Add support for branch.sort configuration

Implements sorting functionality for branch listing based on the
branch.sort configuration variable. Supports refname (default),
committerdate, and authordate sorting with optional reverse order.

dulwich/porcelain.py

@@ -2338,9 +2338,55 @@ def branch_list(repo):
 
     Args:
       repo: Path to the repository
+    Returns:
+      List of branch names (without refs/heads/ prefix)
     """
     with open_repo_closing(repo) as r:
-        return r.refs.keys(base=LOCAL_BRANCH_PREFIX)
+        branches = list(r.refs.keys(base=LOCAL_BRANCH_PREFIX))
+
+        # Check for branch.sort configuration
+        config = r.get_config_stack()
+        try:
+            sort_key = config.get((b"branch",), b"sort").decode()
+        except KeyError:
+            # Default is refname (alphabetical)
+            sort_key = "refname"
+
+        # Parse sort key
+        reverse = False
+        if sort_key.startswith("-"):
+            reverse = True
+            sort_key = sort_key[1:]
+
+        # Apply sorting
+        if sort_key == "refname":
+            # Simple alphabetical sort (default)
+            branches.sort(reverse=reverse)
+        elif sort_key in ("committerdate", "authordate"):
+            # Sort by date
+            def get_commit_date(branch_name):
+                ref = LOCAL_BRANCH_PREFIX + branch_name
+                sha = r.refs[ref]
+                commit = r.object_store[sha]
+                if sort_key == "committerdate":
+                    return commit.commit_time
+                else:  # authordate
+                    return commit.author_time
+
+            # Sort branches by date
+            # Note: Python's sort naturally orders smaller values first (ascending)
+            # For dates, this means oldest first by default
+            # Use a stable sort with branch name as secondary key for consistent ordering
+            if reverse:
+                # For reverse sort, we want newest dates first but alphabetical names second
+                branches.sort(key=lambda b: (-get_commit_date(b), b))
+            else:
+                branches.sort(key=lambda b: (get_commit_date(b), b))
+        else:
+            # Unknown sort key, fall back to default
+            branches.sort()
+
+        return branches
 
 
 def active_branch(repo):

tests/test_porcelain.py

@@ -4739,6 +4739,118 @@ class BranchListTests(PorcelainTestCase):
         porcelain.branch_create(self.repo, b"foo")
         self.assertEqual({b"master", b"foo"}, set(porcelain.branch_list(self.repo)))
 
+    def test_sort_by_refname(self) -> None:
+        """Test branch.sort=refname (default alphabetical)."""
+        [c1] = build_commit_graph(self.repo.object_store, [[1]])
+        self.repo[b"HEAD"] = c1.id
+
+        # Create branches in non-alphabetical order
+        porcelain.branch_create(self.repo, b"zebra")
+        porcelain.branch_create(self.repo, b"alpha")
+        porcelain.branch_create(self.repo, b"beta")
+
+        # Set branch.sort to refname (though it's the default)
+        config = self.repo.get_config()
+        config.set((b"branch",), b"sort", b"refname")
+        config.write_to_path()
+
+        # Should be sorted alphabetically
+        branches = porcelain.branch_list(self.repo)
+        self.assertEqual([b"alpha", b"beta", b"master", b"zebra"], branches)
+
+    def test_sort_by_refname_reverse(self) -> None:
+        """Test branch.sort=-refname (reverse alphabetical)."""
+        [c1] = build_commit_graph(self.repo.object_store, [[1]])
+        self.repo[b"HEAD"] = c1.id
+
+        # Create branches
+        porcelain.branch_create(self.repo, b"zebra")
+        porcelain.branch_create(self.repo, b"alpha")
+        porcelain.branch_create(self.repo, b"beta")
+
+        # Set branch.sort to -refname
+        config = self.repo.get_config()
+        config.set((b"branch",), b"sort", b"-refname")
+        config.write_to_path()
+
+        # Should be sorted reverse alphabetically
+        branches = porcelain.branch_list(self.repo)
+        self.assertEqual([b"zebra", b"master", b"beta", b"alpha"], branches)
+
+    def test_sort_by_committerdate(self) -> None:
+        """Test branch.sort=committerdate."""
+        # Use build_commit_graph to create proper commits with specific times
+        c1, c2, c3 = build_commit_graph(
+            self.repo.object_store,
+            [[1], [2], [3]],
+            attrs={
+                1: {"commit_time": 1000},  # oldest
+                2: {"commit_time": 2000},  # newest
+                3: {"commit_time": 1500},  # middle
+            },
+        )
+
+        self.repo[b"HEAD"] = c1.id
+
+        # Create branches pointing to different commits
+        self.repo.refs[b"refs/heads/master"] = c1.id  # master points to oldest
+        self.repo.refs[b"refs/heads/oldest"] = c1.id
+        self.repo.refs[b"refs/heads/newest"] = c2.id
+        self.repo.refs[b"refs/heads/middle"] = c3.id
+
+        # Set branch.sort to committerdate
+        config = self.repo.get_config()
+        config.set((b"branch",), b"sort", b"committerdate")
+        config.write_to_path()
+
+        # Should be sorted by commit time (oldest first)
+        branches = porcelain.branch_list(self.repo)
+        self.assertEqual([b"master", b"oldest", b"middle", b"newest"], branches)
+
+    def test_sort_by_committerdate_reverse(self) -> None:
+        """Test branch.sort=-committerdate."""
+        # Use build_commit_graph to create proper commits with specific times
+        c1, c2, c3 = build_commit_graph(
+            self.repo.object_store,
+            [[1], [2], [3]],
+            attrs={
+                1: {"commit_time": 1000},  # oldest
+                2: {"commit_time": 2000},  # newest
+                3: {"commit_time": 1500},  # middle
+            },
+        )
+
+        self.repo[b"HEAD"] = c1.id
+
+        # Create branches pointing to different commits
+        self.repo.refs[b"refs/heads/master"] = c1.id  # master points to oldest
+        self.repo.refs[b"refs/heads/oldest"] = c1.id
+        self.repo.refs[b"refs/heads/newest"] = c2.id
+        self.repo.refs[b"refs/heads/middle"] = c3.id
+
+        # Set branch.sort to -committerdate
+        config = self.repo.get_config()
+        config.set((b"branch",), b"sort", b"-committerdate")
+        config.write_to_path()
+
+        # Should be sorted by commit time (newest first)
+        branches = porcelain.branch_list(self.repo)
+        self.assertEqual([b"newest", b"middle", b"master", b"oldest"], branches)
+
+    def test_sort_default(self) -> None:
+        """Test default sorting (no config)."""
+        [c1] = build_commit_graph(self.repo.object_store, [[1]])
+        self.repo[b"HEAD"] = c1.id
+
+        # Create branches in non-alphabetical order
+        porcelain.branch_create(self.repo, b"zebra")
+        porcelain.branch_create(self.repo, b"alpha")
+        porcelain.branch_create(self.repo, b"beta")
+
+        # No config set - should default to alphabetical
+        branches = porcelain.branch_list(self.repo)
+        self.assertEqual([b"alpha", b"beta", b"master", b"zebra"], branches)
+
 
 class BranchCreateTests(PorcelainTestCase):
     def test_branch_exists(self) -> None: