Dotty generates code that cause Exception in thread "main" java.lang.IllegalAccessError during runtime.

[megri]

Compiler version

All versions of Dotty seem to be affected.
Java 8 and 11, possibly newer ones as well.

Minimized code

build.sbt

scalaVersion := "3.1.0"
// scalaVersion := "3.0.0"
// scalaVersion := "2.13.6" // 2.13.6 not affected
classLoaderLayeringStrategy := ClassLoaderLayeringStrategy.Flat // recommended by sbt; does not change outcome
libraryDependencies += "com.google.cloud" % "google-cloud-datastore" % "2.1.0"

Program

package bugreport

import com.google.cloud.datastore.Query

object Main {
  def main(args: Array[String]): Unit = {
    val query = Query.newEntityQueryBuilder.setKind("Bug").setLimit(10) // One "setX"-call seems ok.
    println(s"query: $query")
  }
}

Output

Compilation succeeds. Fails at runtime with

sbt:bugreport-illegalaccesserror> run
[info] running bugreport.Main
[error] (run-main-7) java.lang.IllegalAccessError: Error running public static void bugreport.Main.main(java.lang.String[]).
[error] java.lang.IllegalAccessError: failed to access class com.google.cloud.datastore.StructuredQuery$BuilderImpl from class bugreport.Main$ (com.google.cloud.datastore.StructuredQuery$BuilderImpl and bugreport.Main$ are in unnamed module of loader sbt.internal.FlatLoader @65e7072e)
[error] If using a layered classloader, this can occur if jvm package private classes are accessed across layers. This can be fixed by changing to the Flat or ScalaInstance class loader layering strategies.
[error] java.lang.IllegalAccessError: Error running public static void bugreport.Main.main(java.lang.String[]).
[error] java.lang.IllegalAccessError: failed to access class com.google.cloud.datastore.StructuredQuery$BuilderImpl from class bugreport.Main$ (com.google.cloud.datastore.StructuredQuery$BuilderImpl and bugreport.Main$ are in unnamed module of loader sbt.internal.FlatLoader @65e7072e)
[error] If using a layered classloader, this can occur if jvm package private classes are accessed across layers. This can be fixed by changing to the Flat or ScalaInstance class loader layering strategies.
[error] stack trace is suppressed; run last Compile / bgRun for the full output
[error] Nonzero exit code: 1
[error] (Compile / run) Nonzero exit code: 1
[error] Total time: 1 s, completed 7 Nov 2021, 11:07:28

Expectation

Should work as in 2.13.6

[megri]

This is the decompiled bytecode

2.13.6

Compiled from "Main.scala"
public final class bugreport.Main$ {
  public static final bugreport.Main$ MODULE$;

  public static {};
    Code:
       0: new           #2                  // class bugreport/Main$
       3: dup
       4: invokespecial #22                 // Method "<init>":()V
       7: putstatic     #24                 // Field MODULE$:Lbugreport/Main$;
      10: return

  public void main(java.lang.String[]);
    Code:
       0: invokestatic  #33                 // Method com/google/cloud/datastore/Query.newEntityQueryBuilder:()Lcom/google/cloud/datastore/EntityQuery$Builder;
       3: ldc           #35                 // String Bug
       5: invokevirtual #39                 // Method com/google/cloud/datastore/EntityQuery$Builder.setKind:(Ljava/lang/String;)Lcom/google/cloud/datastore/StructuredQuery$BuilderImpl;
       8: checkcast     #7                  // class com/google/cloud/datastore/EntityQuery$Builder
      11: getstatic     #44                 // Field scala/Predef$.MODULE$:Lscala/Predef$;
      14: bipush        10
      16: invokevirtual #48                 // Method scala/Predef$.int2Integer:(I)Ljava/lang/Integer;
      19: invokevirtual #52                 // Method com/google/cloud/datastore/EntityQuery$Builder.setLimit:(Ljava/lang/Integer;)Lcom/google/cloud/datastore/StructuredQuery$BuilderImpl;
      22: checkcast     #7                  // class com/google/cloud/datastore/EntityQuery$Builder
      25: astore_2
      26: getstatic     #44                 // Field scala/Predef$.MODULE$:Lscala/Predef$;
      29: new           #54                 // class java/lang/StringBuilder
      32: dup
      33: ldc           #55                 // int 7
      35: invokespecial #58                 // Method java/lang/StringBuilder."<init>":(I)V
      38: ldc           #60                 // String query:
      40: invokevirtual #64                 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      43: aload_2
      44: invokevirtual #67                 // Method java/lang/StringBuilder.append:(Ljava/lang/Object;)Ljava/lang/StringBuilder;
      47: invokevirtual #71                 // Method java/lang/StringBuilder.toString:()Ljava/lang/String;
      50: invokevirtual #75                 // Method scala/Predef$.println:(Ljava/lang/Object;)V
      53: return
}

