[WIP PATCH] fast-export: emit deletions first

["Raymond E. Pasco" <ray@ameretat.dev>]

fast-export chooses its output order by pathname, sorting longer
paths earlier. However, this causes faulty output when the deleted
path is a prefix of the added one. For example, deleting a file 'a' and
creating a file 'a/b' emits:

from :prev_label
M 100644 :blob_label a/b
D a

Fix this by sorting deletions to come before other types of change.

Signed-off-by: Raymond E. Pasco <ray@ameretat.dev>
---

This is a quick and dirty fix for the bug. However, I do want to spend a
little more time on it - it may be that we only want to reverse the sort
when the deletion is specifically the prefix of some addition, and I
want to fence this off with new tests.

 builtin/fast-export.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/builtin/fast-export.c b/builtin/fast-export.c
index b90da5e616..82d73b2f43 100644
--- a/builtin/fast-export.c
+++ b/builtin/fast-export.c
@@ -354,6 +354,12 @@ static int depth_first(const void *a_, const void *b_)
 	int len_a, len_b, len;
 	int cmp;
 
+	/* emit deletions first */
+	int a_deletes = (a->status == DIFF_STATUS_DELETED);
+	int b_deletes = (b->status == DIFF_STATUS_DELETED);
+	if (a_deletes != b_deletes)
+		return b_deletes - a_deletes;
+
 	name_a = a->one ? a->one->path : a->two->path;
 	name_b = b->one ? b->one->path : b->two->path;
 
-- 
2.54.0.rc0.605.g598a273b03.dirty