porcelain: respect 'abbrev' argument when describing annotated-tagless repositories (#1482)

Resolves #1477.

dulwich/porcelain.py

@@ -2184,7 +2184,7 @@ def find_unique_abbrev(object_store, object_id):
     return object_id.decode("ascii")[:7]
 
 
-def describe(repo, abbrev=7):
+def describe(repo, abbrev=None):
     """Describe the repository version.
 
     Args:
@@ -2194,6 +2194,7 @@ def describe(repo, abbrev=7):
 
     Examples: "gabcdefh", "v0.1" or "v0.1-5-gabcdefh".
     """
+    abbrev_slice = slice(0, abbrev if abbrev is not None else 7)
     # Get the repository
     with open_repo_closing(repo) as r:
         # Get a list of all tags
@@ -2220,16 +2221,18 @@ def describe(repo, abbrev=7):
 
         sorted_tags = sorted(tags.items(), key=lambda tag: tag[1][0], reverse=True)
 
-        # If there are no tags, return the current commit
+        # Get the latest commit
+        latest_commit = r[r.head()]
+
+        # If there are no tags, return the latest commit
         if len(sorted_tags) == 0:
-            return f"g{find_unique_abbrev(r.object_store, r[r.head()].id)}"
+            if abbrev is not None:
+                return "g{}".format(latest_commit.id.decode("ascii")[abbrev_slice])
+            return f"g{find_unique_abbrev(r.object_store, latest_commit.id)}"
 
         # We're now 0 commits from the top
         commit_count = 0
 
-        # Get the latest commit
-        latest_commit = r[r.head()]
-
         # Walk through all commits
         walker = r.get_walker()
         for entry in walker:
@@ -2245,13 +2248,13 @@ def describe(repo, abbrev=7):
                         return "{}-{}-g{}".format(
                             tag_name,
                             commit_count,
-                            latest_commit.id.decode("ascii")[:abbrev],
+                            latest_commit.id.decode("ascii")[abbrev_slice],
                         )
 
             commit_count += 1
 
         # Return plain commit if no parent tag can be found
-        return "g{}".format(latest_commit.id.decode("ascii")[:abbrev])
+        return "g{}".format(latest_commit.id.decode("ascii")[abbrev_slice])
 
 
 def get_object_by_path(repo, path, committish=None):

tests/test_porcelain.py

@@ -3403,6 +3403,19 @@ class DescribeTests(PorcelainTestCase):
             porcelain.describe(self.repo.path, abbrev=40),
         )
 
+    def test_untagged_commit_abbreviation(self) -> None:
+        _, _, c3 = build_commit_graph(self.repo.object_store, [[1], [2, 1], [3, 1, 2]])
+        self.repo.refs[b"HEAD"] = c3.id
+        brief_description, complete_description = (
+            porcelain.describe(self.repo),
+            porcelain.describe(self.repo, abbrev=40),
+        )
+        self.assertTrue(complete_description.startswith(brief_description))
+        self.assertEqual(
+            "g{}".format(c3.id.decode("ascii")),
+            complete_description,
+        )
+
 
 class PathToTreeTests(PorcelainTestCase):
     def setUp(self) -> None: