[amtool] (#10231) Prevent pushes if there are uncommitted changes in the tree

Author: ojhunt

apple-ci/amtool

@@ -327,6 +327,15 @@ def main():
         except GitError:
             pass
 
+        # Check if we have any unstaged or uncommitted changes in the tree.
+        try:
+            if len(git('diff-index', 'HEAD')):
+                log.error('Looks like you have unstaged or uncommitted changes.')
+                log.error('Please make sure everything has been added to the commit.')
+                return 1
+        except GitError:
+            pass
+
         # Save the commit sha so that we can include it in the output message.
         merge_commit = git('rev-parse', 'HEAD')