From e99a3925e0f62d6d699544bb973fa8604c9d2dc8 Mon Sep 17 00:00:00 2001
From: Max Brunsfeld <maxbrunsfeld@gmail.com>
Date: Sun, 24 Apr 2016 00:55:19 -0700
Subject: [PATCH] Merge all versions created in a given reduce operation

---
 src/runtime/parser.c |  3 +++
 src/runtime/stack.c  | 10 +++++++---
 src/runtime/stack.h  |  2 ++
 3 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/src/runtime/parser.c b/src/runtime/parser.c
index 17411929..b7c0848d 100644
--- a/src/runtime/parser.c
+++ b/src/runtime/parser.c
@@ -342,6 +342,7 @@ static Reduction ts_parser__reduce(TSParser *self, StackVersion version,
                count, BOOL_STRING(fragile));
   }
 
+  size_t initial_version_count = ts_stack_version_count(self->stack);
   StackPopResult pop = ts_stack_pop_count(self->stack, version, count);
   switch (pop.status) {
     case StackPopFailed:
@@ -414,6 +415,8 @@ static Reduction ts_parser__reduce(TSParser *self, StackVersion version,
     }
   }
 
+  ts_stack_merge_from(self->stack, initial_version_count);
+
   return (Reduction){ ReduceSucceeded, pop.slices.contents[0] };
 
 error:
diff --git a/src/runtime/stack.c b/src/runtime/stack.c
index d780e9e1..56af6de3 100644
--- a/src/runtime/stack.c
+++ b/src/runtime/stack.c
@@ -401,10 +401,10 @@ void ts_stack_renumber_version(Stack *self, StackVersion v1, StackVersion v2) {
   array_erase(&self->heads, v1);
 }
 
-void ts_stack_merge(Stack *self) {
-  for (size_t i = 0; i < self->heads.size; i++) {
+void ts_stack_merge_from(Stack *self, StackVersion start_version) {
+  for (size_t i = start_version + 1; i < self->heads.size; i++) {
     StackNode *node = self->heads.contents[i];
-    for (size_t j = 0; j < i; j++) {
+    for (size_t j = start_version; j < i; j++) {
       StackNode *prior_node = self->heads.contents[j];
       if (prior_node->state == node->state &&
           prior_node->position.chars == node->position.chars) {
@@ -419,6 +419,10 @@ void ts_stack_merge(Stack *self) {
   }
 }
 
+void ts_stack_merge(Stack *self) {
+  ts_stack_merge_from(self, 0);
+}
+
 void ts_stack_clear(Stack *self) {
   stack_node_retain(self->base_node);
   for (size_t i = 0; i < self->heads.size; i++)
diff --git a/src/runtime/stack.h b/src/runtime/stack.h
index bf95cc2d..d5761650 100644
--- a/src/runtime/stack.h
+++ b/src/runtime/stack.h
@@ -94,6 +94,8 @@ StackPopResult ts_stack_pop_pending(Stack *, StackVersion);
 
 StackPopResult ts_stack_pop_all(Stack *, StackVersion);
 
+void ts_stack_merge_from(Stack *, StackVersion);
+
 void ts_stack_merge(Stack *);
 
 void ts_stack_renumber_version(Stack *, StackVersion, StackVersion);