Storing module reference in module causes resolve to stack overflow (500USD Bounty) #3715
Description
From the maintainer Li Haoyi: I'm putting a 500USD bounty on this issue, payable by bank transfer on a merged PR implementing this.
The task is to appropriately detect module cycles during task resolution time, report a nice user-friendly error, and direct the user towards use of ModuleRef to fix the issue. This should be covered by unit tests, and we should verify that the module cycles in the code sample below gets properly recognized and handled.
I'm trying to work out a pattern that would allow the consumer of a foreign module swap out dependencies of modules. Given the following module definition:
import mill._, scalalib._
trait CommonModule extends ScalaModule {
def scalaVersion = "2.13.12"
def m1 = mym1
def m2 = mym2
}
object mym1 extends M1
trait M1 extends CommonModule
object mym2 extends M2
trait M2 extends CommonModule {
override def moduleDeps = super.moduleDeps ++ Agg(m1)
}One can then define another build.sc, import the above, instantiate new M1 and M2 (for example with new Scala versions), and then have the newly instantiated M2 depend on M1:
import mill._, scalalib._
import $file.dep.build
trait MyModules {
def m1 = newm1
def m2 = newm2
}
object newm1 extends dep.build.M1 with MyModules
object newm2 extends dep.build.M2 with MyModulesHowever this breaks resolve with a stack overflow error:
$ mill resolve __
No mill version specified.
You should provide a version via '.mill-version' file or --mill-version option.
Using mill version 0.11.12
[1/1] resolve
Exception in thread "MillServerActionRunner" java.lang.StackOverflowError
at java.base/java.security.AccessController.doPrivileged(Native Method)
at java.base/java.lang.Class.getClasses(Class.java:1752)
at mill.define.Reflect$.reflectNestedObjects0(Reflect.scala:77)
at mill.resolve.ResolveCore$.resolveDirectChildren0(ResolveCore.scala:349)
at mill.resolve.ResolveCore$.$anonfun$resolveDirectChildren$3(ResolveCore.scala:300)
at scala.util.Either.flatMap(Either.scala:360)
at mill.resolve.ResolveCore$.resolveDirectChildren(ResolveCore.scala:295)
at mill.resolve.ResolveCore$.resolveTransitiveChildren(ResolveCore.scala:223)
at mill.resolve.ResolveCore$$anonfun$1.applyOrElse(ResolveCore.scala:229)
at mill.resolve.ResolveCore$$anonfun$1.applyOrElse(ResolveCore.scala:228)
at scala.collection.StrictOptimizedIterableOps.collect(StrictOptimizedIterableOps.scala:151)
at scala.collection.StrictOptimizedIterableOps.collect$(StrictOptimizedIterableOps.scala:136)
at scala.collection.immutable.HashSet.collect(HashSet.scala:34)
at mill.resolve.ResolveCore$.$anonfun$resolveTransitiveChildren$2(ResolveCore.scala:228)
at scala.util.Either.map(Either.scala:390)
at mill.resolve.ResolveCore$.$anonfun$resolveTransitiveChildren$1(ResolveCore.scala:226)
at scala.util.Either.flatMap(Either.scala:360)
at mill.resolve.ResolveCore$.resolveTransitiveChildren(ResolveCore.scala:224)
at mill.resolve.ResolveCore$$anonfun$1.applyOrElse(ResolveCore.scala:229)
at mill.resolve.ResolveCore$$anonfun$1.applyOrElse(ResolveCore.scala:228)
at scala.collection.StrictOptimizedIterableOps.collect(StrictOptimizedIterableOps.scala:151)
at scala.collection.StrictOptimizedIterableOps.collect$(StrictOptimizedIterableOps.scala:136)
at scala.collection.immutable.HashSet.collect(HashSet.scala:34)
at mill.resolve.ResolveCore$.$anonfun$resolveTransitiveChildren$2(ResolveCore.scala:228)
at scala.util.Either.map(Either.scala:390)
at mill.resolve.ResolveCore$.$anonfun$resolveTransitiveChildren$1(ResolveCore.scala:226)
at scala.util.Either.flatMap(Either.scala:360)
at mill.resolve.ResolveCore$.resolveTransitiveChildren(ResolveCore.scala:224)
at mill.resolve.ResolveCore$$anonfun$1.applyOrElse(ResolveCore.scala:229)
at mill.resolve.ResolveCore$$anonfun$1.applyOrElse(ResolveCore.scala:228)
at scala.collection.StrictOptimizedIterableOps.collect(StrictOptimizedIterableOps.scala:151)
at scala.collection.StrictOptimizedIterableOps.collect$(StrictOptimizedIterableOps.scala:136)
at scala.collection.immutable.HashSet.collect(HashSet.scala:34)
at mill.resolve.ResolveCore$.$anonfun$resolveTransitiveChildren$2(ResolveCore.scala:228)
at scala.util.Either.map(Either.scala:390)
at mill.resolve.ResolveCore$.$anonfun$resolveTransitiveChildren$1(ResolveCore.scala:226)
at scala.util.Either.flatMap(Either.scala:360)
at mill.resolve.ResolveCore$.resolveTransitiveChildren(ResolveCore.scala:224)
at mill.resolve.ResolveCore$$anonfun$1.applyOrElse(ResolveCore.scala:229)
at mill.resolve.ResolveCore$$anonfun$1.applyOrElse(ResolveCore.scala:228)
at scala.collection.StrictOptimizedIterableOps.collect(StrictOptimizedIterableOps.scala:151)
at scala.collection.StrictOptimizedIterableOps.collect$(StrictOptimizedIterableOps.scala:136)
at scala.collection.immutable.HashSet.collect(HashSet.scala:34)
at mill.resolve.ResolveCore$.$anonfun$resolveTransitiveChildren$2(ResolveCore.scala:228)
at scala.util.Either.map(Either.scala:390)
[...]After experimenting around a bit, it seems like the def m1 and def m2 module references are somehow picked up as submodules and thus resulted in an infinite loop. Wrapping the module references in Some(..) works just ok, however it's quite cumbersome to write and feels hacky. Can this be fixed somehow?