From 2db7945d6f6672648f56dfad1b5cab990c3aa562 Mon Sep 17 00:00:00 2001
From: Calvin Rose <calsrose@gmail.com>
Date: Thu, 20 May 2021 21:57:22 -0500
Subject: [PATCH] Fix peg bug when there is no default grammar set.

This could result in a segfault when we attempt to
read from a NULL pointer.
---
 src/core/peg.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/core/peg.c b/src/core/peg.c
index 49b8088e..eb2a2265 100644
--- a/src/core/peg.c
+++ b/src/core/peg.c
@@ -1148,7 +1148,9 @@ static uint32_t peg_compile1(Builder *b, Janet peg) {
     for (; i > 0 && janet_checktype(peg, JANET_KEYWORD); --i) {
         Janet nextPeg = janet_table_get_ex(grammar, peg, &grammar);
         if (!grammar || janet_checktype(nextPeg, JANET_NIL)) {
-            nextPeg = janet_table_get(b->default_grammar, peg);
+            nextPeg = (b->default_grammar == NULL)
+                ? janet_wrap_nil()
+                : janet_table_get(b->default_grammar, peg);
             if (janet_checktype(nextPeg, JANET_NIL)) {
                 peg_panic(b, "unknown rule");
             }