Mirahc cannot deal with type parameters which refer to type parameters

[felixvf]

Consider this Java code

package org.foo;

import java.util.List;
import java.util.concurrent.CompletableFuture;

public class TypeFixture {
    public CompletableFuture<List<Runnable>> load(List filter, int flags){
        return null;
    }
}

to be called using this Mirah code

      import org.foo.TypeFixture
      import java.util.function.BiConsumer
      import java.util.Map
      import java.util.List

      class Issue417Test

         def initialize(filters:List, flags:int)
            @filters = filters
            @flags = flags
            @loader = TypeFixture.new
            @future = nil
         end

         def run():void
             @future = @loader.load(@filters, @flags)
         end

         def handle(block:BiConsumer):Issue417Test
            @future.whenComplete(block)
            self
         end

         def join():void
            @future.join
         end

      end

(taken from here and here).

Then the compiler may fail (at least in this version) with a NullPointerException:

java.lang.NullPointerException
        at org.mirah.jvm.mirrors.generics.BaseSignatureReader.finishTypeParam(xx_base_signature_reader.mirah:53)
        at org.mirah.jvm.mirrors.generics.BaseSignatureReader.visitFormalTypeParameter(xx_base_signature_reader.mirah:72)
        at org.objectweb.asm.signature.SignatureReader.accept(Unknown Source)
        at org.mirah.jvm.mirrors.generics.BaseSignatureReader.read(xx_base_signature_reader.mirah:94)
        at org.mirah.jvm.mirrors.BytecodeMirror.link_internal(bytecode_mirror.mirah:86)
        at org.mirah.jvm.mirrors.BytecodeMirror.ensure_linked(bytecode_mirror.mirah:77)
        at org.mirah.jvm.mirrors.SimpleMirrorLoader.loadMirror(mirror_loaders.mirah:119)
        at org.mirah.jvm.mirrors.SimpleMirrorLoader.findMirror(mirror_loaders.mirah:127)

[felixvf]

Further analysis reveals that the NullPointerException is triggered by trying to read 00this signature:

<T:Ljava/lang/Object;U:TT;V:Ljava/lang/Object;>Ljava/util/concurrent/CompletableFuture$BiCompletion<TT;TU;TV;>;

The situation where the failure occurs is U:TT;: Type variable U is not bound to a proper class (e.g. Ljava/lang/Object;), but to another local type variable T. The current signature reader code does not seem to be prepared for that.

[felixvf]

Apparently, the Java 1.8 compiler allows producing this signature

<U:TT;T:Ljava/lang/Object;>Ljava/lang/Object;

(e.g. using Java source code

        public class Someclass<U extends T,T> {
        }

).

This means that type variables are allowed to depend on type variables which are defined later.

[ribrdb]

Oh, now that's lovely.

On Fri, Mar 4, 2016 at 8:11 AM Felix von Ferey notifications@github.com
wrote:

Apparently, the Java 1.8 compiler allows producing this signature

<U:TT;T:Ljava/lang/Object;>Ljava/lang/Object;

(e.g. using Java source code

    public class Someclass<U extends T,T> {
    }

).

This means that type variables are allowed to depend on type variables
which are defined later.

—
Reply to this email directly or view it on GitHub
#433 (comment).

[baroquebobcat]

Fun. I guess that makes sense.