Size the dump buffer of a small value by its own extent

The source extent of a value was read from the next node, falling back to the rest of the document when that node held a decoded string. dump() of a small value could thus allocate a buffer as large as the document. Skip a few such nodes, cap the fallback estimate, and shrink a buffer that is much larger than its output.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

include/nlohmann/detail/view/serializer.hpp

@@ -44,7 +44,13 @@ class output_buffer
 
     void finish()
     {
-        m_out.resize(static_cast<std::size_t>(m_pos - m_out.data()));
+        const auto size = static_cast<std::size_t>(m_pos - m_out.data());
+        m_out.resize(size);
+        // do not keep a buffer that was sized for a much larger output
+        if (m_out.capacity() > 1024 && m_out.capacity() / 2 > size)
+        {
+            m_out.shrink_to_fit();
+        }
     }
 
     NLOHMANN_VIEW_ALWAYS_INLINE void reserve(std::size_t n)