[Issue 13155] New: Disallow final abstract classes

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=13155

          Issue ID: 13155
           Summary: Disallow final abstract classes
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: DMD
          Assignee: nobody at puremagic.com
          Reporter: verylonglogin.reg at gmail.com

This code should NOT compile:
---
final abstract class C { }
---

Such classes are almost useless and generally indicate an error. Note unless
enhancement Issue 2946 is fixed the class may be derived as `abstract`:
---
final class C: B { }
---
`C` may or may no be `abstract` here depending on `B`. And one have to look
through every ancestor of `C` to determine whether it contains an unimplemented
`abstract` method.

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