jq_next: simplify CALL_BUILTIN implementation

Author: emanuele6

src/execute.c

@@ -341,8 +341,6 @@ static void set_error(jq_state *jq, jv value) {
 #define ON_BACKTRACK(op) ((op)+NUM_OPCODES)
 
 jv jq_next(jq_state *jq) {
-  jv cfunc_input[MAX_CFUNCTION_ARGS];
-
   jv_nomem_handler(jq->nomem_handler, jq->nomem_handler_data);
 
   uint16_t* pc = stack_restore(jq);
@@ -909,33 +907,27 @@ jv jq_next(jq_state *jq) {
 
     case CALL_BUILTIN: {
       int nargs = *pc++;
-      jv top = stack_pop(jq);
-      jv* in = cfunc_input;
-      in[0] = top;
-      for (int i = 1; i < nargs; i++) {
-        in[i] = stack_pop(jq);
-      }
       struct cfunction* function = &frame_current(jq)->bc->globals->cfunctions[*pc++];
+      jv in[MAX_CFUNCTION_ARGS];
+      for (int i = 0; i < nargs; ++i)
+        in[i] = stack_pop(jq);
+
+      jv top;
       switch (function->nargs) {
       case 1: top = function->fptr.a1(jq, in[0]); break;
       case 2: top = function->fptr.a2(jq, in[0], in[1]); break;
       case 3: top = function->fptr.a3(jq, in[0], in[1], in[2]); break;
       case 4: top = function->fptr.a4(jq, in[0], in[1], in[2], in[3]); break;
-      // FIXME: a) up to 7 arguments (input + 6), b) should assert
-      // because the compiler should not generate this error.
-      default: return jv_invalid_with_msg(jv_string("Function takes too many arguments"))
+      default: assert(0 && "Invalid number of arguments");
       }
 
-      if (jv_is_valid(top)) {
-        stack_push(jq, top);
-      } else if (jv_invalid_has_msg(jv_copy(top))) {
-        set_error(jq, top);
-        goto do_backtrack;
-      } else {
-        // C-coded function returns invalid w/o msg? -> backtrack, as if
-        // it had returned `empty`
+      if (!jv_is_valid(top)) {
+        if (jv_invalid_has_msg(jv_copy(top)))
+          set_error(jq, top);
         goto do_backtrack;
       }
+
+      stack_push(jq, top);
       break;
     }