Cloud storage: merge local and remote changes if there is no conflict

We still punt if there are any conflicts (which are likely to occur if we
have touched dive sites in both changes). But in my testing at least for
fairly simple, non-conflicting changes this works and creates a correctly
merged tree.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

1 files changed, 35 insertions, 10 deletions

diff --git a/git-access.c b/git-access.c
index c6a1648b1..ff00b85a3 100644
--- a/git-access.c
+++ b/git-access.c
@@ -214,16 +214,41 @@ static int try_to_update(git_repository *repo, git_remote *origin, git_reference
 	if (git_branch_is_head(local) != 1)
 		return report_error("Local and remote do not match, local branch not HEAD - cannot update");
 
-	/*
-	 * Some day we migth try a clean merge here.
-	 *
-	 * But I couldn't find any good examples of this, so for now
-	 * you'd need to merge divergent histories manually. But we've
-	 * at least verified above that we have a working tree and the
-	 * current branch is checked out and clean, so we *could* try
-	 * to merge.
-	 */
-	return report_error("Local and remote have diverged, need to merge");
+	/* Ok, let's try to merge these */
+	git_tree *local_tree, *remote_tree, *base_tree;
+	git_commit *local_commit, *remote_commit, *base_commit;
+	git_index *merged_index;
+	if (git_commit_lookup(&local_commit, repo, local_id))
+		return report_error(translate("gettextFromC", "Remote storage and local data diverged. Error: can't get commit (%s)"), giterr_last()->message);
+	if (git_commit_tree(&local_tree, local_commit))
+		return report_error(translate("gettextFromC", "Remote storage and local data diverged. Error: failed local tree lookup (%s)"), giterr_last()->message);
+	if (git_commit_lookup(&remote_commit, repo, remote_id))
+		return report_error(translate("gettextFromC", "Remote storage and local data diverged. Error: can't get commit (%s)"), giterr_last()->message);
+	if (git_commit_tree(&remote_tree, remote_commit))
+		return report_error(translate("gettextFromC", "Remote storage and local data diverged. Error: failed remote tree lookup (%s)"), giterr_last()->message);
+	if (git_commit_lookup(&base_commit, repo, &base))
+		return report_error(translate("gettextFromC", "Remote storage and local data diverged. Error: can't get commit: (%s)"), giterr_last()->message);
+	if (git_commit_tree(&base_tree, base_commit))
+		return report_error(translate("gettextFromC", "Remote storage and local data diverged. Error: failed base tree lookup: (%s)"), giterr_last()->message);
+	if (git_merge_trees(&merged_index, repo, base_tree, local_tree, remote_tree, 0))
+		return report_error(translate("gettextFromC", "Remote storage and local data diverged. Error: merge failed (%s)"), giterr_last()->message);
+	if (git_index_has_conflicts(merged_index)) {
+		return report_error(translate("gettextFromC", "Remote storage and local data diverged. Error: merge conflict - manual intervention needed"));
+	} else {
+		git_oid merge_oid, commit_oid;
+		git_tree *merged_tree;
+		git_signature *author;
+
+		if (git_index_write_tree_to(&merge_oid, merged_index, repo))
+			return report_error(translate("gettextFromC", "Remote storage and local data diverged. Error: writing the tree failed (%s)"), giterr_last()->message);
+		if (git_tree_lookup(&merged_tree, repo, &merge_oid))
+			return report_error(translate("gettextFromC", "Remote storage and local data diverged. Error: tree lookup failed (%s)"), giterr_last()->message);
+		if (git_signature_default(&author, repo) < 0)
+			return report_error(translate("gettextFromC", "Failed to get author: (%s)"), giterr_last()->message);
+		if (git_commit_create_v(&commit_oid, repo, "HEAD", author, author, NULL, "automatic merge", merged_tree, 2, local_commit, remote_commit))
+			return report_error(translate("gettextFromC", "Remote storage and local data diverged. Error: git commit create failed (%s)"), giterr_last()->message);
+	}
+	return 0;
 }
 
 static int check_remote_status(git_repository *repo, git_remote *origin, const char *branch, enum remote_transport rt)