Detecting method calls where receiver is of given type

[knutwannheden]

I would like to write a rule where I want to check the type of the receiver of the call. Specifically, I want to check that there is no code which calls Object#equals(Object) on any instance of Foo. How do I do this? Please note that my class Foo does not override equals() itself.

Of course this rule can only be expected to catch cases where the type of the receiver can statically be determined to be of type Foo. So if I have a variable like Object foo = new Foo(); and then at some point call foo.equals(whatever) then the rule won't be able to catch that, but that is fine for my use case.

[hankem]

I fear that the byte code might not contain the information that Object#equals(Object) was called on a Foo:
In the example

class Foo {
   boolean eq() {
     Foo foo = new Foo();
     return foo.equals(new Object());
   }
}

the method eq is compiled to the byte code (cf. javap -c -p -v Foo.class):

         0: new           #7                  // class Foo
         3: dup
         4: invokespecial #9                  // Method "<init>":()V
         7: astore_1
         8: aload_1
         9: new           #2                  // class java/lang/Object
        12: dup
        13: invokespecial #1                  // Method java/lang/Object."<init>":()V
        16: invokevirtual #10                 // Method java/lang/Object.equals:(Ljava/lang/Object;)Z
        19: ireturn

[knutwannheden]

I see. I forgot that ArchUnit is bytecode-based and not AST-based. Thanks for clarifying!