<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/106988>106988</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            `std::reverse_iterator<Incomplete*>` causes a compilation failure when checking `input_iterator`
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          strega-nil
      </td>
    </tr>
</table>

<pre>
    The following code:

```cxx
int main() {
  struct Incomplete;
 static_assert((std::input_iterator<std::reverse_iterator<Incomplete*>>, true));
}
```

causes a compilation failure:

```
# | In file included from /.../libcxx/test/std/containers/views/views.span/span.cons/copy.pass.cpp:15:
# | In file included from /.../span:163:
# | /.../__iterator/reverse_iterator.h:184:76: error: arithmetic on a pointer to an incomplete type 'Incomplete'
# | is_nothrow_copy_constructible_v<_Iter> && noexcept(ranges::iter_move(--std::declval<_Iter&>()))) {
# | ^ ~~~~~~~~~~~~~~~~~~~~~~
# | /.../__iterator/iter_move.h:43:3: note: in instantiation of exception specification for 'iter_move' requested here
# |   iter_move(std::forward<_Tp>(__t));
# |   ^
# | /.../__iterator/iter_move.h:43:3: note: in instantiation of requirement here
# |   iter_move(std::forward<_Tp>(__t));
# | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# | /.../__iterator/iter_move.h:41:75: note: while substituting template arguments into constraint expression here
# | concept __unqualified_iter_move = __class_or_enum<remove_cvref_t<_Tp>> && requires(_Tp&& __t) {
# | ^~~~~~~~~~~~~~~~~~~~~
# | /.../__iterator/iter_move.h:63:14: note: while checking the satisfaction of concept '__unqualified_iter_move<std::reverse_iterator<Incomplete *> &>' requested here
# |     requires __unqualified_iter_move<_Ip>
# | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
# | /.../__iterator/iter_move.h:63:14: note: while substituting template arguments into constraint expression here
# | requires __unqualified_iter_move<_Ip>
# | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
# | /.../__iterator/iter_move.h:93:7: note: (skipping 5 contexts in backtrace; use -ftemplate-backtrace-limit=0 to see all)
# |     { ranges::iter_move(__t) } -> __can_reference;
# | ^
# | /.../__iterator/concepts.h:58:7: note: in instantiation of requirement here
# |       typename iter_rvalue_reference_t<_In>;
# | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# | /.../__iterator/concepts.h:55:5: note: while substituting template arguments into constraint expression here
# |     requires(const _In __i) {
# | ^~~~~~~~~~~~~~~~~~~~~~~~~
# | /.../__iterator/concepts.h:66:31: note: while checking the satisfaction of concept '__indirectly_readable_impl<std::reverse_iterator<Incomplete *>>' requested here
# | concept indirectly_readable = __indirectly_readable_impl<remove_cvref_t<_In>>;
# | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# | /.../__iterator/concepts.h:66:31: note: while substituting template arguments into constraint expression here
# | concept indirectly_readable = __indirectly_readable_impl<remove_cvref_t<_In>>;
# | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# | /.../libcxx/test/std/containers/views/views.span/span.cons/copy.pass.cpp:105:19: note: while checking the satisfaction of concept 'indirectly_readable<std::reverse_iterator<Incomplete *>>' requested here
# | static_assert(std::indirectly_readable<std::reverse_iterator<Incomplete*>>);
# | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# | /.../libcxx/test/std/containers/views/views.span/span.cons/copy.pass.cpp:100:12: note: forward declaration of 'Incomplete'
# |     struct Incomplete;
# |            ^
# | In file included from /.../libcxx/test/std/containers/views/views.span/span.cons/copy.pass.cpp:15:
# | In file included from /.../span:163:
# | /.../__iterator/reverse_iterator.h:186:30: error: arithmetic on a pointer to an incomplete type 'Incomplete'
# |     return ranges::iter_move(--__tmp);
# |                              ^ ~~~~~
# | /.../__iterator/iter_move.h:66:12: note: in instantiation of member function 'std::iter_move' requested here
# |     return iter_move(std::forward<_Ip>(__i));
# |            ^
# | /.../__iterator/iter_move.h:93:7: note: in instantiation of function template specialization 'std::ranges::__iter_move::__fn::operator()<std::reverse_iterator<Incomplete *> &>' requested here
# |     { ranges::iter_move(__t) } -> __can_reference;
# |       ^
# | /.../__iterator/iter_move.h:93:7: note: in instantiation of requirement here
# |     { ranges::iter_move(__t) } -> __can_reference;
# | ^~~~~~~~~~~~~~~~~~~~~~
# | /.../__iterator/iter_move.h:92:12: note: while substituting template arguments into constraint expression here
# | requires requires(_Tp& __t) {
# |            ^~~~~~~~~~~~~~~~~~~~
# | /.../__iterator/concepts.h:58:16: note: while checking constraint satisfaction for template 'iter_rvalue_reference_t<std::reverse_iterator<Incomplete *>>' required here
# |       typename iter_rvalue_reference_t<_In>;
# | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
# | /.../__iterator/concepts.h:58:7: note: in instantiation of requirement here
# |       typename iter_rvalue_reference_t<_In>;
# | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# | /.../__iterator/concepts.h:55:5: note: while substituting template arguments into constraint expression here
# |     requires(const _In __i) {
# | ^~~~~~~~~~~~~~~~~~~~~~~~~
# | /.../__iterator/concepts.h:66:31: note: while checking the satisfaction of concept '__indirectly_readable_impl<std::reverse_iterator<Incomplete *>>' requested here
# | concept indirectly_readable = __indirectly_readable_impl<remove_cvref_t<_In>>;
# | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# | /.../__iterator/concepts.h:66:31: note: while substituting template arguments into constraint expression here
# | concept indirectly_readable = __indirectly_readable_impl<remove_cvref_t<_In>>;
# | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# | /.../libcxx/test/std/containers/views/views.span/span.cons/copy.pass.cpp:105:19: note: while checking the satisfaction of concept 'indirectly_readable<std::reverse_iterator<Incomplete *>>' requested here
# | static_assert(std::indirectly_readable<std::reverse_iterator<Incomplete*>>);
# | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# | /.../libcxx/test/std/containers/views/views.span/span.cons/copy.pass.cpp:100:12: note: forward declaration of 'Incomplete'
# |     struct Incomplete;
```
</pre>
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