str: introduce `git_str` for internal, `git_buf` is externalethomson/gitstr

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, 7 insertions, 2 deletions

diff --git a/src/commit_graph.h b/src/commit_graph.h
index 9d0a827de..4d2be431c 100644
--- a/src/commit_graph.h
+++ b/src/commit_graph.h
@@ -92,7 +92,7 @@ typedef struct git_commit_graph_entry {
 /* A wrapper for git_commit_graph_file to enable lazy loading in the ODB. */
 struct git_commit_graph {
 	/* The path to the commit-graph file. Something like ".git/objects/info/commit-graph". */
-	git_buf filename;
+	git_str filename;
 
 	/* The underlying commit-graph file. */
 	git_commit_graph_file *file;
@@ -127,12 +127,17 @@ struct git_commit_graph_writer {
 	 * The path of the `objects/info` directory where the `commit-graph` will be
 	 * stored.
 	 */
-	git_buf objects_info_dir;
+	git_str objects_info_dir;
 
 	/* The list of packed commits. */
 	git_vector commits;
 };
 
+int git_commit_graph__writer_dump(
+	git_str *cgraph,
+	git_commit_graph_writer *w,
+	git_commit_graph_writer_options *opts);
+
 /*
  * Returns whether the git_commit_graph_file needs to be reloaded since the
  * contents of the commit-graph file have changed on disk.