https://issues.dlang.org/show_bug.cgi?id=20753

          Issue ID: 20753
           Summary: "Error: unknown" with structs of arrays, speculative
                    instantiation and recursive types
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Keywords: ice, rejects-valid
          Severity: regression
          Priority: P1
         Component: dmd
          Assignee: nobody@puremagic.com
          Reporter: dlang-bugzilla@thecybershadow.net

//////////////// test.d ////////////////
struct HashCollection()
{
    struct Item
    {
        IniFragment value;
    }
    Item[] items;

    ref lookupToReturnValue()
    {
        return items[0].value;
    }

    enum canDup = is(typeof(items.dup));
}

struct IniFragment
{
    HashCollection!() children;
}
////////////////////////////////////////

Works in DMD 2.085 but not newer.

Bisecting shows that the error message begins manifesting when it was introduced ( https://github.com/dlang/dmd/pull/9425 ), however debug versions of DMD have been failing with an assertion failure before that change. The assertion failures began after https://github.com/dlang/dmd/pull/5500 .

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