use feature qw(declared_refs) doesn't seem to make sense without the other feature.
Yes, but the refaliasing does make sense without declared_refs, so it's possible that refaliasing could be accepted without declared_refs.
Upd: Removed incorrect claim once present here. Bad test.
Use of refalising and declared_refs:
$ perl -M5.022 -e'
my $x = 123; \my $y = \$x; say $y;
'
Experimental aliasing via reference not enabled at -e line 2.
$ perl -M5.022 -e'
use feature qw( refaliasing );
my $x = 123; \my $y = \$x; say $y;
'
Aliasing via reference is experimental at -e line 3.
123
$ perl -M5.022 -e'
use feature qw( refaliasing );
no warnings qw( experimental::refaliasing );
my $x = 123; \my $y = \$x; say $y;
'
123
$ perl -M5.022 -e'
use experimental qw( refaliasing );
my $x = 123; \my $y = \$x; say $y;
'
123
$ perl -M5.026 -e'
my $x = 123; my \$y = \$x; say $y;
'
The experimental declared_refs feature is not enabled at -e line 2.
$ perl -M5.026 -e'
use feature qw( declared_refs );
my $x = 123; my \$y = \$x; say $y;
'
Declaring references is experimental at -e line 3.
Experimental aliasing via reference not enabled at -e line 3.
$ perl -M5.026 -e'
use feature qw( refaliasing declared_refs );
my $x = 123; my \$y = \$x; say $y;
'
Declaring references is experimental at -e line 3.
Aliasing via reference is experimental at -e line 3.
123
$ perl -M5.026 -e'
use feature qw( refaliasing declared_refs );
no warnings qw( experimental::refaliasing experimental::declared_re
+fs );
my $x = 123; my \$y = \$x; say $y;
'
123
$ perl -M5.026 -e'
use experimental qw( refaliasing declared_refs );
my $x = 123; my \$y = \$x; say $y;
'
123
Upd: Dropped requirement to 5.22 for refaliasing part.