From 6a8addb84f4dd2745e1d1298e66ce1255cd231a3 Mon Sep 17 00:00:00 2001
From: Max Brunsfeld <maxbrunsfeld@gmail.com>
Date: Wed, 23 Jul 2014 18:26:10 -0700
Subject: [PATCH] Fix segfault when grammar consists of a single token

---
 spec/compiler/compile_spec.cc                 | 22 +++++++++++++++++++
 .../build_tables/build_parse_table.cc         |  5 ++++-
 2 files changed, 26 insertions(+), 1 deletion(-)
 create mode 100644 spec/compiler/compile_spec.cc

diff --git a/spec/compiler/compile_spec.cc b/spec/compiler/compile_spec.cc
new file mode 100644
index 00000000..772ce006
--- /dev/null
+++ b/spec/compiler/compile_spec.cc
@@ -0,0 +1,22 @@
+#include "compiler/compiler_spec_helper.h"
+#include "tree_sitter/compiler.h"
+
+using namespace rules;
+
+START_TEST
+
+describe("Compile", []() {
+  describe("when the grammar's start symbol is a token", [&]() {
+    it("does not fail", [&]() {
+      Grammar grammar({
+        { "rule1", str("the-value") }
+      });
+
+      auto result = compile(grammar, "test_grammar");
+      const GrammarError *error = get<2>(result);
+      AssertThat(error, Equals<const GrammarError *>(nullptr));
+    });
+  });
+});
+
+END_TEST
diff --git a/src/compiler/build_tables/build_parse_table.cc b/src/compiler/build_tables/build_parse_table.cc
index 6f1cb4de..b11b0967 100644
--- a/src/compiler/build_tables/build_parse_table.cc
+++ b/src/compiler/build_tables/build_parse_table.cc
@@ -135,7 +135,10 @@ class ParseTableBuilder {
         conflict_manager(ParseConflictManager(grammar, lex_grammar)) {}
 
   pair<ParseTable, vector<Conflict> > build() {
-    ParseItem start_item(rules::START(), make_shared<Symbol>(0), 0);
+    auto start_symbol = grammar.rules.empty() ?
+        make_shared<Symbol>(0, rules::SymbolOptionToken) :
+        make_shared<Symbol>(0);
+    ParseItem start_item(rules::START(), start_symbol, 0);
     add_parse_state(
         item_set_closure(start_item, { rules::END_OF_INPUT() }, grammar));