[LLVMbugs] [Bug 22806] New: Move from destroyed object in tuple_cat of nested tuples

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=22806

            Bug ID: 22806
           Summary: Move from destroyed object in tuple_cat of nested
                    tuples
           Product: libc++
           Version: 3.6
          Hardware: Macintosh
                OS: MacOS X
            Status: NEW
          Severity: normal
          Priority: P
         Component: All Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: ldionne.2 at gmail.com
                CC: llvmbugs at cs.uiuc.edu, mclow.lists at gmail.com
    Classification: Unclassified

This bug concerns libc++ trunk (git-svn ID 230867).

In the following code, `Tracked{}` is destroyed and is then moved-from.

    std::tuple_cat(std::make_tuple(std::make_tuple(Tracked{})));

Here's a self-contained test program:

    #include <cassert>
    #include <tuple>

    struct Tracked {
        enum class State { CONSTRUCTED, MOVED_FROM, DESTROYED };
        State state;

        Tracked() : state{State::CONSTRUCTED} { }

        Tracked(Tracked const& t) : state{State::CONSTRUCTED} {
            assert(t.state != State::MOVED_FROM && "copying a moved-from
object");
            assert(t.state != State::DESTROYED && "copying a destroyed
object");
        }

        Tracked(Tracked&& t) : state{State::CONSTRUCTED} {
            assert(t.state != State::MOVED_FROM && "double moving from an
object");
            assert(t.state != State::DESTROYED && "moving from a destroyed
object");
            t.state = State::MOVED_FROM;
        }

        ~Tracked() {
            assert(state != State::DESTROYED && "double-destroying an object");
            state = State::DESTROYED;
        }
    };

    int main() {
        std::tuple_cat(std::make_tuple(std::make_tuple(Tracked{})));
    }

Compiling and then running this will produce:

    Assertion failed: (t.state != State::DESTROYED && "moving from a destroyed
object")

I don't have the time to investigate this further right now, unfortunately.

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