Use local branch if newer than remote branch (#33)

* Use local branch if newer than remote branch

If upstream is a user's fork that doesn't get updated, we want to
instead use the local branch, which is more likely to be up to date.

* Try same-name remote branches even if local branch exists

* Add explanation comments, simplify logic

src/rapids_pre_commit_hooks/copyright.py

@@ -177,21 +177,30 @@ def get_target_branch(repo, args):
 
 
 def get_target_branch_upstream_commit(repo, args):
+    # If no target branch can be determined, use HEAD if it exists
     target_branch_name = get_target_branch(repo, args)
     if target_branch_name is None:
         try:
             return repo.head.commit
         except ValueError:
             return None
 
+    commits_to_try = []
+
     try:
         target_branch = repo.heads[target_branch_name]
     except IndexError:
-        target_branch = None
-    if target_branch:
-        target_branch_upstream = target_branch.tracking_branch()
-        if target_branch_upstream:
-            return target_branch_upstream.commit
+        pass
+    else:
+        # Try the branch specified by the branch name
+        commits_to_try.append(target_branch.commit)
+
+        # If the branch has an upstream, try it and exit
+        if target_branch_upstream := target_branch.tracking_branch():
+            return max(
+                [target_branch.commit, target_branch_upstream.commit],
+                key=lambda commit: commit.committed_datetime,
+            )
 
     def try_get_ref(remote):
         try:
@@ -200,15 +209,21 @@ def try_get_ref(remote):
             return None
 
     try:
-        return max(
+        # Try branches in all remotes that have the branch name
+        upstream_commit = max(
             (upstream for remote in repo.remotes if (upstream := try_get_ref(remote))),
             key=lambda upstream: upstream.commit.committed_datetime,
         ).commit
     except ValueError:
         pass
+    else:
+        commits_to_try.append(upstream_commit)
+
+    if commits_to_try:
+        return max(commits_to_try, key=lambda commit: commit.committed_datetime)
 
-    if target_branch:
-        return target_branch.commit
+    # No branch with the specified name, local or remote, can be found, so return HEAD
+    # if it exists
     try:
         return repo.head.commit
     except ValueError:

test/rapids_pre_commit_hooks/test_copyright.py

@@ -283,6 +283,7 @@ def mock_target_branch(branch):
         write_file(remote_repo_1, "file4.txt", "File 4")
         write_file(remote_repo_1, "file5.txt", "File 5")
         write_file(remote_repo_1, "file6.txt", "File 6")
+        write_file(remote_repo_1, "file7.txt", "File 7")
         remote_repo_1.index.add(
             [
                 "file1.txt",
@@ -291,6 +292,7 @@ def mock_target_branch(branch):
                 "file4.txt",
                 "file5.txt",
                 "file6.txt",
+                "file7.txt",
             ]
         )
         remote_repo_1.index.commit("Initial commit")
@@ -302,7 +304,10 @@ def mock_target_branch(branch):
         remote_repo_1.head.reset(index=True, working_tree=True)
         write_file(remote_repo_1, "file1.txt", "File 1 modified")
         remote_repo_1.index.add(["file1.txt"])
-        remote_repo_1.index.commit("Update file1.txt")
+        remote_repo_1.index.commit(
+            "Update file1.txt",
+            commit_date=datetime.datetime(2024, 2, 1, tzinfo=datetime.timezone.utc),
+        )
 
         remote_1_branch_2 = remote_repo_1.create_head(
             "branch-2", remote_1_master.commit
@@ -337,6 +342,18 @@ def mock_target_branch(branch):
             commit_date=datetime.datetime(2024, 1, 1, tzinfo=datetime.timezone.utc),
         )
 
+        remote_1_branch_7 = remote_repo_1.create_head(
+            "branch-7", remote_1_master.commit
+        )
+        remote_repo_1.head.reference = remote_1_branch_7
+        remote_repo_1.head.reset(index=True, working_tree=True)
+        write_file(remote_repo_1, "file7.txt", "File 7 modified")
+        remote_repo_1.index.add(["file7.txt"])
+        remote_repo_1.index.commit(
+            "Update file7.txt",
+            commit_date=datetime.datetime(2024, 1, 1, tzinfo=datetime.timezone.utc),
+        )
+
         remote_2_1 = remote_repo_2.create_remote("remote-1", remote_dir_1)
         remote_2_1.fetch(["master"])
         remote_2_master = remote_repo_2.create_head("master", remote_2_1.refs["master"])
@@ -387,6 +404,7 @@ def mock_target_branch(branch):
             "branch-2",
             "branch-3",
             "branch-4",
+            "branch-7",
         ])
         remote_2 = git_repo.create_remote("unconventional/remote/name/2", remote_dir_2)
         remote_2.fetch(["branch-3", "branch-4", "branch-5"])
@@ -400,14 +418,29 @@ def mock_target_branch(branch):
         git_repo.head.reference = branch_1
         git_repo.head.reset(index=True, working_tree=True)
         git_repo.index.remove("file1.txt", working_tree=True)
-        git_repo.index.commit("Remove file1.txt")
+        git_repo.index.commit(
+            "Remove file1.txt",
+            commit_date=datetime.datetime(2024, 1, 1, tzinfo=datetime.timezone.utc),
+        )
 
         branch_6 = git_repo.create_head("branch-6", remote_1.refs["master"])
         git_repo.head.reference = branch_6
         git_repo.head.reset(index=True, working_tree=True)
         git_repo.index.remove(["file6.txt"], working_tree=True)
         git_repo.index.commit("Remove file6.txt")
 
+        branch_7 = git_repo.create_head("branch-7", remote_1.refs["master"])
+        with branch_7.config_writer() as w:
+            w.set_value("remote", "unconventional/remote/name/1")
+            w.set_value("merge", "branch-7")
+        git_repo.head.reference = branch_7
+        git_repo.head.reset(index=True, working_tree=True)
+        git_repo.index.remove(["file7.txt"], working_tree=True)
+        git_repo.index.commit(
+            "Remove file7.txt",
+            commit_date=datetime.datetime(2024, 2, 1, tzinfo=datetime.timezone.utc),
+        )
+
         git_repo.head.reference = main
         git_repo.head.reset(index=True, working_tree=True)
 
@@ -448,6 +481,12 @@ def mock_target_branch(branch):
             )
 
         with mock_target_branch("branch-7"):
+            assert (
+                copyright.get_target_branch_upstream_commit(git_repo, None)
+                == branch_7.commit
+            )
+
+        with mock_target_branch("nonexistent-branch"):
             assert (
                 copyright.get_target_branch_upstream_commit(git_repo, None)
                 == main.commit