+/*
+ * Read the tree specified with --with-tree option
+ * (typically, HEAD) into stage #1 and then
+ * squash them down to stage #0. This is used for
+ * --error-unmatch to list and check the path patterns
+ * that were given from the command line. We are not
+ * going to write this index out.
+ */
+static void overlay_tree(const char *tree_name, const char *prefix)
+{
+ struct tree *tree;
+ unsigned char sha1[20];
+ const char **match;
+ struct cache_entry *last_stage0 = NULL;
+ int i;
+
+ if (get_sha1(tree_name, sha1))
+ die("tree-ish %s not found.", tree_name);
+ tree = parse_tree_indirect(sha1);
+ if (!tree)
+ die("bad tree-ish %s", tree_name);
+
+ /* Hoist the unmerged entries up to stage #3 to make room */
+ for (i = 0; i < active_nr; i++) {
+ struct cache_entry *ce = active_cache[i];
+ if (!ce_stage(ce))
+ continue;
+ ce->ce_flags |= htons(CE_STAGEMASK);
+ }
+
+ if (prefix) {
+ static const char *(matchbuf[2]);
+ matchbuf[0] = prefix;
+ matchbuf [1] = NULL;
+ match = matchbuf;
+ } else
+ match = NULL;
+ if (read_tree(tree, 1, match))
+ die("unable to read tree entries %s", tree_name);
+
+ for (i = 0; i < active_nr; i++) {
+ struct cache_entry *ce = active_cache[i];
+ switch (ce_stage(ce)) {
+ case 0:
+ last_stage0 = ce;
+ /* fallthru */
+ default:
+ continue;
+ case 1:
+ /*
+ * If there is stage #0 entry for this, we do not
+ * need to show it. We use CE_UPDATE bit to mark
+ * such an entry.
+ */
+ if (last_stage0 &&
+ !strcmp(last_stage0->name, ce->name))
+ ce->ce_flags |= htons(CE_UPDATE);
+ }
+ }
+}
+