strictures
strictures(3pm) User Contributed Perl Documentation strictures(3pm)
NAME
strictures - Turn on strict and make most warnings fatal
SYNOPSIS
use strictures 2;
is equivalent to
use strict;
use warnings FATAL => 'all';
use warnings NONFATAL => qw(
exec
recursion
internal
malloc
newline
experimental
deprecated
portable
);
no warnings 'once';
except when called from a file which matches:
(caller)[1] =~ /^(?:t|xt|lib|blib)[\\\/]/
and when either ".git", ".svn", ".hg", or ".bzr" is present in the
current directory (with the intention of only forcing extra tests on
the author side) -- or when ".git", ".svn", ".hg", or ".bzr" is present
two directories up along with "dist.ini" (which would indicate we are
in a "dzil test" operation, via Dist::Zilla) -- or when the
"PERL_STRICTURES_EXTRA" environment variable is set, in which case it
also does the equivalent of
no indirect 'fatal';
no multidimensional;
no bareword::filehandles;
Note that "PERL_STRICTURES_EXTRA" may at some point add even more
tests, with only a minor version increase, but any changes to the
effect of "use strictures" in normal mode will involve a major version
bump.
If any of the extra testing modules are not present, strictures will
complain loudly, once, via "warn()", and then shut up. But you really
should consider installing them, they're all great anti-footgun tools.
DESCRIPTION
I've been writing the equivalent of this module at the top of my code
for about a year now. I figured it was time to make it shorter.
Things like the importer in "use Moose" don't help me because they turn
warnings on but don't make them fatal -- which from my point of view is
useless because I want an exception to tell me my code isn't warnings-
clean.
Any time I see a warning from my code, that indicates a mistake.
Any time my code encounters a mistake, I want a crash -- not spew to
STDERR and then unknown (and probably undesired) subsequent behaviour.
I also want to ensure that obvious coding mistakes, like indirect
object syntax (and not so obvious mistakes that cause things to
accidentally compile as such) get caught, but not at the cost of an XS
dependency and not at the cost of blowing things up on another machine.
Therefore, strictures turns on additional checking, but only when it
thinks it's running in a test file in a VCS checkout -- although if
this causes undesired behaviour this can be overridden by setting the
"PERL_STRICTURES_EXTRA" environment variable.
If additional useful author side checks come to mind, I'll add them to
the "PERL_STRICTURES_EXTRA" code path only -- this will result in a
minor version increase (e.g. 1.000000 to 1.001000 (1.1.0) or similar).
Any fixes only to the mechanism of this code will result in a sub-
version increase (e.g. 1.000000 to 1.000001 (1.0.1)).
CATEGORY SELECTIONS
strictures does not enable fatal warnings for all categories.
exec
Includes a warning that can cause your program to continue running
unintentionally after an internal fork. Not safe to fatalize.
recursion
Infinite recursion will end up overflowing the stack eventually
anyway.
internal
Triggers deep within perl, in places that are not safe to trap.
malloc
Triggers deep within perl, in places that are not safe to trap.
newline
Includes a warning for using stat on a valid but suspect filename,
ending in a newline.
experimental
Experimental features are used intentionally.
deprecated
Deprecations will inherently be added to in the future in
unexpected ways, so making them fatal won't be reliable.
portable
Doesn't indicate an actual problem with the program, only that it
may not behave properly if run on a different machine.
once
Can't be fatalized. Also triggers very inconsistently, so we just
disable it.
VERSIONS
Depending on the version of strictures requested, different warnings
will be enabled. If no specific version is requested, the current
version's behavior will be used. Versions can be requested using
perl's standard mechanism:
use strictures 2;
Or, by passing in a "version" option:
use strictures version => 2;
VERSION 2
Equivalent to:
use strict;
use warnings FATAL => 'all';
use warnings NONFATAL => qw(
exec
recursion
internal
malloc
newline
experimental
deprecated
portable
);
no warnings 'once';
# and if in dev mode:
no indirect 'fatal';
no multidimensional;
no bareword::filehandles;
Additionally, any warnings created by modules using warnings::register
or "warnings::register_categories()" will not be fatalized.
