[META] Upgrading Folly

[hramos]

For Discussion

The Folly version used in open source is very old. We're looking for volunteers interested in making the necessary changes to upgrade Folly in React Native.

Known Incompatibilities

This is in no way an exhaustive list, but be aware you'll need to tackle the following when upgrading Folly:

• folly::Optional's has_value() doesn't exist
• No template named 'Optional' in namespace 'folly' stuff

[fkgozali]

to upgrade Folly in React Native

Ideally, we'd want to pull the latest folly directly from https://github.com/facebook/folly - or at least use the latest version for each RN release - automatically.

This will involve updating/changing the integration with CocoaPods + gradle that react-native repo has today, e.g. making them run the build scripts already provided by folly repo, instead of making their own wrapper scripts / build steps.

[dulmandakh]

I would like to volunteer to upgrade Folly in Android, and I think this experience will help me better learn C++.

Also it might be better to prepare RN for Clang and libc++ support, as it'll be the only compiler and STL in next NDK release. I tried to build RN with Clang and got many warnings, errors in Folly. So I think that it might be better to upgrade C++ or native tools beforehand, maybe merge #20357 which would land latest Android NDK version.

[dulmandakh]

maybe it's better to switch to CMake to build jni code on Android, because boost, glob and folly supports it, but also many C++ libraries.

[gengjiawen]

@dulmandakh Good idea. And with it we can also have better IDE support.

[yinhangfeng]

I have tried building with cmake
https://github.com/yinhangfeng/react-native/blob/0.53-stable-cmake/ReactAndroid/CMakeLists.txt
maybe have some reference value
i don't understand c++ but this does work.

for the convenience of testing I put all the libraries in ReactAndroid/third-party-ndk
Folly version 2018.02.05.00

problem:

1. c++_shared conflict with jsc-android-buildscripts
   https://github.com/yinhangfeng/react-native/blob/0.53-stable-cmake/ReactAndroid/build.gradle#L255
2. JSC_JSGlobalContextEnableDebugger does not exist https://github.com/yinhangfeng/react-native/blob/0.53-stable-cmake/ReactCommon/cxxreact/JSCExecutor.cpp#L224

[dulmandakh]

@yinhangfeng could you please try to build master with CMake as is, or without bumping libraries. Once finished it will be easy to bump libraries to latest versions. Thank you.

[Kudo]

I am going to upgrade folly and build the code with clang.
So far the build is passed with folly's patch facebook/folly#953.
But there is still a bottleneck for runtime crash, that current prebuilt android-jsc (libjsc.so and libicu_common.so) are still built by GCC.
Both original JSC on jcenter and current upstream one are linked to libgnustl_shared.so.

It seems that the community maintained android-jsc builder could build JSC with clang.
I would clarify if there are any plans to upgrade android-jsc that built by clang.
or maybe @gengjiawen could share the steps that how you build the android-jsc at #18754.

[dulmandakh]

I think that it might be better to start with clang then upgrade folly, because clang is default toolchain for XCode so we'll have identical toolchains for Folly upgrade. But it's your choice, good luck 👍

[Kudo]

I've tried before and the old folly does not support NDK with clang build.
This issue relates to this facebook/folly#75.
That's why I upgrade folly directly.

[Kudo]

Just create #21863 to show my changes in case if someone has interests.