[Bug libstdc++/109474] New: chunk_by doesn't work for ranges of proxy references

[Bug libstdc++/109474] New: chunk_by doesn't work for ranges of proxy references

[barry.revzin at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109474

            Bug ID: 109474
           Summary: chunk_by doesn't work for ranges of proxy references
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: barry.revzin at gmail dot com
  Target Milestone: ---

Reduced example from Conor's tweet
(https://twitter.com/code_report/status/1645831980473282560):

#include <vector>
#include <ranges>

void f(std::vector<bool> v) {
    auto z = std::views::chunk_by(
        v,
        [](auto&& lhs, auto&& rhs){
            return true;
        });
    auto i = z.begin();
}

This fails because the find_next implementation right now
(https://github.com/gcc-mirror/gcc/blob/0c5e64c4249322a178e1a0e843874e4d6b43b992/libstdc%2B%2B-v3/include/std/ranges#L6741-L6750)
passes a predicate into adjacent_find that requires both parameters be the same
type, but in this case indirect_binary_predicate is checking that it's
invocable with both value_type& (bool&) and reference
(vector<bool>::reference), which in this case are different types.

The original example was a zip_view of two ranges - which likewise would have
value_type& and reference be different.

[Bug libstdc++/109474] chunk_by doesn't work for ranges of proxy references

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109474

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |DUPLICATE

--- Comment #1 from Patrick Palka <ppalka at gcc dot gnu.org> ---
D'oh, thanks for the bug report.  Looks like a dup of PR108291, which
unfortunately slipped through the cracks..

*** This bug has been marked as a duplicate of bug 108291 ***

[Bug libstdc++/109474] chunk_by doesn't work for ranges of proxy references

[barry.revzin at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109474

--- Comment #2 from Barry Revzin <barry.revzin at gmail dot com> ---
Serves me right for only checking vector<int> (which worked) and vector<bool>
(which didn't) and not bothering to check vector<int> const (which also doesn't
work) and thus overly complicating the bug report.

I got too excited that vector<bool> played an important role I guess.