attr: tighten const correctness with git_attr and match_attr

Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

attr.c

@@ -220,7 +220,7 @@ static void report_invalid_attr(const char *name, size_t len,
  * dictionary.  If no entry is found, create a new attribute and store it in
  * the dictionary.
  */
-static struct git_attr *git_attr_internal(const char *name, int namelen)
+static const struct git_attr *git_attr_internal(const char *name, int namelen)
 {
 	struct git_attr *a;
 
@@ -244,14 +244,14 @@ static struct git_attr *git_attr_internal(const char *name, int namelen)
 	return a;
 }
 
-struct git_attr *git_attr(const char *name)
+const struct git_attr *git_attr(const char *name)
 {
 	return git_attr_internal(name, strlen(name));
 }
 
 /* What does a matched pattern decide? */
 struct attr_state {
-	struct git_attr *attr;
+	const struct git_attr *attr;
 	const char *setto;
 };
 
@@ -278,7 +278,7 @@ struct pattern {
 struct match_attr {
 	union {
 		struct pattern pat;
-		struct git_attr *attr;
+		const struct git_attr *attr;
 	} u;
 	char is_macro;
 	unsigned num_attr;
@@ -898,7 +898,7 @@ static int fill_one(const char *what, struct all_attrs_item *all_attrs,
 	int i;
 
 	for (i = a->num_attr - 1; rem > 0 && i >= 0; i--) {
-		struct git_attr *attr = a->state[i].attr;
+		const struct git_attr *attr = a->state[i].attr;
 		const char **n = &(all_attrs[attr->attr_nr].value);
 		const char *v = a->state[i].setto;
 
@@ -922,7 +922,7 @@ static int fill(const char *path, int pathlen, int basename_offset,
 	const char *base = stk->origin ? stk->origin : "";
 
 	for (i = stk->num_matches - 1; 0 < rem && 0 <= i; i--) {
-		struct match_attr *a = stk->attrs[i];
+		const struct match_attr *a = stk->attrs[i];
 		if (a->is_macro)
 			continue;
 		if (path_matches(path, pathlen, basename_offset,

attr.h

@@ -11,7 +11,7 @@ struct all_attrs_item;
  * Given a string, return the gitattribute object that
  * corresponds to it.
  */
-struct git_attr *git_attr(const char *);
+const struct git_attr *git_attr(const char *);
 
 /* Internal use */
 extern const char git_attr__true[];

builtin/check-attr.c

@@ -166,7 +166,8 @@ int cmd_check_attr(int argc, const char **argv, const char *prefix)
 	check = attr_check_alloc();
 	if (!all_attrs) {
 		for (i = 0; i < cnt; i++) {
-			struct git_attr *a = git_attr(argv[i]);
+			const struct git_attr *a = git_attr(argv[i]);
+
 			if (!a)
 				return error("%s: not a valid attribute name",
 					     argv[i]);