[Issue 23073] New: [dip1000] scope inference from pure doesn't consider self-assignment

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=23073

          Issue ID: 23073
           Summary: [dip1000] scope inference from pure doesn't consider
                    self-assignment
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: dkorpel at live.nl

```
@safe:

class C 
{
    C next;
}

void assignNext(C c) pure nothrow @nogc 
{
    c.next = c;
}

C escape() @nogc
{
    scope C c = new C();
    assignNext(c);
    return c.next;
}

void main()
{
    C dangling = escape();
}

```

`assignNext` should not be callable on a `scope` parameter. The compiler sees
no other parameters that c could be assigned to, but doesn't consider that
mutable aggregates may have extra pointer layers, allowing you to escape a
scope pointer because of the lack of transitive scope.

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