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/unpack-trees.c b/unpack-trees.c
index b27f2a62e..bf0171701 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -179,7 +179,7 @@ static void display_error_msgs(struct unpack_trees_options *o)
  * Unlink the last component and schedule the leading directories for
  * removal, such that empty directories get removed.
  */
-static void unlink_entry(struct cache_entry *ce)
+static void unlink_entry(const struct cache_entry *ce)
 {
 	if (!check_leading_path(ce->name, ce_namelen(ce)))
 		return;
@@ -199,7 +199,7 @@ static int check_updates(struct unpack_trees_options *o)
 
 	if (o->update && o->verbose_update) {
 		for (total = cnt = 0; cnt < index->cache_nr; cnt++) {
-			struct cache_entry *ce = index->cache[cnt];
+			const struct cache_entry *ce = index->cache[cnt];
 			if (ce->ce_flags & (CE_UPDATE | CE_WT_REMOVE))
 				total++;
 		}
@@ -212,7 +212,7 @@ static int check_updates(struct unpack_trees_options *o)
 	if (o->update)
 		git_attr_set_direction(GIT_ATTR_CHECKOUT, &o->result);
 	for (i = 0; i < index->cache_nr; i++) {
-		struct cache_entry *ce = index->cache[i];
+		const struct cache_entry *ce = index->cache[i];
 
 		if (ce->ce_flags & CE_WT_REMOVE) {
 			display_progress(progress, ++cnt);
@@ -376,7 +376,7 @@ static struct cache_entry *next_cache_entry(struct unpack_trees_options *o)
 	return NULL;
 }
 
-static void add_same_unmerged(struct cache_entry *ce,
+static void add_same_unmerged(const struct cache_entry *ce,
 			      struct unpack_trees_options *o)
 {
 	struct index_state *index = o->src_index;
@@ -650,7 +650,7 @@ static int find_cache_pos(struct traverse_info *info,
 	int p_len = tree_entry_len(p);
 
 	for (pos = o->cache_bottom; pos < index->cache_nr; pos++) {
-		struct cache_entry *ce = index->cache[pos];
+		const struct cache_entry *ce = index->cache[pos];
 		const char *ce_name, *ce_slash;
 		int cmp, ce_len;
 
@@ -1353,7 +1353,7 @@ static int verify_clean_subdirectory(const struct cache_entry *ce,
  */
 static int icase_exists(struct unpack_trees_options *o, const char *name, int len, struct stat *st)
 {
-	struct cache_entry *src;
+	const struct cache_entry *src;
 
 	src = index_name_exists(o->src_index, name, len, 1);
 	return src && !ie_match_stat(o->src_index, src, st, CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE);
@@ -1364,7 +1364,7 @@ static int check_ok_to_remove(const char *name, int len, int dtype,
 			      enum unpack_trees_error_types error_type,
 			      struct unpack_trees_options *o)
 {
-	struct cache_entry *result;
+	const struct cache_entry *result;
 
 	/*
 	 * It may be that the 'lstat()' succeeded even though