fix(tag): resolve `commit` objects deeply.

As TagObjects can point to other TagObjects, we need
to keep going in order to resolve the final commit.

Fixes #503

2 files changed, 13 insertions, 7 deletions

diff --git a/doc/source/changes.rst b/doc/source/changes.rst
index bba538be..1feacab8 100644
--- a/doc/source/changes.rst
+++ b/doc/source/changes.rst
@@ -2,6 +2,12 @@
 Changelog
 =========
 
+2.0.9 - Bugfixes
+=============================
+
+* `tag.commit` will now resolve commits deeply.
+
+* `DiffIndex.iter_change_type(...)` produces better results when diffing
 2.0.8 - Features and Bugfixes
 =============================
 
diff --git a/git/refs/tag.py b/git/refs/tag.py
index 3334e53c..11dbab97 100644
--- a/git/refs/tag.py
+++ b/git/refs/tag.py
@@ -24,13 +24,13 @@ class TagReference(Reference):
     def commit(self):
         """:return: Commit object the tag ref points to"""
         obj = self.object
-        if obj.type == "commit":
-            return obj
-        elif obj.type == "tag":
-            # it is a tag object which carries the commit as an object - we can point to anything
-            return obj.object
-        else:
-            raise ValueError("Tag %s points to a Blob or Tree - have never seen that before" % self)
+        while obj.type != 'commit':
+            if obj.type == "tag":
+                # it is a tag object which carries the commit as an object - we can point to anything
+                obj = obj.object
+            else:
+                raise ValueError("Tag %s points to a Blob or Tree - have never seen that before" % self)
+        return obj
 
     @property
     def tag(self):