Update iterators for consistency across library

This updates all the `foreach()` type functions across the library
that take callbacks from the user to have a consistent behavior.
The rules are:

* A callback terminates the loop by returning any non-zero value
* Once the callback returns non-zero, it will not be called again
  (i.e. the loop stops all iteration regardless of state)
* If the callback returns non-zero, the parent fn returns GIT_EUSER
* Although the parent returns GIT_EUSER, no error will be set in
  the library and `giterr_last()` will return NULL if called.

This commit makes those changes across the library and adds tests
for most of the iteration APIs to make sure that they follow the
above rules.

1 files changed, 2 insertions, 2 deletions

diff --git a/include/git2/status.h b/include/git2/status.h
index 9e7b5de4a..cc94d7680 100644
--- a/include/git2/status.h
+++ b/include/git2/status.h
@@ -38,11 +38,11 @@ enum {
  *
  * The callback is passed the path of the file, the status and the data
  * pointer passed to this function. If the callback returns something other
- * than 0, this function will return that value.
+ * than 0, this function will stop looping and return GIT_EUSER.
  *
  * @param repo a repository object
  * @param callback the function to call on each file
- * @return 0 on success or the return value of the callback that was non-zero
+ * @return 0 on success, GIT_EUSER on non-zero callback, or error code
  */
 GIT_EXTERN(int) git_status_foreach(
 	git_repository *repo,