#99: Gate empty initial commit behavior to Git 2.7+

Author: mtkennerly

CHANGELOG.md

@@ -1,10 +1,10 @@
 ## Unreleased
 
-* Changed: Previously, if the initial commit were both tagged and empty,
+* Changed: Previously, if Git's initial commit were both tagged and empty,
   Dunamai would raise an exception due to Git not reporting that tag in
   `git log --simplify-by-decoration`.
-  Now, if a tag is missing from that list, Dunamai treats it as the oldest tag,
-  since, in practice, this only seems to affect the initial commit.
+  Now, if a tag is missing from that list, Dunamai treats it as the oldest tag.
+  This new behavior is only enabled for Git 2.7+.
 
 ## v1.23.2 (2025-05-06)
 

dunamai/__init__.py

@@ -458,19 +458,21 @@ def best_date(self) -> Optional[dt.datetime]:
         else:
             return self.creatordate
 
-    @property
-    def commit_offset(self) -> int:
+    def commit_offset(self, git_version: List[int]) -> int:
         try:
             return self.tag_topo_lookup[self.fullref]
         except KeyError:
-            # This mainly happens when the initial commit is both empty and tagged.
-            # People can't really fix this in an old/existing repository,
-            # so we just sort the tag to the oldest position.
-            return sys.maxsize
+            if git_version < [2, 7]:
+                raise RuntimeError(
+                    "Unable to determine commit offset for ref {}. Is the initial commit both tagged and empty? Data: {}".format(
+                        self.fullref, self.tag_topo_lookup
+                    )
+                )
+            else:
+                return sys.maxsize
 
-    @property
-    def sort_key(self) -> Tuple[int, Optional[dt.datetime]]:
-        return (-self.commit_offset, self.best_date())
+    def sort_key(self, git_version: List[int]) -> Tuple[int, Optional[dt.datetime]]:
+        return (-self.commit_offset(git_version), self.best_date())
 
     @property
     def ref(self) -> str:
@@ -1243,7 +1245,7 @@ def from_git(
                     continue
                 detailed_tags.append(_GitRefInfo(*parts).with_tag_topo_lookup(tag_topo_lookup))
 
-            tags = [t.ref for t in sorted(detailed_tags, key=lambda x: x.sort_key, reverse=True)]
+            tags = [t.ref for t in sorted(detailed_tags, key=lambda x: x.sort_key(git_version), reverse=True)]
             matched_pattern = _match_version_pattern(pattern, tags, latest_tag, strict, pattern_prefix)
 
         if matched_pattern is None:

tests/integration/test_dunamai.py

@@ -534,22 +534,24 @@ def test__version__from_git__initial_commit_empty_and_tagged(tmp_path) -> None:
         run("git init")
         run("git commit --no-gpg-sign --allow-empty -m Initial")
         run("git tag v0.1.0 -m Release")
-        assert run("dunamai from git") == "0.1.0"
 
-        run("git commit --no-gpg-sign --allow-empty -m Second")
-        assert run("dunamai from git").startswith("0.1.0.post1.dev0+")
+        if is_git_legacy():
+            with pytest.raises(RuntimeError):
+                Version.from_git()
+        else:
+            assert run("dunamai from git") == "0.1.0"
 
-        run("git tag v0.2.0 -m Release")
-        if _get_git_version() < [2, 7]:
+            run("git commit --no-gpg-sign --allow-empty -m Second")
             assert run("dunamai from git").startswith("0.1.0.post1.dev0+")
-        else:
+
+            run("git tag v0.2.0 -m Release")
             assert run("dunamai from git") == "0.2.0"
 
-        (vcs / "foo.txt").write_text("hi")
-        run("git add .")
-        run("git commit --no-gpg-sign -m Third")
-        run("git tag v0.3.0 -m Release")
-        assert run("dunamai from git") == "0.3.0"
+            (vcs / "foo.txt").write_text("hi")
+            run("git add .")
+            run("git commit --no-gpg-sign -m Third")
+            run("git tag v0.3.0 -m Release")
+            assert run("dunamai from git") == "0.3.0"
 
 
 @pytest.mark.skipif(shutil.which("git") is None, reason="Requires Git")