Convert "struct cache_entry *" to "const ..." wherever possible

I attempted to make index_state->cache[] a "const struct cache_entry **"
to find out how existing entries in index are modified and where. The
question I have is what do we do if we really need to keep track of on-disk
changes in the index. The result is

 - diff-lib.c: setting CE_UPTODATE

 - name-hash.c: setting CE_HASHED

 - preload-index.c, read-cache.c, unpack-trees.c and
   builtin/update-index: obvious

 - entry.c: write_entry() may refresh the checked out entry via
   fill_stat_cache_info(). This causes "non-const struct cache_entry
   *" in builtin/apply.c, builtin/checkout-index.c and
   builtin/checkout.c

 - builtin/ls-files.c: --with-tree changes stagemask and may set
   CE_UPDATE

Of these, write_entry() and its call sites are probably most
interesting because it modifies on-disk info. But this is stat info
and can be retrieved via refresh, at least for porcelain
commands. Other just uses ce_flags for local purposes.

So, keeping track of "dirty" entries is just a matter of setting a
flag in index modification functions exposed by read-cache.c. Except
unpack-trees, the rest of the code base does not do anything funny
behind read-cache's back.

The actual patch is less valueable than the summary above. But if
anyone wants to re-identify the above sites. Applying this patch, then
this:

    diff --git a/cache.h b/cache.h
    index 430d021..1692891 100644
    --- a/cache.h
    +++ b/cache.h
    @@ -267,7 +267,7 @@ static inline unsigned int canon_mode(unsigned int mode)
     #define cache_entry_size(len) (offsetof(struct cache_entry,name) + (len) + 1)

     struct index_state {
    -	struct cache_entry **cache;
    +	const struct cache_entry **cache;
     	unsigned int version;
     	unsigned int cache_nr, cache_alloc, cache_changed;
     	struct string_list *resolve_undo;

will help quickly identify them without bogus warnings.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 7 insertions, 7 deletions

diff --git a/builtin/update-index.c b/builtin/update-index.c
index 5c7762eef4..c317981516 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -83,7 +83,7 @@ static int process_lstat_error(const char *path, int err)
 	return error("lstat(\"%s\"): %s", path, strerror(errno));
 }
 
-static int add_one_path(struct cache_entry *old, const char *path, int len, struct stat *st)
+static int add_one_path(const struct cache_entry *old, const char *path, int len, struct stat *st)
 {
 	int option, size;
 	struct cache_entry *ce;
@@ -142,7 +142,7 @@ static int process_directory(const char *path, int len, struct stat *st)
 
 	/* Exact match: file or existing gitlink */
 	if (pos >= 0) {
-		struct cache_entry *ce = active_cache[pos];
+		const struct cache_entry *ce = active_cache[pos];
 		if (S_ISGITLINK(ce->ce_mode)) {
 
 			/* Do nothing to the index if there is no HEAD! */
@@ -158,7 +158,7 @@ static int process_directory(const char *path, int len, struct stat *st)
 	/* Inexact match: is there perhaps a subdirectory match? */
 	pos = -pos-1;
 	while (pos < active_nr) {
-		struct cache_entry *ce = active_cache[pos++];
+		const struct cache_entry *ce = active_cache[pos++];
 
 		if (strncmp(ce->name, path, len))
 			break;
@@ -183,7 +183,7 @@ static int process_path(const char *path)
 {
 	int pos, len;
 	struct stat st;
-	struct cache_entry *ce;
+	const struct cache_entry *ce;
 
 	len = strlen(path);
 	if (has_symlink_leading_path(path, len))
@@ -448,7 +448,7 @@ static int unresolve_one(const char *path)
 		/* already merged */
 		pos = unmerge_cache_entry_at(pos);
 		if (pos < active_nr) {
-			struct cache_entry *ce = active_cache[pos];
+			const struct cache_entry *ce = active_cache[pos];
 			if (ce_stage(ce) &&
 			    ce_namelen(ce) == namelen &&
 			    !memcmp(ce->name, path, namelen))
@@ -462,7 +462,7 @@ static int unresolve_one(const char *path)
 		 */
 		pos = -pos-1;
 		if (pos < active_nr) {
-			struct cache_entry *ce = active_cache[pos];
+			const struct cache_entry *ce = active_cache[pos];
 			if (ce_namelen(ce) == namelen &&
 			    !memcmp(ce->name, path, namelen)) {
 				fprintf(stderr,
@@ -558,7 +558,7 @@ static int do_reupdate(int ac, const char **av,
 		has_head = 0;
  redo:
 	for (pos = 0; pos < active_nr; pos++) {
-		struct cache_entry *ce = active_cache[pos];
+		const struct cache_entry *ce = active_cache[pos];
 		struct cache_entry *old = NULL;
 		int save_nr;