cocci & cache.h: fully apply "active_nr" part of index-compatibility

Apply the "active_nr" part of "index-compatibility.pending.cocci",
which was left out in [1] due to an in-flight conflict. As of [2] the
topic we conflicted with has been merged to "master", so we can fully
apply this rule.

1. dc594180d9 (cocci & cache.h: apply variable section of "pending"
   index-compatibility, 2022-11-19)
2. 9ea1378d04 (Merge branch 'ab/various-leak-fixes', 2022-12-14)

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/commit.c

@@ -991,7 +991,7 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 		struct object_id oid;
 		const char *parent = "HEAD";
 
-		if (!active_nr) {
+		if (!the_index.cache_nr) {
 			discard_cache();
 			if (read_cache() < 0)
 				die(_("Cannot read index"));

cache.h

@@ -454,8 +454,6 @@ extern struct index_state the_index;
 
 #ifndef USE_THE_INDEX_VARIABLE
 #ifdef USE_THE_INDEX_COMPATIBILITY_MACROS
-#define active_nr (the_index.cache_nr)
-
 #define read_cache() repo_read_index(the_repository)
 #define discard_cache() discard_index(&the_index)
 #define cache_name_pos(name, namelen) index_name_pos(&the_index,(name),(namelen))

contrib/coccinelle/index-compatibility.cocci

@@ -1,6 +1,7 @@
 // the_index.* variables
 @@
 identifier AC = active_cache;
+identifier AN = active_nr;
 identifier ACC = active_cache_changed;
 identifier ACT = active_cache_tree;
 @@
@@ -8,6 +9,9 @@ identifier ACT = active_cache_tree;
 - AC
 + the_index.cache
 |
+- AN
++ the_index.cache_nr
+|
 - ACC
 + the_index.cache_changed
 |
@@ -15,15 +19,6 @@ identifier ACT = active_cache_tree;
 + the_index.cache_tree
 )
 
-@@
-identifier AN = active_nr;
-identifier f != prepare_to_commit;
-@@
-  f(...) {<...
-- AN
-+ the_index.cache_nr
-  ...>}
-
 // "the_repository" simple cases
 @@
 @@