cssnode: Refactor node tree modification code

This allows adding more API for it.

It also includes code that tracks modifications and invalidates siblings
and their positions whenever nodes get added or removed.

gtk/gtkcssnode.c

@@ -359,6 +359,110 @@ gtk_css_node_parent_will_be_set (GtkCssNode *node)
     GTK_CSS_NODE_GET_CLASS (node)->dequeue_validate (node);
 }
 
+static void
+gtk_css_node_unlink_from_siblings (GtkCssNode *node)
+{
+  if (GTK_IS_CSS_TRANSIENT_NODE (node))
+    return;
+
+  if (node->previous_sibling)
+    node->previous_sibling->next_sibling = node->next_sibling;
+  else
+    node->parent->first_child = node->next_sibling;
+
+  if (node->next_sibling)
+    node->next_sibling->previous_sibling = node->previous_sibling;
+  else
+    node->parent->last_child = node->previous_sibling;
+
+  node->previous_sibling = NULL;
+  node->next_sibling = NULL;
+}
+
+static void
+gtk_css_node_link_to_siblings (GtkCssNode *node,
+                               GtkCssNode *new_previous)
+{
+  if (GTK_IS_CSS_TRANSIENT_NODE (node))
+    return;
+
+  if (new_previous)
+    {
+      node->previous_sibling = new_previous;
+      node->next_sibling = new_previous->next_sibling;
+      new_previous->next_sibling = node;
+    }
+  else
+    {
+      node->next_sibling = node->parent->first_child;
+      node->parent->first_child = node;
+    }
+
+  if (node->next_sibling)
+    node->next_sibling->previous_sibling = node;
+  else
+    node->parent->last_child = node;
+}
+
+static void
+gtk_css_node_set_children_changed (GtkCssNode *node)
+{
+  if (node->children_changed)
+    return;
+
+  node->children_changed = TRUE;
+  gtk_css_node_set_invalid (node, TRUE);
+}
+
+static void
+gtk_css_node_reposition (GtkCssNode *node,
+                         GtkCssNode *parent,
+                         GtkCssNode *previous)
+{
+  g_assert (! (parent == NULL && previous != NULL));
+
+  /* Take a reference here so the whole function has a reference */
+  g_object_ref (node);
+
+  if (node->parent != NULL)
+    gtk_css_node_unlink_from_siblings (node);
+
+  if (node->parent != parent)
+    {
+      if (node->parent == NULL)
+        {
+          gtk_css_node_parent_will_be_set (node);
+        }
+      else
+        {
+          g_object_unref (node);
+          gtk_css_node_set_children_changed (node->parent);
+        }
+
+      node->parent = parent;
+
+      if (parent)
+        {
+          gtk_css_node_set_children_changed (parent);
+          g_object_ref (node);
+
+          if (node->invalid)
+            gtk_css_node_set_invalid (parent, TRUE);
+        }
+      else
+        {
+          gtk_css_node_parent_was_unset (node);
+        }
+    }
+
+  if (parent)
+    gtk_css_node_link_to_siblings (node, previous);
+
+  gtk_css_node_invalidate (node, GTK_CSS_CHANGE_ANY_PARENT | GTK_CSS_CHANGE_ANY_SIBLING);
+
+  g_object_unref (node);
+}
+
 void
 gtk_css_node_set_parent (GtkCssNode *node,
                          GtkCssNode *parent)
@@ -366,66 +470,7 @@ gtk_css_node_set_parent (GtkCssNode *node,
   if (node->parent == parent)
     return;
 
-  /* Take a reference here so the whole function has a reference */
-  g_object_ref (node);
-
-  if (node->parent != NULL)
-    {
-      if (!GTK_IS_CSS_TRANSIENT_NODE (node))
-        {
-          if (node->previous_sibling)
-            node->previous_sibling->next_sibling = node->next_sibling;
-          else
-            node->parent->first_child = node->next_sibling;
-
-          if (node->next_sibling)
-            node->next_sibling->previous_sibling = node->previous_sibling;
-          else
-            node->parent->last_child = node->previous_sibling;
-
-          node->parent->n_children--;
-        }
-
-      node->parent = NULL;
-      node->next_sibling = NULL;
-      node->previous_sibling = NULL;
-
-      g_object_unref (node);
-
-      if (parent == NULL)
-        gtk_css_node_parent_was_unset (node);
-    }
-
-  if (parent)
-    {
-      if (node->parent == NULL)
-        gtk_css_node_parent_will_be_set (node);
-
-      node->parent = parent;
-
-      if (!GTK_IS_CSS_TRANSIENT_NODE (node))
-        {
-          parent->n_children++;
-
-          if (parent->last_child)
-            {
-              parent->last_child->next_sibling = node;
-              node->previous_sibling = parent->last_child;
-            }
-          parent->last_child = node;
-
-          if (parent->first_child == NULL)
-            parent->first_child = node;
-        }
-
-      if (node->invalid)
-        gtk_css_node_set_invalid (parent, TRUE);
-    }
-
-  gtk_css_node_invalidate (node, GTK_CSS_CHANGE_ANY_PARENT | GTK_CSS_CHANGE_ANY_SIBLING);
-
-  if (node->parent == NULL)
-    g_object_unref (node);
+  gtk_css_node_reposition (node, parent, parent ? parent->last_child : NULL);
 }
 
 GtkCssNode *
@@ -638,6 +683,11 @@ gtk_css_node_propagate_pending_changes (GtkCssNode *cssnode)
     return;
 
   change = _gtk_css_change_for_child (cssnode->pending_changes);
+  if (cssnode->children_changed)
+    {
+      change |= GTK_CSS_CHANGE_POSITION | GTK_CSS_CHANGE_ANY_SIBLING;
+      cssnode->children_changed = FALSE;
+    }
 
   for (child = gtk_css_node_get_first_child (cssnode);
        child;
@@ -671,11 +721,11 @@ gtk_css_node_validate (GtkCssNode            *cssnode,
   if (G_UNLIKELY (gtk_get_debug_flags () & GTK_DEBUG_NO_CSS_CACHE))
     change = GTK_CSS_CHANGE_ANY;
 
+  gtk_css_node_propagate_pending_changes (cssnode);
+
   if (!cssnode->invalid && change == 0 && _gtk_bitmask_is_empty (parent_changes))
     return;
 
-  gtk_css_node_propagate_pending_changes (cssnode);
-
   gtk_css_node_set_invalid (cssnode, FALSE);
 
   change = cssnode->pending_changes;

gtk/gtkcssnodeprivate.h

@@ -43,7 +43,6 @@ struct _GtkCssNode
   GtkCssNode *next_sibling;
   GtkCssNode *first_child;
   GtkCssNode *last_child;
-  guint n_children;
 
   GtkCssNodeDeclaration *decl;
   GtkCssStyle           *style;
@@ -51,6 +50,7 @@ struct _GtkCssNode
   GtkCssChange           pending_changes;       /* changes that accumulated since the style was last computed */
 
   guint                  invalid :1;            /* node or a child needs to be validated (even if just for animation) */
+  guint                  children_changed :1;   /* the children changed since last validation */
 };
 
 struct _GtkCssNodeClass