pointer chain information is not adequate to rebuild data structure

[kortschak]

Given an adequately clever parser and type constructor, we still cannot unambiguously recreate a data structure from the output of utter when there are pointers to non-pointer values.

In the case of pointers to concrete values, there is no address information given for the target, so for example:

c := []interface{}{5, 5, nil, nil}
c[2] = &c[0]
c[3] = &c[0]

ptrDump := utter.NewDefaultConfig()
ptrDump.CommentPointers = true

ptrDump(c)

gives:

[]interface{}{
    int(5),
    int(5),
    &int /*0xc20803e840*/ (5),
    &int /*0xc20803e840*/ (5),
}

To get this information and only report it where necessary we need to walk the structure once before the dump and mark concrete values that are referenced by a pointer.

Another complication is of how to deal with pointers into []byte. To not interfere with []byte formatting, I think the best approach is to add an appendix comment to []byte rendering to list elements that are referenced and their addresss.