[Issue 23552] New: Function `x` does not override any function, but it actually does

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=23552

          Issue ID: 23552
           Summary: Function `x` does not override any function, but it
                    actually does
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Windows
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: grimmaple95 at gmail.com

Consider code below:
```
import std;

abstract class Base
{
    void foo();
}

class Derived : Base
{
    void foo() { writeln("foo"); }
    int data() { return 0; }
}

class DerivedX : Derived
{
    override int data() { return 1; }
}

```

The main issue with this code is missing `override` for `Derived`'s `foo`
function. However, this code produces two errors:
```
onlineapp.d(10): Error: cannot implicitly override base class method
`onlineapp.Base.foo` with `onlineapp.Derived.foo`; add `override` attribute
onlineapp.d(23): Error: function `onlineapp.DerivedX.data` does not override
any function
```

The first error is entirely coorect. But the other one is completely wrong. If
`override` is added, then the second error is gone too.

--