do not check buffer invariant in do_{erase,insert} as this cause O(n²) behaviour

src/buffer.cc

@@ -321,8 +321,6 @@ void Buffer::do_insert(const BufferIterator& pos, const String& content)
         end_it = BufferIterator{*this, { last_line, m_lines[last_line].length() - suffix.length() }};
     }
 
-    check_invariant();
-
     for (auto listener : m_change_listeners)
         listener->on_insert(begin_it, end_it);
 }
@@ -348,8 +346,6 @@ void Buffer::do_erase(const BufferIterator& begin, const BufferIterator& end)
     for (LineCount i = begin.line()+1; i < line_count(); ++i)
         m_lines[i].start -= length;
 
-    check_invariant();
-
     for (auto listener : m_change_listeners)
         listener->on_erase(begin, end);
 }

src/buffer.hh

@@ -168,10 +168,10 @@ public:
     const HookManager&   hooks()   const { return m_hooks; }
 
     std::unordered_set<BufferChangeListener*>& change_listeners() const { return m_change_listeners; }
-private:
-    friend class BufferIterator;
 
     void check_invariant() const;
+private:
+    friend class BufferIterator;
 
     struct Line
     {

src/editor.cc

@@ -88,10 +88,10 @@ void Editor::insert(const String& str, InsertMode mode)
         {
             sel.first() = pos;
             sel.last() = str.empty() ? pos : utf8::character_start(pos + str.length() - 1);
-            sel.check_invariant();
         }
         sel.avoid_eol();
     }
+    check_invariant();
 }
 
 void Editor::insert(const memoryview<String>& strings, InsertMode mode)
@@ -110,10 +110,10 @@ void Editor::insert(const memoryview<String>& strings, InsertMode mode)
         {
             sel.first() = pos;
             sel.last() = str.empty() ? pos : utf8::character_start(pos + str.length() - 1);
-            sel.check_invariant();
         }
         sel.avoid_eol();
     }
+    check_invariant();
 }
 
 std::vector<String> Editor::selections_content() const
@@ -408,6 +408,7 @@ void Editor::check_invariant() const
     assert(not m_selections.empty());
     assert(m_main_sel < m_selections.size());
     m_selections.check_invariant();
+    buffer().check_invariant();
     assert(std::is_sorted(m_selections.begin(), m_selections.end(), compare_selections));
 #endif
 }

src/editor.hh

@@ -87,7 +87,6 @@ public:
                                     size_t cursor_pos = String::npos);
 
     bool is_editing() const { return m_edition_level!= 0; }
-
 private:
     friend struct scoped_edition;
     void begin_edition();