Add configurable stack overflow to prevent infinite recursion

without waiting for out of memory.

lib/pp.dst

@@ -1,3 +1,4 @@
+(def a (fn [] 2))
 #
 # Copyright (c) 2017 Calvin Rose
 #

src/compiler/boot.dst

@@ -75,9 +75,11 @@
   (def end (get head 2))
   (def _inc (get head 3))
   (def inc (if _inc _inc 1))
+  (def endsym (gensym))
   (tuple 'do
     (tuple 'var sym start)
-    (tuple 'while (tuple '< sym end)
+    (tuple 'def endsym end)
+    (tuple 'while (tuple '< sym endsym)
      (tuple-prepend body 'do)
      (tuple 'varset! sym (tuple '+ sym 1))
       )))
@@ -136,7 +138,7 @@
  (fiber (fn [parent]
     (var up parent)
     (def me (fiber-current))
-    (def p (parser)) 
+    (def p (parser 1)) 
     (while true
       (def s (parser-status p)) 
       (if (= s :full)

src/core/vm.c

@@ -541,6 +541,11 @@ static void *op_lookup[255] = {
     VM_OP(DOP_CALL)
     {
         Dst callee = stack[oparg(2, 0xFFFF)];
+#ifdef DST_STACK_MAX
+        if (dst_vm_fiber->stacktop > DST_STACK_MAX) {
+            vm_throw("stack overflow");
+        }
+#endif
         if (dst_checktype(callee, DST_FUNCTION)) {
             func = dst_unwrap_function(callee);
             dst_stack_frame(stack)->pc = pc;

src/include/dst/dstconfig.h

@@ -120,6 +120,11 @@ extern "C" {
  * ands crashing (the parser). Instead, error out. */
 #define DST_RECURSION_GUARD 1024
 
+/* Define max stack size for stacks before raising a stack overflow error.
+ * If this is not defined, fiber stacks can grow without limit (until memory
+ * runs out) */
+#define DST_STACK_MAX 4096
+
 /* Use nanboxed values - uses 8 bytes per value instead of 12 or 16. */
 #define DST_NANBOX
 #define DST_NANBOX_47

src/parser/parse.c

@@ -458,12 +458,12 @@ static int root(DstParser *p, DstParseState *state, uint8_t c) {
 int dst_parser_consume(DstParser *parser, uint8_t c) {
     int consumed = 0;
     if (parser->error) return 0;
+    parser->index++;
     while (!consumed && !parser->error) {
         DstParseState *state = &dst_v_last(parser->states);
         consumed = state->consumer(parser, state, c);
     }
     parser->lookback = c;
-    parser->index++;
     return 1;
 }