`interval<..., dynamic>::operator-` is missing its `return` (undefined behavior)

[mutetea]

Summary

The dynamic interval kind's operator- (interval distance) computes the distance but never returns it. The function is declared to return value_type, so falling off the end is undefined behavior: under -O1 and above it typically returns a garbage value or crashes.

Root cause

// include/interval-tree/interval_tree.hpp:348-351 (dynamic interval kind)
value_type operator-(interval const& other) const
{
 interval_kind::distance(*this, other); // result computed but NOT returned
}

Compare the correct closed-interval implementation in the same header (lines 210–219), which returns in every path:

value_type operator-(interval const& other) const
{
 if (overlaps(other)) return 0;
 if (high_ <= other.low_) return other.low_ - high_;
 else return low_ - other.high_;
}

The bug is also a compile-time diagnostic: -Wreturn-type (on by default in clang/gcc) warns here, and the build fails under -Werror.

Steps to reproduce

#include <interval-tree/interval_tree.hpp>
using namespace lib_interval_tree;
using Dyn = interval<int, dynamic>;
Dyn a(1, 5, interval_border::closed, interval_border::closed);
Dyn b(7, 9, interval_border::closed, interval_border::closed);
auto d = a - b; // non-overlapping; distance should be 2
// EXPECTED: d == 2
// ACTUAL: UBSan: "reached end of value-returning function"; garbage / SIGSEGV under -O1

Compile with -O1 -fsanitize=undefined to observe the report.

Expected vs. actual

• Expected: operator- returns the interval distance (0 for overlapping intervals; a positive gap otherwise), as documented in the header comment ("Calculates the distance between the two intervals").
• Actual: no value is returned; behavior is undefined.

Suggested fix

return interval_kind::distance(*this, other);