patch forces RTTI on everyone, which may not be better either.

[kou]

Everyone? The specified -frtti is only used by Snappy.

[pitrou]

Hmm, that's true. But I have no idea whether some configurations may not like RTTI being enabled. @felipecrv Do you have any insight on this?