Fixed some edge-case bugs having to do with inserting an element

  into a tag it's already inside, and replacing one of a tag's
  children with another. [bug=997529]

3 files changed, 34 insertions, 13 deletions

diff --git a/NEWS.txt b/NEWS.txt
index b9c92fe..16f4598 100644
--- a/NEWS.txt
+++ b/NEWS.txt
@@ -13,6 +13,10 @@
   adding attributes to a tag that didn't originally have
   any. [bug=1002378] Thanks to Oliver Beattie for the patch.
 
+* Fixed some edge-case bugs having to do with inserting an element
+  into a tag it's already inside, and replacing one of a tag's
+  children with another. [bug=997529]
+
 = 4.0.5 (20120427) =
 
 * Added a new method, wrap(), which wraps an element in a tag.
diff --git a/bs4/element.py b/bs4/element.py
index 22b8304..99a3540 100644
--- a/bs4/element.py
+++ b/bs4/element.py
@@ -137,14 +137,6 @@ class PageElement(object):
             raise ValueError("Cannot replace a Tag with its parent.")
         old_parent = self.parent
         my_index = self.parent.index(self)
-        if (hasattr(replace_with, 'parent')
-            and replace_with.parent is self.parent):
-            # We're replacing this element with one of its siblings.
-            if self.parent.index(replace_with) < my_index:
-                # Furthermore, it comes before this element. That
-                # means that when we extract it, the index of this
-                # element will change.
-                my_index -= 1
         self.extract()
         old_parent.insert(my_index, replace_with)
         return self
@@ -212,11 +204,12 @@ class PageElement(object):
             # We're 'inserting' an element that's already one
             # of this object's children.
             if new_child.parent is self:
-                if self.index(new_child) > position:
-                    # Furthermore we're moving it further down the
-                    # list of this object's children. That means that
-                    # when we extract this element, our target index
-                    # will jump down one.
+                current_index = self.index(new_child)
+                if current_index < position:
+                    # We're moving this element further down the list
+                    # of this object's children. That means that when
+                    # we extract this element, our target index will
+                    # jump down one.
                     position -= 1
             new_child.extract()
 
diff --git a/bs4/tests/test_tree.py b/bs4/tests/test_tree.py
index 9a10edf..1e24c29 100644
--- a/bs4/tests/test_tree.py
+++ b/bs4/tests/test_tree.py
@@ -821,6 +821,18 @@ class TestTreeModification(SoupTest):
         self.assertEqual(the.next_element, c_tag)
         self.assertEqual(c_tag.previous_element, the)
 
+    def test_append_child_thats_already_at_the_end(self):
+        data = "<a><b></b></a>"
+        soup = self.soup(data)
+        soup.a.append(soup.b)
+        self.assertEquals(data, soup.decode())
+
+    def test_move_tag_to_beginning_of_parent(self):
+        data = "<a><b></b><c></c><d></d></a>"
+        soup = self.soup(data)
+        soup.a.insert(0, soup.d)
+        self.assertEqual("<a><d></d><b></b><c></c></a>", soup.decode())
+
     def test_insert_works_on_empty_element_tag(self):
         # This is a little strange, since most HTML parsers don't allow
         # markup like this to come through. But in general, we don't
@@ -882,6 +894,18 @@ class TestTreeModification(SoupTest):
         self.assertEqual(no.next_element, "no")
         self.assertEqual(no.next_sibling, " business")
 
+    def test_replace_first_child(self):
+        data = "<a><b></b><c></c></a>"
+        soup = self.soup(data)
+        soup.b.replace_with(soup.c)
+        self.assertEqual("<a><c></c></a>", soup.decode())
+
+    def test_replace_last_child(self):
+        data = "<a><b></b><c></c></a>"
+        soup = self.soup(data)
+        soup.c.replace_with(soup.b)
+        self.assertEqual("<a><b></b></a>", soup.decode())
+
     def test_nested_tag_replace_with(self):
         soup = self.soup(
             """<a>We<b>reserve<c>the</c><d>right</d></b></a><e>to<f>refuse</f><g>service</g></e>""")