Hello wise monks.

I was playing around with features and warnings because I would like to create my own Moose version that not only enables all warnings like Moose does (which is great), but also disables experimental::signatures warnings, because I don't want to repeat writing no warnings 'experimental::signatures'; over and over again.

But my question is only about the strange and unexpected results that I get when I use warnings::enabled() for checking whether enabling and disabling warnings from my import sub works.

In fact, for me it looks like warnings::enabled does not treat the enabled/disabled state of 'standard' warning categories like once or void correctly. I am sure there is a good explanation why the following code behaves as it does, and it would certainly help me if I understood why. 

#!/usr/bin/env perl

use feature 'say';
use feature 'signatures';

# Switch all warnings *off*, and only some warnings *on* explicitly:
no warnings;
use warnings qw( void once experimental::signatures );

# Let's check whether the warnings are generated:

# Checking 'void' warnings:
"hello";
# Results in a 'Useless use of a constant ("hello") in void context'
# warning (as expected).

# Checking 'once' warnings:
$x = 1;
# Results in a 'Name "main::x" used only once: possible typo' warning
# (as expected).

# Checking 'experimental::signatures' warnings:
sub foo( $param ) { say "foo( $param )" }
# Results in a 'The signatures feature is experimental' warning
# (as expected; no warning in perl v5.36 since there, the feature is
# not experimental anymore.)


# Let's see what 'warnings::enabled' returns,
# and let 'warnings::warnif' print an own warning for each enabled
# category (and they should all be enabled!):
for my $category ( qw( void once experimental::signatures ) ) {
    say "warnings::enabled( $category ) returns ",
        warnings::enabled( $category ) ? "TRUE" : "**FALSE**", ".";
    warnings::warnif( $category, "my own warning for $category" );
}

# Prints this:
# warnings::enabled( void ) returns **FALSE**.
# warnings::enabled( once ) returns **FALSE**.
# warnings::enabled( experimental::signatures ) returns TRUE.
# my own warning for experimental::signatures at [...]
#
# But no output for the 'void' or 'once' categories.

1;

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Thank you for a ration of your wisdom!

In reply to Warnings are enabled, but they aren't? by muthm

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