warn() misunderstands UTF8-encoded scalar

# New Ticket Created by  Zefram 
# Please include the string:  [perl #45549]
# in the subject line of all future correspondence about
this issue. 
# <URL: h
ttp://rt.perl.org/rt3/Ticket/Display.html?id=45549 >


This is a bug report for perl from zeframfysh.org,
generated with the help of perlbug 1.35 running under perl
v5.8.8.


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[Please enter your report here]

$ perl -we '$a="xeen"; print STDERR $a; warn $a;
utf8::upgrade($a); print STDERR $a; warn $a'

I won't attempt to reproduce the output directly here,
because it
involves non-ASCII characters, and it is the fate of such
characters
that they always get mangled on the net.  However, here's
what you get
if the output (on stderr) is piped through `od -tx1`:

0000000 ee 0a ee 0a ee 0a c3 ae 0a
0000011

So: print() always outputs the character/byte values that
are *logically*
in the string (that is, 0xee and 0x0a), but warn() always
outputs the
byte values that are *physically* used to represent the
string internally.
I believe warn()'s behaviour is a bug: the visible behaviour
of a string
should not depend on its internal representation.

Emitting the byte values 0xc3 0xae 0x0a for $a is, of
course, appropriate
in some circumstances: namely, when the output stream
involves an encoding
layer to represent characters as bytes using the UTF-8
encoding.  But in
this case I have not set up such a layer, and if I did then
I should get
the UTF-8 output from all four output commands.  The results
should be
consistent either way.

[Please do not change anything below this line]
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---
Flags:
    category=core
    severity=low
---
Site configuration information for perl v5.8.8:

Configured by Debian Project at Wed Dec  6 23:17:41 UTC
2006.

Summary of my perl5 (revision 5 version 8 subversion 8)
configuration:
  Platform:
    osname=linux, osvers=2.6.18.3,
archname=i486-linux-gnu-thread-multi
    uname='linux saens 2.6.18.3 #1 smp sat nov 25 13:39:52
est 2006 i686 gnulinux '
    config_args='-Dusethreads -Duselargefiles
-Dccflags=-DDEBIAN -Dcccdlflags=-fPIC
-Darchname=i486-linux-gnu -Dprefix=/usr
-Dprivlib=/usr/share/perl/5.8 -Darchlib=/usr/lib/perl/5.8
-Dvendorprefix=/usr -Dvendorlib=/usr/share/perl5
-Dvendorarch=/usr/lib/perl5 -Dsiteprefix=/usr/local
-Dsitelib=/usr/local/share/perl/5.8.8
-Dsitearch=/usr/local/lib/perl/5.8.8
-Dman1dir=/usr/share/man/man1 -Dman3dir=/usr/share/man/man3
-Dsiteman1dir=/usr/local/man/man1
-Dsiteman3dir=/usr/local/man/man3 -Dman1ext=1
-Dman3ext=3perl -Dpager=/usr/bin/sensible-pager -Uafs
-Ud_csh -Uusesfio -Uusenm -Duseshrplib
-Dlibperl=libperl.so.5.8.8 -Dd_dosuid -des'
    hint=recommended, useposix=true, d_sigaction=define
    usethreads=define use5005threads=undef
useithreads=define usemultiplicity=define
    useperlio=define d_sfio=undef uselargefiles=define
usesocks=undef
    use64bitint=undef use64bitall=undef uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE
-DTHREADS_HAVE_PIDS -DDEBIAN -fno-strict-aliasing -pipe
-I/usr/local/include -D_LARGEFILE_SOURCE
-D_FILE_OFFSET_BITS=64',
    optimize='-O2',
    cppflags='-D_REENTRANT -D_GNU_SOURCE -DTHREADS_HAVE_PIDS
-DDEBIAN -fno-strict-aliasing -pipe -I/usr/local/include'
    ccversion='', gccversion='4.1.2 20061115 (prerelease)
(Debian 4.1.1-20)', gccosandvers=''
    intsize=4, longsize=4, ptrsize=4, doublesize=8,
byteorder=1234
    d_longlong=define, longlongsize=8, d_longdbl=define,
longdblsize=12
    ivtype='long', ivsize=4, nvtype='double', nvsize=8,
Off_t='off_t', lseeksize=8
    alignbytes=4, prototype=define
  Linker and Libraries:
    ld='cc', ldflags =' -L/usr/local/lib'
    libpth=/usr/local/lib /lib /usr/lib
    libs=-lgdbm -lgdbm_compat -ldb -ldl -lm -lpthread -lc
-lcrypt
    perllibs=-ldl -lm -lpthread -lc -lcrypt
    libc=/lib/libc-2.3.6.so, so=so, useshrplib=true,
libperl=libperl.so.5.8.8
    gnulibc_version='2.3.6'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef,
ccdlflags='-Wl,-E'
    cccdlflags='-fPIC', lddlflags='-shared
-L/usr/local/lib'

Locally applied patches:
    

---
INC
for perl v5.8.8:
    /etc/perl
    /usr/local/lib/perl/5.8.8
    /usr/local/share/perl/5.8.8
    /usr/lib/perl5
    /usr/share/perl5
    /usr/lib/perl/5.8
    /usr/share/perl/5.8
    /usr/local/lib/site_perl
    /usr/local/lib/perl/5.8.4
    /usr/local/share/perl/5.8.4
    .

---
Environment for perl v5.8.8:
    HOME=/home/zefram
    LANG (unset)
    LANGUAGE (unset)
    LC_CTYPE=en_GB
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
   
PATH=/home/zefram/pub/i686-pc-linux-gnu/bin:/home/zefram/pub
/common/bin:/usr/bin:/usr/X11R6/bin:/bin:/usr/local/bin:/usr
/games
    PERL_BADLANG (unset)
    SHELL=/usr/bin/zsh