[PATCH] Make symbolic references diagnostic less cryptic

[p5pRT]

Migrated from rt.perl.org#112542 (status was 'resolved')

Searchable as RT112542$

[p5pRT]

From @Smylers

This is a bug report for perl from Smylers@​stripey.com,
generated with the help of perlbug 1.39 running under perl 5.15.9.

From 34d0e59777e8cf0638f92115e3a31a9d9be5637c Mon Sep 17 00​:00​:00 2001
From​: Smylers <Smylers@​stripey.com>
Date​: Thu, 12 Apr 2012 13​:30​:37 +0100
Subject​: [PATCH] Make symbolic references diagnostic less cryptic

If somebody has accidentally used a symbolic reference with strict enabled and
are looking for diagnostics then it's likely they didn't intend to use a
symbolic reference at all. A beginner may not even know what a symbolic
reference is, or even a reference.

So explain the error in terms of what the user has done, not what sort of
references are allowed. Provide a simple example of how this error can occur,
so even those who don't know about references have a chance of spotting and
fixing their mistake.

---

pod/perldiag.pod | 9 +++++++--
1 files changed, 7 insertions(+), 2 deletions(-)

Inline Patch

diff --git a/pod/perldiag.pod b/pod/perldiag.pod
index 9a8c934..3cf0188 100644
--- a/pod/perldiag.pod
+++ b/pod/perldiag.pod
@@ -1268,8 +1268,13 @@ test the type of the reference, if need be.
 
 =item Can't use string ("%s") as %s ref while "strict refs" in use
 
-(F) Only hard references are allowed by "strict refs".  Symbolic
-references are disallowed.  See L<perlref>.
+(F) You've told Perl to dereference a string, something which C<use strict>
+blocks to prevent it happening accidentally. See
+L<perlref/"Symbolic references">. This can be triggered by an C<@> or C<$> in a
+double-quoted string immediately before interpolating a variable, for example
+in C<"user @$twitter_id">, which says to treat the contents of C<$twitter_id>
+as an array reference; use a C<\> to have a literal C<@> symbol followed by the
+contents of C<$twitter_id>: C<"user \@$twitter_id">.
 
 =item Can't use subscript on %s
 
-- 

1.7.1

---

Flags​:
  category=docs
  severity=low

---

Site configuration information for perl 5.15.9​:

Configured by smyers at Thu Apr 12 12​:48​:17 BST 2012.

Summary of my perl5 (revision 5 version 15 subversion 9) configuration​:
  Derived from​: 2653c1e
  Platform​:
  osname=linux, osvers=2.6.35-32-generic, archname=i686-linux
  uname='linux smyers-laptop 2.6.35-32-generic #67-ubuntu smp mon mar 5 19​:35​:26 utc 2012 i686 gnulinux '
  config_args='-des -Dusedevel'
  hint=recommended, useposix=true, d_sigaction=define
  useithreads=undef, usemultiplicity=undef
  useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=undef
  use64bitint=undef, use64bitall=undef, uselongdouble=undef
  usemymalloc=n, bincompat5005=undef
  Compiler​:
  cc='cc', ccflags ='-fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
  optimize='-O2',
  cppflags='-fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include'
  ccversion='', gccversion='4.4.5', 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 =' -fstack-protector -L/usr/local/lib'
  libpth=/usr/local/lib /lib/../lib /usr/lib/../lib /lib /usr/lib /usr/lib/i686-linux-gnu /usr/lib64
  libs=-lnsl -ldl -lm -lcrypt -lutil -lc
  perllibs=-lnsl -ldl -lm -lcrypt -lutil -lc
  libc=/lib/libc-2.12.1.so, so=so, useshrplib=false, libperl=libperl.a
  gnulibc_version='2.12.1'
  Dynamic Linking​:
  dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
  cccdlflags='-fPIC', lddlflags='-shared -O2 -L/usr/local/lib -fstack-protector'

Locally applied patches​:
 

---

@​INC for perl 5.15.9​:
  lib
  /home/smyers/lib/perl5/site_perl
  /home/smyers/lib/perl5
  /usr/local/lib/perl5/site_perl/5.15.9/i686-linux
  /usr/local/lib/perl5/site_perl/5.15.9
  /usr/local/lib/perl5/5.15.9/i686-linux
  /usr/local/lib/perl5/5.15.9
  .

