Parser: Fix crash on stack overflow when lazy-parsing arrow functions

src/parser.cc

Index: src/parser.cc
diff --git a/src/parser.cc b/src/parser.cc
index 4bcdfdbda7e2233fd25a710caea8f23d9d6d0510..1e5356fc6800ea678c034ef89a49e75564a4bd41 100644
--- a/src/parser.cc
+++ b/src/parser.cc
@@ -1145,8 +1145,20 @@ FunctionLiteral* Parser::ParseLazy(Isolate* isolate, ParseInfo* info,
       // from creating unresolved variables in already-resolved scopes.
       parsing_lazy_arrow_parameters_ = true;
       Expression* expression = ParseExpression(false, &ok);
-      DCHECK(expression->IsFunctionLiteral());
-      result = expression->AsFunctionLiteral();
+      if (ok) {
+        // Scanning must end at the same position that was recorded
+        // previously. If not, parsing has been interrupted due to a
+        // stack overflow, at which point the partially parsed arrow
+        // function concise body happens to be a valid expression.
+        if (scanner()->location().end_pos == shared_info->end_position()) {
+          // The input is known to be a function that is being lazy-parsed.

[wingo, 2015/03/19 13:21:40]

lazy-parsed is not great terminology IMO.  How about

// The pre-parser saw an arrow function here, so the full parser must produce a
FunctionLiteral.

[aperez, 2015/03/19 23:57:39]

Acknowledged.

+          DCHECK(expression->IsFunctionLiteral());
+          result = expression->AsFunctionLiteral();
+        } else {
+          result = NULL;
+          ok = false;
+        }
+      }
     } else if (shared_info->is_default_constructor()) {
       result = DefaultConstructor(IsSubclassConstructor(shared_info->kind()),
                                   scope, shared_info->start_position(),