unpack-trees.c: prepare for looking ahead in the index

This prepares but does not yet implement a look-ahead in the index entries
when traverse-trees.c decides to give us tree entries in an order that
does not match what is in the index.

A case where a look-ahead in the index is necessary happens when merging
branch B into branch A while the index matches the current branch A, using
a tree O as their common ancestor, and these three trees looks like this:

   O        A       B
   t                t
   t-i      t-i     t-i
   t-j      t-j
            t/1
            t/2

The traverse_trees() function gets "t", "t-i" and "t" from trees O, A and
B first, and notices that A may have a matching "t" behind "t-i" and "t-j"
(indeed it does), and tells A to give that entry instead.  After unpacking
blob "t" from tree B (as it hasn't changed since O in B and A removed it,
it will result in its removal), it descends into directory "t/".

The side that walked index in parallel to the tree traversal used to be
implemented with one pointer, o->pos, that points at the next index entry
to be processed.  When this happens, the pointer o->pos still points at
"t-i" that is the first entry.  We should be able to skip "t-i" and "t-j"
and locate "t/1" from the index while the recursive invocation of
traverse_trees() walks and match entries found there, and later come back
to process "t-i".

While that look-ahead is not implemented yet, this adds a flag bit,
CE_UNPACKED, to mark the entries in the index that has already been
processed.  o->pos pointer has been renamed to o->cache_bottom and it
points at the first entry that may still need to be processed.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 0 insertions, 18 deletions

diff --git a/diff-lib.c b/diff-lib.c
index adf1c5f..f759917 100644
--- a/diff-lib.c
+++ b/diff-lib.c
@@ -359,21 +359,6 @@ static void do_oneway_diff(struct unpack_trees_options *o,
 	show_modified(revs, tree, idx, 1, cached, match_missing);
 }
 
-static inline void skip_same_name(struct cache_entry *ce, struct unpack_trees_options *o)
-{
-	int len = ce_namelen(ce);
-	const struct index_state *index = o->src_index;
-
-	while (o->pos < index->cache_nr) {
-		struct cache_entry *next = index->cache[o->pos];
-		if (len != ce_namelen(next))
-			break;
-		if (memcmp(ce->name, next->name, len))
-			break;
-		o->pos++;
-	}
-}
-
 /*
  * The unpack_trees() interface is designed for merging, so
  * the different source entries are designed primarily for
@@ -395,9 +380,6 @@ static int oneway_diff(struct cache_entry **src, struct unpack_trees_options *o)
 	struct cache_entry *tree = src[1];
 	struct rev_info *revs = o->unpack_data;
 
-	if (idx && ce_stage(idx))
-		skip_same_name(idx, o);
-
 	/*
 	 * Unpack-trees generates a DF/conflict entry if
 	 * there was a directory in the index and a tree