[Bug libstdc++/86658] [9 Regression] Debug mode: std::copy(..., std::inserter(...)) causes "Error: attempt to copy-construct an iterator from a singular iterator."

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86658

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2018-07-24
      Known to work|                            |8.1.0
           Assignee|unassigned at gcc dot gnu.org      |redi at gcc dot gnu.org
   Target Milestone|---                         |9.0
            Summary|Debug mode: std::copy(...,  |[9 Regression] Debug mode:
                   |std::inserter(...)) causes  |std::copy(...,
                   |"Error: attempt to          |std::inserter(...)) causes
                   |copy-construct an iterator  |"Error: attempt to
                   |from a singular iterator."  |copy-construct an iterator
                   |                            |from a singular iterator."
     Ever confirmed|0                           |1
      Known to fail|                            |9.0

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The problem is that __niter_wrap takes its argument by value, and in this case
that makes a copy of the output iterator after it's been invalidated.

I'll test this fix:

--- a/libstdc++-v3/include/bits/stl_algobase.h
+++ b/libstdc++-v3/include/bits/stl_algobase.h
@@ -288,7 +288,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   // No need to wrap, iterator already has the right type.
   template<typename _Iterator>
     inline _Iterator
-    __niter_wrap(_Iterator, _Iterator __res)
+    __niter_wrap(const _Iterator&, _Iterator __res)
     { return __res; }

   // All of these auxiliary structs serve two purposes.  (1) Replace