[perl #130668] poor argument parsing in pragma 'use open'

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This is a bug report for perl from sur98ke@gmail.com,
generated with the help of perlbug 1.40 running under perl 5.22.3.

?Today I tried to work with UCS-2-LE-BOM encoded data using ARGV and 
STDOUT filehandles.

To do so I had to use 	binmode (STDOUT, ...)
for STDOUT and 	use open 'IN', ...
for ARGV.

What I found out is that format of argument for "use open" pragma is 
much more strict than format for open and binmode subroutines. i.e.:

binmode(STDOUT, "raw pop encoding(ucs-2le) crlf utf8"); # works well
binmode(STDOUT, " raw pop encoding(ucs-2le) crlf utf8"); # works well
binmode(STDOUT, ":raw:pop:encoding(ucs-2le):crlf:utf8"); # works well

open (F, '<encoding(ucs-2le) crlf utf8', 'vlc-assoc.reg'); # works well
open (F, '< encoding(ucs-2le) crlf utf8', 'vlc-assoc.reg'); # works well
open (F, '<:encoding(ucs-2le):crlf:utf8', 'vlc-assoc.reg'); # works well

use open ('IN' , 'encoding(ucs-2le) crlf utf8'); # works well
use open ('IN' , ' encoding(ucs-2le) crlf utf8'); # Unknown PerlIO layer 
'' at myscript.pl line ...
use open ('IN' , ':encoding(ucs-2le):crlf:utf8'); # Unknown PerlIO layer 
'encoding(ucs-2le):crlf:utf8' at myscript.pl line ...

And this difference in interpreting arguments IS NOT mentioned at
http://perldoc.perl.org/open.html
http://perldoc.perl.org/functions/binmode.html
http://perldoc.perl.org/functions/open.html
http://perldoc.perl.org/PerlIO.html

I couldn't even find the example of proper "use open" usage over 
internet. I had to look into the file "open.pm" to find the line number 73:

https://perl5.git.perl.org/perl.git/blob/HEAD:/lib/open.pm#l73
foreach my $layer (split(/\s+/,$dscp)) {

which splits the argument by spaces.
In both of distributions on my machine files:
<install path>\Strawberry\perl\lib\open.pm
<install path>\cygwin64\lib\perl5\5.22\open.pm
are equal to
https://perl5.git.perl.org/perl.git/blob_plain/HEAD:/lib/open.pm
on 29 Jan 2017.

Could you please fix this in such a way that examples:
use open ('IN' , ' encoding(ucs-2le) crlf utf8');
use open ('IN' , ':encoding(ucs-2le):crlf:utf8');
would work well.

Or, at least add explanation of this limitation to perldoc:
http://perldoc.perl.org/open.html

Thank you.

Best regards,
Artur Mansurov.

---
Flags:
     category=library
     severity=low
     module=open
---
Site configuration information for perl 5.22.3:

Configured by ASSI at Sun Jan 15 13:05:43 CET 2017.

Summary of my perl5 (revision 5 version 22 subversion 3) configuration:
      Platform:
     osname=cygwin, osvers=2.6.1(0.30553), archname=cygwin-thread-multi
     uname='cygwin_nt-6.3 cygwin 2.6.1(0.30553) 2016-12-16 11:55 x86_64 
cygwin '
     config_args='-des -Dprefix=/usr -Dmksymlinks 
-Darchname=x86_64-cygwin-threads -Dlibperl=cygperl5_22.dll -Dcc=gcc 
-Dld=g++ -Accflags=-ggdb -O2 -pipe -Wimplicit-function-declaration 
-fdebug-prefix-map=/mnt/share/maint/perl.x86_64/build=/usr/src/debug/perl-5.22.3-1 
-fdebug-prefix-map=/mnt/share/maint/perl.x86_64/src/perl-5.22.3=/usr/src/debug/perl-5.22.3-1 
-fwrapv'
     hint=recommended, useposix=true, d_sigaction=define
     useithreads=define, usemultiplicity=define
     use64bitint=define, use64bitall=define, uselongdouble=undef
     usemymalloc=n, bincompat5005=undef
   Compiler:
     cc='gcc', ccflags ='-DPERL_USE_SAFE_PUTENV -D_GNU_SOURCE 
-U__STRICT_ANSI__ -ggdb -O2 -pipe -Wimplicit-function-declaration 
-fdebug-prefix-map=/mnt/share/maint/perl.x86_64/build=/usr/src/debug/perl-5.22.3-1 
-fdebug-prefix-map=/mnt/share/maint/perl.x86_64/src/perl-5.22.3=/usr/src/debug/perl-5.22.3-1 
-fwrapv -fno-strict-aliasing -fstack-protector-strong -D_FORTIFY_SOURCE=2',
     optimize='-O3',
     cppflags='-DPERL_USE_SAFE_PUTENV -D_GNU_SOURCE -U__STRICT_ANSI__ 
-ggdb -O2 -pipe -Wimplicit-function-declaration 
-fdebug-prefix-map=/mnt/share/maint/perl.x86_64/build=/usr/src/debug/perl-5.22.3-1 
-fdebug-prefix-map=/mnt/share/maint/perl.x86_64/src/perl-5.22.3=/usr/src/debug/perl-5.22.3-1 
-fwrapv -fno-strict-aliasing -fstack-protector-strong'
     ccversion='', gccversion='5.4.0', gccosandvers=''
     intsize=4, longsize=8, ptrsize=8, doublesize=8, byteorder=12345678, 
doublekind=3
     d_longlong=define, longlongsize=8, d_longdbl=define, 
longdblsize=16, longdblkind=3
     ivtype='long', ivsize=8, nvtype='double', nvsize=8, Off_t='off_t', 
lseeksize=8
     alignbytes=8, prototype=define
   Linker and Libraries:
     ld='g++', ldflags =' -Wl,--enable-auto-import 
-Wl,--export-all-symbols -Wl,--enable-auto-image-base 
-fstack-protector-strong'
     libpth=/usr/lib
     libs=-lpthread -lgdbm -ldb -ldl -lcrypt -lgdbm_compat
     perllibs=-lpthread -ldl -lcrypt
     libc=/usr/lib/libcygwin.a, so=dll, useshrplib=true, 
libperl=cygperl5_22.dll
     gnulibc_version=''
   Dynamic Linking:
     dlsrc=dl_dlopen.xs, dlext=dll, d_dlsymun=undef, ccdlflags=' '
     cccdlflags=' ', lddlflags=' --shared  -Wl,--enable-auto-import 
-Wl,--export-all-symbols -Wl,--enable-auto-image-base 
-fstack-protector-strong'


