Function svn_error_create 

pub unsafe extern "C" fn svn_error_create(
    apr_err: apr_status_t,
    child: *mut svn_error_t,
    message: *const c_char,
) -> *mut svn_error_t

Create a nested exception structure.

Input: an APR or SVN custom error code, a “child” error to wrap, a specific message

Returns: a new error structure (containing the old one).

@note Errors are always allocated in a subpool of the global pool, since an error’s lifetime is generally not related to the lifetime of any convenient pool. Errors must be freed with svn_error_clear(). The specific message should be @c NULL if there is nothing to add to the general message associated with the error code.

   If creating the "bottommost" error in a chain, pass @c NULL for
   the child argument.