[shape] Fail shaping internally if buffer ops exceeded

src/hb-buffer.cc

@@ -311,6 +311,7 @@ hb_buffer_t::enter ()
 {
   deallocate_var_all ();
   serial = 0;
+  shaping_failed = false;
   scratch_flags = HB_BUFFER_SCRATCH_FLAG_DEFAULT;
   if (likely (!hb_unsigned_mul_overflows (len, HB_BUFFER_MAX_LEN_FACTOR)))
   {
@@ -330,6 +331,7 @@ hb_buffer_t::leave ()
   max_ops = HB_BUFFER_MAX_OPS_DEFAULT;
   deallocate_var_all ();
   serial = 0;
+  // Intentionally not reseting shaping_failed, such that it can be inspected.
 }
 
 

src/hb-ot-shape.cc

@@ -1159,8 +1159,6 @@ hb_propagate_flags (hb_buffer_t *buffer)
 static void
 hb_ot_shape_internal (hb_ot_shape_context_t *c)
 {
-  c->buffer->enter ();
-
   /* Save the original direction, we use it later. */
   c->target_direction = c->buffer->props.direction;
 

src/hb-shape.cc

@@ -129,6 +129,8 @@ hb_shape_full (hb_font_t          *font,
   if (unlikely (!buffer->len))
     return true;
 
+  buffer->enter ();
+
   hb_buffer_t *text_buffer = nullptr;
   if (buffer->flags & HB_BUFFER_FLAG_VERIFY)
   {
@@ -140,8 +142,12 @@ hb_shape_full (hb_font_t          *font,
 							      features, num_features,
 							      font->coords, font->num_coords,
 							      shaper_list);
-  buffer->shaping_failed = false;
+
   hb_bool_t res = hb_shape_plan_execute (shape_plan, font, buffer, features, num_features);
+
+  if (buffer->max_ops <= 0)
+    buffer->shaping_failed = true;
+
   hb_shape_plan_destroy (shape_plan);
 
   if (text_buffer)
@@ -157,6 +163,8 @@ hb_shape_full (hb_font_t          *font,
     hb_buffer_destroy (text_buffer);
   }
 
+  buffer->leave ();
+
   return res;
 }