Do not use mrb_funcall() if Hash#default is not overridden; ref #3421

This change reduces the recursion level, but does not solve the stack
overflow issue entirely.

include/mruby.h

@@ -1147,6 +1147,7 @@ MRB_API mrb_value mrb_attr_get(mrb_state *mrb, mrb_value obj, mrb_sym id);
 
 MRB_API mrb_bool mrb_respond_to(mrb_state *mrb, mrb_value obj, mrb_sym mid);
 MRB_API mrb_bool mrb_obj_is_instance_of(mrb_state *mrb, mrb_value obj, struct RClass* c);
+MRB_API mrb_bool mrb_func_basic_p(mrb_state *mrb, mrb_value obj, mrb_sym mid, mrb_func_t func);
 
 
 /*

src/hash.c

@@ -159,6 +159,9 @@ mrb_hash_new(mrb_state *mrb)
   return mrb_hash_new_capa(mrb, 0);
 }
 
+static mrb_value mrb_hash_default(mrb_state *mrb, mrb_value hash);
+static mrb_value hash_default(mrb_state *mrb, mrb_value hash, mrb_value key);
+
 MRB_API mrb_value
 mrb_hash_get(mrb_state *mrb, mrb_value hash, mrb_value key)
 {
@@ -171,7 +174,9 @@ mrb_hash_get(mrb_state *mrb, mrb_value hash, mrb_value key)
       return kh_value(h, k).v;
   }
 
-  /* not found */
+  if (mrb_func_basic_p(mrb, hash, mrb_intern_lit(mrb, "default"), mrb_hash_default)) {
+    return hash_default(mrb, hash, key);
+  }
   /* xxx mrb_funcall_tailcall(mrb, hash, "default", 1, key); */
   return mrb_funcall(mrb, hash, "default", 1, key);
 }
@@ -366,6 +371,20 @@ mrb_hash_aget(mrb_state *mrb, mrb_value self)
   return mrb_hash_get(mrb, self, key);
 }
 
+static mrb_value
+hash_default(mrb_state *mrb, mrb_value hash, mrb_value key)
+{
+  if (MRB_RHASH_DEFAULT_P(hash)) {
+    if (MRB_RHASH_PROCDEFAULT_P(hash)) {
+      return mrb_funcall(mrb, RHASH_PROCDEFAULT(hash), "call", 2, hash, key);
+    }
+    else {
+      return RHASH_IFNONE(hash);
+    }
+  }
+  return mrb_nil_value();
+}
+
 /* 15.2.13.4.5  */
 /*
  *  call-seq:

src/kernel.c

@@ -28,15 +28,21 @@ typedef enum {
   NOEX_RESPONDS  = 0x80
 } mrb_method_flag_t;
 
-static mrb_bool
-mrb_obj_basic_to_s_p(mrb_state *mrb, mrb_value obj)
+MRB_API mrb_bool
+mrb_func_basic_p(mrb_state *mrb, mrb_value obj, mrb_sym mid, mrb_func_t func)
 {
-  struct RProc *me = mrb_method_search(mrb, mrb_class(mrb, obj), mrb_intern_lit(mrb, "to_s"));
-  if (MRB_PROC_CFUNC_P(me) && (me->body.func == mrb_any_to_s))
+  struct RProc *me = mrb_method_search(mrb, mrb_class(mrb, obj), mid);
+  if (MRB_PROC_CFUNC_P(me) && (me->body.func == func))
     return TRUE;
   return FALSE;
 }
 
+static mrb_bool
+mrb_obj_basic_to_s_p(mrb_state *mrb, mrb_value obj)
+{
+  return mrb_func_basic_p(mrb, obj, mrb_intern_lit(mrb, "to_s"), mrb_any_to_s);
+}
+
 /* 15.3.1.3.17 */
 /*
  *  call-seq: