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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