Fix pretty-printing nested empty lists and add test suite

The earlier "test" was just hitting the code without actually checking the
output.  This new suite is a set of pretty-printed documents which serd must
reproduce from a model exactly to pass.  This should make it easy to add cases
in the future, since each case is just a document, as it should look.

3 files changed, 15 insertions, 7 deletions

diff --git a/src/describe.c b/src/describe.c
index 9bd9d3ae..718eaf1c 100644
--- a/src/describe.c
+++ b/src/describe.c
@@ -204,7 +204,7 @@ write_range_statement(const SerdSink* const             sink,
       // First write inline list subject, which this statement will follow
       if (zix_hash_insert(list_subjects, subject) != ZIX_STATUS_EXISTS) {
         st = write_list(
-          sink, model, list_subjects, 2, SERD_LIST_S, subject, graph);
+          sink, model, list_subjects, 2, flags | SERD_LIST_S, subject, graph);
       }
     }
   }
@@ -226,9 +226,12 @@ write_range_statement(const SerdSink* const             sink,
     serd_cursor_free(iter);
 
   } else if (object_style == LIST_O) { // Write list object like "( ... )"
-    flags |= SERD_LIST_O;
-    if (!(st = serd_sink_write_statement(sink, flags, statement))) {
-      st = write_list(sink, model, list_subjects, depth + 1, 0, object, graph);
+    if (!(st =
+            serd_sink_write_statement(sink, flags | SERD_LIST_O, statement))) {
+      flags = flags & ~((unsigned)SERD_LIST_S);
+
+      st =
+        write_list(sink, model, list_subjects, depth + 1, flags, object, graph);
     }
 
   } else {
diff --git a/src/n3.c b/src/n3.c
index ff142976..3b12dfec 100644
--- a/src/n3.c
+++ b/src/n3.c
@@ -866,11 +866,11 @@ read_collection(SerdReader* const reader,
     return SERD_ERR_OVERFLOW;
   }
 
-  if (ctx.subject) {
-    // subject predicate _:head
+  if (ctx.subject) { // Reading a collection object
     *ctx.flags |= (end ? 0 : SERD_LIST_O);
     TRY(st, emit_statement(reader, ctx, *dest));
-  } else {
+    *ctx.flags &= ~((unsigned)SERD_LIST_O);
+  } else { // Reading a collection subject
     *ctx.flags |= (end ? 0 : SERD_LIST_S);
   }
 
diff --git a/src/writer.c b/src/writer.c
index 5f9fdaab..452d3679 100644
--- a/src/writer.c
+++ b/src/writer.c
@@ -1064,6 +1064,11 @@ write_list_statement(SerdWriter* const        writer,
   SerdStatus st     = SERD_SUCCESS;
   bool       is_end = false;
 
+  if (serd_node_equals(predicate, writer->world->rdf_first) &&
+      serd_node_equals(object, writer->world->rdf_nil)) {
+    return esink("()", 2, writer);
+  }
+
   TRY(st, write_list_obj(writer, flags, predicate, object, &is_end));
   if (is_end) {
     pop_context(writer);