softwaremill / softwaremill/macwire

Incremental Build Fails - Cannot Find Implementation

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Scala
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Description

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]
}

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by reproducing the incremental rebuild in the Play application, then inspect InstanceLookup.scala:13 and Wired.scala:10 alongside Global.scala:41. Compare the class loaders at the reported stack frames. Done means adding or removing a controller class resolves without deleting the build output or forcing a complete rebuild.

Written by the indexing model from the issue text.

Assessment

Tech stack
scala
Domain
backend
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
30/100

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