Convert "struct cache_entry *" to "const ..." wherever possiblend/const-struct-cache-entry

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, 10 insertions, 9 deletions

diff --git a/cache-tree.c b/cache-tree.c
index 37e4d008b5..0bbec43216 100644
--- a/cache-tree.c
+++ b/cache-tree.c
@@ -149,7 +149,7 @@ void cache_tree_invalidate_path(struct cache_tree *it, const char *path)
 		cache_tree_invalidate_path(down->cache_tree, slash + 1);
 }
 
-static int verify_cache(struct cache_entry **cache,
+static int verify_cache(const struct cache_entry * const *cache,
 			int entries, int flags)
 {
 	int i, funny;
@@ -158,7 +158,7 @@ static int verify_cache(struct cache_entry **cache,
 	/* Verify that the tree is merged */
 	funny = 0;
 	for (i = 0; i < entries; i++) {
-		struct cache_entry *ce = cache[i];
+		const struct cache_entry *ce = cache[i];
 		if (ce_stage(ce)) {
 			if (silent)
 				return -1;
@@ -234,7 +234,7 @@ int cache_tree_fully_valid(struct cache_tree *it)
 }
 
 static int update_one(struct cache_tree *it,
-		      struct cache_entry **cache,
+		      const struct cache_entry * const *cache,
 		      int entries,
 		      const char *base,
 		      int baselen,
@@ -265,7 +265,7 @@ static int update_one(struct cache_tree *it,
 	 */
 	i = 0;
 	while (i < entries) {
-		struct cache_entry *ce = cache[i];
+		const struct cache_entry *ce = cache[i];
 		struct cache_tree_sub *sub;
 		const char *path, *slash;
 		int pathlen, sublen, subcnt, subskip;
@@ -312,7 +312,7 @@ static int update_one(struct cache_tree *it,
 
 	i = 0;
 	while (i < entries) {
-		struct cache_entry *ce = cache[i];
+		const struct cache_entry *ce = cache[i];
 		struct cache_tree_sub *sub;
 		const char *path, *slash;
 		int pathlen, entlen;
@@ -397,7 +397,7 @@ static int update_one(struct cache_tree *it,
 }
 
 int cache_tree_update(struct cache_tree *it,
-		      struct cache_entry **cache,
+		      const struct cache_entry * const *cache,
 		      int entries,
 		      int flags)
 {
@@ -599,8 +599,8 @@ int write_cache_as_tree(unsigned char *sha1, int flags, const char *prefix)
 	was_valid = cache_tree_fully_valid(active_cache_tree);
 	if (!was_valid) {
 		if (cache_tree_update(active_cache_tree,
-				      active_cache, active_nr,
-				      flags) < 0)
+				      (const struct cache_entry * const *)active_cache,
+				      active_nr, flags) < 0)
 			return WRITE_TREE_UNMERGED_INDEX;
 		if (0 <= newfd) {
 			if (!write_cache(newfd, active_cache, active_nr) &&
@@ -701,5 +701,6 @@ int update_main_cache_tree(int flags)
 	if (!the_index.cache_tree)
 		the_index.cache_tree = cache_tree();
 	return cache_tree_update(the_index.cache_tree,
-				 the_index.cache, the_index.cache_nr, flags);
+				 (const struct cache_entry * const *)the_index.cache,
+				 the_index.cache_nr, flags);
 }