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, 6 insertions, 6 deletions

diff --git a/builtin/ls-files.c b/builtin/ls-files.c
index 3a410c35d9..80fff23ad9 100644
--- a/builtin/ls-files.c
+++ b/builtin/ls-files.c
@@ -127,7 +127,7 @@ static void show_killed_files(struct dir_struct *dir)
 	}
 }
 
-static void show_ce_entry(const char *tag, struct cache_entry *ce)
+static void show_ce_entry(const char *tag, const struct cache_entry *ce)
 {
 	int len = max_prefix_len;
 
@@ -165,7 +165,7 @@ static void show_ce_entry(const char *tag, struct cache_entry *ce)
 	}
 	write_name(ce->name, ce_namelen(ce));
 	if (debug_mode) {
-		struct stat_data *sd = &ce->ce_stat_data;
+		const struct stat_data *sd = &ce->ce_stat_data;
 
 		printf("  ctime: %d:%d\n", sd->sd_ctime.sec, sd->sd_ctime.nsec);
 		printf("  mtime: %d:%d\n", sd->sd_mtime.sec, sd->sd_mtime.nsec);
@@ -203,7 +203,7 @@ static void show_ru_info(void)
 	}
 }
 
-static int ce_excluded(struct dir_struct *dir, struct cache_entry *ce)
+static int ce_excluded(struct dir_struct *dir, const struct cache_entry *ce)
 {
 	int dtype = ce_to_dtype(ce);
 	return is_excluded(dir, ce->name, &dtype);
@@ -223,7 +223,7 @@ static void show_files(struct dir_struct *dir)
 	}
 	if (show_cached || show_stage) {
 		for (i = 0; i < active_nr; i++) {
-			struct cache_entry *ce = active_cache[i];
+			const struct cache_entry *ce = active_cache[i];
 			if ((dir->flags & DIR_SHOW_IGNORED) &&
 			    !ce_excluded(dir, ce))
 				continue;
@@ -237,7 +237,7 @@ static void show_files(struct dir_struct *dir)
 	}
 	if (show_deleted || show_modified) {
 		for (i = 0; i < active_nr; i++) {
-			struct cache_entry *ce = active_cache[i];
+			const struct cache_entry *ce = active_cache[i];
 			struct stat st;
 			int err;
 			if ((dir->flags & DIR_SHOW_IGNORED) &&
@@ -273,7 +273,7 @@ static void prune_cache(const char *prefix)
 	last = active_nr;
 	while (last > first) {
 		int next = (last + first) >> 1;
-		struct cache_entry *ce = active_cache[next];
+		const struct cache_entry *ce = active_cache[next];
 		if (!strncmp(ce->name, prefix, max_prefix_len)) {
 			first = next+1;
 			continue;