Fix rev parsing for refs starting with at

Agent-Logs-Url: https://github.com/gitpython-developers/GitPython/sessions/0273e08f-ead0-4b1e-b148-b103851caca9

Co-authored-by: Byron <63622+Byron@users.noreply.github.com>

Author: Copilot

git/repo/fun.py

@@ -269,6 +269,15 @@ def rev_parse(repo: "Repo", rev: str) -> AnyGitObject:
         if rev[start] not in "^~:@":
             start += 1
             continue
+        if rev[start] == "@":
+            next_char = rev[start + 1] if start + 1 < lr else None
+            if start == 0:
+                if next_char not in (None, "{", "^", "~", ":"):
+                    start += 1
+                    continue
+            elif next_char != "{":
+                start += 1
+                continue
         # END handle start
 
         token = rev[start]
@@ -292,6 +301,12 @@ def rev_parse(repo: "Repo", rev: str) -> AnyGitObject:
 
         start += 1
 
+        if token == "@" and (start >= lr or rev[start] != "{"):
+            obj = cast(AnyGitObject, ref.commit)
+            ref = None
+            parsed_to = start
+            continue
+
         # Try to parse {type}.
         if start < lr and rev[start] == "{":
             end = rev.find("}", start)

test/test_repo.py

@@ -146,6 +146,22 @@ def test_commit_from_revision(self):
         self.assertEqual(commit.type, "commit")
         self.assertEqual(self.rorepo.commit(commit), commit)
 
+    @with_rw_directory
+    def test_commit_from_tag_starting_with_at(self, rw_dir):
+        repo = Repo.init(rw_dir)
+        with repo.config_writer() as writer:
+            writer.set_value("user", "name", "GitPython Tests")
+            writer.set_value("user", "email", "gitpython@example.com")
+
+        tracked_file = Path(rw_dir) / "hello.txt"
+        tracked_file.write_text("hello")
+        repo.index.add([str(tracked_file)])
+        commit = repo.index.commit("init")
+        repo.create_tag("@foo")
+
+        self.assertEqual(repo.commit("@"), commit)
+        self.assertEqual(repo.commit("@foo"), commit)
+
     def test_commits(self):
         mc = 10
         commits = list(self.rorepo.iter_commits("0.1.6", max_count=mc))