[util] Allow setting cli summary / description

util/hb-ot-shape-closure.cc

@@ -37,6 +37,7 @@ struct shape_closure_consumer_t
 {
   void add_options (struct option_parser_t *parser)
   {
+    parser->set_summary ("Find glyph set from input text under shaping closure.");
     shaper.add_options (parser);
 
     GOptionEntry entries[] =

util/hb-shape.cc

@@ -40,6 +40,7 @@ struct output_buffer_t : output_options_t<>
 {
   void add_options (option_parser_t *parser)
   {
+    parser->set_summary ("Shape text with given font.");
     output_options_t::add_options (parser, hb_buffer_serialize_list_formats ());
     format.add_options (parser);
   }

util/hb-subset.cc

@@ -586,6 +586,8 @@ subset_main_t::collect_rest (const char *name,
 void
 subset_main_t::add_options ()
 {
+  set_summary ("Subset fonts to specification.");
+
   face_options_t::add_options (this);
 
   GOptionEntry glyphset_entries[] =

util/options.hh

@@ -72,8 +72,8 @@ fail (hb_bool_t suggest_help, const char *format, ...)
 
 struct option_parser_t
 {
-  option_parser_t (const char *usage = nullptr)
+  option_parser_t (const char *parameter_string = nullptr)
-  : context (g_option_context_new (usage)),
+  : context (g_option_context_new (parameter_string)),
     to_free (g_ptr_array_new ())
   {}
 
@@ -130,6 +130,15 @@ struct option_parser_t
     g_option_context_set_main_group (context, group);
   }
 
+  void set_summary (const char *summary)
+  {
+    g_option_context_set_summary (context, summary);
+  }
+  void set_description (const char *description)
+  {
+    g_option_context_set_description (context, description);
+  }
+
   void free_later (char *p) {
     g_ptr_array_add (to_free, p);
   }

util/view-cairo.hh

@@ -40,6 +40,7 @@ struct view_cairo_t : view_options_t, output_options_t<>
 
   void add_options (option_parser_t *parser)
   {
+    parser->set_summary ("View text with given font.");
     view_options_t::add_options (parser);
     output_options_t::add_options (parser, helper_cairo_supported_formats);
   }