[util] List supported output formats in --help output

util/hb-shape.cc

@@ -31,7 +31,8 @@
 struct output_buffer_t
 {
   output_buffer_t (option_parser_t *parser)
-		  : options (parser),
+		  : options (parser,
+			     g_strjoinv (" / ", (gchar**) hb_buffer_serialize_list_formats ())),
 		    format (parser) {}
 
   void init (const font_options_t *font_opts)
@@ -49,8 +50,7 @@ struct output_buffer_t
     {
       if (options.explicit_output_format)
 	fail (false, "Unknown output format `%s'; supported formats are: %s",
-	      options.output_format,
-	      g_strjoinv (" / ", (gchar**) hb_buffer_serialize_list_formats ()));
+	      options.output_format, options.supported_formats);
       else
 	/* Just default to TEXT if not explicitly requested and the
 	 * file extension is not recognized. */

util/helper-cairo.cc

@@ -246,7 +246,7 @@ stdio_write_func (void                *closure,
   return CAIRO_STATUS_SUCCESS;
 }
 
-static const char helper_cairo_supported_formats[] =
+const char helper_cairo_supported_formats[] =
   "ansi"
   #ifdef CAIRO_HAS_PNG_FUNCTIONS
   "/png"

util/helper-cairo.hh

@@ -36,6 +36,7 @@ cairo_scaled_font_t *
 helper_cairo_create_scaled_font (const font_options_t *font_opts,
 				 double font_size);
 
+extern const char helper_cairo_supported_formats[];
 
 cairo_t *
 helper_cairo_create_context (double w, double h,

util/options.cc

@@ -367,10 +367,17 @@ text_options_t::add_options (option_parser_t *parser)
 void
 output_options_t::add_options (option_parser_t *parser)
 {
+  const char *text;
+
+  if (NULL == supported_formats)
+    text = "Set output format";
+  else
+    text = g_strdup_printf ("Set output format\n\n    Supported formats are: %s", supported_formats);
+
   GOptionEntry entries[] =
   {
     {"output-file",	0, 0, G_OPTION_ARG_STRING,	&this->output_file,		"Set output file-name (default: stdout)","filename"},
-    {"output-format",	0, 0, G_OPTION_ARG_STRING,	&this->output_format,		"Set output format",			"format"},
+    {"output-format",	0, 0, G_OPTION_ARG_STRING,	&this->output_format,		text,					"format"},
     {NULL}
   };
   parser->add_group (entries,

util/options.hh

@@ -310,9 +310,11 @@ struct text_options_t : option_group_t
 
 struct output_options_t : option_group_t
 {
-  output_options_t (option_parser_t *parser) {
+  output_options_t (option_parser_t *parser,
+		    const char *supported_formats_ = NULL) {
     output_file = NULL;
     output_format = NULL;
+    supported_formats = supported_formats_;
     explicit_output_format = false;
 
     fp = NULL;
@@ -345,6 +347,7 @@ struct output_options_t : option_group_t
 
   const char *output_file;
   const char *output_format;
+  const char *supported_formats;
   bool explicit_output_format;
 
   mutable FILE *fp;

util/view-cairo.hh

@@ -33,7 +33,7 @@
 
 struct view_cairo_t {
   view_cairo_t (option_parser_t *parser)
-	       : output_options (parser),
+	       : output_options (parser, helper_cairo_supported_formats),
 	         view_options (parser) {}
   ~view_cairo_t (void) {
     if (debug)