[Bug libstdc++/86292] New: Missing exception safety when constructing vector from input iterator pair

[kristian.spangsege at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86292

            Bug ID: 86292
           Summary: Missing exception safety when constructing vector from
                    input iterator pair
           Product: gcc
           Version: 8.0.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kristian.spangsege at gmail dot com
  Target Milestone: ---

Created attachment 44316
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=44316&action=edit
Code to trigger the bug

When constructing a `std::vector` from a pair of input iterators
(`std::input_iterator_tag`), and the copy constructor for the value type
throws, already constructed copies will never be destroyed. I.e., the mentioned
vector constructor is not exception safe under these circumstances.

See the attached code for a way to trigger and reveal the problem.

The expectation is that it should output `0` (no instances of `X` remain at
exit), but it outputs `1`, meaning that one `X` object was leaked.

I tried this with GCC version 8.0.1 and 5.5.0 on Linux Mint 18.1.