unordered_set rehash breaks insert_commit_data

[paul203948]

Since boost 1.80.0 there is an issue performing insert_check, rehash and then insert_commit. The bucket_idx in insert_commit_data can become invalid. This was changed in commit 3c5c8ce.

The documentation explicitly states that this is allowed:

After a successful rehashing insert_commit_data remains valid.

This worked in Boost 1.79.0.

Example program:

#include <boost/intrusive/unordered_set.hpp>

struct MyClass : boost::intrusive::unordered_set_base_hook<>
{
    int n_;

    MyClass(int n) : n_(n) { }

    friend bool operator==(const MyClass &a, const MyClass &b)
        { return a.n_ == b.n_; }
    friend std::size_t hash_value(const MyClass &value)
        { return std::size_t(value.n_); }
};

int main()
{
    using Set = boost::intrusive::unordered_set<MyClass>;

    MyClass value(101);
    Set::bucket_type buckets100[100];
    Set::bucket_type buckets200[200];

    Set set(Set::bucket_traits(buckets100, 100));

    Set::insert_commit_data commitData;
    set.insert_check(value, commitData);

    set.rehash(Set::bucket_traits(buckets200, 200));

    set.insert_commit(value, commitData);

    assert(1 == set.count(101));

    return 0;
}

[igaztanaga]

This was clearly a regression. To support the faster commit version, a new operation that does not support commit after rehashing is added insert_fast_commit(), and insert_commit is again compatible with rehashing. Many thanks for the report.