cocci & cache.h: apply variable section of "pending" index-compatibility

Mostly apply the part of "index-compatibility.pending.cocci" that
renames the global variables like "active_nr", which are a shorthand
to referencing (in that case) a struct member as "the_index.cache_nr".

In doing so move more of "index-compatibility.pending.cocci" to
"index-compatibility.cocci".

In the case of "active_nr" we'd have a textual conflict with
"ab/various-leak-fixes" in "next"[1]. Let's exclude that specific case
while moving the rule over from "pending".

1. 407b94280f8 (commit: discard partial cache before (re-)reading it,
   2022-11-08)

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/commit.c b/builtin/commit.c
index 10a827b..abbed75 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -272,8 +272,8 @@ static int list_paths(struct string_list *list, const char *with_tree,
 
 	/* TODO: audit for interaction with sparse-index. */
 	ensure_full_index(&the_index);
-	for (i = 0; i < active_nr; i++) {
-		const struct cache_entry *ce = active_cache[i];
+	for (i = 0; i < the_index.cache_nr; i++) {
+		const struct cache_entry *ce = the_index.cache[i];
 		struct string_list_item *item;
 
 		if (ce->ce_flags & CE_UPDATE)
@@ -461,8 +461,8 @@ static const char *prepare_index(const char **argv, const char *prefix,
 	if (!only && !pathspec.nr) {
 		hold_locked_index(&index_lock, LOCK_DIE_ON_ERROR);
 		refresh_cache_or_die(refresh_flags);
-		if (active_cache_changed
-		    || !cache_tree_fully_valid(active_cache_tree))
+		if (the_index.cache_changed
+		    || !cache_tree_fully_valid(the_index.cache_tree))
 			update_main_cache_tree(WRITE_TREE_SILENT);
 		if (write_locked_index(&the_index, &index_lock,
 				       COMMIT_LOCK | SKIP_IF_UNCHANGED))
@@ -998,10 +998,10 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 
 			/* TODO: audit for interaction with sparse-index. */
 			ensure_full_index(&the_index);
-			for (i = 0; i < active_nr; i++)
-				if (ce_intent_to_add(active_cache[i]))
+			for (i = 0; i < the_index.cache_nr; i++)
+				if (ce_intent_to_add(the_index.cache[i]))
 					ita_nr++;
-			committable = active_nr - ita_nr > 0;
+			committable = the_index.cache_nr - ita_nr > 0;
 		} else {
 			/*
 			 * Unless the user did explicitly request a submodule
@@ -1823,7 +1823,7 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 		append_merge_tag_headers(parents, &tail);
 	}
 
-	if (commit_tree_extended(sb.buf, sb.len, &active_cache_tree->oid,
+	if (commit_tree_extended(sb.buf, sb.len, &the_index.cache_tree->oid,
 				 parents, &oid, author_ident.buf, NULL,
 				 sign_commit, extra)) {
 		rollback_index_files();