back-in-time-plugin

No more print debugging, No more repetitive manual debugging.

This plugin helps you to track the changes of application state during its execution. Also, you can easily revert the state to the previous one. We call it "back-in-time" debugging.

This plugin currently intended to be used with Android projects. But we are planning to support other platforms in the future.

Debugging tool is available at flipper-plugin. Want to play with it? Android example is available at back-in-time-demo module in this repository.

Important

This project is still a work in progress, and its API is unstable and may change without any notice. Also, we are planning make back-in-time-debugger implementation independent from Flipper to support other platforms (iOS, Desktop, JS...). Using this plugin for a hobby project is fine, but we do not recommend using it for production projects yet.

How to use

Manual Publishing Artifacts

This plugin is still under development, and its artifacts does not exist on Maven Central yet. You can manually publish them to your local Maven repository by running the following command in the project's root directory:

./gradlew publishToMavenLocal

Configure Gradle

settings.gradle.kts

pluginManagement {
    repositories {
        mavenLocal() // plugin is published to Maven Local
        // ...
    }
    plugins {
        id("io.github.kitakkun.backintime") version "1.0.0" apply false
        kotlin("plugin.serialization") version "2.0.0" apply false // required by the plugin
    }
}

dependencyResolutionManagement {
    repositories {
        mavenLocal() // annotation library and runtime library are also published to Maven Local
        // ...
    }
}

build.gradle.kts

plugins {
    id("io.github.kitakkun.backintime") version "1.0.0"
    kotlin("plugin.serialization")
    ...
}

// add required dependencies
dependencies {
    // Note that annotations and runtime library are automatically added by the back-in-time gradle plugin

    // other dependencies required to use the plugin
    implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:$kotlinxSerializationVersion")
    // debugger is implemented as a Flipper plugin, so you need this
    debugImplementation("com.facebook.flipper:flipper:$flipperVersion")
    debugImplementation("com.facebook.soloader:soloader:$soloaderVersion")
    releaseImplementation("com.facebook.flipper:flipper-noop:$flipperVersion")
}

backInTime {
    enabled = true // default is true
}

Annotate your class

Annotate your class with @BackInTime to make it back-in-time debuggable. Make sure property you want to debug is holding serializable value by kotlinx.serialization.

@BackInTime
class CounterViewModel : ViewModel() {
    var count = 0

    fun increment() {
        count++
    }
}

One more step (Setup Flipper)

Currently, this plugin is completely dependent on Flipper. You need to setup Flipper to use this plugin. See Flipper for more information.

You can use pre-built FlipperPlugin implementation class BackInTimeDebugFlipperPlugin to add the back-in-time debugging feature to your Flipper. Also, debugging tool is available at flipper-plugin-back-in-time.

How it works

This plugin comes with two phases: compile-time and runtime.

Compile-time

At compile-time, this plugin finds the classes annotated with @BackInTime and generates the code to track the changes of its state. For example, if you have the following class:

@BackInTime
class CounterViewModel {
    var count = 0

    fun increment() {
        count++
    }
}

The plugin modify the class as follows(not exact the same, just for explanation):

@BackInTime
class CounterViewModel : BackInTimeDebuggable {
    var count = 0
    // other required properties for debugging...

    init {
        BackInTimeDebugService.emitEvent(DebuggableStateHolderEvent.RegisterInstance(...))
    }

    fun increment() {
        val callUUID = UUID.randomUUID().toString()
        BackInTimeDebugService.emitEvent(DebuggableStateHolderEvent.MethodCall(...))
        count++
        BackInTimeDebugService.emitEvent(DebuggableStateHolderEvent.PropertyValueChange(...))
    }

    fun forceSetValue(propertyName: String, value: Any?) {
        when (propertyName) {
            "count" -> if (value is Int) count = value
        }
    }

    // other required methods for debugging...
}

Runtime

At runtime, inserted code works to enable the back-in-time debugging. The debugger is implemented as a Flipper plugin, so you can debug your app via Flipper.