Restore intitial ref after symbol walk

comma/util/symbols.py

@@ -47,34 +47,44 @@ def map_symbols_to_patch(
     commits: SHA of all commits in database
     prev_commit: SHA of start of HyperV patch to track
     """
-    repo.head.reference = repo.commit(prev_commit)
-    repo.head.reset(index=True, working_tree=True)
-    before_patch_apply = None
 
-    # Iterate through commits
-    for commit in commits:
-        # Get symbols before patch is applied
-        if before_patch_apply is None:
-            before_patch_apply = set(get_symbols(repo.working_tree_dir, files))
+    # Preserve initial reference
+    initial_reference = repo.head.reference
 
-        # Checkout commit
-        repo.head.reference = repo.commit(commit)
+    try:
+        repo.head.reference = repo.commit(prev_commit)
         repo.head.reset(index=True, working_tree=True)
+        before_patch_apply = None
 
-        # Get symbols after patch is applied
-        after_patch_apply = set(get_symbols(repo.working_tree_dir, files))
+        # Iterate through commits
+        for commit in commits:
+            # Get symbols before patch is applied
+            if before_patch_apply is None:
+                before_patch_apply = set(get_symbols(repo.working_tree_dir, files))
 
-        # Compare symbols before and after patch
-        diff_symbols = after_patch_apply - before_patch_apply
-        print(f"Commit: {commit} -> {''.join(diff_symbols)}")
+            # Checkout commit
+            repo.head.reference = repo.commit(commit)
+            repo.head.reset(index=True, working_tree=True)
 
-        # Save symbols to database
-        with DatabaseDriver.get_session() as session:
-            patch = session.query(PatchData).filter_by(commitID=commit).one()
-            patch.symbols = " ".join(diff_symbols)
+            # Get symbols after patch is applied
+            after_patch_apply = set(get_symbols(repo.working_tree_dir, files))
 
-        # Use symbols from current commit to compare to next commit
-        before_patch_apply = after_patch_apply
+            # Compare symbols before and after patch
+            diff_symbols = after_patch_apply - before_patch_apply
+            print(f"Commit: {commit} -> {''.join(diff_symbols)}")
+
+            # Save symbols to database
+            with DatabaseDriver.get_session() as session:
+                patch = session.query(PatchData).filter_by(commitID=commit).one()
+                patch.symbols = " ".join(diff_symbols)
+
+            # Use symbols from current commit to compare to next commit
+            before_patch_apply = after_patch_apply
+
+    finally:
+        # Reset reference
+        repo.head.reference = initial_reference
+        repo.head.reset(index=True, working_tree=True)
 
 
 def get_hyperv_patch_symbols():