sexp: Fix broken gcry_sexp_nth.

* src/sexp.c (_gcry_sexp_nth): Return a valid S-expression for a data
element.
(NODE): Remove unused typedef.
(ST_HINT): Comment unused macro.

* tests/t-sexp.c (bug_1594): New.
(main): Run new test.
--

Before 1.6.0 gcry_sexp_nth (list, 0) with a LIST of "(a (b 3:pqr) (c
3:456) (d 3:xyz))" returned the entire list.  1.6.0 instead returned
NULL.  However, this is also surprising and the expected value would
be "(a)".  This patch fixes this.

Somewhat related to that gcry_sexp_nth returned a broken list if
requesting index 1 of a list like "(n foo)".  It returned just the
"foo" but not as a list which is required by the S-expression specs.
Due to this patch the returned value is now "(foo)".

Thanks to Ludovic Courtès for pointing out these problems.

GnuPG-bug-id: 1594

1 files changed, 3 insertions, 2 deletions

diff --git a/doc/gcrypt.texi b/doc/gcrypt.texi
index 4a917901..c5c3b452 100644
--- a/doc/gcrypt.texi
+++ b/doc/gcrypt.texi
@@ -4064,8 +4064,9 @@ no such element, @code{NULL} is returned.
 @deftypefun gcry_sexp_t gcry_sexp_car (@w{const gcry_sexp_t @var{list}})
 
 Create and return a new S-expression from the first element in
-@var{list}; this called the "type" and should always exist and be a
-string. @code{NULL} is returned in case of a problem.
+@var{list}; this is called the "type" and should always exist per
+S-expression specification and in general be a string.  @code{NULL} is
+returned in case of a problem.
 @end deftypefun
 
 @deftypefun gcry_sexp_t gcry_sexp_cdr (@w{const gcry_sexp_t @var{list}})