Add "experimental" mode to local echo (always predict even when incorrect)

scripts/mosh

@@ -47,9 +47,10 @@ qq{Usage: $0 [options] [--] [user@]host [command...]
         --server=COMMAND     mosh server on remote machine
                                 (default: "mosh-server")
 
-        --predict=adaptive   local echo for slower links [default]
--a      --predict=always     use local echo even on fast links
--n      --predict=never      never use local echo
+        --predict=adaptive      local echo for slower links [default]
+-a      --predict=always        use local echo even on fast links
+-n      --predict=never         never use local echo
+        --predict=experimental  aggressively echo even when incorrect
 
 -p NUM  --port=NUM           server-side UDP port
 
@@ -72,7 +73,8 @@ There is NO WARRANTY, to the extent permitted by law.\n};
 sub predict_check {
   my ( $predict, $env_set ) = @_;
 
-  if ( not exists { adaptive => 0, always => 0, never => 0 }->{ $predict } ) {
+  if ( not exists { adaptive => 0, always => 0,
+		    never => 0, experimental => 0 }->{ $predict } ) {
     my $explanation = $env_set ? " (MOSH_PREDICTION_DISPLAY in environment)" : "";
     print STDERR qq{$0: Unknown mode \"$predict\"$explanation.\n\n};
 

src/frontend/stmclient.h

@@ -82,6 +82,8 @@ public:
 	overlays.get_prediction_engine().set_display_preference( Overlay::PredictionEngine::Never );
       } else if ( !strcmp( predict_mode, "adaptive" ) ) {
 	overlays.get_prediction_engine().set_display_preference( Overlay::PredictionEngine::Adaptive );
+      } else if ( !strcmp( predict_mode, "experimental" ) ) {
+	overlays.get_prediction_engine().set_display_preference( Overlay::PredictionEngine::Experimental );
       } else {
 	fprintf( stderr, "Unknown prediction mode %s.\n", predict_mode );
 	exit( 1 );

src/frontend/terminaloverlay.cc

@@ -325,7 +325,8 @@ void PredictionEngine::apply( Framebuffer &fb ) const
 {
   bool show = (display_preference != Never) && ( srtt_trigger
 						 || glitch_trigger
-						 || (display_preference == Always) );
+						 || (display_preference == Always)
+						 || (display_preference == Experimental) );
 
   if ( show ) {
     for ( cursors_type::const_iterator it = cursors.begin();
@@ -461,7 +462,11 @@ void PredictionEngine::cull( const Framebuffer &fb )
 		   );
 	  */
 
-	  kill_epoch( j->tentative_until_epoch, fb );
+	  if ( display_preference == Experimental ) {
+	    j->reset();
+	  } else {
+	    kill_epoch( j->tentative_until_epoch, fb );
+	  }
 	  /*
 	  if ( j->display_time != uint64_t(-1) ) {
 	    fprintf( stderr, "TIMING %ld - %ld (TENT)\n", time(NULL), now - j->display_time );
@@ -481,8 +486,12 @@ void PredictionEngine::cull( const Framebuffer &fb )
 	  }
 	  */
 
-	  reset();
-	  return;
+	  if ( display_preference == Experimental ) {
+	    j->reset();
+	  } else {
+	    reset();
+	    return;
+	  }
 	}
 	break;
       case Correct:
@@ -548,8 +557,12 @@ void PredictionEngine::cull( const Framebuffer &fb )
 	       cursor().expiration_time,
 	       now );
       */
-      reset();
-      return;
+      if ( display_preference == Experimental ) {
+	cursors.clear();
+      } else {
+	reset();
+	return;
+      }
     }
   }
 
@@ -590,6 +603,8 @@ void PredictionEngine::new_user_byte( char the_byte, const Framebuffer &fb )
 {
   if ( display_preference == Never ) {
     return;
+  } else if ( display_preference == Experimental ) {
+    prediction_epoch = confirmed_epoch;
   }
 
   cull( fb );
@@ -810,7 +825,9 @@ void PredictionEngine::newline_carriage_return( const Framebuffer &fb )
 
 void PredictionEngine::become_tentative( void )
 {
-  prediction_epoch++;
+  if ( display_preference != Experimental ) {
+    prediction_epoch++;
+  }
 
   /*
   fprintf( stderr, "Now tentative in epoch %lu (confirmed=%lu)\n",

src/frontend/terminaloverlay.h

@@ -231,7 +231,8 @@ namespace Overlay {
     enum DisplayPreference {
       Always,
       Never,
-      Adaptive
+      Adaptive,
+      Experimental
     };
 
   private: