tree.h API: expose read_tree_1() as read_tree_at()

Rename the static read_tree_1() function to read_tree_at(). This
function works just like read_tree_recursive(), except you provide
your own strbuf.

This step doesn't make much sense now, but in follow-up commits I'll
remove the base/baselen/stage arguments to read_tree_recursive(). At
that point an anticipated in-tree user[1] for the old
read_tree_recursive() couldn't provide a path to start the
traversal.

Let's give them a function to do so with an API that makes more sense
for them, by taking a strbuf we should be able to avoid more casting
and/or reallocations in the future.

1. https://lore.kernel.org/git/xmqqft106sok.fsf@gitster.g

Signed-off-by: Junio C Hamano <gitster@pobox.com>

tree.c

@@ -11,10 +11,11 @@
 
 const char *tree_type = "tree";
 
-static int read_tree_1(struct repository *r,
-		       struct tree *tree, struct strbuf *base,
-		       int stage, const struct pathspec *pathspec,
-		       read_tree_fn_t fn, void *context)
+int read_tree_at(struct repository *r,
+		 struct tree *tree, struct strbuf *base,
+		 int stage,
+		 const struct pathspec *pathspec,
+		 read_tree_fn_t fn, void *context)
 {
 	struct tree_desc desc;
 	struct name_entry entry;
@@ -71,9 +72,9 @@ static int read_tree_1(struct repository *r,
 		len = tree_entry_len(&entry);
 		strbuf_add(base, entry.path, len);
 		strbuf_addch(base, '/');
-		retval = read_tree_1(r, lookup_tree(r, &oid),
-				     base, stage, pathspec,
-				     fn, context);
+		retval = read_tree_at(r, lookup_tree(r, &oid),
+				      base, stage, pathspec,
+				      fn, context);
 		strbuf_setlen(base, oldlen);
 		if (retval)
 			return -1;
@@ -91,7 +92,7 @@ int read_tree_recursive(struct repository *r,
 	int ret;
 
 	strbuf_add(&sb, base, baselen);
-	ret = read_tree_1(r, tree, &sb, stage, pathspec, fn, context);
+	ret = read_tree_at(r, tree, &sb, stage, pathspec, fn, context);
 	strbuf_release(&sb);
 	return ret;
 }

tree.h

@@ -33,6 +33,12 @@ int cmp_cache_name_compare(const void *a_, const void *b_);
 #define READ_TREE_RECURSIVE 1
 typedef int (*read_tree_fn_t)(const struct object_id *, struct strbuf *, const char *, unsigned int, int, void *);
 
+int read_tree_at(struct repository *r,
+		 struct tree *tree, struct strbuf *base,
+		 int stage,
+		 const struct pathspec *pathspec,
+		 read_tree_fn_t fn, void *context);
+
 int read_tree_recursive(struct repository *r,
 			struct tree *tree,
 			const char *base, int baselen,