expo-build-flags
v0.7.0
Published
A module to make feature-flagging easier for expo projects.
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expo-build-flags
A module to make feature-flagging easier for expo projects.
This module is in active development and is not stable or well documented yet.
Getting Started
yarn add expo-build-flags
Add a flags file to the root of your repo in the form of the test example, or run yarn build-flags init
.
Run yarn build-flags override +secretFeature -newFeature
sometime before your bundle server or build start to generate the runtime typescript module. This path is defined by mergePath
and you should add it to your project gitignore.
The arguments after the override command are the flags you want to +
enable or -
disable. No comparison with the default value is done, so if it's already enabled and you +enable
it, it's a no-op.
You can run yarn build-flags ota-override
instead of "override" to do the same but also consider the branch name in two supported CI environments: Github and Gitlab. Use the ota.branches
array in the flags.yml to setup that matching and branch-based enablement.
Set Flags in CI & for Static Builds
To set flags for EAS builds, set the EXPO_BUILD_FLAGS
environment variable in eas.json
for your profile. This value will be available to the config plugin at build time in EAS when you add it to your app.json
plugins array:
{
"expo": {
+ "plugins": ["expo-build-flags"]
}
}
Using the EXPO_BUILD_FLAGS
environment variable, the config plugin will:
- add a
<meta-data android:name="EXBuildFlags" />
tag to your AndroidManifest.xml - add a
EXBuildFlags
array to your Info.plist - generate the runtime build flags module for your javascript bundle
The variable value is a comma-separated list of flag names you want to enable, ie: EXPO_BUILD_FLAGS=newFeature,secretFeature
.
Enable Tree Shaking
To benefit from tree shaking, add the babel plugin to your project's babel config:
{
presets: ["babel-preset-expo"],
plugins: [
+ ["expo-build-flags/babel-plugin", { flagsModule: "./constants/buildFlags.ts" }],
],
}
The flagsModule
path must match the runtime mergePath
in your committed flags.yml file. This plugin replaces the BuildFlags
imports with the literal boolean values which allows the build pipeline to strip unreachable paths.
Flagged Autolinking
If your feature relies on native module behaviour, you may want to avoid linking that module if the build flag is off. To do so, specify the absolute name or relative path to the module in the base definition for your flag:
Example for flags.yml definition:
flags:
featureWithNativeStuff:
value: false
modules:
- react-native-device-info
In the above example, react-native-device-info
would be excluded from autolinking. If you want to allow builds to occur on a specific branch, you can specify it:
modules:
- react-native-device-info:
branch: some-branch-with-build
Locally-referenced modules aren't currently supported (until this 'exclude' exclusion can be overridden).
Goals
- [x] allow defining a base set of flags that are available at runtime in one place
- [x] allow for overriding a flag's value locally during development (without having to change the default value committed to source control)
- [x] allow for running OTA updates with the flag on for specific CI branches
- [x] allow for overriding a flag's value for any native build for one-off testing
- [x] allow for referencing flag values in JS
- [ ] allow for referencing flag values from native code on iOS or Android
- [x] allow for tree-shaking of the JS bundle and dead code path elimination
- [x] allow for typescript to see the specific flags available
- [ ] add metro resolver w/ proxy to surface better flagged autolinking error messages
- [ ] add android integration spec for flagged autolinking
- [ ] doc site & readme cleanup to reference