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>

10 files changed, 33 insertions, 32 deletions

diff --git a/builtin/apply.c b/builtin/apply.c
index 0e9b631db..023bb3aad 100644
--- a/builtin/apply.c
+++ b/builtin/apply.c
@@ -2999,7 +2999,7 @@ static int read_blob_object(struct strbuf *buf, const unsigned char *sha1, unsig
 	return 0;
 }
 
-static int read_file_or_gitlink(struct cache_entry *ce, struct strbuf *buf)
+static int read_file_or_gitlink(const struct cache_entry *ce, struct strbuf *buf)
 {
 	if (!ce)
 		return 0;
@@ -3117,7 +3117,7 @@ static struct patch *previous_patch(struct patch *patch, int *gone)
 	return previous;
 }
 
-static int verify_index_match(struct cache_entry *ce, struct stat *st)
+static int verify_index_match(const struct cache_entry *ce, struct stat *st)
 {
 	if (S_ISGITLINK(ce->ce_mode)) {
 		if (!S_ISDIR(st->st_mode))
@@ -3130,7 +3130,7 @@ static int verify_index_match(struct cache_entry *ce, struct stat *st)
 #define SUBMODULE_PATCH_WITHOUT_INDEX 1
 
 static int load_patch_target(struct strbuf *buf,
-			     struct cache_entry *ce,
+			     const struct cache_entry *ce,
 			     struct stat *st,
 			     const char *name,
 			     unsigned expected_mode)
@@ -3160,7 +3160,8 @@ static int load_patch_target(struct strbuf *buf,
  * we read from the result of a previous diff.
  */
 static int load_preimage(struct image *image,
-			 struct patch *patch, struct stat *st, struct cache_entry *ce)
+			 struct patch *patch, struct stat *st,
+			 const struct cache_entry *ce)
 {
 	struct strbuf buf = STRBUF_INIT;
 	size_t len;
@@ -3273,7 +3274,7 @@ static int load_current(struct image *image, struct patch *patch)
 }
 
 static int try_threeway(struct image *image, struct patch *patch,
-			struct stat *st, struct cache_entry *ce)
+			struct stat *st, const struct cache_entry *ce)
 {
 	unsigned char pre_sha1[20], post_sha1[20], our_sha1[20];
 	struct strbuf buf = STRBUF_INIT;
@@ -3343,7 +3344,7 @@ static int try_threeway(struct image *image, struct patch *patch,
 	return 0;
 }
 
-static int apply_data(struct patch *patch, struct stat *st, struct cache_entry *ce)
+static int apply_data(struct patch *patch, struct stat *st, const struct cache_entry *ce)
 {
 	struct image image;
 
diff --git a/builtin/checkout.c b/builtin/checkout.c
index 3be001882..69f9efa75 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -97,7 +97,7 @@ static int read_tree_some(struct tree *tree, const char **pathspec)
 	return 0;
 }
 
-static int skip_same_name(struct cache_entry *ce, int pos)
+static int skip_same_name(const struct cache_entry *ce, int pos)
 {
 	while (++pos < active_nr &&
 	       !strcmp(active_cache[pos]->name, ce->name))
@@ -105,7 +105,7 @@ static int skip_same_name(struct cache_entry *ce, int pos)
 	return pos;
 }
 
-static int check_stage(int stage, struct cache_entry *ce, int pos)
+static int check_stage(int stage, const struct cache_entry *ce, int pos)
 {
 	while (pos < active_nr &&
 	       !strcmp(active_cache[pos]->name, ce->name)) {
@@ -119,7 +119,7 @@ static int check_stage(int stage, struct cache_entry *ce, int pos)
 		return error(_("path '%s' does not have their version"), ce->name);
 }
 
-static int check_stages(unsigned stages, struct cache_entry *ce, int pos)
+static int check_stages(unsigned stages, const struct cache_entry *ce, int pos)
 {
 	unsigned seen = 0;
 	const char *name = ce->name;
@@ -321,7 +321,7 @@ static int checkout_paths(const struct checkout_opts *opts,
 
 	/* Any unmerged paths? */
 	for (pos = 0; pos < active_nr; pos++) {
-		struct cache_entry *ce = active_cache[pos];
+		const struct cache_entry *ce = active_cache[pos];
 		if (ce->ce_flags & CE_MATCHED) {
 			if (!ce_stage(ce))
 				continue;
diff --git a/builtin/clean.c b/builtin/clean.c
index 04e396b17..e344137ef 100644
--- a/builtin/clean.c
+++ b/builtin/clean.c
@@ -221,7 +221,7 @@ int cmd_clean(int argc, const char **argv, const char *prefix)
 		struct dir_entry *ent = dir.entries[i];
 		int len, pos;
 		int matches = 0;
-		struct cache_entry *ce;
+		const struct cache_entry *ce;
 		struct stat st;
 
