[Issue 24657] New: 0-sized struct should be rejected in @safe mode

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=24657

          Issue ID: 24657
           Summary: 0-sized struct should be rejected in @safe mode
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: bugzilla at digitalmars.com

The following:

    struct S { }
    pragma(msg, s.sizeof);

prints 1. But:

    extern (C) struct S { }
    pragma(msg, s.sizeof);

prints 0. extern(C++) results in a size of 1.

The size 1 comes from C++, which (correctly) decided that individual objects
should have distinct addresses.

This does have the potential to be memory unsafe, and a struct with no data
members should be rejected in @safe mode.

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