diff-cache: fix handling of unmerged files.

We've always warned about them properly, but we would then do the
wrong thing if that filename existed in the tree we were comparing
against (we'd think the file has been deleted, because we forgot
about the unmerged cases).

diff-cache.c

@@ -47,41 +47,58 @@ static int diff_cache(struct cache_entry **ac, int entries)
 {
 	while (entries) {
 		struct cache_entry *ce = *ac;
+		int same = (entries > 1) && same_name(ce, ac[1]);
 
-		/* No matching 0-stage (current) entry? Show it as deleted */
-		if (ce_stage(ce)) {
-			show_file("-", ce);
-			ac++;
-			entries--;
-			continue;
+		switch (ce_stage(ce)) {
+		case 0:
+			/* No stage 1 entry? That means it's a new file */
+			if (!same) {
+				show_file("+", ce);
+				break;
+			}
+			/* Show difference between old and new */
+			show_modified(ac[1], ce);
+			break;
+		case 1:
+			/* No stage 3 (merge) entry? That means it's been deleted */
+			if (!same) {
+				show_file("-", ce);
+				break;
+			}
+			/* Otherwise we fall through to the "unmerged" case */
+		case 3:
+			printf("U %s%c", ce->name, line_termination);
+			break;
+
+		default:
+			die("impossible cache entry stage");
 		}
-		/* No matching 1-stage (tree) entry? Show the current one as added */
-		if (entries == 1 || !same_name(ce, ac[1])) {
-			show_file("+", ce);
+
+		/*
+		 * Ignore all the different stages for this file,
+		 * we've handled the relevant cases now.
+		 */
+		do {
 			ac++;
 			entries--;
-			continue;
-		}
-		show_modified(ac[1], ce);
-		ac += 2;
-		entries -= 2;
-		continue;
+		} while (entries && same_name(ce, ac[0]));
 	}
 	return 0;
 }
 
-static void remove_merge_entries(void)
+/*
+ * This turns all merge entries into "stage 3". That guarantees that
+ * when we read in the new tree (into "stage 1"), we won't lose sight
+ * of the fact that we had unmerged entries.
+ */
+static void mark_merge_entries(void)
 {
 	int i;
 	for (i = 0; i < active_nr; i++) {
 		struct cache_entry *ce = active_cache[i];
 		if (!ce_stage(ce))
 			continue;
-		printf("U %s%c", ce->name, line_termination);
-		while (remove_entry_at(i)) {
-			if (!ce_stage(active_cache[i]))
-				break;
-		}
+		ce->ce_flags |= htons(CE_STAGEMASK);
 	}
 }
 
@@ -116,7 +133,7 @@ int main(int argc, char **argv)
 	if (argc != 2 || get_sha1_hex(argv[1], tree_sha1))
 		usage(diff_cache_usage);
 
-	remove_merge_entries();
+	mark_merge_entries();
 
 	tree = read_tree_with_tree_or_commit_sha1(tree_sha1, &size, 0);
 	if (!tree)