Kotlin Suspend Interface reversal

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Generate platform-compatible extension types for interfaces or abstract classes that contain suspend functions, based on KSP.

Summary

Suppose: You have an interface like the following:

interface Foo {
    /** get value */
    suspend fun value(): Int
    
    /** get name */
    val name: String
}

Now, you want this interface to be implemented by your users, but it's not directly available to Java users!

At this point, you provide two additional interfaces to accommodate blocking and asynchrony, as follows:

import java.util.concurrent.CompletableFuture

interface Foo {
    /** get value */
    @JvmSynthetic
    suspend fun value(): Int

    /** get name */
    val name: String
}

/** Provided to Java */
interface JBlockingFoo : Foo {
    fun valueBlocking(): Int

    @JvmSynthetic
    override suspend fun value(): Int = valueBlocking()
}

/** Provided to Java */
interface JAsyncFoo : Foo {
    fun valueAsync(): CompletableFuture<out Int>

    @JvmSynthetic
    override suspend fun value(): Int = valueAsync().await()
}

In this way, Java users can implement it:

public class FooImpl implements JBlockingFoo {
    @Override
    public int valueBlocking() {
        return 1;
    }

    @Override
    public String getName() {
        return "name";
    }
}

Usage

JVM

plugins {
    id("org.jetbrains.kotlin.jvm") version "$KOTLIN_VERSION"
    id("com.google.devtools.ksp") version "$KSP_VERSION"
}

repositories {
    mavenCentral()
}

dependencies {
    implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:$COROUTINES_VERSION")
    // annotation
    compileOnly("love.forte.suspend-interface-reversal:annotations:$VERSION")
    // ksp processor
    ksp("love.forte.suspend-interface-reversal:processor:$VERSION")
}

Multiplatform

Note

Support JVM and JS.

plugins {
    id("org.jetbrains.kotlin.multiplatform") version "$KOTLIN_VERSION"
    id("com.google.devtools.ksp") version "$KSP_VERSION"
}

repositories {
    mavenCentral()
}

kotlin {
    jvm {
        // ...
    }
    js(IR) {
        // ...
    }

    linuxX64()
    macosX64()
    mingwX64()
    // ...
    sourceSets {
        commonMain.dependencies {
            implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:$COROUTINES_VERSION")
            compileOnly("love.forte.suspend-interface-reversal:annotations:$VERSION")
        }

        jsMain.dependencies {
            implementation("love.forte.suspend-interface-reversal:annotations:$VERSION")
        }
    }
}

// ksp
dependencies {
    add("kspJvm", "love.forte.suspend-interface-reversal:processor:$VERSION") // process JVM
    add("kspJs", "love.forte.suspend-interface-reversal:processor:$VERSION")  // process JS
}

Code

Add @SuspendReversal to the interfaces or abstract classes.

@SuspendReversal
interface Foo {
    val age: Int get() = 5 // Will be skipped

    @JvmSynthetic
    suspend fun run()      // Will generated blocking and async function
    
    @JvmSynthetic
    suspend fun get(): Int // Will generated blocking and async function

    val name: String       // Will be skipped
}

Note

If SuspendReversal.markJvmSynthetic = true, then @JvmSynthetic must (or is strongly recommended) be added to the suspend function.

Cautions

1. The processor will only handle the abstract suspend function.

2. In Java, functions with a return value of Unit are treated as CompletableFuture<Void?> (for async)

3. Will copy the annotations @kotlin.Throws and @kotlin.jvm.Throws.

4. Will roughly calculate whether the generated function needs to be inherited or not.

e.g.

interface Foo {
    suspend fun run()
    fun runBlocking() { /*...*/ }
}

// Generated 👇

interface JBlockingFoo : Foo {
    override fun runBlocking() // Will be marked `override`
    suspend fun run() {
        runBlocking()
    }
}

Warning

The judgment is very rough and not very reliable. For example, it won't determine if it's final or not, if the parameters are inherited or not, and so on.

Useful Links

Kotlin suspend transform compiler plugin : Kotlin compiler plugin for converting suspend functions to platform-compatible functions.

License

see LICENSE .

Copyright (c) 2024 ForteScarlet

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