[PATCH v3 04/11] rerere: delay the recording of preimage

[Junio C Hamano <gitster@pobox.com>]

We record the preimage only when there is no directory to record the
conflict we encountered, i.e. when $GIT_DIR/rr-cache/$ID does not
exist.  As the plan is to allow multiple <preimage,postimage> pairs
as variants for the same conflict ID eventually, this logic needs to
go.

As the first step in that direction, stop the "did we create the
directory?  Then we record the preimage" logic.  Instead, we record
if a preimage does not exist when we saw a conflict in a path.  Also
make sure that we remove a stale postimage, which most likely is
totally unrelated to the resolution of this new conflict, when we
create a new preimage under $ID when $GIT_DIR/rr-cache/$ID already
exists.

In later patches, we will further update this logic to be "do we
have <preimage,postimage> pair that cleanly resolve the current
conflicts?  If not, record a new preimage as a new variant", but
that does not happen at this stage yet.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 rerere.c | 52 +++++++++++++++++++++++++---------------------------
 1 file changed, 25 insertions(+), 27 deletions(-)

diff --git a/rerere.c b/rerere.c
index a1e2963..33b1348 100644
--- a/rerere.c
+++ b/rerere.c
@@ -122,6 +122,11 @@ static int has_rerere_resolution(const struct rerere_id *id)
 	return ((id->collection->status & both) == both);
 }
 
+static int has_rerere_preimage(const struct rerere_id *id)
+{
+	return (id->collection->status & RR_HAS_PREIMAGE);
+}
+
 static struct rerere_id *new_rerere_id_hex(char *hex)
 {
 	struct rerere_id *id = xmalloc(sizeof(*id));
@@ -749,8 +754,24 @@ static void do_rerere_one_path(struct string_list_item *rr_item,
 	const char *path = rr_item->string;
 	const struct rerere_id *id = rr_item->util;
 
-	/* Is there a recorded resolution we could attempt to apply? */
-	if (has_rerere_resolution(id)) {
+	if (!has_rerere_preimage(id)) {
+		/*
+		 * We are the first to encounter this conflict.  Ask
+		 * handle_file() to write the normalized contents to
+		 * the "preimage" file.
+		 */
+		handle_file(path, NULL, rerere_path(id, "preimage"));
+		if (id->collection->status & RR_HAS_POSTIMAGE) {
+			const char *path = rerere_path(id, "postimage");
+			if (unlink(path))
+				die_errno("cannot unlink stray '%s'", path);
+			id->collection->status &= ~RR_HAS_POSTIMAGE;
+		}
+		id->collection->status |= RR_HAS_PREIMAGE;
+		fprintf(stderr, "Recorded preimage for '%s'\n", path);
+		return;
+	} else if (has_rerere_resolution(id)) {
+		/* Is there a recorded resolution we could attempt to apply? */
 		if (merge(id, path))
 			return; /* failed to replay */
 
@@ -807,31 +828,8 @@ static int do_plain_rerere(struct string_list *rr, int fd)
 		id = new_rerere_id(sha1);
 		string_list_insert(rr, path)->util = id;
 
-		/*
-		 * Ensure that the directory exists.
-		 * mkdir_in_gitdir() will fail with EEXIST if there
-		 * already is one.
-		 */
-		if (mkdir_in_gitdir(rerere_path(id, NULL)) &&
-		    errno != EEXIST)
-			continue; /* NEEDSWORK: perhaps we should die? */
-
-		if (id->collection->status & RR_HAS_PREIMAGE) {
-			;
-		} else {
-			/*
-			 * We are the first to encounter this
-			 * conflict.  Ask handle_file() to write the
-			 * normalized contents to the "preimage" file.
-			 *
-			 * NEEDSWORK: what should happen if we had a
-			 * leftover postimage that is totally
-			 * unrelated?  Perhaps we should unlink it?
-			 */
-			handle_file(path, NULL, rerere_path(id, "preimage"));
-			id->collection->status |= RR_HAS_PREIMAGE;
-			fprintf(stderr, "Recorded preimage for '%s'\n", path);
-		}
+		/* Ensure that the directory exists. */
+		mkdir_in_gitdir(rerere_path(id, NULL));
 	}
 
 	for (i = 0; i < rr->nr; i++)
-- 
2.8.1-273-ga2cd0f9