Support sorting and merging overlapping separately, fix bug in move

Fixes #754

src/normal.cc

@@ -1513,10 +1513,12 @@ void move(Context& context, NormalParams params)
         sel.anchor() = mode == SelectMode::Extend ? sel.anchor() : cursor;
         sel.cursor() = cursor;
     }
+    selections.sort();
+
     if (std::is_same<Type, LineCount>::value)
         selections.avoid_eol();
 
-    selections.sort_and_merge_overlapping();
+    selections.merge_overlapping();
 }
 
 void select_whole_buffer(Context& context, NormalParams)

src/selection.cc

@@ -419,7 +419,7 @@ void SelectionList::check_invariant() const
 #endif
 }
 
-void SelectionList::sort_and_merge_overlapping()
+void SelectionList::sort()
 {
     if (size() == 1)
         return;
@@ -434,7 +434,21 @@ void SelectionList::sort_and_merge_overlapping()
                                    return begin < main_begin;
                            });
     std::stable_sort(begin(), end(), compare_selections);
-    m_selections.erase(merge_overlapping(begin(), end(), m_main, overlaps), end());
+}
+
+void SelectionList::merge_overlapping()
+{
+    if (size() == 1)
+        return;
+
+    m_selections.erase(Kakoune::merge_overlapping(begin(), end(),
+                                                  m_main, overlaps), end());
+}
+
+void SelectionList::sort_and_merge_overlapping()
+{
+    sort();
+    merge_overlapping();
 }
 
 static inline void _avoid_eol(const Buffer& buffer, ByteCoord& coord)
@@ -547,9 +561,7 @@ void SelectionList::insert(ConstArrayView<String> strings, InsertMode mode,
 void SelectionList::erase()
 {
     update();
-
+    merge_overlapping();
-    m_selections.erase(merge_overlapping(begin(), end(), m_main, overlaps),
-                       end());
 
     ForwardChangesTracker changes_tracker;
     for (auto& sel : m_selections)

src/selection.hh

@@ -124,6 +124,8 @@ struct SelectionList
     bool operator==(const SelectionList& other) const { return m_buffer == other.m_buffer and m_selections == other.m_selections; }
     bool operator!=(const SelectionList& other) const { return not ((*this) == other); }
 
+    void sort();
+    void merge_overlapping();
     void sort_and_merge_overlapping();
 
     Buffer& buffer() const { return *m_buffer; }