aunkrig
commented
1 year ago Hey Emil,
you are right, that problem cannot be reproduced with Java code alone, because Scala produces bytecode here that a Java compiler would never generate. Instead it must (!) issue an error message "The return type is incompatible with ReportedBugsTest.Base.value()", because the JLS dictates that the return type of the overriding method must be a subtype of the return type of the overridden method, and int is not a subtype of Object. In other words: This is a limitation that is enforced by the Java compiler, not the JVM.
Consequently, JAVAC should refuse to compile CallValue2 just like Janino does. Did you try that=
eejbyfeldt
I was not able to reproduce this error with only java code. Perhaps someone with more java knowledge could figure out what might produce similar bytecode. But the example below will sadly involve using scalac to reproduce the issue.
Scala allows one to override a method returning
Anywith a return value ofIntwhen this is done like thisThe interface of the compiled class
DerivedbecomesSo there are two methods called
valuewhich takes no arguments, one returningintand one returningObject.Then we want to call the
valuemethod from a java file:Compiling this code using openjdk works fine. But trying to compile it using janino 3.1.7 using the SimplerCompiler results in a
Incompatible return typesexception:Changing the java code slightly to expect a
Objectinstead ofintalso compiles fine using openjdk but gives the same error when using janino.
The java version used:
Scala version used:
Also some indication that we are not the only one hitting this issue: https://stackoverflow.com/questions/63250313/create-dataset-for-case-class-that-implements-a-generic-trait