March generator: enhance error handling

tools/gen_marching_cubes_conf.py

@@ -7,6 +7,7 @@
 """
 
 from functools import reduce
+import sys
 
 
 class Vert:
@@ -203,9 +204,13 @@ def do_main(base_cases):
                 if index[code] is None:
                     index[code] = tr_case
 
+    has_unbound = False
     for (val, tri) in enumerate(index):
         if tri is None:
-            print(">> UNBOUND {}".format(val))
+            print(">> UNBOUND {}".format(val), file=sys.stderr)
+            has_unbound = True
+    if has_unbound:
+        raise RuntimeError("Some cases were not generated.")
 
     print(("static const std::vector<MarchingCubes::CubeTri> "
            "edges_of_intersection[256] = {"))