+ cached = o->index_only;
+ match_missing = !revs->ignore_merges;
+
+ if (cached && idx && ce_stage(idx)) {
+ if (tree)
+ diff_unmerge(&revs->diffopt, idx->name, idx->ce_mode, idx->sha1);
+ return;
+ }
+
+ /*
+ * Something added to the tree?
+ */
+ if (!tree) {
+ show_new_file(revs, idx, cached, match_missing);
+ return;
+ }
+
+ /*
+ * Something removed from the tree?
+ */
+ if (!idx) {
+ diff_index_show_file(revs, "-", tree, tree->sha1, tree->ce_mode);
+ return;
+ }
+
+ /* Show difference between old and new */
+ 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
+ * the source trees, with the old index being really mainly
+ * used for being replaced by the result.
+ *
+ * For diffing, the index is more important, and we only have a
+ * single tree.
+ *
+ * We're supposed to return how many index entries we want to skip.
+ *
+ * This wrapper makes it all more readable, and takes care of all
+ * the fairly complex unpack_trees() semantic requirements, including
+ * the skipping, the path matching, the type conflict cases etc.
+ */
+static int oneway_diff(struct cache_entry **src, struct unpack_trees_options *o)
+{
+ struct cache_entry *idx = src[0];
+ 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
+ * in the tree. From a diff standpoint, that's a
+ * delete of the tree and a create of the file.
+ */
+ if (tree == o->df_conflict_entry)
+ tree = NULL;
+
+ if (ce_path_match(idx ? idx : tree, revs->prune_data))
+ do_oneway_diff(o, idx, tree);
+
+ return 0;
+}
+
+int run_diff_index(struct rev_info *revs, int cached)
+{
+ struct object *ent;
+ struct tree *tree;
+ const char *tree_name;
+ struct unpack_trees_options opts;
+ struct tree_desc t;