From 1d9d6f37ad770df8eed4c8ff80dc8863616f6ef3 Mon Sep 17 00:00:00 2001
From: Max Brunsfeld <maxbrunsfeld@gmail.com>
Date: Mon, 2 Apr 2018 11:52:34 -0700
Subject: [PATCH] Introduce an error cost per error instance to favor fewer
 errors

---
 src/runtime/error_costs.h |  1 +
 src/runtime/stack.c       | 10 +++++++---
 src/runtime/tree.c        | 11 +++++++----
 3 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/src/runtime/error_costs.h b/src/runtime/error_costs.h
index f543b3ff..d6420488 100644
--- a/src/runtime/error_costs.h
+++ b/src/runtime/error_costs.h
@@ -2,6 +2,7 @@
 #define RUNTIME_ERROR_COSTS_H_
 
 #define ERROR_STATE 0
+#define ERROR_COST_PER_RECOVERY 500
 #define ERROR_COST_PER_MISSING_TREE 110
 #define ERROR_COST_PER_SKIPPED_TREE 100
 #define ERROR_COST_PER_SKIPPED_LINE 30
diff --git a/src/runtime/stack.c b/src/runtime/stack.c
index f993f59f..17a301fe 100644
--- a/src/runtime/stack.c
+++ b/src/runtime/stack.c
@@ -399,7 +399,9 @@ void ts_stack_set_last_external_token(Stack *self, StackVersion version, Tree *t
 
 unsigned ts_stack_error_cost(const Stack *self, StackVersion version) {
   StackHead *head = array_get(&self->heads, version);
-  return head->node->error_cost;
+  unsigned result = head->node->error_cost;
+  if (head->node->state == ERROR_STATE) result += ERROR_COST_PER_RECOVERY;
+  return result;
 }
 
 unsigned ts_stack_node_count_since_error(const Stack *self, StackVersion version) {
@@ -668,8 +670,10 @@ bool ts_stack_print_dot_graph(Stack *self, const char **symbol_names, FILE *f) {
       fprintf(f, "color=red ");
     }
     fprintf(f,
-      "label=%u, fontcolor=blue, weight=10000, labeltooltip=\"node_count: %u",
-      i, head->node->node_count - head->node_count_at_last_error
+      "label=%u, fontcolor=blue, weight=10000, labeltooltip=\"node_count: %u\nerror_cost: %u",
+      i,
+      ts_stack_node_count_since_error(self, i),
+      ts_stack_error_cost(self, i)
     );
 
     if (head->last_external_token) {
diff --git a/src/runtime/tree.c b/src/runtime/tree.c
index c58c987a..f88895d2 100644
--- a/src/runtime/tree.c
+++ b/src/runtime/tree.c
@@ -354,11 +354,14 @@ void ts_tree_set_children(Tree *self, uint32_t child_count, Tree **children,
   }
 
   if (self->symbol == ts_builtin_sym_error) {
-    self->error_cost += ERROR_COST_PER_SKIPPED_CHAR * self->size.bytes +
+    self->error_cost += ERROR_COST_PER_RECOVERY +
+                        ERROR_COST_PER_SKIPPED_CHAR * self->size.bytes +
                         ERROR_COST_PER_SKIPPED_LINE * self->size.extent.row;
-    for (uint32_t i = 0; i < child_count; i++)
-      if (!self->children[i]->extra)
+    for (uint32_t i = 0; i < child_count; i++) {
+      if (!self->children[i]->extra) {
         self->error_cost += ERROR_COST_PER_SKIPPED_TREE;
+      }
+    }
   }
 
   if (child_count > 0) {
@@ -418,7 +421,7 @@ Tree *ts_tree_make_error_node(TreePool *pool, TreeArray *children, const TSLangu
 Tree *ts_tree_make_missing_leaf(TreePool *pool, TSSymbol symbol, const TSLanguage *language) {
   Tree *result = ts_tree_make_leaf(pool, symbol, length_zero(), length_zero(), language);
   result->is_missing = true;
-  result->error_cost = ERROR_COST_PER_MISSING_TREE;
+  result->error_cost = ERROR_COST_PER_MISSING_TREE + ERROR_COST_PER_RECOVERY;
   return result;
 }