 		/*
diff --git a/builtin/commit.c b/builtin/commit.c
index 6b693c16d..c9cbb811b 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -205,7 +205,7 @@ static int list_paths(struct string_list *list, const char *with_tree,
 	}
 
 	for (i = 0; i < active_nr; i++) {
-		struct cache_entry *ce = active_cache[i];
+		const struct cache_entry *ce = active_cache[i];
 		struct string_list_item *item;
 
 		if (ce->ce_flags & CE_UPDATE)
diff --git a/builtin/grep.c b/builtin/grep.c
index 159e65d47..0223d701a 100644
--- a/builtin/grep.c
+++ b/builtin/grep.c
@@ -376,7 +376,7 @@ static int grep_cache(struct grep_opt *opt, const struct pathspec *pathspec, int
 	read_cache();
 
 	for (nr = 0; nr < active_nr; nr++) {
-		struct cache_entry *ce = active_cache[nr];
+		const struct cache_entry *ce = active_cache[nr];
 		if (!S_ISREG(ce->ce_mode))
 			continue;
 		if (!match_pathspec_depth(pathspec, ce->name, ce_namelen(ce), 0, NULL))
diff --git a/builtin/ls-files.c b/builtin/ls-files.c
index 3a410c35d..80fff23ad 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;
diff --git a/builtin/merge-index.c b/builtin/merge-index.c
index be5e51432..b416d9284 100644
--- a/builtin/merge-index.c
+++ b/builtin/merge-index.c
@@ -16,7 +16,7 @@ static int merge_entry(int pos, const char *path)
 		die("git merge-index: %s not in the cache", path);
 	found = 0;
 	do {
-		struct cache_entry *ce = active_cache[pos];
+		const struct cache_entry *ce = active_cache[pos];
 		int stage = ce_stage(ce);
 
 		if (strcmp(ce->name, path))
@@ -58,7 +58,7 @@ static void merge_all(void)
 {
 	int i;
 	for (i = 0; i < active_nr; i++) {
-		struct cache_entry *ce = active_cache[i];
+		const struct cache_entry *ce = active_cache[i];
 		if (!ce_stage(ce))
 			continue;
 		i += merge_entry(i, ce->name)-1;
diff --git a/builtin/merge.c b/builtin/merge.c
index 2ebe73289..74c0746a9 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -889,7 +889,7 @@ static int suggest_conflicts(int renormalizing)
 		die_errno(_("Could not open '%s' for writing"), filename);
 	fprintf(fp, "\nConflicts:\n");
 	for (pos = 0; pos < active_nr; pos++) {
-		struct cache_entry *ce = active_cache[pos];
+		const struct cache_entry *ce = active_cache[pos];
 
 		if (ce_stage(ce)) {
 			fprintf(fp, "\t%s\n", ce->name);
diff --git a/builtin/rm.c b/builtin/rm.c
index 06025a2e7..18916e022 100644
--- a/builtin/rm.c
+++ b/builtin/rm.c
@@ -67,7 +67,7 @@ static int check_submodules_use_gitfiles(void)
 	for (i = 0; i < list.nr; i++) {
 		const char *name = list.entry[i].name;
 		int pos;
-		struct cache_entry *ce;
+		const struct cache_entry *ce;
 		struct stat st;
 
 		pos = cache_name_pos(name, strlen(name));
@@ -120,7 +120,7 @@ static int check_local_mod(unsigned char *head, int index_only)
 	for (i = 0; i < list.nr; i++) {
 		struct stat st;
 		int pos;
-		struct cache_entry *ce;
+		const struct cache_entry *ce;
 		const char *name = list.entry[i].name;
 		unsigned char sha1[20];
 		unsigned mode;
@@ -321,7 +321,7 @@ int cmd_rm(int argc, const char **argv, const char *prefix)
 	seen = xcalloc(i, 1);
 
 	for (i = 0; i < active_nr; i++) {
-		struct cache_entry *ce = active_cache[i];
+		const struct cache_entry *ce = active_cache[i];
 		if (!match_pathspec(pathspec, ce->name, ce_namelen(ce), 0, seen))
 			continue;
 		ALLOC_GROW(list.entry, list.nr + 1, list.alloc);
diff --git a/builtin/update-index.c b/builtin/update-index.c
index 5c7762eef..c31798151 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;