From dcc75348c720acd6c2a0587bca34f7851e6c1283 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Sun, 6 Sep 2015 22:50:52 -0700
Subject: Reset flex scanner if exception thrown during read.

We must tear down and rebuild the Flex scanner, otherwise
it is left in a bad state causing it to abort.

* parser.c (parser_cleanup): After destroying scanner,
null out the pointer.
(parser_reset): Destroy the Flex scanner, and
instantiate a new one in its place.
(lisp_parse): Set up an unwind catch which will
reset the parser if it was aborted by an exception.

* parser.h (parser_reset): Declared.
---
 parser.c | 23 ++++++++++++++++++++++-
 parser.h |  1 +
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/parser.c b/parser.c
index 035291f6..37255ae0 100644
--- a/parser.c
+++ b/parser.c
@@ -120,6 +120,16 @@ void parser_cleanup(parser_t *p)
 {
   if (p->scanner != 0)
     yylex_destroy(p->scanner);
+  p->scanner = 0;
+}
+
+void parser_reset(parser_t *p)
+{
+  yyscan_t yyscan;
+  parser_cleanup(p);
+  yylex_init(&yyscan);
+  p->scanner = convert(scanner_t *, yyscan);
+  yyset_extra(p, p->scanner);
 }
 
 val parser(val stream, val lineno)
@@ -279,6 +289,9 @@ val lisp_parse(val source_in, val error_stream, val error_return_val,
   val parser = ensure_parser(input_stream);
   val saved_dyn = dyn_env;
   parser_t *pi = get_parser_impl(parser);
+  volatile val parsed = nil;
+
+  uw_simple_catch_begin;
 
   dyn_env = make_env(nil, nil, dyn_env);
 
@@ -295,9 +308,17 @@ val lisp_parse(val source_in, val error_stream, val error_return_val,
     int gc = gc_state(0);
     parse(pi, if3(std_error != std_null, name, lit("")), prime_lisp);
     gc_state(gc);
+    parsed = t;
+  }
+
+  uw_unwind {
+    dyn_env = saved_dyn;
+    if (!parsed) {
+      parser_reset(pi);
+    }
   }
 
-  dyn_env = saved_dyn;
+  uw_catch_end;
 
   if (pi->errors || pi->syntax_tree == nao) {
     if (missingp(error_return_val))
diff --git a/parser.h b/parser.h
index bc6a3364..efbaa351 100644
--- a/parser.h
+++ b/parser.h
@@ -86,6 +86,7 @@ int parse(parser_t *parser, val name, enum prime_parser);
 val source_loc(val form);
 val source_loc_str(val form, val alt);
 val rlset(val form, val info);
+void parser_reset(parser_t *);
 INLINE val rlcp(val to, val from)
 {
   return rlset(to, source_loc(from));
-- 
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