str: introduce `git_str` for internal, `git_buf` is external

libgit2 has two distinct requirements that were previously solved by
`git_buf`.  We require:

1. A general purpose string class that provides a number of utility APIs
   for manipulating data (eg, concatenating, truncating, etc).
2. A structure that we can use to return strings to callers that they
   can take ownership of.

By using a single class (`git_buf`) for both of these purposes, we have
confused the API to the point that refactorings are difficult and
reasoning about correctness is also difficult.

Move the utility class `git_buf` to be called `git_str`: this represents
its general purpose, as an internal string buffer class.  The name also
is an homage to Junio Hamano ("gitstr").

The public API remains `git_buf`, and has a much smaller footprint.  It
is generally only used as an "out" param with strict requirements that
follow the documentation.  (Exceptions exist for some legacy APIs to
avoid breaking callers unnecessarily.)

Utility functions exist to convert a user-specified `git_buf` to a
`git_str` so that we can call internal functions, then converting it
back again.

1 files changed, 3 insertions, 3 deletions

diff --git a/tests/iterator/tree.c b/tests/iterator/tree.c
index f7fb9a7ee..4145c8dea 100644
--- a/tests/iterator/tree.c
+++ b/tests/iterator/tree.c
@@ -623,7 +623,7 @@ static void build_test_tree(
 	const char *scan = fmt, *next;
 	char type, delimiter;
 	git_filemode_t mode = GIT_FILEMODE_BLOB;
-	git_buf name = GIT_BUF_INIT;
+	git_str name = GIT_STR_INIT;
 	va_list arglist;
 
 	cl_git_pass(git_treebuilder_new(&builder, repo, NULL)); /* start builder */
@@ -640,7 +640,7 @@ static void build_test_tree(
 		delimiter = *scan++; /* read and skip delimiter */
 		for (next = scan; *next && *next != delimiter; ++next)
 			/* seek end */;
-		cl_git_pass(git_buf_set(&name, scan, (size_t)(next - scan)));
+		cl_git_pass(git_str_set(&name, scan, (size_t)(next - scan)));
 		for (scan = next; *scan && (*scan == delimiter || *scan == ','); ++scan)
 			/* skip delimiter and optional comma */;
 
@@ -653,7 +653,7 @@ static void build_test_tree(
 	cl_git_pass(git_treebuilder_write(out, builder));
 
 	git_treebuilder_free(builder);
-	git_buf_dispose(&name);
+	git_str_dispose(&name);
 }
 
 void test_iterator_tree__case_conflicts_0(void)