Even if we goto another routine, we can't trash an output.

HISTORY.md

@@ -7,6 +7,7 @@ History of SixtyPical
 *   `copy` is now understood to trash `a`, thus `copy ..., a` is not valid.
     Indirect addressing is supported in `ld`, as in `ld a, [ptr] + y`, to compensate.
 *   Implements the "union rule for trashes" when analyzing `if` blocks.
+*   Even if we `goto` another routine, we can't trash an output.
 *   Fixed bug where `trash` was not marking the location as being virtually altered.
 
 0.11

eg/proto-game.60p

@@ -35,9 +35,9 @@ typedef routine
          actor_pos, actor_delta, actor_logic,
          screen, screen1, screen2, screen3, screen4, colormap1, colormap2, colormap3, colormap4
   outputs button_down, dispatch_game_state,
-          actor_pos, pos, new_pos, actor_delta, delta, actor_logic,
+          actor_pos, actor_delta, actor_logic,
           screen, screen1, screen2, screen3, screen4, colormap1, colormap2, colormap3, colormap4
-  trashes a, x, y, c, z, n, v, ptr, save_x, compare_target, dispatch_logic
+  trashes a, x, y, c, z, n, v, pos, new_pos, delta, ptr, save_x, compare_target, dispatch_logic
     game_state_routine
 
 //
@@ -402,12 +402,7 @@ define game_state_title_screen game_state_routine
 
     if c {
         call clear_screen
-
-        // FIXME: this seems wrong and we need to investigate it.
-        // init_game trashes `pos` (this is reasonable.)  But pos is declared
-        // as an output to `game_state_routine`.  This should be an error...
         call init_game
-
         copy forward game_state_play, dispatch_game_state
     }
 

src/sixtypical/analyzer.py

@@ -202,13 +202,31 @@ class Analyzer(object):
             return
         type_ = routine.location.type
         context = Context(self.routines, routine, type_.inputs, type_.outputs, type_.trashes)
+
         if self.debug:
             print "at start of routine `{}`:".format(routine.name)
             print context
+
         self.analyze_block(routine.block, context)
+        trashed = set(context.each_touched()) - context._meaningful
+
         if self.debug:
             print "at end of routine `{}`:".format(routine.name)
             print context
+            print "trashed: ", LocationRef.format_set(trashed)
+            print "outputs: ", LocationRef.format_set(type_.outputs)
+            trashed_outputs = type_.outputs & trashed
+            if trashed_outputs:
+                print "TRASHED OUTPUTS: ", LocationRef.format_set(trashed_outputs)
+            print ''
+            print '-' * 79
+            print ''
+
+        # even if we goto another routine, we can't trash an output.
+        for ref in trashed:
+            if ref in type_.outputs:
+                raise UnmeaningfulOutputError('%s in %s' % (ref.name, routine.name))
+
         if not self.has_encountered_goto:
             for ref in type_.outputs:
                 context.assert_meaningful(ref, exception_class=UnmeaningfulOutputError)