in reply to A plague on all your features

Interesting. You can maybe figure out why 'c' and 'd' differ so much using this:

use strict;
use warnings;
no strict 'refs';

use Data::Dumper;
$Data::Dumper::Sortkeys = 1;
$Data::Dumper::Deparse = 1;
print Dumper( { map { $_ => $_->() } 'a' .. 'g' } );

sub dumphints {
    my @caller = caller(0);
    $caller[10];
}
                                         sub a {dumphints()}
{use feature ':5.10';                    sub b {dumphints()}}
{use 5.010;                              sub c {dumphints()}}
{no feature ':all'; use feature ':5.10'; sub d {dumphints()}}

{use feature 'say';                   sub e {dumphints()}}
{                   no feature 'say'; sub f {dumphints()}}
{use feature 'say'; no feature 'say'; sub g {dumphints()}}

[download]

I find the output for 'c' honestly surprising.

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Re^2: A plague on all your features
by ikegami (Patriarch) on Mar 07, 2023 at 00:43 UTC 
    $VAR1 = {
          'a' => undef,
          'b' => {
                   'feature_bareword_filehandles' => 1,
                   'feature_indirect' => 1,
                   'feature_multidimensional' => 1,
                   'feature_say' => 1,
                   'feature_state' => 1,
                   'feature_switch' => 1
                 },
          'c' => undef,
          'd' => {
                   'feature_bareword_filehandles' => 1,
                   'feature_indirect' => 1,
                   'feature_multidimensional' => 1,
                   'feature_say' => 1,
                   'feature_state' => 1,
                   'feature_switch' => 1
                 },
          'e' => {
                   'feature_bareword_filehandles' => 1,
                   'feature_indirect' => 1,
                   'feature_multidimensional' => 1,
                   'feature_say' => 1
                 },
          'f' => {
                   'feature_bareword_filehandles' => 1,
                   'feature_indirect' => 1,
                   'feature_multidimensional' => 1
                 },
          'g' => {
                   'feature_bareword_filehandles' => 1,
                   'feature_indirect' => 1,
                   'feature_multidimensional' => 1
                 }
        };

    [download]
[reply]
[d/l]

      I don't know why the hints are undef for c, but I can confirm it's accurate. 

      $ diff -u \
   <( perl -MO=Concise,b b.pl 2>&1 ) \
   <( perl -MO=Concise,c b.pl 2>&1 )
--- /dev/fd/63  2023-03-06 20:59:39.932888013 -0400
+++ /dev/fd/62  2023-03-06 20:59:39.932888013 -0400
@@ -1,8 +1,8 @@
 b.pl syntax OK
-main::b:
+main::c:
 5  <1> leavesub[1 ref] K/REFC,1 ->(end)
 -     <@> lineseq KP ->5
-1        <;> nextstate(main 1252 b.pl:15) v:%,*,&,x*,x&,x$,fea=15 ->2
+1        <;> nextstate(main 1257 b.pl:16) v:*,&,x*,x&,x$,fea=1 ->2
 4        <1> entersub KS ->5
 -           <1> ex-list K ->4
 2              <0> pushmark s ->3

      [download]

      Note the different value of the hints (fea= for "feature") for the two lines.

[reply]
[d/l]
[select]

        Actually, the whole v: thing is the hints, not just the fea= portion. And we see another difference: The %. Not sure what it means, but it relates to %^H. Presumably the presence of %^H. Again, present for b but not c.

[reply]
[d/l]
[select]

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