[Guide] Speeding up your Android/iOS Build

docs/build-speed.md

@@ -0,0 +1,200 @@
+---
+id: build-speed
+title: Speeding up your Build
+---
+
+Building your React Native app could be **expensive** and take several minutes of developers time.
+This can be problematic as your project grows and generally in bigger organizations with multiple React Native developers.
+
+With [the New React Native Architecture](/docs/next/new-architecture-app-modules-android), this problem is becoming more critical
+as you might have to compile some native C++ code in your project with the Android NDK in addition to the native code already necessary for the iOS and Android platforms.
+
+To mitigate this performance hit, this page shares some suggestions on how to **improve your build time**.
+
+## Android
+
+### Build only one ABI
+
+When building your android app locally, you build all the 4 ABIs by default: `armeabi-v7a`, `arm64-v8a`, `x86` & `x86_64`.
+
+However, you probably don't need to build all of them if you're building locally and testing your emulator or on a physical device.
+
+This should reduce your build time by a **~75% factor**.
+
+If you're using the React Native CLI, you can use the `--active-arch-only` flag together with the `run-android` command.
+This flag will make sure the correct ABI is picked up from either the running emulator or the plugged in phone.
+To confirm that this approach is working fine, you'll see a message like `info Detected architectures arm64-v8a` on console.
+
+```
+$ yarn react-native run-android --active-arch-only
+
+[ ... ]
+info Running jetifier to migrate libraries to AndroidX. You can disable it using "--no-jetifier" flag.
+Jetifier found 1037 file(s) to forward-jetify. Using 32 workers...
+info JS server already running.
+info Detected architectures arm64-v8a
+info Installing the app...
+```
+
+This mechanism relies on the `reactNativeArchitectures` Gradle property.
+
+Therefore, if you're building directly with Gradle from the command line and without the CLI, you can specify the ABI you want to build as follows:
+
+```
+$ ./gradlew :app:assembleDebug -PreactNativeArchitectures=x86,x86_64
+```
+
+This can be useful if you wish to build your Android App on a CI and use a matrix to parallelize the build of the different architectures.
+
+If you wish, you can also override this value locally, using the `gradle.properties` file you have in the [top level folder](https://github.com/facebook/react-native/blob/19cf70266eb8ca151aa0cc46ac4c09cb987b2ceb/template/android/gradle.properties#L30-L33) of your project:
+
+```
+# Use this property to specify which architecture you want to build.
+# You can also override it from the CLI using
+# ./gradlew <task> -PreactNativeArchitectures=x86_64
+reactNativeArchitectures=armeabi-v7a,arm64-v8a,x86,x86_64
+```
+
+Once you build a **release version** of your app, don't forget to remove those flags as you want to build an apk/app bundle that works for all the ABIs and not only for the one you're using in your daily development workflow.
+
+## Use a compiler cache
+
+If you're running frequent native builds, you might benefit from using a compiler cache.
+Specifically you can use two type of caches: local compiler caches and distributed compiler caches.
+
+### Local caches
+
+We suggest to use [**ccache**](https://ccache.dev/) to cache the compilation of your native builds.
+Ccache works by wrapping the C++ compilers, storing the compilation results, and skipping the compilation
+if an intermediate compilation result was originally stored.
+
+To install it, you can follow the [official installation instructions](https://github.com/ccache/ccache/blob/master/doc/INSTALL.md).
+
+On Mac OS, we recommend to install ccache with `brew install ccache`.
+Once installed you can configure it as follows to cache NDK compile results:
+
+```
+ln -s ccache /usr/local/bin/gcc
+ln -s ccache /usr/local/bin/g++
+ln -s ccache /usr/local/bin/cc
+ln -s ccache /usr/local/bin/c++
+```
+
+This will create symbolic links to `ccache` inside the `/usr/local/bin/` which are called `gcc`, `g++`, `cc` and `c++`.
+
+This works as long as `/usr/local/bin/` comes first than `/usr/bin/` inside your `$PATH` variable, which is the default.
+
+You can verify that it works using the `which` command:
+
+```
+$ which gcc
+/usr/local/bin/gcc
+```
+
+If the results is `/usr/local/bin/gcc`, then you're effectively calling `ccache` which will wrap the `gcc` calls.
+
+You can then do two Android clean builds. You will notice that the second build was way faster than the first one (it should take seconds rather than minutes).
+While building, you can verify that `ccache` works correctly and check the cache hits/miss rate `ccache -s`
+
+```
+$ ccache -s
+Summary:
+  Hits:             196 /  3068 (6.39 %)
+    Direct:           0 /  3068 (0.00 %)
+    Preprocessed:   196 /  3068 (6.39 %)
+  Misses:          2872
+    Direct:        3068
+    Preprocessed:  2872
+  Uncacheable:        1
+Primary storage:
+  Hits:             196 /  6136 (3.19 %)
+  Misses:          5940
+  Cache size (GB): 0.60 / 20.00 (3.00 %)
+```
+
+Should you need to wipe your cache, you can do so with `ccache --clear`
+
+#### Using this approach on a CI
+
+Ccache uses the `/Users/$USER/Library/Caches/ccache` folder on macOS to store the cache.
