From 7d85092bc4e1b3d2a204af50906adb144502571f Mon Sep 17 00:00:00 2001
From: dearblue <dearblue@users.osdn.me>
Date: Sun, 13 Mar 2022 15:20:12 +0900
Subject: [PATCH] Reorganize the `struct RException::mesg` member

There is no need to limit the type to `struct RString`.
Also, the `MRB_EXC_MESG_STRING_FLAG` flag can be eliminated by checking if `struct RException::mesg` is `NULL` or not.

ref. #2485
---
 include/mruby/error.h |  3 +--
 src/error.c           | 17 ++++++-----------
 src/gc.c              |  4 ++--
 3 files changed, 9 insertions(+), 15 deletions(-)

diff --git a/include/mruby/error.h b/include/mruby/error.h
index fb3557405..01082f931 100644
--- a/include/mruby/error.h
+++ b/include/mruby/error.h
@@ -17,11 +17,10 @@ MRB_BEGIN_DECL
 struct RException {
   MRB_OBJECT_HEADER;
   struct iv_tbl *iv;
-  struct RString *mesg;
+  struct RObject *mesg;         // NULL or probably RString
 };
 
 #define mrb_exc_ptr(v) ((struct RException*)mrb_ptr(v))
-#define MRB_EXC_MESG_STRING_FLAG 0x100
 
 MRB_API void mrb_sys_fail(mrb_state *mrb, const char *mesg);
 MRB_API mrb_value mrb_exc_new_str(mrb_state *mrb, struct RClass* c, mrb_value str);
diff --git a/src/error.c b/src/error.c
index 46d26bece..1a8f65dbf 100644
--- a/src/error.c
+++ b/src/error.c
@@ -20,26 +20,21 @@
 void
 mrb_exc_mesg_set(mrb_state *mrb, struct RException *exc, mrb_value mesg)
 {
-  if (mrb_string_p(mesg)) {
-    exc->flags |= MRB_EXC_MESG_STRING_FLAG;
-    exc->mesg = RSTRING(mesg);
+  if (!mrb_immediate_p(mesg)) {
+    exc->mesg = mrb_obj_ptr(mesg);
     mrb_field_write_barrier_value(mrb, (struct RBasic*)exc, mesg);
+    mrb_iv_remove(mrb, mrb_obj_value(exc), MRB_SYM(mesg));
   }
   else {
-    exc->flags &= ~MRB_EXC_MESG_STRING_FLAG;
-    if (mrb_nil_p(mesg)) {
-      exc->mesg = 0;
-    }
-    else {
-      mrb_obj_iv_set(mrb, (struct RObject*)exc, MRB_SYM(mesg), mesg);
-    }
+    exc->mesg = NULL;
+    mrb_obj_iv_set(mrb, (struct RObject*)exc, MRB_SYM(mesg), mesg);
   }
 }
 
 mrb_value
 mrb_exc_mesg_get(mrb_state *mrb, struct RException *exc)
 {
-  if ((exc->flags & MRB_EXC_MESG_STRING_FLAG) != 0) {
+  if (exc->mesg) {
     return mrb_obj_value(exc->mesg);
   }
   else {
diff --git a/src/gc.c b/src/gc.c
index a6ff0c588..1a139fcf9 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -760,7 +760,7 @@ gc_mark_children(mrb_state *mrb, mrb_gc *gc, struct RBasic *obj)
 
   case MRB_TT_EXCEPTION:
     mrb_gc_mark_iv(mrb, (struct RObject*)obj);
-    if ((obj->flags & MRB_EXC_MESG_STRING_FLAG) != 0) {
+    if (((struct RException*)obj)->mesg) {
       mrb_gc_mark(mrb, (struct RBasic*)((struct RException*)obj)->mesg);
     }
     break;
@@ -1049,7 +1049,7 @@ gc_gray_counts(mrb_state *mrb, mrb_gc *gc, struct RBasic *obj)
 
   case MRB_TT_EXCEPTION:
     children += mrb_gc_mark_iv_size(mrb, (struct RObject*)obj);
-    if ((obj->flags & MRB_EXC_MESG_STRING_FLAG) != 0) {
+    if (((struct RException*)obj)->mesg) {
       children++;
     }
     break;