https://issues.dlang.org/show_bug.cgi?id=21198

          Issue ID: 21198
           Summary: Inout copy constructor on union field does not prevent
                    copy-initialization of union
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody@puremagic.com
          Reporter: snarwin+bugzilla@gmail.com

Example program:

---
struct S
{
    this(ref inout(S) other) inout {}
}

union U
{
    S s;
}

static assert(!__traits(compiles,
    (U original) { U copy = original; }
));
---

The language spec says:

> If a union S has fields that define a copy constructor, whenever an object of type S is initialized by copy, an error will be issued. The same rule applies to overlapped fields (anonymous unions).

According to this paragraph, the static assert above should pass. However, as of DMD 2.093.1, it fails.

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