Several changes:

 - Fix #5843: Make sure zIndex is higher than any sibling with same or lower baseZIndex,
   and at least equal to baseZIndex
 - Add virtual destructor to Session/Transaction, make sure they're not copyable/movable
 - Issue #5841: allow MySQL operation to continue when connection lost
   Also, err_nb == CR_SERVER_LOST can also occur, apparently.
   return statement after connect allows action to continue.
 - src/Wt/Dbo/backend/Postgres.C: That type of for loop is a C++11 feature
 - Added unwind support to release notes

ReleaseNotes.html

@@ -102,6 +102,7 @@ <h2>Release 3.3.8 (July 2017)</h2>
           RESTful services is planned in a future release.</li>
       <li>Added <a href="classWt_1_1Dbo_1_1FixedSqlConnectionPool.html#a955e2ce03d8d45e8738f6ff718614601">Wt::Dbo::FixedSqlConnectionPool::setTimeout()</a>, to set a timeout for obtaining a connection.</li>
       <li>Added <a href="classWt_1_1Dbo_1_1backend_1_1Postgres.html#acb13461474cc43bc9e8a51b844a051f3">Wt::Dbo::backend::Postgres::setTimeout()</a>, to set a timeout for queries.</li>
+      <li>Added libunwind support for printing stacktraces. Enable this with the <tt>ENABLE_UNWIND</tt> CMake option.</li>
     </ul>
   </dd>
 </dl>

src/Wt/Dbo/Session

@@ -136,7 +136,17 @@ public:
    * through it, and will warning during this destructor if there are
    * still database objects that are being referenced from a ptr.
    */
-  ~Session();
+  virtual ~Session();
+
+#ifdef WT_CXX11
+  // Sessions are not copyable
+  Session(const Session &) = delete;
+  Session& operator=(const Session &) = delete;
+
+  // Sessions are not movable
+  Session(Session &&) = delete;
+  Session& operator=(Session &&) = delete;
+#endif // WT_CXX11
 
   /*! \brief Sets a dedicated connection.
    *
@@ -483,11 +493,15 @@ public:
   void setFlushMode(FlushMode mode) { flush(); flushMode_ = mode; }
 
 private:
-
   mutable std::string longlongType_;
   mutable std::string intType_;
   mutable bool haveSupportUpdateCascade_;
+
+#ifndef WT_CXX11
+  // Sessions are not copyable
   Session(const Session& s);
+  Session& operator=(const Session& s);
+#endif // WT_CXX11
 
   typedef boost::multi_index::multi_index_container<
     MetaDboBase *,

src/Wt/Dbo/Transaction

@@ -82,7 +82,17 @@ public:
    *
    * If the transaction is still active, it is rolled back.
    */
-  ~Transaction() WT_CXX11ONLY(noexcept(false));
+  virtual ~Transaction() WT_CXX11ONLY(noexcept(false));
+
+#ifdef WT_CXX11
+  // Transactions are not copyable
+  Transaction(const Transaction&) = delete;
+  Transaction& operator=(const Transaction&) = delete;
+
+  // Transactions are not movable
+  Transaction(Transaction&&) = delete;
+  Transaction& operator=(Transaction&&) = delete;
+#endif // WT_CXX11
 
   /*! \brief Returns whether the transaction is still active.
    *
@@ -126,6 +136,12 @@ public:
   SqlConnection *connection() const;
 
 private:
+#ifndef WT_CXX11
+  // Transactions should not be copied
+  Transaction(const Transaction& other);
+  Transaction& operator=(const Transaction& other);
+#endif // WT_CXX11
+
   struct Impl {
     Session& session_;
     bool active_;

src/Wt/Dbo/backend/MySQL.C

@@ -994,12 +994,14 @@ void MySQL::checkConnection()
     err_nb = mysql_errno(impl_->mysql);
     err = std::string(mysql_error(impl_->mysql));
   }
-  if (err_nb == CR_SERVER_GONE_ERROR) {
+  if (err_nb == CR_SERVER_GONE_ERROR ||
+      err_nb == CR_SERVER_LOST) {
     clearStatementCache();
     mysql_close(impl_->mysql);
     impl_->mysql = 0;
     try {
       connect(dbname_, dbuser_, dbpasswd_, dbhost_, dbport_, dbsocket_);
+      return;
     } catch (MySQLException e) {
       throw MySQLException("checkConnection: Error when reconnecting: " + std::string(e.what()));
     }

src/Wt/Dbo/backend/Postgres.C

@@ -641,7 +641,8 @@ void Postgres::disconnect()
   /* Evict also the statements -- the statements themselves can stay,
      only running statements behavior is affected (but we are dealing with
      that while calling disconnect) */
-  for (auto s : statements) {
+  for (std::size_t i = 0; i < statements.size(); ++i) {
+    SqlStatement *s = statements[i];
     PostgresStatement *ps = dynamic_cast<PostgresStatement *>(s);
     ps->rebuild();
   }

src/Wt/WWebWidget.C

@@ -709,19 +709,16 @@ void WWebWidget::calcZIndex()
 
   WWebWidget *ww = parentWebWidget();
   if (ww) {
-    if (ww == Wt::WApplication::instance()->domRoot()) {
-      layoutImpl_->zIndex_ = baseZIndex();
-    } else {
-      const std::vector<WWidget *>& children = ww->children();
+    const std::vector<WWidget *>& children = ww->children();
 
-      int maxZ = 0;
-      for (unsigned i = 0; i < children.size(); ++i) {
-        WWebWidget *wi = children[i]->webWidget();
+    int maxZ = 0;
+    for (unsigned i = 0; i < children.size(); ++i) {
+      WWebWidget *wi = children[i]->webWidget();
+      if (wi->baseZIndex() <= baseZIndex())
         maxZ = std::max(maxZ, wi->zIndex());
-      }
-
-      layoutImpl_->zIndex_ = maxZ + 100;
     }
+
+    layoutImpl_->zIndex_ = std::max(baseZIndex(), maxZ + 100);
   }
 }