VERSION 1
Equivalent to:
use strict;
use warnings FATAL => 'all';
# and if in dev mode:
no indirect 'fatal';
no multidimensional;
no bareword::filehandles;
METHODS
import
This method does the setup work described above in "DESCRIPTION".
Optionally accepts a "version" option to request a specific version's
behavior.
VERSION
This method traps the "strictures->VERSION(1)" call produced by a use
line with a version number on it and does the version check.
EXTRA TESTING RATIONALE
Every so often, somebody complains that they're deploying via "git
pull" and that they don't want strictures to enable itself in this case
-- and that setting "PERL_STRICTURES_EXTRA" to 0 isn't acceptable
(additional ways to disable extra testing would be welcome but the
discussion never seems to get that far).
In order to allow us to skip a couple of stages and get straight to a
productive conversation, here's my current rationale for turning the
extra testing on via a heuristic:
The extra testing is all stuff that only ever blows up at compile time;
this is intentional. So the oft-raised concern that it's different code
being tested is only sort of the case -- none of the modules involved
affect the final optree to my knowledge, so the author gets some
additional compile time crashes which he/she then fixes, and the rest
of the testing is completely valid for all environments.
The point of the extra testing -- especially "no indirect" -- is to
catch mistakes that newbie users won't even realise are mistakes
without help. For example,
foo { ... };
where foo is an & prototyped sub that you forgot to import -- this is
pernicious to track down since all seems fine until it gets called and
you get a crash. Worse still, you can fail to have imported it due to a
circular require, at which point you have a load order dependent bug
which I've seen before now only show up in production due to tiny
differences between the production and the development environment. I
wrote <http://shadow.cat/blog/matt-s-trout/indirect-but-still-fatal/>
to explain this particular problem before strictures itself existed.
As such, in my experience so far strictures' extra testing has avoided
production versus development differences, not caused them.
Additionally, strictures' policy is very much "try and provide as much
protection as possible for newbies -- who won't think about whether
there's an option to turn on or not" -- so having only the environment
variable is not sufficient to achieve that (I get to explain that you
need to add "use strict" at least once a week on freenode #perl --
newbies sometimes completely skip steps because they don't understand
that that step is important).
I make no claims that the heuristic is perfect -- it's already been
evolved significantly over time, especially for 1.004 where we changed
things to ensure it only fires on files in your checkout (rather than
strictures-using modules you happened to have installed, which was just
silly). However, I hope the above clarifies why a heuristic approach is
not only necessary but desirable from a point of view of providing new
users with as much safety as possible, and will allow any future
discussion on the subject to focus on "how do we minimise annoyance to
people deploying from checkouts intentionally".
SEE ALSO
o indirect
o multidimensional
o bareword::filehandles
COMMUNITY AND SUPPORT
IRC channel
irc.perl.org #toolchain
(or bug 'mst' in query on there or freenode)
Git repository
Gitweb is on http://git.shadowcat.co.uk/ and the clone URL is:
git clone git://git.shadowcat.co.uk/p5sagit/strictures.git
The web interface to the repository is at:
http://git.shadowcat.co.uk/gitweb/gitweb.cgi?p=p5sagit/strictures.git
AUTHOR
mst - Matt S. Trout (cpan:MSTROUT) <mst@shadowcat.co.uk>
CONTRIBUTORS
Karen Etheridge (cpan:ETHER) <ether@cpan.org>
Mithaldu - Christian Walde (cpan:MITHALDU) <walde.christian@gmail.com>
haarg - Graham Knop (cpan:HAARG) <haarg@haarg.org>
COPYRIGHT
Copyright (c) 2010 the strictures "AUTHOR" and "CONTRIBUTORS" as listed
above.
LICENSE
This library is free software and may be distributed under the same
terms as perl itself.
perl v5.28.1 2019-07-15 strictures(3pm)
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