+Therefore you could save & restore this folder also on CI to speedup your builds.
+
+However, there are a couple of things to be aware:
+
+1. On CI, we recommend to do a full clean build, to avoid poisoned cache problems. If you follow the approach mentioned in the previous paragraph, you should be able to parallelize the native build on 4 different ABIs and you will most likely not need `ccache` on CI.
+
+2. `ccache` relies on timestamps to compute a cache hit. This doesn't work well on CI as files are re-downloaded at every CI run. To overcome this, you'll need to use the `compiler_check content` option which relies instead on [hashing the content of the file](https://ccache.dev/manual/4.3.html).
+
+### Distributed caches
+
+Similar to local caches, you might want to consider using a distributed cache for your native builds.
+This could be specifically useful in bigger organizations that are doing frequent native builds.
+
+We recommend to use [sccache](https://github.com/mozilla/sccache) to achieve this.
+We defer to the sccache [distributed compilation quickstart](https://github.com/mozilla/sccache/blob/main/docs/DistributedQuickstart.md) for instructions on how to setup and use this tool.
+
+## iOS
+
+### Use a compiler cache
+
+Compilation of Objective-C/C++ and Swift files may also be accelerated by a compiler cache.
+
+Similar to the Android compiler cache section above, we recommend using `ccache`, and you should install it in the same way.
+
+For Xcode to take advantage of a compiler cache three steps are required:
+
+1. You must make symbolic links to the compilers that xcodebuild needs, similar to the links made above for `gcc` and `g++` but Xcode uses `clang` and `clang++`:
+
+```
+ln -s ccache /usr/local/bin/clang
+ln -s ccache /usr/local/bin/clang++
+```
+
+This will create symbolic links to `ccache` inside the `/usr/local/bin/` which are called `clang` and `clang++`.
+
+This works as long as `/usr/local/bin/` comes first than `/usr/bin/` inside your `$PATH` variable, which is the default.
+
+You can verify that it works using the `which` command:
+
+```
+$ which clang
+/usr/local/bin/clang
+```
+
+If the result is `/usr/local/bin/clang`, then you're effectively calling `ccache` which will wrap the `clang` calls.
+
+2. You must alter the way Xcode and `xcodebuild` call for the compiler command. By default they use _fully specified paths_ to the compiler binaries, so the symbolic links installed in `/usr/local/bin` will not be used. You may configure Xcode to use _relative_ names for the compilers using either of these two options:
+
+- environment variables prefixed on the command line if you use a direct command line: `CLANG=clang CLANGPLUSPLUS=clang++ LD=clang LDPLUSPLUS=clang++ xcodebuild <rest of xcodebuild command line>`
+- A `post_install` section in your `ios/Podfile` that alters the compiler in your Xcode workspace during the `pod install` step:
+
+```ruby
+  post_install do |installer|
+    react_native_post_install(installer)
+
+    # ...possibly other post_install items here
+
+    installer.pods_project.targets.each do |target|
+      target.build_configurations.each do |config|
+        # Using the un-qualified names means you can swap in different implementations, for example ccache
+        config.build_settings["CC"] = "clang"
+        config.build_settings["LD"] = "clang"
+        config.build_settings["CXX"] = "clang++"
+        config.build_settings["LDPLUSPLUS"] = "clang++"
+      end
+    end
+
+    __apply_Xcode_12_5_M1_post_install_workaround(installer)
+  end
+```
+
+3. A `ccache` configuration that allows for a certain level of sloppiness and cache behavior such that ccache registers cache hits during Xcode compiles. The ccache configuration variables that are different from standard are as follows if configured by environment variable:
+
+```bash
+export CCACHE_SLOPPINESS=clang_index_store,file_stat_matches,include_file_ctime,include_file_mtime,ivfsoverlay,pch_defines,modules,system_headers,time_macros
+export CCACHE_FILECLONE=true
+export CCACHE_DEPEND=true
+export CCACHE_INODECACHE=true
+```
+
+The same may be configured in a `ccache.conf` file or any other mechanism ccache provides. More on this can be found in the [official ccache manual](https://ccache.dev/manual/4.3.html).

docs/new-architecture-app-modules-android.md

@@ -13,7 +13,8 @@ Make sure your application meets all the [prerequisites](new-architecture-app-in
 
 :::caution
 
-In this iteration of the guide we’re setting up the project to let you build from source. You might notice an increase in your build time because of this. We’re looking into what would be the preferred approach here so please feel free to share your feedbacks.
+In this iteration of the guide we’re setting up the project to let you build from source. You might notice an increase in your build time because of this.
+You can mitigate this by following the approach described in this guide: [Speeding up your Android Build](/docs/next/build-speed-android)
 
 :::
 

website/sidebars.json

@@ -66,7 +66,8 @@
       "optimizing-flatlist-configuration",
       "ram-bundles-inline-requires",
       "profiling",
-      "profile-hermes"
+      "profile-hermes",
+      "build-speed"
     ],
     "JavaScript Runtime": ["javascript-environment", "timers", "hermes"],
     "Native Modules": [