cache.h: drop LOCAL_REPO_ENV_SIZE

We keep a static array of variables that should be cleared
when invoking a sub-process on another repo. We statically
size the array with the LOCAL_REPO_ENV_SIZE macro so that
any readers do not have to count it themselves.

As it turns out, no readers actually use the macro, and it
creates a maintenance headache, as modifications to the
array need to happen in two places (one to add the new
element, and another to bump the size).

Since it's NULL-terminated, we can just drop the size macro
entirely. While we're at it, we'll clean up some comments
around it, and add a new mention of it at the top of the
list of environment variable macros. Even though
local_repo_env is right below that list, it's easy to miss,
and additions to that list should consider local_repo_env.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

cache.h

@@ -341,6 +341,7 @@ static inline enum object_type object_type(unsigned int mode)
 		OBJ_BLOB;
 }
 
+/* Double-check local_repo_env below if you add to this list. */
 #define GIT_DIR_ENVIRONMENT "GIT_DIR"
 #define GIT_NAMESPACE_ENVIRONMENT "GIT_NAMESPACE"
 #define GIT_WORK_TREE_ENVIRONMENT "GIT_WORK_TREE"
@@ -364,13 +365,12 @@ static inline enum object_type object_type(unsigned int mode)
 #define GIT_NOTES_REWRITE_MODE_ENVIRONMENT "GIT_NOTES_REWRITE_MODE"
 
 /*
- * Repository-local GIT_* environment variables
- * The array is NULL-terminated to simplify its usage in contexts such
- * environment creation or simple walk of the list.
- * The number of non-NULL entries is available as a macro.
+ * Repository-local GIT_* environment variables; these will be cleared
+ * when git spawns a sub-process that runs inside another repository.
+ * The array is NULL-terminated, which makes it easy to pass in the "env"
+ * parameter of a run-command invocation, or to do a simple walk.
  */
-#define LOCAL_REPO_ENV_SIZE 9
-extern const char *const local_repo_env[LOCAL_REPO_ENV_SIZE + 1];
+extern const char * const local_repo_env[];
 
 extern int is_bare_repository_cfg;
 extern int is_bare_repository(void);

environment.c

@@ -76,11 +76,9 @@ static const char *git_dir;
 static char *git_object_dir, *git_index_file, *git_graft_file;
 
 /*
- * Repository-local GIT_* environment variables
- * Remember to update local_repo_env_size in cache.h when
- * the size of the list changes
+ * Repository-local GIT_* environment variables; see cache.h for details.
  */
-const char * const local_repo_env[LOCAL_REPO_ENV_SIZE + 1] = {
+const char * const local_repo_env[] = {
 	ALTERNATE_DB_ENVIRONMENT,
 	CONFIG_ENVIRONMENT,
 	CONFIG_DATA_ENVIRONMENT,