Incremental Build Fails - Cannot Find Implementation

先在 Play 应用中复现增量构建，然后结合 Global.scala:41 检查 InstanceLookup.scala:13 和 Wired.scala:10。比较报告的堆栈帧中的类加载器。完成的标准是：添加或删除一个 controller 类即可解决问题，而无需删除构建输出或强制执行完整重建。

MacWire Version: 2.11-2.2.0
Play! Version: 2.11-2.3.10

The incremental compilation fails when adding/removing a class file with:

java.lang.RuntimeException: Cannot find implementations of class class controllers.FooBarGong!
at com.softwaremill.macwire.InstanceLookup$class.lookupSingleOrThrow(InstanceLookup.scala:13) ~[util_2.11-2.2.0.jar:2.2.0]
at com.softwaremill.macwire.Wired.lookupSingleOrThrow(Wired.scala:10) ~[util_2.11-2.2.0.jar:2.2.0]
at Global$.getControllerInstance(Global.scala:41) ~[na:na]
...

Resolution succeeds provided I delete the build output folder do a complete project rebuild.

Upon further investigation, I have learned of an inconsistent classloader state between stack frames as indicated by calling the following from the subject stack frame:

((ClassLoader)this.getClass().getClassLoader()).loadClass("controllers.FooBarGong")

Lookup succeeds from stack frame Global$.getControllerInstance(Global.scala:41) ~[na:na] (class loader ReloadableClassLoader(v1)) but fails to find the class from the deeper stack frame com.softwaremill.macwire.Wired.lookupSingleOrThrow(Wired.scala:10) (class loader PlayDependencyClassLoader)

The call site is fairly simple:

package modules

import play.api.Play
import play.api.libs.ws.WS

import controllers._

import com.softwaremill.macwire._
import services._

object ApplicationModule extends ControllerModule with ServiceModule

trait ControllerModule extends ServiceModule {
  import Play.current

  lazy val fooBarGongController = wire[FooBarGong]
}