Fix redrawing of windows when only the status line changes

src/client.cc

@@ -88,16 +88,21 @@ void Client::change_buffer(Buffer& buffer)
 
 void Client::redraw_ifn()
 {
-    if (context().window().timestamp() != context().buffer().timestamp())
+    DisplayLine mode_line = generate_mode_line();
+    const bool buffer_changed = context().window().timestamp() != context().buffer().timestamp();
+    if (buffer_changed or mode_line.atoms() != m_mode_line.atoms())
+    {
+        if (buffer_changed)
         {
             CharCoord dimensions = context().ui().dimensions();
             if (dimensions == CharCoord{0,0})
                 return;
             context().window().set_dimensions(dimensions);
             context().window().update_display_buffer(context());
-
+        }
+        m_mode_line = std::move(mode_line);
         context().ui().draw(context().window().display_buffer(),
-                            m_status_line, generate_mode_line());
+                            m_status_line, m_mode_line);
     }
     context().ui().refresh();
 }

src/client.hh

@@ -53,6 +53,7 @@ private:
     InputHandler m_input_handler;
 
     DisplayLine m_status_line;
+    DisplayLine m_mode_line;
 };
 
 }

src/display_buffer.hh

@@ -105,6 +105,13 @@ public:
     void trim_end(CharCount count);
 
     void check_invariant() const;
+
+    bool operator==(const DisplayAtom& other) const
+    {
+        return colors == other.colors or attribute == other.attribute or
+               content() == other.content();
+    }
+
 public:
     ColorPair      colors = {Colors::Default, Colors::Default};
     Attribute      attribute = Normal;