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Nick Gerleman e5a4003af5 Breaking: Use C++ 20 (#1382) 
Summary:
Pull Request resolved: https://github.com/facebook/yoga/pull/1382

X-link: https://github.com/facebook/react-native/pull/39437

Have been running into places where C++ 20 makes life easier for use like `std::bit_cast` (that one is easy to polyfill), in-class member initializer support for bitfields, designated initializers, defaulted comparison operator, concepts instead of SFINAE, and probably more.

Our other infra is in the process of making this jump, or already has. This tests it out everywhere, across the various reference builds, to see if we have any issues.

This is a bit more aggressive than I had previously communicated, but n - 1 is going to be a better long term place than n - 2.

If we wanted to use `std::bit_cast` we would need one of:
1. GCC 11+ (~2.5 years old)
1. Clang 14 (~2.5 years old)
1. VS 16.11 (~2 years old)

For mobile this means:
1. NDK 26 (still in Beta 😭)
1. XCode 14.3.0 (~6 months old)

https://en.cppreference.com/w/cpp/compiler_support/20

That isn't quite doable yet, but we can start taking advantage of language features in the meantime. More of these will be supported in older toolchains.

Anyone needing support for older C++ versions can lag behind on more recent changes. E.g. Yoga 2.0 supports C++ 14.

bypass-github-export-checks

Changelog: [Internal]

Reviewed By: cortinico

Differential Revision: D49261607

fbshipit-source-id: 38301204d56b7bc8410c2dda9c291da1b8d61ec1
2023-09-19 00:29:50 -07:00

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Yoga Support Ukraine CocoaPods npm Maven Central

Yoga is an embeddable and performant flexbox layout engine with bindings for multiple languages.

Building

Yoga's main implementation targets C++ 20 with accompanying build logic in CMake. A wrapper is provided to build the main library and run unit tests.

./unit_tests <Debug|Release>

While not required, this script will use ninja if it is installed for faster builds.

Yoga is additionally part of the vcpkg collection of ports maintained by Microsoft and community contributors. If the version is out of date, please create an issue or pull request on the vcpkg repository.

Adding Tests

Many of Yoga's tests are automatically generated, using HTML fixtures describing node structure. These are rendered in Chrome to generate an expected layout result for the tree. New fixtures can be added to gentest/fixtures.

<div id="my_test" style="width: 100px; height: 100px; align-items: center;">
  <div style="width: 50px; height: 50px;"></div>
</div>

To generate new tests from added fixtures:

  1. Run bundle install in the gentest directory to install dependencies of the test generator.
  2. Run ruby gentest.rb in the gentest directory.

Debugging

Yoga provides a VSCode "launch.json" configuration which allows debugging unit tests. Simply add your breakpoints, and run "Debug C++ Unit tests (lldb)" (or "Debug C++ Unit tests (vsdbg)" on Windows).