[Issue 20492] New: __traits(getOverloads) and covariant return types in interfaces

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20492

          Issue ID: 20492
           Summary: __traits(getOverloads) and covariant return types in
                    interfaces
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: regression
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: destructionator at gmail.com

Easier to explain with code:

---
interface A {
        A foo();
}

interface B : A {
        B foo();
}

class C : B {
        C foo() { return this; }
}

void main() {
        static foreach(overload; __traits(getOverloads, B, "foo"))
                pragma(msg, typeof(overload));
}
---

* * *

Up to      2.080.1: Success with output: B()
Since      2.081.2: Success with output:
-----
B()
A()
-----


You can see there that getOverloads is considering both interface methods to be
overloaded on each other, despite the fact that they have identical arguments
(in this case, none).

The class, C, shows that the language proper considers them to have just one
slot. But getOverloads is returning both. I contend getOverloads should only
return the most derived version. It did that prior to 2.80.1, so I'm calling
this a regression. It is also blocking the currently most promising approach
for my auto-gen java bindings.

I suspect this was introduced in this PR https://github.com/dlang/dmd/pull/7959

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