Disable $[ under 5.16

This adds the array_base feature to feature.pm

Perl_feature_is_enabled has been modified to use PL_curcop, rather
than PL_hintgv, so it can work with run-time hints as well.
(PL_curcop holds the current state op at run time, and &PL_compiling
at compile time, so it works for both.)  The hints in $^H are not
stored in the same place at compile time and run time, so the FEATURE_IS_ENABLED macro has been modified to check first whether
PL_curop == &PL_compiling.

Since array_base is on by default with no hint for it in %^H, it is
a ‘negative’ feature, whose entry in %^H turns it off.  feature.pm
has been modified to support such negative features.  The new FEATURE_IS_ENABLED_d can check whether such default features
are enabled.

This does make things less efficient, as every version declaration
now loads feature.pm to disable all features (including turning off
array_base, which entails adding an entry to %^H) before loading the
new bundle.  I have plans to make this more efficient.

1 files changed, 4 insertions, 5 deletions

diff --git a/t/op/override.t b/t/op/override.t
index be39cf9330..b38c3938a1 100644
--- a/t/op/override.t
+++ b/t/op/override.t
@@ -49,13 +49,12 @@ is( $r, "Foo.pm" );
 eval "use Foo::Bar";
 is( $r, join($dirsep, "Foo", "Bar.pm") );
 
-# Under PERL_UNICODE, %^H is set, causing Perl_utilize to require
-# feature.pm after 5.006, in order to turn off features.  Stop that
-# from interfering with this test by unsetting HINT_LOCALIZE_HH.
+# use VERSION also loads feature.pm.
 {
-    BEGIN { $^H &= ~0x00020000 } # HINT_LOCALIZE_HH
+    my @r;
+    local *CORE::GLOBAL::require = sub { push @r, shift; 1; };
     eval "use 5.006";
-    is( $r, "5.006" );
+    like( " @r ", qr " 5\.006 " );
 }
 
 {