---

Environment for perl 5.15.9​:
  HOME=/home/smyers
  LANG=en_GB.utf8
  LANGUAGE (unset)
  LC_COLLATE=C
  LD_LIBRARY_PATH (unset)
  LOGDIR (unset)
  PATH=/home/smyers/bin​:/usr/local/sbin​:/usr/local/bin​:/sbin​:/bin​:/usr/sbin​:/usr/bin​:/usr/X11R6/bin​:/usr/games
  PERL5LIB=/home/smyers/lib/perl5/site_perl​:/home/smyers/lib/perl5
  PERL_BADLANG (unset)
  PERL_CPANM_OPT=--sudo --prompt
  SHELL=/bin/bash

[p5pRT]

From @cpansprout

On Thu Apr 19 05​:10​:21 2012, smylers@​stripey.com wrote​:

This is a bug report for perl from Smylers@​stripey.com,
generated with the help of perlbug 1.39 running under perl 5.15.9.

From 34d0e59777e8cf0638f92115e3a31a9d9be5637c Mon Sep 17 00​:00​:00 2001
From​: Smylers <Smylers@​stripey.com>
Date​: Thu, 12 Apr 2012 13​:30​:37 +0100
Subject​: [PATCH] Make symbolic references diagnostic less cryptic

If somebody has accidentally used a symbolic reference with strict
enabled and
are looking for diagnostics then it's likely they didn't intend to use
a
symbolic reference at all. A beginner may not even know what a
symbolic
reference is, or even a reference.

So explain the error in terms of what the user has done, not what sort
of
references are allowed. Provide a simple example of how this error can
occur,
so even those who don't know about references have a chance of
spotting and
fixing their mistake.
---
pod/perldiag.pod | 9 +++++++--
1 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/pod/perldiag.pod b/pod/perldiag.pod
index 9a8c934..3cf0188 100644
--- a/pod/perldiag.pod
+++ b/pod/perldiag.pod
@​@​ -1268,8 +1268,13 @​@​ test the type of the reference, if need be.

=item Can't use string ("%s") as %s ref while "strict refs" in use

-(F) Only hard references are allowed by "strict refs". Symbolic
-references are disallowed. See L<perlref>.
+(F) You've told Perl to dereference a string, something which C<use
strict>
+blocks to prevent it happening accidentally. See
+L<perlref/"Symbolic references">. This can be triggered by an C<@​> or
C<$> in a
+double-quoted string immediately before interpolating a variable, for
example
+in C<"user @​$twitter_id">, which says to treat the contents of
C<$twitter_id>
+as an array reference; use a C<\> to have a literal C<@​> symbol
followed by the
+contents of C<$twitter_id>​: C<"user \@​$twitter_id">.

=item Can't use subscript on %s

That sounds good. We are currently in code freeze, but I hope to apply
it after the release of 5.16.

--

Father Chrysostomos

[p5pRT]

The RT System itself - Status changed from 'new' to 'open'

[p5pRT]

From perl-diddler@tlinx.org

Smylers (via RT) wrote​:

So explain the error in terms of what the user has done, not what sort of
references are allowed. Provide a simple example of how this error can occur,
so even those who don't know about references have a chance of spotting and
fixing their mistake.

---

  Anything that increases the clarity of perl error messages is, IMO,
a beautiful
thing (and my major was CS!)... $jargon="bad";

[p5pRT]

From @cpansprout

On Thu Apr 19 05​:10​:21 2012, smylers@​stripey.com wrote​:

This is a bug report for perl from Smylers@​stripey.com,
generated with the help of perlbug 1.39 running under perl 5.15.9.

From 34d0e59777e8cf0638f92115e3a31a9d9be5637c Mon Sep 17 00​:00​:00 2001
From​: Smylers <Smylers@​stripey.com>
Date​: Thu, 12 Apr 2012 13​:30​:37 +0100
Subject​: [PATCH] Make symbolic references diagnostic less cryptic

Thank you. Applied as 3f38d37.

--

Father Chrysostomos

[p5pRT]

@cpansprout - Status changed from 'open' to 'resolved'