Add git_diff_patch_print

This adds a `git_diff_patch_print()` API which is more like the
existing API to "print" a patch from an entire `git_diff_list`
but operates on a single `git_diff_patch` object.

Also, it rewrites the `git_diff_patch_to_str()` API to use that
function (making it very small).

1 files changed, 18 insertions, 1 deletions

diff --git a/include/git2/diff.h b/include/git2/diff.h
index 1c2a2f83a..4e80bed56 100644
--- a/include/git2/diff.h
+++ b/include/git2/diff.h
@@ -604,10 +604,27 @@ GIT_EXTERN(int) git_diff_patch_get_line_in_hunk(
 	size_t line_of_hunk);
 
 /**
+ * Serialize the patch to text via callback.
+ *
+ * Returning a non-zero value from the callback will terminate the iteration
+ * and cause this return `GIT_EUSER`.
+ *
+ * @param patch A git_diff_patch representing changes to one file
+ * @param cb_data Reference pointer that will be passed to your callbacks.
+ * @param print_cb Callback function to output lines of the patch.  Will be
+ *                 called for file headers, hunk headers, and diff lines.
+ * @return 0 on success, GIT_EUSER on non-zero callback, or error code
+ */
+GIT_EXTERN(int) git_diff_patch_print(
+	git_diff_patch *patch,
+	void *cb_data,
+	git_diff_data_fn print_cb);
+
+/**
  * Get the content of a patch as a single diff text.
  *
  * @param string Allocated string; caller must free.
- * @param patch The patch to generate a string from.
+ * @param patch A git_diff_patch representing changes to one file
  * @return 0 on success, <0 on failure.
  */
 GIT_EXTERN(int) git_diff_patch_to_str(