Type Inference is Causing Verification Error

[Maurizio Cimadamore]

Thanks for the report.
Please send me (if that's possible) a zipfile containing the problematic 
sources, so that I can reproduce the problem.

Maurizio

On 03/09/10 17:58, Ming-Yee Iu wrote:
> I have a piece of code that seems to compile fine, but when I run it,
> it generates a verification error.
>
> I'm putting together a LINQish system for Java7, but the my system is
> based only on bytecode analysis and uses no bytecode rewriting, so it
> looks like a compiler problem (in fact, I haven't implemented nested
> queries yet, so this piece of code was not successfully translated
> into SQL by my system and was simply running directly).
>
> Here is the code fragment that fails:
>
> DBSet<Pair<Tuple3<Integer, String, String>, Integer>>  matches =
>   db.allDBOrderLine()
>     .group(
>       #(ol)
>       {
>         DBItem i = ol.getItem();
>         DBAuthor a = i.getAuthor();
>         return new Tuple3<Integer, String, String>(i.getItemId(),
> i.getTitle(), a.getFirstName());
>       },
>       #(key, olset) {
>         new Pair<Tuple3<Integer, String, String>, Integer>(
>           key, olset.sumInt(#(ol){ol.getQuantity()}))}
>     );
>
> ------
> The definition of the group() method is
>
> interface DBSet<T>  extends Collection<T>  {
> ...
>    public static interface AggregateInteger<U>  {
>       public int aggregate(U val);
>    }
>    public int sumInt(AggregateInteger<T>  aggregate);
>
>   ...
>    public static interface AggregateSelect<U, V>  {
>       public V aggregateSelect(DBSet<U>  val);
>    }
>    public static interface AggregateGroup<W, U, V>  {
>       public V aggregateSelect(W key, DBSet<U>  val);
>    }
>    public<U, V>  DBSet<Pair<U, V>>  group(Select<T, U>  select,
> AggregateGroup<U, T, V>  aggregate);
> }
>
> ------
> The verification error is
>
> Exception in thread "main" java.lang.VerifyError: Bad return type in
> method Test$2.aggregateSelect(Lch/epfl/labos/iu/orm/Tuple3;Lch/epfl/labos/iu/orm/DBSet;)Ljava/lang/Integer;
> at offset 25
>         at Test.main(Test.java:12)
>
>
> -----
> The javap of Test$2 is
>
>
> class Test$2 extends java.lang.Object implements
> ch.epfl.labos.iu.orm.DBSet$AggregateGroup<ch.epfl.labos.iu.orm.Tuple3<java.lang.Integer,
> java.lang.String, java.lang.String>,
> ch.epfl.labos.iu.tpcw.entities.DBOrderLine, java.lang.Integer>  {
>   public java.lang.Integer
> aggregateSelect(ch.epfl.labos.iu.orm.Tuple3<java.lang.Integer,
> java.lang.String, java.lang.String>,
> ch.epfl.labos.iu.orm.DBSet<ch.epfl.labos.iu.tpcw.entities.DBOrderLine>);
>     Code:
>        0: new           #2                  // class ch/epfl/labos/iu/orm/Pair
>        3: dup
>        4: aload_1
>        5: aload_2
>        6: new           #3                  // class Test$2$1
>        9: dup
>       10: aload_0
>       11: invokespecial #4                  // Method
> Test$2$1."<init>":(LTest$2;)V
>       14: invokeinterface #5,  2            // InterfaceMethod
> ch/epfl/labos/iu/orm/DBSet.sumInt:(Lch/epfl/labos/iu/orm/DBSet$AggregateInteger;)I
>       19: invokestatic  #6                  // Method
> java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
>       22: invokespecial #7                  // Method
> ch/epfl/labos/iu/orm/Pair."<init>":(Ljava/lang/Object;Ljava/lang/Object;)V
>       25: areturn
>
>   Test$2();
>     Code:
>        0: aload_0
>        1: invokespecial #1                  // Method
> java/lang/Object."<init>":()V
>        4: return
>
>   public java.lang.Object aggregateSelect(java.lang.Object,
> ch.epfl.labos.iu.orm.DBSet);
>     Code:
>        0: aload_0
>        1: aload_1
>        2: checkcast     #8                  // class ch/epfl/labos/iu/orm/Tuple3
>        5: aload_2
>        6: invokevirtual #9                  // Method
> aggregateSelect:(Lch/epfl/labos/iu/orm/Tuple3;Lch/epfl/labos/iu/orm/DBSet;)Ljava/lang/Integer;
>        9: areturn
> }
>
> ----
>
> I may have gotten the generics in my definition of group() mixed up,
> but my intention was for Test$2.aggregateSelect() to return a Pair and
> not an Integer (in any case, the compiler should not generate code
> that does not verify).
>
> -Ming
>
>