Add empty syntax type for suppressing output

3 files changed, 19 insertions, 11 deletions

diff --git a/src/serdi.c b/src/serdi.c
index 75599ac7..8a4a52cf 100644
--- a/src/serdi.c
+++ b/src/serdi.c
@@ -65,7 +65,7 @@ print_usage(const char* const name, const bool error)
     "  -i SYNTAX    Input syntax: turtle/ntriples/trig/nquads.\n"
     "  -k BYTES     Parser stack size.\n"
     "  -l           Lax (non-strict) parsing.\n"
-    "  -o SYNTAX    Output syntax: turtle/ntriples/nquads.\n"
+    "  -o SYNTAX    Output syntax: empty/turtle/ntriples/nquads.\n"
     "  -p PREFIX    Add PREFIX to blank node IDs.\n"
     "  -q           Suppress all output except data.\n"
     "  -r ROOT_URI  Keep relative URIs within ROOT_URI.\n"
@@ -100,13 +100,14 @@ main(int argc, char** argv)
 {
   const char* const prog = argv[0];
 
-  SerdSyntax      input_syntax  = (SerdSyntax)0;
-  SerdSyntax      output_syntax = (SerdSyntax)0;
+  SerdSyntax      input_syntax  = SERD_SYNTAX_EMPTY;
+  SerdSyntax      output_syntax = SERD_SYNTAX_EMPTY;
   SerdWriterFlags writer_flags  = 0;
   bool            from_string   = false;
   bool            from_stdin    = false;
   bool            bulk_read     = true;
   bool            lax           = false;
+  bool            osyntax_set   = false;
   bool            quiet         = false;
   size_t          stack_size    = 1048576U;
   const char*     add_prefix    = NULL;
@@ -182,12 +183,15 @@ main(int argc, char** argv)
         stack_size = (size_t)size;
         break;
       } else if (opt == 'o') {
+        osyntax_set = true;
         if (argv[a][o + 1] || ++a == argc) {
           return missing_arg(prog, 'o');
         }
 
-        if (!(output_syntax = serd_syntax_by_name(argv[a]))) {
-          return print_usage(prog, true);
+        if (!strcmp(argv[a], "empty")) {
+          output_syntax = SERD_SYNTAX_EMPTY;
+        } else if (!(output_syntax = serd_syntax_by_name(argv[a]))) {
+          return print_usage(argv[0], true);
         }
         break;
       } else if (opt == 'p') {
@@ -228,7 +232,7 @@ main(int argc, char** argv)
   }
 
   const bool input_has_graphs = serd_syntax_has_graphs(input_syntax);
-  if (!output_syntax) {
+  if (!output_syntax && !osyntax_set) {
     output_syntax = input_has_graphs ? SERD_NQUADS : SERD_NTRIPLES;
   }
 
diff --git a/src/syntax.c b/src/syntax.c
index 1599df08..d75865b1 100644
--- a/src/syntax.c
+++ b/src/syntax.c
@@ -19,7 +19,7 @@ static const Syntax syntaxes[] = {
   {"ntriples", ".nt", SERD_NTRIPLES},
   {"nquads", ".nq", SERD_NQUADS},
   {"trig", ".trig", SERD_TRIG},
-  {NULL, NULL, (SerdSyntax)0},
+  {NULL, NULL, SERD_SYNTAX_EMPTY},
 };
 
 SerdSyntax
@@ -33,7 +33,7 @@ serd_syntax_by_name(const char* const name)
       }
     }
   }
-  return (SerdSyntax)0;
+  return SERD_SYNTAX_EMPTY;
 }
 
 SerdSyntax
@@ -43,12 +43,12 @@ serd_guess_syntax(const char* const filename)
   if (ext && ext[1]) {
     const size_t ext_len = strlen(ext);
     for (const Syntax* s = syntaxes; s->name; ++s) {
-      if (!serd_strncasecmp(s->extension, ext, ext_len)) {
+      if (s->extension && !serd_strncasecmp(s->extension, ext, ext_len)) {
         return s->syntax;
       }
     }
   }
-  return (SerdSyntax)0;
+  return SERD_SYNTAX_EMPTY;
 }
 
 bool
diff --git a/src/writer.c b/src/writer.c
index 5603e9ca..a1d91ff8 100644
--- a/src/writer.c
+++ b/src/writer.c
@@ -1003,6 +1003,10 @@ serd_writer_write_statement(SerdWriter* const          writer,
   assert(!((flags & SERD_ANON_O) && (flags & SERD_LIST_O)));
   assert(!((flags & SERD_EMPTY_O) && (flags & SERD_LIST_O)));
 
+  if (writer->syntax == SERD_SYNTAX_EMPTY) {
+    return SERD_SUCCESS;
+  }
+
   SerdStatus            st        = SERD_SUCCESS;
   const SerdNode* const subject   = serd_statement_subject(statement);
   const SerdNode* const predicate = serd_statement_predicate(statement);
@@ -1149,7 +1153,7 @@ serd_writer_end_anon(SerdWriter* writer, const SerdNode* node)
 {
   SerdStatus st = SERD_SUCCESS;
 
-  if (writer->syntax == SERD_NTRIPLES || writer->syntax == SERD_NQUADS) {
+  if (writer->syntax != SERD_TURTLE && writer->syntax != SERD_TRIG) {
     return SERD_SUCCESS;
   }