Fix handling of main selection when copying selection to next/previous lines

Fixes #1095

src/normal.cc

@@ -1100,12 +1100,17 @@ void copy_selections_on_next_lines(Context& context, NormalParams params)
     auto& buffer = context.buffer();
     const ColumnCount tabstop = context.options()["tabstop"].get<int>();
     Vector<Selection> result;
+    size_t main_index = 0;
     for (auto& sel : selections)
     {
+        const bool is_main = (&sel == &selections.main());
         auto anchor = sel.anchor();
         auto cursor = sel.cursor();
         ColumnCount cursor_col = get_column(buffer, tabstop, cursor);
         ColumnCount anchor_col = get_column(buffer, tabstop, anchor);
+
+        if (is_main)
+            main_index = result.size();
         result.push_back(std::move(sel));
         for (int i = 0; i < std::max(params.count, 1); ++i)
         {
@@ -1123,11 +1128,15 @@ void copy_selections_on_next_lines(Context& context, NormalParams params)
 
             if (anchor_byte != buffer[anchor_line].length() and
                 cursor_byte != buffer[cursor_line].length())
+            {
+                if (is_main)
+                    main_index = result.size();
                 result.emplace_back(BufferCoord{anchor_line, anchor_byte},
                                     BufferCoordAndTarget{cursor_line, cursor_byte, cursor.target});
             }
         }
-    selections = std::move(result);
+    }
+    selections.set(std::move(result), main_index);
     selections.sort_and_merge_overlapping();
 }
 

src/selection.hh

@@ -101,12 +101,18 @@ struct SelectionList
 
     SelectionList& operator=(Vector<Selection> list)
     {
+        set(std::move(list), list.size()-1);
+        return *this;
+    }
+
+    void set(Vector<Selection> list, size_t main)
+    {
+        kak_assert(main < list.size());
         m_selections = std::move(list);
-        m_main = size()-1;
+        m_main = main;
         sort_and_merge_overlapping();
         update_timestamp();
         check_invariant();
-        return *this;
     }
 
     using iterator = Vector<Selection>::iterator;