Add highlight.janet tool which can highlight

janet source code and output html or terminal escaped code.
Also made re entrant calls into the vm provide better
error messages.

src/core/core.janet

@@ -92,7 +92,7 @@
 (defn function? "Check if x is a function (not a cfunction)." [x]
   (= (type x) :function))
 (defn cfunction? "Check if x a cfunction." [x] (= (type x) :cfunction))
-(defn table? "Check if x a table." [x] (= (type x) :table ))
+(defn table? "Check if x a table." [x] (= (type x) :table))
 (defn struct? "Check if x a struct." [x] (= (type x) :struct))
 (defn array? "Check if x is an array." [x] (= (type x) :array))
 (defn tuple? "Check if x is a tuple." [x] (= (type x) :tuple))

src/core/peg.c

@@ -53,6 +53,7 @@ typedef enum {
     RULE_REPLACE,      /* [rule, constant, tag] */
     RULE_MATCHTIME,    /* [rule, constant, tag] */
     RULE_ERROR,        /* [rule] */
+    RULE_DROP,         /* [rule] */
 } Opcode;
 
 /* Hold captured patterns and match state */
@@ -350,6 +351,17 @@ tail:
                 return result;
             }
 
+        case RULE_DROP:
+            {
+                CapState cs = cap_save(s);
+                down1(s);
+                const uint8_t *result = peg_rule(s, s->bytecode + rule[1], text);
+                up1(s);
+                if (!result) return NULL;
+                cap_load(s, cs);
+                return result;
+            }
+
         case RULE_GROUP:
             {
                 uint32_t tag = rule[2];
@@ -750,6 +762,9 @@ static void spec_not(Builder *b, int32_t argc, const Janet *argv) {
 static void spec_error(Builder *b, int32_t argc, const Janet *argv) {
     spec_onerule(b, argc, argv, RULE_ERROR);
 }
+static void spec_drop(Builder *b, int32_t argc, const Janet *argv) {
+    spec_onerule(b, argc, argv, RULE_DROP);
+}
 
 /* Rule of the form [rule, tag] */
 static void spec_cap1(Builder *b, int32_t argc, const Janet *argv, uint32_t op) {
@@ -854,6 +869,7 @@ static const SpecialPair specials[] = {
     {"choice", spec_choice},
     {"cmt", spec_matchtime},
     {"constant", spec_constant},
+    {"drop", spec_drop},
     {"error", spec_error},
     {"group", spec_group},
     {"if", spec_if},

src/core/vm.c

@@ -758,18 +758,30 @@ Janet janet_call(JanetFunction *fun, int32_t argc, const Janet *argv) {
     JanetFiber *fiber = janet_fiber(fun, 64, argc, argv);
     if (!fiber)
         janet_panic("arity mismatch");
+    JanetFiber *old_fiber = janet_vm_fiber;
+    janet_vm_fiber = fiber;
+    janet_gcroot(janet_wrap_fiber(fiber));
+    int32_t oldn = janet_vm_stackn++;
     int handle = janet_gclock();
 
-    JanetFiber *old_fiber = janet_vm_fiber;
-    old_fiber->child = fiber;
-    janet_vm_fiber = fiber;
-    memcpy(fiber->buf, janet_vm_fiber->buf,  sizeof(jmp_buf));
-    run_vm(fiber, janet_wrap_nil(), JANET_STATUS_NEW);
-    old_fiber->child = NULL;
-    janet_vm_fiber = old_fiber;
+    JanetSignal signal;
+    if (setjmp(fiber->buf)) {
+        signal = JANET_SIGNAL_ERROR;
+    } else {
+        signal = run_vm(fiber, janet_wrap_nil(), JANET_STATUS_NEW);
+    }
 
+    janet_vm_stackn = oldn;
+    janet_vm_fiber = old_fiber;
+    Janet ret = fiber->data[fiber->stacktop - 1];
+    janet_gcunroot(janet_wrap_fiber(fiber));
     janet_gcunlock(handle);
-    return fiber->data[fiber->stacktop - 1];
+    if (signal == JANET_SIGNAL_ERROR) {
+        old_fiber->child = fiber;
+        janet_fiber_set_status(fiber, signal);
+        janet_panicv(ret);
+    }
+    return ret;
 }
 
 /* Enter the main vm loop */