git object format: make sure parenthood isn't lost when saving

This makes subsurface remember the git source commit of the dive data.

If you save to an existing branch, subsurface will now complain and
refuse to save if you try to save if the existing branch is not related
to the original source.  That would destroy the history of the dive
data, which in turn would make it impossible to do sane merging of the
data.

If you save to a new branch, it will see if the previous parent commit
is known in the repository you are saving to, and will save parenthood
information if so.  Otherwise it will save it as a new parentless commit
("root commit" in git parlance).

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

1 files changed, 25 insertions, 5 deletions

diff --git a/load-git.c b/load-git.c
index c268cf1ef..12bf66141 100644
--- a/load-git.c
+++ b/load-git.c
@@ -14,6 +14,8 @@
 #include "device.h"
 #include "membuffer.h"
 
+const char *saved_git_id = NULL;
+
 struct keyword_action {
 	const char *keyword;
 	void (*fn)(char *, struct membuffer *, void *);
@@ -1198,11 +1200,25 @@ static int load_dives_from_tree(git_repository *repo, git_tree *tree)
 	return 0;
 }
 
+void clear_git_id(void)
+{
+	saved_git_id = NULL;
+}
+
+void set_git_id(const struct git_oid * id)
+{
+	static char git_id_buffer[GIT_OID_HEXSZ+1];
+
+	git_oid_tostr(git_id_buffer, sizeof(git_id_buffer), id);
+	saved_git_id = git_id_buffer;
+}
+
 static int do_git_load(git_repository *repo, const char *branch)
 {
 	int ret;
 	git_reference *ref;
-	git_object *tree;
+	git_commit *commit;
+	git_tree *tree;
 
 	ret = git_branch_lookup(&ref, repo, branch, GIT_BRANCH_LOCAL);
 	if (ret) {
@@ -1210,10 +1226,14 @@ static int do_git_load(git_repository *repo, const char *branch)
 		if (ret)
 			return report_error("Unable to look up branch '%s'", branch);
 	}
-	if (git_reference_peel(&tree, ref, GIT_OBJ_TREE))
-		return report_error("Could not look up tree of branch '%s'", branch);
-	ret = load_dives_from_tree(repo, (git_tree *) tree);
-	git_object_free(tree);
+	if (git_reference_peel((git_object **)&commit, ref, GIT_OBJ_COMMIT))
+		return report_error("Could not look up commit of branch '%s'", branch);
+	if (git_commit_tree(&tree, commit))
+		return report_error("Could not look up tree of commit in branch '%s'", branch);
+	ret = load_dives_from_tree(repo, tree);
+	if (!ret)
+		set_git_id(git_commit_id(commit));
+	git_object_free((git_object *)tree);
 	return ret;
 }