Use helper function for copying index entry information

We used to just memcpy() the index entry when we copied the stat() and
SHA1 hash information, which worked well enough back when the index
entry was just an exact bit-for-bit representation of the information on
disk.

However, these days we actually have various management information in
the cache entry too, and we should be careful to not overwrite it when
we copy the stat information from another index entry.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

cache.h

@@ -110,7 +110,6 @@ struct ondisk_cache_entry {
 };
 
 struct cache_entry {
-	struct cache_entry *next;
 	unsigned int ce_ctime;
 	unsigned int ce_mtime;
 	unsigned int ce_dev;
@@ -121,6 +120,7 @@ struct cache_entry {
 	unsigned int ce_size;
 	unsigned int ce_flags;
 	unsigned char sha1[20];
+	struct cache_entry *next;
 	char name[FLEX_ARRAY]; /* more */
 };
 
@@ -137,6 +137,22 @@ struct cache_entry {
 #define CE_HASHED    (0x100000)
 #define CE_UNHASHED  (0x200000)
 
+/*
+ * Copy the sha1 and stat state of a cache entry from one to
+ * another. But we never change the name, or the hash state!
+ */
+#define CE_STATE_MASK (CE_HASHED | CE_UNHASHED)
+static inline void copy_cache_entry(struct cache_entry *dst, struct cache_entry *src)
+{
+	unsigned int state = dst->ce_flags & CE_STATE_MASK;
+
+	/* Don't copy hash chain and name */
+	memcpy(dst, src, offsetof(struct cache_entry, next));
+
+	/* Restore the hash state */
+	dst->ce_flags = (dst->ce_flags & ~CE_STATE_MASK) | state;
+}
+
 /*
  * We don't actually *remove* it, we can just mark it invalid so that
  * we won't find it in lookups.

unpack-trees.c

@@ -590,7 +590,7 @@ static int merged_entry(struct cache_entry *merge, struct cache_entry *old,
 		 * a match.
 		 */
 		if (same(old, merge)) {
-			memcpy(merge, old, offsetof(struct cache_entry, name));
+			copy_cache_entry(merge, old);
 		} else {
 			verify_uptodate(old, o);
 			invalidate_ce_path(old);