https://issues.dlang.org/show_bug.cgi?id=24247

          Issue ID: 24247
           Summary: Improve constructor not callable using $modifier
                    object error
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: dmd
          Assignee: nobody@puremagic.com
          Reporter: nick@geany.org

struct S1
{
    this(ref const S1 s) immutable {
    }
    int i;
}

void main()
{
    const(S1) s1;
    S1 ms1 = s1;
}

Error: `immutable` method `immutable_ctor.S1.this` is not callable using a mutable object

This should be changed to:

Error: `immutable` constructor `immutable_ctor.S1.this` cannot construct a mutable object

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