grafts: make `from_file` be `open_or_refresh`

The semantics of `from_file` are weird - it looks like a function that
just opens a file, but it actually inspects the pointer, which is
unexpected and could make things very crashy.

Make an `open` function that just does an open, and move the magic to
`open_or_refresh` whose name better indicates that it may do weird
stuff.

src/libgit2/grafts.c

@@ -44,7 +44,7 @@ int git_grafts_new(git_grafts **out, git_oid_t oid_type)
 	return 0;
 }
 
-int git_grafts_from_file(
+int git_grafts_open(
 	git_grafts **out,
 	const char *path,
 	git_oid_t oid_type)
@@ -52,10 +52,7 @@ int git_grafts_from_file(
 	git_grafts *grafts = NULL;
 	int error;
 
-	GIT_ASSERT_ARG(path && oid_type);
-
-	if (*out)
-		return git_grafts_refresh(*out);
+	GIT_ASSERT_ARG(out && path && oid_type);
 
 	if ((error = git_grafts_new(&grafts, oid_type)) < 0)
 		goto error;
@@ -67,12 +64,24 @@ int git_grafts_from_file(
 		goto error;
 
 	*out = grafts;
+
 error:
 	if (error < 0)
 		git_grafts_free(grafts);
+
 	return error;
 }
 
+int git_grafts_open_or_refresh(
+	git_grafts **out,
+	const char *path,
+	git_oid_t oid_type)
+{
+	GIT_ASSERT_ARG(out && path && oid_type);
+
+	return *out ? git_grafts_refresh(*out) : git_grafts_open(out, path, oid_type);
+}
+
 void git_grafts_free(git_grafts *grafts)
 {
 	if (!grafts)

src/libgit2/grafts.h

@@ -20,7 +20,8 @@ typedef struct {
 typedef struct git_grafts git_grafts;
 
 int git_grafts_new(git_grafts **out, git_oid_t oid_type);
-int git_grafts_from_file(git_grafts **out, const char *path, git_oid_t oid_type);
+int git_grafts_open(git_grafts **out, const char *path, git_oid_t oid_type);
+int git_grafts_open_or_refresh(git_grafts **out, const char *path, git_oid_t oid_type);
 void git_grafts_free(git_grafts *grafts);
 void git_grafts_clear(git_grafts *grafts);
 

src/libgit2/repository.c

@@ -852,13 +852,13 @@ static int load_grafts(git_repository *repo)
 
 	if ((error = git_repository__item_path(&path, repo, GIT_REPOSITORY_ITEM_INFO)) < 0 ||
 	    (error = git_str_joinpath(&path, path.ptr, "grafts")) < 0 ||
-	    (error = git_grafts_from_file(&repo->grafts, path.ptr, repo->oid_type)) < 0)
+	    (error = git_grafts_open_or_refresh(&repo->grafts, path.ptr, repo->oid_type)) < 0)
 		goto error;
 
 	git_str_clear(&path);
 
 	if ((error = git_str_joinpath(&path, repo->gitdir, "shallow")) < 0 ||
-	    (error = git_grafts_from_file(&repo->shallow_grafts, path.ptr, repo->oid_type)) < 0)
+	    (error = git_grafts_open_or_refresh(&repo->shallow_grafts, path.ptr, repo->oid_type)) < 0)
 		goto error;
 
 error: