[PATCH 1/2] merge-recursive: sometimes, d/f conflict is not an issue

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

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When a merge has a d/f conflict on a path which was not touched
between the merge base(s) and the remote HEAD, and the index and
HEAD contain the same version for that path (even if empty), it
is not really a conflict.

Noticed by Rémi Vanicat, reported to the Git list by Gerrit Pape.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---

	Turns out I was wrong with my "this is only half of it" remark.
	AFAICT "merge-tree -u -m" does not touch the files which have
	unmerged entries, but merge-recursive does.  And since
	fix_up_df_conflicts() is called before any of that, it just works.

 merge-recursive.c |   87 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 87 insertions(+), 0 deletions(-)

diff --git a/merge-recursive.c b/merge-recursive.c
index c8539ec..fb487ba 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -243,6 +243,91 @@ static int git_merge_trees(int index_only,
 	return rc;
 }
 
+/*
+ * If there were dir/file conflicts, which are not really dir/file
+ * conflicts, because only one side changed anything, take that
+ * side instead of outputting silly conflicts.
+ *
+ * We keep it nice and easy, in that we only fix the conflicts if one
+ * side was renamed without changing the contents _at all_.  We check that
+ * by comparing the hash.
+ */
+static inline int is_df(struct cache_entry *in_dir, struct cache_entry *file)
+{
+	int len = ce_namelen(file);
+	const char *name = in_dir->name;
+	return !memcmp(name, file->name, len) && name[len] == '/';
+}
+
+static int fix_up_df_conflicts(const unsigned char *base,
+		const unsigned char *head, const unsigned char *merge)
+{
+	int i;
+	for (i = 0; i + 2 < active_nr; i++) {
+		int last;
+		unsigned char sha1[20], sha2[20];
+		unsigned dummy;
+		char *name;
+		struct cache_entry *ce = active_cache[i], *ce1, *ce2;
+
+		if (ce_stage(ce) == 0)
+			continue;
+		ce1 = active_cache[i + 1];
+		ce2 = active_cache[i + 2];
+		if (ce_same_name(ce, ce2) || !is_df(ce2, ce)) {
+			/* not a d/f conflict */
+			i += 2;
+			continue;
+		}
+		for (last = i + 3; last < active_nr &&
+				is_df(active_cache[last], ce); last++)
+			; /* do nothing */
+		/* check if unchanged in HEAD */
+		if (ce_same_name(ce, ce1)) {
+			if (ce_stage(ce) != 1 ||
+					hashcmp(ce->sha1, ce1->sha1)) {
+				/* file was changed */
+				i = last - 1;
+				continue;
+			}
+			/* other side removed file, added dir */
+			if (!remove_file_from_cache(ce->name))
+				return error("index error");
+			for (i -= 2, last -= 2; i < last; i++)
+				active_cache[i]->ce_flags &=
+					~ntohs(CE_STAGEMASK);
+			i--;
+			continue;
+		}
+		if (i + 1 == last)
+			continue;
+		/* check if HEAD changed type (e.g. dir->file) */
+		if (ce_stage(ce) == 1) {
+			i = last - 1;
+			continue;
+		}
+		name = xstrndup(ce->name, ce_namelen(ce));
+		if (get_tree_entry(base, name, sha1, &dummy) ||
+				get_tree_entry(ce_stage(ce) == 2 ?
+					merge : head,
+					name, sha2, &dummy)) {
+			free(name);
+			i = last - 1;
+			continue;
+		}
+		free(name);
+		if (!hashcmp(sha1, sha2)) {
+			/* remove tree */
+			memmove(active_cache + i + 1, active_cache + last,
+				(active_nr - last) *
+				sizeof(struct cache_entry *));
+			active_nr -= last - i - 1;
+			ce->ce_flags &= ~ntohs(CE_STAGEMASK);
+		}
+	}
+	return 0;
+}
+
 static int unmerged_index(void)
 {
 	int i;
@@ -1542,6 +1627,8 @@ static int merge_trees(struct tree *head,
 		    sha1_to_hex(head->object.sha1),
 		    sha1_to_hex(merge->object.sha1));
 
+	fix_up_df_conflicts(common->object.sha1,
+			head->object.sha1, merge->object.sha1);
 	if (unmerged_index()) {
 		struct path_list *entries, *re_head, *re_merge;
 		int i;
-- 
1.5.3.rc1.16.g9d6f-dirty