From 14bae584d4ff91acecbb0467bd6279e2f02407c3 Mon Sep 17 00:00:00 2001
From: Timothy Clem <timothy.clem@gmail.com>
Date: Tue, 18 Oct 2016 13:03:41 -0700
Subject: [PATCH] WIP: New check for mergable symbols in merge_state

---
 src/compiler/build_tables/build_parse_table.cc | 6 +++++-
 src/compiler/parse_table.cc                    | 4 ++++
 src/compiler/parse_table.h                     | 2 ++
 3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/compiler/build_tables/build_parse_table.cc b/src/compiler/build_tables/build_parse_table.cc
index 93820424..387a1baa 100644
--- a/src/compiler/build_tables/build_parse_table.cc
+++ b/src/compiler/build_tables/build_parse_table.cc
@@ -112,7 +112,11 @@ class ParseTableBuilder {
   void build_error_parse_state() {
     ParseState error_state;
 
-    for (const Symbol &symbol : recovery_tokens(lexical_grammar))
+    auto recovery_symbols = recovery_tokens(lexical_grammar);
+
+    parse_table.mergeable_symbols.insert(recovery_symbols.begin(), recovery_symbols.end());
+
+    for (const Symbol &symbol : recovery_symbols)
       add_out_of_context_parse_state(&error_state, symbol);
 
     for (const Symbol &symbol : grammar.extra_tokens)
diff --git a/src/compiler/parse_table.cc b/src/compiler/parse_table.cc
index d345f0e4..b63d472b 100644
--- a/src/compiler/parse_table.cc
+++ b/src/compiler/parse_table.cc
@@ -206,6 +206,8 @@ bool ParseTable::merge_state(size_t i, size_t j) {
 
     const auto &other_entry = other.entries.find(symbol);
     if (other_entry == other.entries.end()) {
+      if (mergeable_symbols.count(symbol) == 0)
+        return false;
       if (actions.back().type != ParseActionTypeReduce)
         return false;
       if (!has_entry(other, entry.second))
@@ -222,6 +224,8 @@ bool ParseTable::merge_state(size_t i, size_t j) {
     const vector<ParseAction> &actions = entry.second.actions;
 
     if (!state.entries.count(symbol)) {
+      if (mergeable_symbols.count(symbol) == 0)
+        return false;
       if (actions.back().type != ParseActionTypeReduce)
         return false;
       if (!has_entry(state, entry.second))
diff --git a/src/compiler/parse_table.h b/src/compiler/parse_table.h
index 1a00b273..cd24d32a 100644
--- a/src/compiler/parse_table.h
+++ b/src/compiler/parse_table.h
@@ -97,6 +97,8 @@ class ParseTable {
 
   std::vector<ParseState> states;
   std::map<rules::Symbol, ParseTableSymbolMetadata> symbols;
+
+  std::set<rules::Symbol> mergeable_symbols;
 };
 
 }  // namespace tree_sitter