kotlin-power-assert

Kotlin Compiler Plugin which high-jacks Kotlin assert function calls and transforms them similar to Groovy's Power Assert feature. This plugin uses the IR backend for the Kotlin compiler and supports all platforms: JVM, JS, and Native!

Example

Given following code:

val hello = "Hello"
assert(hello.length == "World".substring(1, 4).length)

Normally the assertion message would look like:

java.lang.AssertionError: Assertion failed
	at <stacktrace>

A custom assertion message can be provided:

val hello = "Hello"
assert(hello.length == "World".substring(1, 4).length) { "Incorrect length" }

But this just replaces the message:

java.lang.AssertionError: Incorrect length
	at <stacktrace>

With kotlin-power-assert included, the error message for the previous example will be transformed:

java.lang.AssertionError: Incorrect length
assert(hello.length == "World".substring(1, 4).length)
       |     |      |          |               |
       |     |      |          |               3
       |     |      |          orl
       |     |      false
       |     5
       Hello
	at <stacktrace>

Complex, multi-line, boolean expression are also supported:

Assertion failed
assert(
  (text != null && text.toLowerCase() == text) ||
   |    |
   |    false
   null
      text == "Hello"
      |    |
      |    false
      null
)

Gradle Plugin

Builds of the Gradle plugin are available through the Gradle Plugin Portal.

plugins {
  kotlin("jvm") version "1.4.0"
  id("com.bnorm.power.kotlin-power-assert") version "0.5.0"
}

The plugin by default will transform assert function call but can also transform other functions like require, check, and/or assertTrue. The function needs to validate the Boolean expression evaluates to true and has a form which also takes a String or String producing lambda.

configure<com.bnorm.power.PowerAssertGradleExtension> {
  functions = listOf("kotlin.test.assertTrue", "kotlin.require")
}

Kotlin IR

Using this compiler plugin only works if the code is compiled using Kotlin 1.4.0 and IR is enabled. This includes all IR based compiler backends: JVM, JS, and Native! As Kotlin IR is still experimental, mileage may vary.

Kotlin/JVM

tasks.withType<KotlinCompile>().configureEach {
  kotlinOptions {
    useIR = true
  }
}

Kotlin/JS

target {
  js(IR) {
  }
}

Kotlin/Native

IR already enabled by default!