Issue #1 - Reference at ... does not exist

git_unneeded.py

@@ -179,10 +179,22 @@ def repository_safe_to_delete(repo: git.Repo, fetch: bool = True) -> Generator[S
                 )
             continue
 
-        # branch b tracks remote branch
-        if tracking_branch.commit == b.commit:
-            # common & fast path
-            bl.info(f"Branch {b.path} and remote {tracking_branch.path} point to same commit {b.commit}")
+        try:
+            # branch b tracks remote branch
+            if tracking_branch.commit == b.commit:
+                # common & fast path
+                bl.info(f"Branch {b.path} and remote {tracking_branch.path} point to same commit {b.commit}")
+                continue
+        except ValueError as e:
+            bl.info(f"Branch {b.path} cites {tracking_branch.path}, but {tracking_branch.path} isn't known. It was probably deleted: {e}")
+            yield Safe(
+                repo,
+                f"Local branch {b.path} cites {tracking_branch.path}",
+                suggestions=[
+                    f"{e}.",
+                    "It was probably deleted from the remote. If so, delete the local branch."
+                ]
+            )
             continue
 
         bl.info(f"Local branch {b.path} points to commit {b.commit}")

tests/conftest.py

@@ -70,7 +70,7 @@ def cloned_repo(tmp_path: Path) -> Iterable[Repo]:
     upstream_path = tmp_path / "Upstream"
     upstream_path.mkdir()
 
-    repo = Repo.init(upstream_path)
+    repo = Repo.init(upstream_path, initial_branch="main")
 
     original_branch = repo.active_branch
 

tests/test_repos.py

@@ -1,7 +1,8 @@
 from datetime import UTC, datetime, timedelta
 from pathlib import Path
 
-from git import Repo
+import pytest
+from git import RemoteReference, Repo
 
 import git_unneeded
 from git_unneeded import Safe, Unsafe, repository_safe_to_delete
@@ -149,3 +150,33 @@ def test_local_branch_unknown_to_remote(cloned_repo: Repo) -> None:
                 assert "branch localbranch is not known to remotes" in r.reason
                 assert "has commits" in r.reason
                 assert git_unneeded.describe_commit_one_line(local_commit) in r.suggestions
+
+
+def test_upstream_is_gone(cloned_repo: Repo) -> None:
+    """Issue #1"""
+
+    # Deleting like vvv doesn't result in the state where "... but the upstream is gone" is seen.
+    # remote_git_repo.delete_head("new-b", force=True)  # git branch -D new-b
+
+    cloned_repo.refs["main"].checkout()
+    pil = cloned_repo.remote("origin").push("new-b", delete=True)
+    assert pil[0].summary == "[deleted]\n"  # delete remote ref
+
+    switch_result = cloned_repo.git.switch("new-b")
+    assert "but the upstream is gone" in switch_result
+
+    new_b = cloned_repo.branches["new-b"]
+    tracking_branch = new_b.tracking_branch()
+
+    assert isinstance(tracking_branch, RemoteReference)
+    assert tracking_branch.path == "refs/remotes/origin/new-b"
+
+    with pytest.raises(ValueError):
+        tracking_branch.commit
+
+    with pytest.raises(ValueError) as e:
+        tracking_branch.dereference_recursive(tracking_branch.repo, tracking_branch.path)
+    assert e.value.args[0] == "Reference at 'refs/remotes/origin/new-b' does not exist"
+
+    reasons = list(repository_safe_to_delete(cloned_repo, fetch=True))
+    assert "It was probably deleted" in str(reasons[0])