git notes merge: Add automatic conflict resolvers (ours, theirs, union)

The new -s/--strategy command-line option to 'git notes merge' allow the user
to choose how notes merge conflicts should be resolved. There are four valid
strategies to choose from:

1. "manual" (the default): This will let the user manually resolve conflicts.
   This option currently fails with an error message. It will be implemented
   properly in future patches.

2. "ours": This automatically chooses the local version of a conflict, and
   discards the remote version.

3. "theirs": This automatically chooses the remote version of a conflict, and
   discards the local version.

4. "union": This automatically resolves the conflict by appending the remote
   version to the local version.

The strategies are implemented using the combine_notes_* functions from the
notes.h API.

The patch also includes testcases verifying the correct implementation of
these strategies.

This patch has been improved by the following contributions:
- Jonathan Nieder: Future-proof by always checking add_note() return value
- Stephen Boyd: Use test_commit
- Stephen Boyd: Use correct option name

Thanks-to: Jonathan Nieder <jrnieder@gmail.com>
Thanks-to: Stephen Boyd <bebarino@gmail.com>
Signed-off-by: Johan Herland <johan@herland.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 31 insertions, 1 deletions

diff --git a/notes-merge.c b/notes-merge.c
index b1afb7e52c..2c0b25b369 100644
--- a/notes-merge.c
+++ b/notes-merge.c
@@ -263,6 +263,36 @@ static void diff_tree_local(struct notes_merge_options *o,
 	diff_tree_release_paths(&opt);
 }
 
+static int merge_one_change(struct notes_merge_options *o,
+			    struct notes_merge_pair *p, struct notes_tree *t)
+{
+	/*
+	 * Return 0 if change was resolved (and added to notes_tree),
+	 * 1 if conflict
+	 */
+	switch (o->strategy) {
+	case NOTES_MERGE_RESOLVE_MANUAL:
+		return 1;
+	case NOTES_MERGE_RESOLVE_OURS:
+		OUTPUT(o, 2, "Using local notes for %s", sha1_to_hex(p->obj));
+		/* nothing to do */
+		return 0;
+	case NOTES_MERGE_RESOLVE_THEIRS:
+		OUTPUT(o, 2, "Using remote notes for %s", sha1_to_hex(p->obj));
+		if (add_note(t, p->obj, p->remote, combine_notes_overwrite))
+			die("BUG: combine_notes_overwrite failed");
+		return 0;
+	case NOTES_MERGE_RESOLVE_UNION:
+		OUTPUT(o, 2, "Concatenating local and remote notes for %s",
+		       sha1_to_hex(p->obj));
+		if (add_note(t, p->obj, p->remote, combine_notes_concatenate))
+			die("failed to concatenate notes "
+			    "(combine_notes_concatenate)");
+		return 0;
+	}
+	die("Unknown strategy (%i).", o->strategy);
+}
+
 static int merge_changes(struct notes_merge_options *o,
 			 struct notes_merge_pair *changes, int *num_changes,
 			 struct notes_tree *t)
@@ -292,7 +322,7 @@ static int merge_changes(struct notes_merge_options *o,
 		} else {
 			/* need file-level merge between local and remote */
 			trace_printf("\t\t\tneed content-level merge\n");
-			conflicts += 1; /* TODO */
+			conflicts += merge_one_change(o, p, t);
 		}
 	}