block_given? should work; close #262

src/kernel.c

@@ -269,12 +269,6 @@ mrb_f_send(mrb_state *mrb, mrb_value self)
   return mrb_funcall_with_block(mrb,self, mrb_string_value_ptr(mrb, name), argc, argv, block);
 }
 
-static mrb_value
-mrb_f_block_given_p(void)
-{
-  return mrb_false_value(); /* dummy */
-}
-
 /* 15.3.1.2.2  */
 /* 15.3.1.2.5  */
 /* 15.3.1.3.6  */
@@ -302,7 +296,18 @@ mrb_f_block_given_p(void)
 static mrb_value
 mrb_f_block_given_p_m(mrb_state *mrb, mrb_value self)
 {
-  return mrb_f_block_given_p();
+  mrb_callinfo *ci = mrb->ci;
+  mrb_value *bp, *p;
+
+  p = mrb->stbase + ci->stackidx;
+  bp = mrb->stbase + ci->stackidx + 1;
+  ci--;
+  if (ci <= mrb->cibase) return mrb_false_value();
+  if (ci->argc > 0) {
+    bp += ci->argc;
+  }
+  if (mrb_nil_p(*bp)) return mrb_false_value();
+  return mrb_true_value();
 }
 
 /* 15.3.1.3.7  */

test/t/kernel.rb

@@ -6,7 +6,14 @@ assert('Kernel', '15.3.1') do
 end
 
 assert('Kernel.block_given?', '15.3.1.2.2') do
-  Kernel.block_given? == false
+  def bg_try(&b)
+    if block_given?
+      yield
+    else
+      "no block"
+    end
+  end
+  (Kernel.block_given? == false) && (bg_try == "no block") && ((bg_try { "block" }) == "block") && ((bg_try do "block" end) == "block")
 end
 
 assert('Kernel.global_variables', '15.3.1.2.4') do