Ubuntu Manpage: Perl::Critic::Policy::Compatibility::PerlMinimumVersionAndWhy

Provided by: libperl-critic-pulp-perl_99-1_all

NAME

       Perl::Critic::Policy::Compatibility::PerlMinimumVersionAndWhy - explicit Perl version for
       features used

DESCRIPTION

This policy is part of the "Perl::Critic::Pulp" add-on. It requires that you have an
explicit "use 5.XXX" etc for the Perl syntax features you use, as determined by
"Perl::MinimumVersion".

use 5.010; # the // operator is new in perl 5.010
print $x // $y; # ok

If you don't have the "Perl::MinimumVersion" module then nothing is reported. Certain
nasty hacks are used to extract reasons and locations from "Perl::MinimumVersion".

This policy is under the "compatibility" theme (see "POLICY THEMES" in Perl::Critic). Its
best use is when it picks up things like "//" or "qr" which are only available in a newer
Perl than you meant to target.

An explicit "use 5.xxx" can be a little tedious, but has the advantage of making it clear
what's needed (or supposed to be needed) and it gives a good error message if run on an
older Perl.

Disabling
The config options below let you limit how far back to go. Or if you don't care at all
about this sort of thing you can always disable the policy completely from your
~/.perlcriticrc file in the usual way (see "CONFIGURATION" in Perl::Critic),

[-Compatibility::PerlMinimumVersionAndWhy]

MinimumVersion Mangling
Some mangling is applied to what "Perl::MinimumVersion" normally reports (as of its
version 1.28).

• A multi-constant hash with the "constant" module is not reported, since that's covered
better by Compatibility::ConstantPragmaHash.

• Module requirements for things like "use Errno" are dropped, since you might get a
back-port from CPAN etc and the need for a module is better expressed in a
distribution "prereq".

But pragma modules like "use warnings" are still reported. They're normally an
interface to a feature new in the Perl version it comes with and can't be back-ported.
(See "OTHER NOTES" below too.)

MinimumVersion Extras
The following extra checks are added to "Perl::MinimumVersion".

5.12 for
• new "keys @array", "values @array" and "each @array"

5.10 for
• "qr//m", since "m" modifier doesn't propagate correctly on a "qr" until 5.10

• "-e -f -x" stacked filetest operators.

• "pack()" new "<" and ">" endianness.

• new "UNIVERSAL.pm" method "DOES()"

5.8 for
• new "word [newline] =>" fat comma quoting across a newline

For earlier Perl "word" ended up a function call. It's presumed such code is
meant to quote in the 5.8 style, and thus requires 5.8 or higher.

• "eval '#line ...'" with "#line" the very first thing

In earlier Perl a "#line" as the very first thing in an "eval" doesn't take
effect. Adding a blank line so it's not first is enough.

• "pack()" new "F" native NV, "D" long double, "i" IV, "j" UV, "()" group, "[]"
repeat count

5.6 for
• new "exists &subr", "exists $array[0]" and "delete $array[0]"

• new "0b110011" binary number literals

• new "open(my $fh,...)" etc auto-creation of filehandle

• "syswrite()" length parameter optional

• "Foo->$method" no-args call without parens

For earlier Perl a no-args call to a method named in a variable must be
"Foo->$method()". The parens are optional in 5.6 up.

• "pack()" new "Z" asciz, "q","Q" quads, "!" native size, "/" counted string, "#"
comment

5.005 for
• new "Foo::Bar::" double-colon package name quoting

• new "my ($x, undef, $y) = @values", using "undef" as a dummy in a "my" list

5.004 for
• new "use 5.xxx" Perl version check through "use". For earlier Perl it can be
"BEGIN { require 5.000 }" etc

• new "__PACKAGE__" special literal

• new "foreach my $foo" lexical loop variable

• new "$coderef->()" call with "->"

• new "sysseek()" builtin function

• "pack()" new "w" BER integer

• new "UNIVERSAL.pm" with "VERSION()", "isa()" and "can()" methods

"pack()" and "unpack()" format strings are only checked if they're literal strings or
here-documents without interpolations, or "." operator concats of those.

The "qr//m" report concerns a misfeature fixed in perl 5.10.0 (see perl5101delta). In
earlier versions a regexp like "$re = qr/^x/m" within another regexp like "/zz|$re/" loses
the "/m" attribute from $re, changing the interpretation of the "^" (and "$" similarly).
Forms like "(\A|\n)" are a possible workaround, though are uncommon so may be a little
obscure. "RegularExpressions::RequireLineBoundaryMatching" asks for "/m" in all cases so
if think you want that then you probably want Perl 5.10 or up for the fix too.

"Modern::Perl"
"use Modern::Perl" is taken to mean Perl 5.10. This is slightly experimental and in
principle the actual minimum it implies is forever rising, and even now could be more, or
depends on it date argument scheme. Maybe if could say its actual current desire then an
installed version could be queried.

CONFIGURATION

       "above_version" (version string, default none)
           Set a minimum version of Perl you always use, so that reports are only about things
           higher than this and higher than what the document declares.  The value is anything
           the "version.pm" module can parse.

               [Compatibility::PerlMinimumVersionAndWhy]
               above_version = 5.006

           For example if you always use Perl 5.6 and set 5.006 like this then you can have "our"
           package variables without an explicit "use 5.006".

       "skip_checks" (list of check names, default none)
           Skip the given MinimumVersion checks (a space separated list).  The check names are
           shown in the violation message and come from "Perl::MinimumVersion::CHECKS".  For
           example,

               [Compatibility::PerlMinimumVersionAndWhy]
               skip_checks = _some_thing _another_thing

           This can be used for checks you believe are wrong, or where the compatibility matter
           only affects limited circumstances which you understand.

           The check names are likely to be a moving target, especially the Pulp additions.
           Unknown checks in the list are quietly ignored.

OTHER NOTES

       "use warnings" is reported as a Perl 5.6 feature since the lexically-scoped fine grain
       warnings control it gives is new in that version.  If targeting earlier versions then it's
       often enough to drop "use warnings", ensure your code runs cleanly under "perl -w", and
       leave it to applications to use "-w" (or set $^W) if they desire.

       "warnings::compat" offers a "use warnings" for earlier Perl, but it's not lexical, instead
       setting $^W globally.  In a script this might be an alternative to "#!/usr/bin/perl -w"
       (per perlrun), but in a module it's probably not a good idea to change global settings.

       The "UNIVERSAL.pm" methods "VERSION()", "isa()", "can()" or "DOES()" might in principle be
       implemented explicitly by a particular class, but it's assumed that's not so and that any
       call to those requires the respective minimum Perl version.

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