merge revision(s) 99d8c4832a7133ca52578d015e3ddcfd94820f4a: [Backport #18160]

	Preserve the encoding of the argument in IndexError [Bug #18160]

	---
	 re.c                     | 20 ++++++++++----------
	 test/ruby/test_regexp.rb |  7 ++++++-
	 2 files changed, 16 insertions(+), 11 deletions(-)

1 files changed, 10 insertions, 10 deletions

diff --git a/re.c b/re.c
index 9e9df700cf..718a66b031 100644
--- a/re.c
+++ b/re.c
@@ -1141,6 +1141,14 @@ match_size(VALUE match)
 }
 
 static int name_to_backref_number(struct re_registers *, VALUE, const char*, const char*);
+NORETURN(static void name_to_backref_error(VALUE name));
+
+static void
+name_to_backref_error(VALUE name)
+{
+    rb_raise(rb_eIndexError, "undefined group name reference: % "PRIsVALUE,
+	     name);
+}
 
 static int
 match_backref_number(VALUE match, VALUE backref)
@@ -1160,10 +1168,10 @@ match_backref_number(VALUE match, VALUE backref)
     }
     name = StringValueCStr(backref);
 
-    num = name_to_backref_number(regs, regexp, name, name + strlen(name));
+    num = name_to_backref_number(regs, regexp, name, name + RSTRING_LEN(backref));
 
     if (num < 1) {
-        rb_raise(rb_eIndexError, "undefined group name reference: %s", name);
+        name_to_backref_error(backref);
     }
 
     return num;
@@ -1910,14 +1918,6 @@ name_to_backref_number(struct re_registers *regs, VALUE regexp, const char* name
 	(const unsigned char *)name, (const unsigned char *)name_end, regs);
 }
 
-NORETURN(static void name_to_backref_error(VALUE name));
-static void
-name_to_backref_error(VALUE name)
-{
-    rb_raise(rb_eIndexError, "undefined group name reference: % "PRIsVALUE,
-	     name);
-}
-
 #define NAME_TO_NUMBER(regs, re, name, name_ptr, name_end)	\
     (NIL_P(re) ? 0 : \
      !rb_enc_compatible(RREGEXP_SRC(re), (name)) ? 0 : \