fix: fallback to HEAD when remote tag lookup fails

copier/_vcs.py

@@ -140,9 +140,19 @@ def get_latest_tag(url: str, use_prereleases: OptBool = False) -> str:
         The latest git tag, or `HEAD` if no valid tags are found.
     """
     git = get_git()
+    try:
+        tags_output = git("ls-remote", "--tags", "--refs", url)
+    except ProcessExecutionError:
+        print(
+            colors.warn
+            | "Could not list remote tags from template; using HEAD as ref",
+            file=sys.stderr,
+        )
+        return "HEAD"
+
     all_tags = (
         tag.split("\t", 1)[1].removeprefix("refs/tags/")
-        for tag in git("ls-remote", "--tags", "--refs", url).splitlines()
+        for tag in tags_output.splitlines()
     )
     all_tags = (tag for tag in all_tags if valid_version(tag))
     if not use_prereleases:

tests/test_vcs.py

@@ -12,7 +12,13 @@
 from copier import run_copy, run_update
 from copier._main import Worker
 from copier._user_data import load_answersfile_data
-from copier._vcs import clone, get_git_version, get_latest_tag, get_repo
+from copier._vcs import (
+    ProcessExecutionError,
+    clone,
+    get_git_version,
+    get_latest_tag,
+    get_repo,
+)
 from copier.errors import DirtyLocalWarning, ShallowCloneWarning
 
 from .helpers import build_file_tree, git, git_save
@@ -213,6 +219,15 @@ def test_invalid_version(tmp_path: Path) -> None:
         assert get_latest_tag(str(tmp_path)) == "v2"
 
 
+def test_get_latest_tag_falls_back_to_head_on_ls_remote_error() -> None:
+    mock_git = mock.MagicMock(
+        side_effect=ProcessExecutionError(["git", "ls-remote"], 128, "", "auth")
+    )
+
+    with mock.patch("copier._vcs.get_git", return_value=mock_git):
+        assert get_latest_tag("https://x-access-token:token@github.com/org/private.git") == "HEAD"
+
+
 @pytest.mark.parametrize("sorter", [iter, reversed])
 def test_select_latest_version_tag(
     tmp_path_factory: pytest.TempPathFactory,