Method Resolution doesn't handle user-defined implicit coercions correctly.

Here's what Vijay wrote about method resolution:

1. List all the exact methods that could possibly be used (generic type
inferencing performed; implicit coercions not performed; if DYNAMIC_CHECKS
is on, then constraints need not match exactly)

2. Determine the most specific ones.

3. If there is one; this is the method, stop.

4. If there are more than one, declare an ambiguity error and stop.
5. Repeat steps 1-4, this time with implicit coercions performed.
6. If method is not found, declare no method found and stop.

That doesn't seem to be what X10 is doing.

class Res2 {
  interface Surface {}
  public static class Ace implements Surface {
    public static operator (Byte) : Ace = new Ace();
  }
  def m(x:Int) = {Console.OUT.println("Int x=" + x + " type=" + x.typeName());return 1;}
  def m(x:Surface) = {Console.OUT.println("Surface x=" + x + " type=" + x.typeName());return 3;}
    
  def example() {
     assert m(100) == 1 : "Int"; 
     // An Ace is a Surface, unambiguous best choice
     assert m(new Ace()) == 3 : "Ace";

     assert m(1y) == 3 : "Byte";
     
  }
  public static def main(argv:Array[String](1)) {
     (new Res2()).example();
     Console.OUT.println("That's all!");    
  }
}

There are implicit coercions from Byte to Int and Ace, so, by the above rules, this ought to be a static error. Instead, it's not; X10 silently picks the Byte->Int coercion:

x10c Res2.x10
~/x10/tmp: x10 Res2
Int x=100 type=x10.lang.Int
Surface x=Res2.Ace@32bf7190 type=Res2.Ace
Int x=1 type=x10.lang.Int
x10.lang.AssertionError: Byte
at Res2.example(Res2.java:130)
at Res2.main(Res2.java:154)
at Res2$$Main.runtimeCallback(Res2.java:144)
at x10.runtime.impl.java.Runtime$$Closure$Main.$apply(Runtime.java:92)
at x10.lang.Runtime$$Closure$146.$apply(Runtime.java:3966)
at x10.lang.Activity.run(Activity.java:590)
at x10.lang.Runtime$Worker.loop(Runtime.java:1087)
at x10.lang.Runtime$Worker.$apply(Runtime.java:1022)
at x10.lang.Runtime$Pool.$apply(Runtime.java:1540)
at x10.lang.Runtime.start(Runtime.java:2237)
at x10.runtime.impl.java.Runtime.$apply(Runtime.java:132)
at x10.runtime.impl.java.Thread.run(Thread.java:48)
~/x10/tmp:

Here's a similar program, differing only in that the method m looks for an instance of class Ace rather than interface Surface:

class Res3 {
  interface Surface {}
  public static class Ace implements Surface {
    public static operator (Byte) : Ace = new Ace();
  }
  def m(x:Int) = {Console.OUT.println("Int x=" + x + " type=" + x.typeName());return 1;}
  def m(x:Ace) = {Console.OUT.println("Ace x=" + x + " type=" + x.typeName());return 3;}
    
  def example() {
     assert m(100) == 1 : "Int"; 
     assert m(new Ace()) == 3 : "Ace";

     assert m(1y) == 3 : "Byte";
     
  }
  public static def main(argv:Array[String](1)) {
     (new Res3()).example();
     Console.OUT.println("That's all!");    
  }
}

This doesn't compile, but the error message doesn't seem to indicate that it's failing to compile for the right reason:

x10c Res3.x10
/Users/bard/x10/tmp/Res3.x10:13: Method m(x: x10.lang.Int): x10.lang.Int

Unknown macro: {self==1}

in Res3

Unknown macro: {self==Res3#this}

cannot be called with arguments (x10.lang.Byte

); Invalid Parameter.
Expected type: x10.lang.Int
Found type: x10.lang.Byte

Unknown macro: {self==1}

1 error.
~/x10/tmp: