YAML::Nodes alias rather than moving when using std::vector::erase, std::iter_swap and similar methods.

[Mark Johnson]

The following unit test fails

#include "gtest/gtest.h"
#include <yaml-cpp/yaml.h>
#include <vector>

TEST(VectorErase, ProducesVectorContainingCorrectElements) {
    YAML::Node a;
    a["name"] = "a";
    YAML::Node b;
    b["name"] = "b";
    YAML::Node c;
    c["name"] = "c";
    std::vector<YAML::Node> vec{a, b, c};
    vec.erase(vec.begin());
    EXPECT_EQ(vec[0]["name"].as<std::string>(), "b");
}

When vec.erase(vec.begin()) is called, instead of vec containing names {"b", "c"}, it instead contains names {"c", "c"}.

My guess is that this is something to do with aliasing rather than copying when the vector elements are moved. This is likely an issue with the move constructor or move assignment of the Node.

I am using libcpp-yaml0.6, as I am currently limited to Ubuntu 20.04.

[Mark Johnson]

Some other std::vector operations fail in the same way, including

std::iter_swap(vec.begin(), vec.begin()+1);

[Mark Johnson]

This is likely a duplicate of #721, and that issue is probably easier to test with.

[Mark Johnson]

I think this issue will be resolved by #810