[Issue 21653] New: Inheriting from an interface then a class generates a wrong error

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21653

          Issue ID: 21653
           Summary: Inheriting from an interface then a class generates a
                    wrong error
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Keywords: industry, rejects-valid
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: pro.mathias.lang at gmail.com

```
interface A {}
class C { int a; }

class Works : C, A {}
class Doesnt : A, C {}
```

This seems like a pointless limitation. It produces the following error:
```
multi.d(5): Error: multi.Doesnt: multiple class inheritance is not supported.
Use multiple interface inheritance and/or composition.
multi.d(5):        multi.C has fields, consider making it a member of
multi.Doesnt
```

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