curds: Give nodes a first-child notification

The UI has been guessing this during scanning, but we can easily figure
this out and tell them when a tree node is given their first child.

Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>

curds/test_tree.py

@@ -7,14 +7,20 @@ import unittest
 class TestETree(unittest.TestCase):
     def setUp(self):
         notify.register("child-inserted", self.on_child_inserted)
+        notify.register("first-child",    self.on_first_child)
 
     def tearDown(self):
         notify.cancel("child-inserted", self.on_child_inserted)
+        notify.cancel("first-child",    self.on_first_child)
 
     def on_child_inserted(self, child, path):
         self.cb_child = child
         self.cb_path  = path
 
+    def on_first_child(self, parent, path):
+        self.cb_first = parent
+        self.cb_fpath = path
+
     def test_etree_init(self):
         etree = tree.ETree("Test Tree", "test-icon")
         self.assertEqual(etree.name, "Test Tree")
@@ -113,12 +119,16 @@ class TestETree(unittest.TestCase):
         self.assertEqual(a.parent, root)
         self.assertEqual(self.cb_child, a)
         self.assertEqual(self.cb_path, [ 0 ])
+        self.assertEqual(self.cb_first, root)
+        self.assertEqual(self.cb_fpath, [ ])
 
+        self.cb_first = None
         c = root.insert_child(tree.ETree("C", "icon"))
         self.assertEqual(root.children, [ a, c ])
         self.assertEqual(a.sibling, c)
         self.assertEqual(self.cb_child, c)
         self.assertEqual(self.cb_path, [ 1 ])
+        self.assertIsNone(self.cb_first)
 
         b = root.insert_child(tree.ETree("B", "icon"))
         self.assertEqual(root.children, [ a, b, c ])

curds/tree.py

@@ -28,6 +28,8 @@ class ETree:
             with prev.tree_lock:
                 prev.sibling = child
 
+        if len(self.children) == 1:
+            notify.notify("first-child", self, self.get_path())
         notify.notify("child-inserted", child, self.get_path() + [ index ])
         return child