From 4f125a3f19f66cb3739bf93302be92acb33a4d64 Mon Sep 17 00:00:00 2001
From: "Yukihiro \"Matz\" Matsumoto" <matz@ruby.or.jp>
Date: Tue, 11 Apr 2023 14:26:35 +0900
Subject: [PATCH] mruby-struct/struct.c: allow struct size differ from
 `members`

The situation may be caused by `Struct.new(...).alloc` etc.
---
 mrbgems/mruby-struct/src/struct.c | 28 +++++++++++++++++++---------
 1 file changed, 19 insertions(+), 9 deletions(-)

diff --git a/mrbgems/mruby-struct/src/struct.c b/mrbgems/mruby-struct/src/struct.c
index 94b3dd159..43d3890a8 100644
--- a/mrbgems/mruby-struct/src/struct.c
+++ b/mrbgems/mruby-struct/src/struct.c
@@ -58,14 +58,16 @@ struct_s_members(mrb_state *mrb, struct RClass *c)
 static mrb_value
 struct_members(mrb_state *mrb, mrb_value s)
 {
-  if (!mrb_struct_p(s) || RSTRUCT_LEN(s) == 0) {
+  if (!mrb_struct_p(s)) {
     struct_corrupted(mrb);
   }
   mrb_value members = struct_s_members(mrb, mrb_obj_class(mrb, s));
-  if (RSTRUCT_LEN(s) != RARRAY_LEN(members)) {
+  mrb_int len = RSTRUCT_LEN(s);
+  mrb_int mlen = RARRAY_LEN(members);
+  if (len > 0 && len != mlen) {
     mrb_raisef(mrb, E_TYPE_ERROR,
                "struct size differs (%i required %i given)",
-               RARRAY_LEN(members), RSTRUCT_LEN(s));
+               mlen, len);
   }
   return members;
 }
@@ -350,18 +352,20 @@ struct_aref_sym(mrb_state *mrb, mrb_value obj, mrb_sym id)
 {
   mrb_value members, *ptr;
   const mrb_value *ptr_members;
-  mrb_int i, len;
+  mrb_int i, len, plen;
 
   members = struct_members(mrb, obj);
   ptr_members = RARRAY_PTR(members);
   len = RARRAY_LEN(members);
   ptr = RSTRUCT_PTR(obj);
-  for (i=0; i<len; i++) {
+  plen = RARRAY_LEN(obj);
+  for (i=0; i<len && i<plen; i++) {
     mrb_value slot = ptr_members[i];
     if (mrb_symbol_p(slot) && mrb_symbol(slot) == id) {
       return ptr[i];
     }
   }
+  if (i<len) return mrb_nil_value();
   mrb_name_error(mrb, id, "no member '%n' in struct", id);
   return mrb_nil_value();       /* not reached */
 }
@@ -424,18 +428,24 @@ mrb_struct_aref(mrb_state *mrb, mrb_value s)
 static mrb_value
 mrb_struct_aset_sym(mrb_state *mrb, mrb_value s, mrb_sym id, mrb_value val)
 {
-  mrb_value members, *ptr;
+  mrb_value members;
   const mrb_value *ptr_members;
-  mrb_int i, len;
+  mrb_int i, len, plen;
 
   members = struct_members(mrb, s);
   len = RARRAY_LEN(members);
-  ptr = RSTRUCT_PTR(s);
+  plen = RSTRUCT_LEN(s);
   ptr_members = RARRAY_PTR(members);
   for (i=0; i<len; i++) {
     if (mrb_symbol(ptr_members[i]) == id) {
       mrb_struct_modify(mrb, s);
-      ptr[i] = val;
+      if (i < plen) {
+        mrb_value *ptr = RSTRUCT_PTR(s);
+        ptr[i] = val;
+      }
+      else {
+        mrb_ary_set(mrb, s, i, val);
+      }
       mrb_field_write_barrier_value(mrb, mrb_basic_ptr(s), val);
       return val;
     }