\U and \L in interpolated strings don't actually stack

[snoopyjc]

Description
Perl the documentation, in string interpolation \U and \L stack, but it doesn't actually work. "\L, \U, \F, and \Q can stack, in which case you need one \E for each"

Steps to Reproduce
print "\UUpPeR\LLOWER\EuPpEr\E\n";
UPPERloweruPpEr

Expected behavior
UPPERlowerUPPER

The first \E should pop the \L, leaving the \U operator in effect until the second \E.

Perl configuration

Summary of my perl5 (revision 5 version 34 subversion 0) configuration:

  Platform:
    osname=msys
    osvers=3.1.7-340.x86_64
    archname=x86_64-msys-thread-multi
    uname='msys_nt-10.0-14393 fv-az123-95 3.1.7-340.x86_64 2021-03-26 22:17 utc x86_64 msys '
    config_args='-des -Dusethreads -Doptimize=-march=x86-64 -mtune=generic -O2 -pipe -Dprefix=/usr -Dvendorprefix=/usr -Dprivlib=/usr/share/perl5/core_perl -Darchlib=/usr/lib/perl5/core_perl -Dsitelib=/usr/share/perl5/site_perl -Dsitearch=/usr/lib/perl5/site_perl -Dvendorlib=/usr/share/perl5/vendor_perl -Dvendorarch=/usr/lib/perl5/vendor_perl -Dscriptdir=/usr/bin/core_perl -Dsitescript=/usr/bin/site_perl -Dvendorscript=/usr/bin/vendor_perl -Dinc_version_list=none -Dman1ext=1perl -Dman3ext=3perl -Darchname=-msys-threads -Dmyarchname=-msys -Dlibperl=msys-perl5_34.dll -Dcc=gcc -Dld=g++ -Accflags=-march=x86-64 -mtune=generic -O2 -pipe -fwrapv'
    hint=recommended
    useposix=true
    d_sigaction=define
    useithreads=define
    usemultiplicity=define
    use64bitint=define
    use64bitall=define
    uselongdouble=undef
    usemymalloc=n
    default_inc_excludes_dot=define
  Compiler:
    cc='gcc'
    ccflags ='-DPERL_USE_SAFE_PUTENV -U__STRICT_ANSI__ -D_GNU_SOURCE -march=x86-64 -mtune=generic -O2 -pipe -fwrapv -fno-strict-aliasing -fstack-protector-strong -D_FORTIFY_SOURCE=2'
    optimize='-march=x86-64 -mtune=generic -O2 -pipe'
    cppflags='-DPERL_USE_SAFE_PUTENV -U__STRICT_ANSI__ -D_GNU_SOURCE -march=x86-64 -mtune=generic -O2 -pipe -fwrapv -fno-strict-aliasing -fstack-protector-strong'
    ccversion=''
    gccversion='10.2.0'
    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 -ldl -lcrypt
    perllibs=-lpthread -ldl -lcrypt
    libc=/usr/lib/libmsys-2.0.a
    so=dll
    useshrplib=true
    libperl=msys-perl5_34.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'


Characteristics of this binary (from libperl):
  Compile-time options:
    HAS_TIMES
    MULTIPLICITY
    PERLIO_LAYERS
    PERL_COPY_ON_WRITE
    PERL_DONT_CREATE_GVSV
    PERL_IMPLICIT_CONTEXT
    PERL_OP_PARENT
    PERL_PRESERVE_IVUV
    PERL_USE_SAFE_PUTENV
    USE_64_BIT_ALL
    USE_64_BIT_INT
    USE_ITHREADS
    USE_LARGE_FILES
    USE_LOCALE
    USE_LOCALE_COLLATE
    USE_LOCALE_CTYPE
    USE_LOCALE_NUMERIC
    USE_LOCALE_TIME
    USE_PERLIO
    USE_PERL_ATOF
    USE_REENTRANT_API
    USE_THREAD_SAFE_LOCALE
  Built under msys
  Compiled at Jul 22 2021 12:31:47
  @INC:
    /usr/lib/perl5/site_perl
    /usr/share/perl5/site_perl
    /usr/lib/perl5/vendor_perl
    /usr/share/perl5/vendor_perl
    /usr/lib/perl5/core_perl
    /usr/share/perl5/core_perl

[iabyn]

On Mon, Apr 25, 2022 at 09:21:00PM -0700, Joe Cool wrote: **Description** Perl the [documentation](https://perldoc.perl.org/perlop#Quote-and-Quote-like-Operators), in string interpolation \U and \L stack, but it doesn't actually work. "\L, \U, \F, and \Q can stack, in which case you need one \E for each"

Looking at the src code in yyl_interpcasemod(), in the case of a new \L, \U or \F, it quite explicitly looks for any existing L/U/F on the casestack, and if so, pops it before pushing the new one. So it appears to be deliberate behaviour not to stack. (and has been like that since 5.000.) I guess we need to fix the docs rather than change perl's behaviour.

…

-- More than any other time in history, mankind faces a crossroads. One path leads to despair and utter hopelessness. The other, to total extinction. Let us pray we have the wisdom to choose correctly. -- Woody Allen

[khwilliamson]

On 4/28/22 03:41, iabyn wrote: On Mon, Apr 25, 2022 at 09:21:00PM -0700, Joe Cool wrote: > **Description** > Perl the > [documentation](https://perldoc.perl.org/perlop#Quote-and-Quote-like-Operators), > in string interpolation \U and \L stack, but it doesn't actually work. > "\L, \U, \F, and \Q can stack, in which case you need one \E for each" Looking at the src code in yyl_interpcasemod(), in the case of a new \L, \U or \F, it quite explicitly looks for any existing L/U/F on the casestack, and if so, pops it before pushing the new one. So it appears to be deliberate behaviour not to stack. (and has been like that since 5.000.) I guess we need to fix the docs rather than change perl's behaviour.

This is actually a sore point. The behavior is inconsistent. There are plenty of tickets on it; this one may well be a duplicate. It is on my todo list, but quite low in priority, to go through them and propose an approach to making things consistent, which might very well lead to some deprecation cycles. rjbs was quite keen at one time to have this done, IIRC. Anyone who wants to take this on, I owe you a beer or two.

[snoopyjc]

Maybe just document that only \Q and {\L, \U, \F} can be nested and that \L \U and \F each get an implicit \E if another command from that set is seen?

[khwilliamson]

It's worse than that

[khwilliamson]

Here are some tickets #8848 #11145 #18981

[bram-perl]

Issue #8848 looks unrelated, I think it was typo'ed and that it should've been: #8846