Check whether in shallow repo. If so, do not trust git.

insert_license_header/insert_license.py

@@ -832,6 +832,22 @@ def _get_existing_year_range(filepath: str) -> tuple[int, int] | None:
     return None  # File exists but no license header found
 
 
+def _is_shallow_git_repo() -> bool:
+    """Check if the current directory is a shallow git repo.
+    If it is, we cannot use git log to get the year range of the file.
+    """
+    command = "git rev-parse --is-shallow-repository"
+
+    try:
+        result = subprocess.run(
+            command, shell=True, text=True, capture_output=True, check=True
+        )
+    except subprocess.CalledProcessError:
+        return False
+
+    return result.stdout.strip() == "true"
+
+
 def _get_git_file_year_range(filepath: str) -> tuple[datetime, datetime] | None:
     """Uses git log formatting to extract start and end year from the commits.
     Take the start year from the first commit and the end year from the last.
@@ -844,6 +860,12 @@ def _get_git_file_year_range(filepath: str) -> tuple[datetime, datetime] | None:
     """
     command = f'git log --follow --format="%aI" -- "{filepath}"'
 
+    if _is_shallow_git_repo():
+        # Shallow git repo, don't trust git log as the life cycle of a file
+        # may not be fully captured. In this case, just pretend the file
+        # is not tracked with Git.
+        return None
+
     try:
         result = subprocess.run(
             command, shell=True, text=True, capture_output=True, check=True

tests/insert_license_test.py

@@ -806,14 +806,21 @@ def test_dynamic_years_with_existing_license_header(
         assert updated_content == expected_content
 
 
-# TESTCASES:
-# File's last_year is now 2024 (prev 2023)
-# File's last_year is still 2023 (current year = 2024)
-# File's start_year
+def test_git_ignored_in_shallow_repo(monkeypatch, tmp_path):
+    """Mock subprocess.run to throw an exception. Expect the returned datetime to have this year!"""
+
+    def mock_shallow_test(cmd, **kwargs):
+        assert "git rev-parse --is-shallow-repository" in cmd
+        return type("mock", (), {"stdout": "true"})
 
-# 1. File has no license header:
-#   - Git tracked: take from git
-#   - Not Git tracked: take current-current
+    monkeypatch.setattr(
+        subprocess,
+        "run",
+        mock_shallow_test,
+    )
+
+    result = _get_git_file_year_range("some-non-existant-file.py")
+    assert result is None
 
 
 def test_git_file_creation_date(monkeypatch):