Fix Interface method handling

[krakowski]

Description

From FunctionalInterface's JavaDoc:

If an interface declares an abstract method overriding one of the public methods of java.lang.Object, that also does not count toward the interface's abstract method count since any implementation of the interface will have an implementation from java.lang.Object or elsewhere.

CtLambdaImpl doesn't take this into account resulting in Exceptions whenever an Interface declaring one or more of java.lang.Object's methods is used in combination with a Lambda Expression.

Related Issues

• Fixes SpoonException when computing imports #2003

[pvojtechovsky]

Filip, welcome! And thank you for this high quality PR 👍

[pvojtechovsky]

I am just not sure whether we can check whether method overrides Object method this way. I guess CtMethod equals compares everythink including body of method. So this fix will probably fail on the class whose sources are in spoon model. Because this method will have body and therefore will be not equal to Object method.
What is correct and fast enough? I am not sure ...
A) to compare method signatures?
B) to use isoverriding method
C) ...

[krakowski]

Thanks for the incredibly fast feedback!

I just tried using CtMethod.isOverriding.

for (CtMethod<?> method : lambdaTypeMethods) {
    if (getFactory().Method().OBJECT_METHODS.stream().anyMatch(method::isOverriding)) {
        continue;
    }
...

Unfortunately the method does not return true since the Interface is no subtype of java.lang.Object (Reference).

It seems the only solution is comparing method signatures, as you said.

[spoon-bot]

API changes: 1 (Detected by Revapi)

Old API: fr.inria.gforge.spoon:spoon-core:jar:6.3.0-20180601.225315-107 / New API: fr.inria.gforge.spoon:spoon-core:jar:6.3.0-SNAPSHOT

	Method was added to an interface.
Old	none
New	method CtMethod#hasSameSignature(CtMethod)
Breaking	binary: non_breaking

[pvojtechovsky]

CtMethod.isOverriding.
Unfortunately the method does not return true since the Interface is no subtype of java.lang.Object

I think it is a bug, which should be fixed first (in another PR). Then we can use isOverriding here too.
@monperrus WDYT?

[pvojtechovsky]

The comparation of signatures doesn't work with java generics

class B<T> extends A<T> {
void m(T arg){}
}
class A<U> {
void m(U arg){}
}

here B#m overrides A#m, but they have different signatures.

So do not invest more effort on signatures, because it is probably wrong way.

[krakowski]

CtLambdaImpl now checks if the interface's methods are overriding java.lang.Object methods. Once #2025 is merged this should work.

[pvojtechovsky]

#2025 was merged, please do some little change in your PR so the next CI build is triggered using latest sources.

[krakowski]

Thanks Pavel!

I rebased on top of master and the test succeeded on my local machine.

[pvojtechovsky]

please add contract to the first line of the test body. Something like
//contract: Lambda expression works on interfaces with methods inherited from java.lang.Object

[krakowski]

Done :)

[pvojtechovsky]

Thank You Filip 👍