3.1.0

Compiled from "Main.scala"
public final class bugreport.Main$ implements java.io.Serializable {
  public static final bugreport.Main$ MODULE$;

  public static {};
    Code:
       0: new           #2                  // class bugreport/Main$
       3: dup
       4: invokespecial #26                 // Method "<init>":()V
       7: putstatic     #28                 // Field MODULE$:Lbugreport/Main$;
      10: return

  public void main(java.lang.String[]);
    Code:
       0: invokestatic  #44                 // Method com/google/cloud/datastore/Query.newEntityQueryBuilder:()Lcom/google/cloud/datastore/EntityQuery$Builder;
       3: ldc           #46                 // String Bug
       5: invokevirtual #50                 // Method com/google/cloud/datastore/EntityQuery$Builder.setKind:(Ljava/lang/String;)Lcom/google/cloud/datastore/StructuredQuery$BuilderImpl;
       8: getstatic     #55                 // Field scala/Predef$.MODULE$:Lscala/Predef$;
      11: bipush        10
      13: invokevirtual #59                 // Method scala/Predef$.int2Integer:(I)Ljava/lang/Integer;
      16: invokevirtual #63                 // Method com/google/cloud/datastore/StructuredQuery$BuilderImpl.setLimit:(Ljava/lang/Integer;)Lcom/google/cloud/datastore/StructuredQuery$BuilderImpl;
      19: checkcast     #9                  // class com/google/cloud/datastore/EntityQuery$Builder
      22: astore_2
      23: getstatic     #55                 // Field scala/Predef$.MODULE$:Lscala/Predef$;
      26: new           #65                 // class java/lang/StringBuilder
      29: dup
      30: ldc           #66                 // int 7
      32: invokespecial #69                 // Method java/lang/StringBuilder."<init>":(I)V
      35: ldc           #71                 // String query:
      37: invokevirtual #75                 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      40: aload_2
      41: invokevirtual #78                 // Method java/lang/StringBuilder.append:(Ljava/lang/Object;)Ljava/lang/StringBuilder;
      44: invokevirtual #82                 // Method java/lang/StringBuilder.toString:()Ljava/lang/String;
      47: invokevirtual #86                 // Method scala/Predef$.println:(Ljava/lang/Object;)V
      50: return
}

So 2.13.6 does an extra 8: checkcast #7 // class com/google/cloud/datastore/EntityQuery$Builder. I have no idea if this is what's making the difference.

[nicolasstucki]

We need a version that does not have the dependency

[megri]

We need a version that does not have the dependency

I managed to minimize it.

Bar.java

package com.a.b;

public class Bar<V> {
    abstract static class BuilderImpl<V, B extends BuilderImpl<V, B>> {
        public B call() {
            return (B) this;
        }
    }
}

Baz.java

package com.a.b;

public final class Baz extends Bar<String> {
    public static final class Builder extends Bar.BuilderImpl<String, Builder> {}
}

Main.scala

package bugreport

import com.a.b.Baz

object Main {
  def main(args: Array[String]): Unit = {
    val b = new Baz.Builder()
    b.call() // works
    val x = b.call(); val y = x.call() // also works
    b.call().call() // works on 2.13, fails on Scala 3
  }
}

edit: shrunk it further

[som-snytt]

Possibly duplicates #13841 like two ships passing in the night.

[eed3si9n]

Closing this as duplicate.