"no feature" now means reset to defaultsmoke-me/no-feature

See https://rt.perl.org/rt3/Ticket/Display.html?id=108776

"no feature" now resets to the default feature set.  To disable all
features (which is likely to be a pretty special-purpose request, since
it presumably won't match any named set of semantics) you can now
write "no feature ':all'"

3 files changed, 38 insertions, 16 deletions

diff --git a/lib/feature.pm b/lib/feature.pm
index fe88c8c47d..33f48dc021 100644
--- a/lib/feature.pm
+++ b/lib/feature.pm
@@ -5,7 +5,7 @@
 
 package feature;
 
-our $VERSION = '1.26';
+our $VERSION = '1.27';
 
 our %feature = (
     fc              => 'feature_fc',
@@ -23,6 +23,7 @@ our %feature_bundle = (
     "5.10"    => [qw(array_base say state switch)],
     "5.11"    => [qw(array_base say state switch unicode_strings)],
     "5.15"    => [qw(current_sub evalbytes fc say state switch unicode_eval unicode_strings)],
+    "all"     => [qw(array_base current_sub evalbytes fc say state switch unicode_eval unicode_strings)],
     "default" => [qw(array_base)],
 );
 
@@ -98,7 +99,8 @@ has lexical effect.
     }
     say "Yet it is here.";
 
-C<no feature> with no features specified will turn off all features.
+C<no feature> with no features specified will reset to the default group.  To
+disable I<all> features (an unusual request!) use C<no feature ':all'>.
 
 =head1 AVAILABLE FEATURES
 
@@ -277,7 +279,7 @@ the C<use VERSION> construct.  That is,
 
 will do an implicit
 
-    no feature;
+    no feature ':all';
     use feature ':5.10';
 
 and so on.  Note how the trailing sub-version
@@ -351,11 +353,10 @@ sub unimport {
 	normalise_hints $features;
     }
 
-    # A bare C<no feature> should disable *all* features
+    # A bare C<no feature> should reset to the default bundle
     if (!@_) {
-        delete @^H{ values(%feature) };
-        $^H &= ~ $hint_uni8bit;
-        return;
+	$^H &= ~($hint_uni8bit|$hint_mask);
+	return;
     }
 
     while (@_) {
diff --git a/regen/feature.pl b/regen/feature.pl
index 445c8b3a6e..f362396943 100755
--- a/regen/feature.pl
+++ b/regen/feature.pl
@@ -38,6 +38,7 @@ my %feature = (
 #       be changed to account.
 
 my %feature_bundle = (
+     all     => [ keys %feature ],
      default =>	[qw(array_base)],
     "5.9.5"  =>	[qw(say state switch array_base)],
     "5.10"   =>	[qw(say state switch array_base)],
@@ -331,7 +332,7 @@ read_only_bottom_close_and_rename($h);
 __END__
 package feature;
 
-our $VERSION = '1.26';
+our $VERSION = '1.27';
 
 FEATURES
 
@@ -392,7 +393,8 @@ has lexical effect.
     }
     say "Yet it is here.";
 
-C<no feature> with no features specified will turn off all features.
+C<no feature> with no features specified will reset to the default group.  To
+disable I<all> features (an unusual request!) use C<no feature ':all'>.
 
 =head1 AVAILABLE FEATURES
 
@@ -561,7 +563,7 @@ the C<use VERSION> construct.  That is,
 
 will do an implicit
 
-    no feature;
+    no feature ':all';
     use feature ':5.10';
 
 and so on.  Note how the trailing sub-version
@@ -635,11 +637,10 @@ sub unimport {
 	normalise_hints $features;
     }
 
-    # A bare C<no feature> should disable *all* features
+    # A bare C<no feature> should reset to the default bundle
     if (!@_) {
-        delete @^H{ values(%feature) };
-        $^H &= ~ $hint_uni8bit;
-        return;
+	$^H &= ~($hint_uni8bit|$hint_mask);
+	return;
     }
 
     while (@_) {
diff --git a/t/lib/feature/bundle b/t/lib/feature/bundle
index 7e1479f4e3..429e68ebd0 100644
--- a/t/lib/feature/bundle
+++ b/t/lib/feature/bundle
@@ -85,9 +85,9 @@ no feature;
 use feature ":default";
 $[ = 1;
 print qw[a b c][2], "\n";
-use feature ":5.16"; # should not disable anything; no feature does that
+use feature ":5.16"; # should not disable anything; no feature ':all' does that
 print qw[a b c][2], "\n";
-no feature;
+no feature ':all';
 print qw[a b c][2], "\n";
 use feature ":5.16";
 print qw[a b c][2], "\n";
@@ -97,3 +97,23 @@ b
 b
 c
 c
+########
+# "no feature"
+use feature ':5.16'; # turns array_base off
+no feature; # resets to :default, thus turns array_base on
+$[ = 1;
+print qw[a b c][2], "\n";
+EXPECT
+Use of assignment to $[ is deprecated at - line 4.
+b
+########
+# "no feature 'all"
+$[ = 1;
+print qw[a b c][2], "\n";
+no feature ':all'; # turns array_base (and everything else) off
+$[ = 1;
+print qw[a b c][2], "\n";
+EXPECT
+Use of assignment to $[ is deprecated at - line 2.
+Assigning non-zero to $[ is no longer possible at - line 5.
+b