[Issue 21251] New: parameter UDA type not equal to itself

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21251

          Issue ID: 21251
           Summary: parameter UDA type not equal to itself
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: elpenguino+D at gmail.com

```
enum A;
static if (is(typeof(& func) Fsym : Fsym*)) {
    static if (is(Fsym P == function)) {
        static assert(is(A == A)); //okay
        static assert(is(__traits(getAttributes, P[0 .. 1])[0] == A)); //wait,
what? A != A?
    }
}

void func(@A int) {}
```

The static asserts in this code should both pass. Interestingly, DMD 2.084 -
2.091 seem to crash instead of producing any errors.

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