b1c749075d
Summary: @public Limit child cloning to layout calculation. This also allows for mixing shared and owned children. Rationale: We do allow for shared children if the caller manages themselves. The single known use case is React Native. So far, we have cloned children eagerly whenever child lists are mutated, or layout is run. This was to allow for a quick check of the owner of any first child, assuming that either *all* or *no* child of a node are shared. For Yoga/Java, we want to get rid of global weak JNI refs, and these are also used to invoke clone callbacks. We can achieve that goal by switching to an alternative approach, passing additional data to the layout pass. This additional data has to be passed to any configured cloning callback. Therefore, it is desirable to **only call cloning functions during the layout pass.** The obvious solution seems to be to not uphold the invariant of the first child determining shared/owned state of all siblings, and allow for a mix of shared and own children. Reviewed By: shergin Differential Revision: D14136223 fbshipit-source-id: 34490cfeeb2170c99d6ed1b9bdcbcedb316813af
Yoga 
Building
Yoga builds with buck. Make sure you install buck before contributing to Yoga. Yoga's main implementation is in C, with bindings to supported languages and frameworks. When making changes to Yoga please ensure the changes are also propagated to these bindings when applicable.
Testing
For testing we rely on gtest as a submodule. After cloning Yoga run git submodule init followed by git submodule update.
For any changes you make you should ensure that all the tests are passing. In case you make any fixes or additions to the library please also add tests for that change to ensure we don't break anything in the future. Tests are located in the tests directory. Run the tests by executing buck test //:yoga.
Instead of manually writing a test which ensures parity with web implementations of Flexbox you can run gentest/gentest.rb to generate a test for you. You can write html which you want to verify in Yoga, in gentest/fixtures folder, such as the following.
<div id="my_test" style="width: 100px; height: 100px; align-items: center;">
<div style="width: 50px; height: 50px;"></div>
</div>
Run gentest/gentest.rb to generate test code and re-run buck test //:yoga to validate the behavior. One test case will be generated for every root div in the input html.
You may need to install the latest watir-webdriver gem (gem install watir-webdriver) and ChromeDriver to run gentest/gentest.rb Ruby script.
.NET
.NET testing is not integrated in buck yet, you might need to set up .NET testing environment. We have a script which to launch C# test on macOS, csharp/tests/Facebook.Yoga/test_macos.sh.
Benchmarks
Benchmarks are located in benchmark/YGBenchmark.c and can be run with buck run //benchmark:benchmark. If you think your change has affected performance please run this before and after your change to validate that nothing has regressed. Benchmarks are run on every commit in CI.
JavaScript
Installing through NPM
npm install yoga-layout
By default this will install the library and try to build for all platforms (node, browser asm, and standalone webpack). You may receive errors if you do not have the required platform development tools already installed. To preset the platform you'd like to build for you can set a .npmrc property first.
npm config set yoga-layout:platform standalone
This will now only run the standalone webpack build upon install.
Build Platforms
| name | description |
|---|---|
| all (default) | Builds all of these platforms. |
| browser | Builds asm js browser version. |
| node | Builds node js version. |
| standalone | Runs webpack. |
| none | Does nothing. You can use the prepackaged libs. |