A `launch` for IDEA scratches

scratch-launch.kt

import kotlin.coroutines.*

/**
 * Minimal, probably-borked implementation of `launch()`, just good enough
 * for running in a IDEA scratch.
 *
 * ### Usage
 *
 * ```kt
 * suspend fun main() {
 *   ...crazy coroutine stuff
 * }
 *
 * launch {
 *   main()
 * }
 * ```
 */
fun launch(block: suspend () -> Unit) =
  Launch().run {
    block.startCoroutine(this)
    await()
  }

private class Launch : Continuation<Unit> {
  var done = false
  var failure: Throwable? = null

  override val context: CoroutineContext get() = EmptyCoroutineContext

  override fun resumeWith(result: Result<Unit>) = synchronized(this) {
    done = true
    try {
      result.getOrThrow()
    } catch (failure: Throwable) {
      this.failure = failure
    }
    (this as Object).notifyAll()
  }

  fun await() = synchronized(this) {
    while (true) {
      when (val done = this.done) {
        false -> {
          (this as Object).wait()
        }
        else -> {
          failure?.let {
            throw it
          }
          return
        }
      }
    }
  }
}