From c3e4ee0bf292d9e48eaa5646410b1d424efc557b Mon Sep 17 00:00:00 2001
From: "Yukihiro \"Matz\" Matsumoto" <matz@ruby.or.jp>
Date: Fri, 6 May 2022 16:21:39 +0900
Subject: [PATCH] error.c: store error message converted as a string.

This is controversial since this change alters the `raise` behavior.
Previously, when an object that cannot be converted to a string, it just
ignore message when it's printed (using `Exception#inspect`). But after
this change, `raise` (more precisly `Exception.new`) raises TypeError
exception. I think the new behavior is clearer, more intuitive.
---
 src/error.c | 20 ++++++--------------
 1 file changed, 6 insertions(+), 14 deletions(-)

diff --git a/src/error.c b/src/error.c
index 916109cb1..0fb951390 100644
--- a/src/error.c
+++ b/src/error.c
@@ -21,26 +21,18 @@
 void
 mrb_exc_mesg_set(mrb_state *mrb, struct RException *exc, mrb_value 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->mesg = NULL;
-    mrb_obj_iv_set(mrb, (struct RObject*)exc, MRB_SYM(mesg), mesg);
+  if (!mrb_string_p(mesg)) {
+    mesg = mrb_obj_as_string(mrb, mesg);
   }
+  exc->mesg = mrb_obj_ptr(mesg);
+  mrb_field_write_barrier_value(mrb, (struct RBasic*)exc, mesg);
 }
 
 mrb_value
 mrb_exc_mesg_get(mrb_state *mrb, struct RException *exc)
 {
-  if (exc->mesg) {
-    return mrb_obj_value(exc->mesg);
-  }
-  else {
-    return mrb_obj_iv_get(mrb, (struct RObject*)exc, MRB_SYM(mesg));
-  }
+  if (exc->mesg == NULL) return mrb_nil_value();
+  return mrb_obj_value(exc->mesg);
 }
 
 MRB_API mrb_value