Description Jens Lideström 2018-07-11 07:33:19 EDT

Created attachment 274935 [details]
Code example that demonstrates the problem.

The ejc compiler seems to give priority to methods from class of the reference type when resolving method overloads. The result is that ejc accepts some method calls which should be considered to be ambiguous.

This is compared to javac, which rejects these calls.

### Software verions

ejc version: I20180710
javac version: 1.8.0_92

Also tested with the same result with JDT 3.13.4, Eclipse Oxygen.3a Release (4.7.3a) Build id: 20180405-1200

### Output from the compilers

Output from the compilers when compiling the example code:

$ java -jar ecj-I20180710-2000.jar -classpath rt.jar -source 1.9 OverloadExtensionGenericsBug.java 
$ 
$ javac OverloadExtensionGenericsBug.java 
OverloadExtensionGenericsBug.java:34: error: reference to m is ambiguous
        b.m(i); // Works in ejc, compile error in javac: Method is ambiguous
         ^
  both method m(T) in A and method m(Integer) in B match
  where T is a type-variable:
    T extends Object declared in class A
1 error

### Example code

class A<T> {
    void m(T a) {}
    void m(Integer a) {}
}

class B<T> extends A<T> {
    @Override
    void m(Integer a) {}
    
    // Adding this makes both calls to m result in compile errors
//    @Override
//    public void m(T a) {
//        System.out.println("B#m(T)");
//    }
}

public class OverloadExtensionGenericsBug {
    public static void main(String[] args) {
        Integer i = 0;
        
        B<Integer> b = new B<>();
        b.m(i); // Works in ejc, compile error in javac: Method is ambiguous

//        A<Integer> a = b;
//        a.m(i); // Compile error in  both ejc and javac: Method is ambiguous
    }
}