[llvm-bugs] [Bug 38504] New: std::filesystem::path::iterator::iterator_category is non-comformingly "bidirectional_iterator_tag"

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=38504

            Bug ID: 38504
           Summary: std::filesystem::path::iterator::iterator_category is
                    non-comformingly "bidirectional_iterator_tag"
           Product: libc++
           Version: 7.0
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: All Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: Casey at Carter.net
                CC: llvm-bugs at lists.llvm.org, mclow.lists at gmail.com

std::filesystem::path::iterator's member iterator_category is an alias for
bidirectional_iterator_tag, despite that it does not satisfy the requirement in
[forward.iterators]/6:

  If a and b are both dereferenceable, then a == b if and only if *a and *b
  are bound to the same object.

An iterator cannot be bidirectional if it is not forward, so the
iterator_category should in fact be input_iterator_tag, or - as a conforming
extension - some other type which is convertible to input_iterator_tag but not
convertible to forward_iterator_tag.

Note that if path::iterator::operator* were to return a prvalue it would
conform to the BidirectionalIterator concept in the Ranges proposal, and could
conformingly define its member iterator_concept as an alias for
std::bidirectional_iterator_tag.

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