---
@INC for perl 5.22.3:
     /usr/lib/perl5/site_perl/5.22/x86_64-cygwin-threads
     /usr/lib/perl5/site_perl/5.22
     /usr/lib/perl5/vendor_perl/5.22/x86_64-cygwin-threads
     /usr/lib/perl5/vendor_perl/5.22
     /usr/lib/perl5/5.22/x86_64-cygwin-threads
     /usr/lib/perl5/5.22

---
Environment for perl 5.22.3:
     CYGWIN_HOME=c:\home\sur
     HOME=/home/sur
     LANG=ru_RU.UTF-8
     LANGUAGE (unset)
     LD_LIBRARY_PATH (unset)
     LOGDIR (unset)
 
PATH=/usr/local/bin:/usr/bin:/win/c/Windows/system32:/win/c/Windows:/win/c/Windows/System32/Wbem:/win/c/Windows/System32/WindowsPowerShell/v1.0:/win/c/bin:/win/c/prog32/SysinternalsSuite:/win/c/Program 
Files/Microsoft/Web Platform Installer:/win/c/Program Files 
(x86)/Microsoft ASP.NET/ASP.NET Web Pages/v1.0:/win/c/Program Files 
(x86)/Windows Kits/8.0/Windows Performance Toolkit:/win/c/Program 
Files/Microsoft SQL 
Server/110/Tools/Binn:/win/c/prog32/MATLAB/R2014a/runtime/win32:/win/c/prog32/MATLAB/R2014a/bin:/win/c/prog32/MATLAB/R2014a/polyspace/bin:/win/c/prog64/Python34:/win/c/prog64/Python34/Scripts:/win/c/prog32/Borland/CBUILD~1/Bin:/win/c/prog32/Borland/CBUILD~1/Projects/Bpl:/win/c/Program 
Files (x86)/Microsoft SDKs/Windows/v8.0A/bin/NETFX 4.0 
Tools:/win/c/Program Files (x86)/Microsoft SQL 
Server/110/Tools/Binn:/win/c/Program Files/Microsoft SQL 
Server/110/DTS/Binn:/win/c/Program Files (x86)/Microsoft SQL 
Server/110/DTS/Binn:/win/c/prog32/GnuPG/pub:/win/c/home/ProgramData/Oracle/Java/javapath:/win/c/prog64/Strawberry/c/bin:/win/c/prog64/Strawberry/perl/site/bin:/win/c/prog64/Strawberry/perl/bin:/win/c/prog32/Skype/Phone:/win/c/prog64/Java/jdk1.8.0_45:/win/c/Program 
Files/TortoiseGit/bin:/win/c/home/sur/scripts:/win/c/home/sur/bin:/win/c/prog32/GMT4/bin:/media/pri1/intelFPGA_lite/16.1/modelsim_ase/win32aloem:/usr/lib/lapack
     PERL_BADLANG (unset)
     SHELL=/bin/bash

• [perl #130668] poor argument parsing in pragma 'use open' by perlbug-followup