From 3a18813b31ea9acdba52560ab9409ec6880b7f71 Mon Sep 17 00:00:00 2001
From: Father Chrysostomos <sprout@cpan.org>
Date: Sat, 29 Oct 2011 01:13:54 -0700
Subject: Make all keywords overridable

---
 lib/feature.pm  | 11 ++++++++++-
 t/op/override.t | 35 ++++++++++++++++++++++++++++++++++-
 toke.c          |  5 +++--
 3 files changed, 47 insertions(+), 4 deletions(-)

diff --git a/lib/feature.pm b/lib/feature.pm
index e20285d595..a17b65684e 100644
--- a/lib/feature.pm
+++ b/lib/feature.pm
@@ -8,6 +8,7 @@ my %feature = (
     state           => 'feature_state',
     switch          => 'feature_switch',
     unicode_strings => 'feature_unicode',
+    overrides       => 'feature_overrides',
 );
 
 # This gets set (for now) in $^H as well as in %^H,
@@ -23,7 +24,7 @@ my %feature_bundle = (
     "5.12" => [qw(say state switch unicode_strings)],
     "5.13" => [qw(say state switch unicode_strings)],
     "5.14" => [qw(say state switch unicode_strings)],
-    "5.15" => [qw(say state switch unicode_strings)],
+    "5.15" => [qw(say state switch unicode_strings overrides)],
 );
 
 # special case
@@ -126,6 +127,14 @@ C<use feature 'unicode_strings'> subpragma is B<strongly> recommended.
 This subpragma is available starting with Perl 5.11.3, but was not fully
 implemented until 5.13.8.
 
+=head2 the 'overrides' feature
+
+C<use feature 'overrides'> tells the compiler to allow all Perl keywords to
+be overridden with user-defined subroutines.  See
+L<perlsub/Overriding Built-in Functions>.
+
+This subpragma is available from Perl 5.16 onwards.
+
 =head1 FEATURE BUNDLES
 
 It's possible to load a whole slew of features in one go, using
diff --git a/t/op/override.t b/t/op/override.t
index 413ba77e84..d0829cc44e 100644
--- a/t/op/override.t
+++ b/t/op/override.t
@@ -6,7 +6,36 @@ BEGIN {
     require './test.pl';
 }
 
-plan tests => 26;
+
+# Test that every keyword is overridable under 5.16.
+
+use File::Spec::Functions;
+use subs ();
+
+my $keywords_file = catfile(updir,'regen','keywords.pl');
+open my $kh, $keywords_file
+   or die "$0 cannot open $keywords_file: $!";
+
+my $keyword_count;
+
+while($_ = CORE::readline $kh) {
+  if (m?__END__?..${\0} and /^\+/) {
+    chomp(my $word = $');
+    next if $word =~ /^[A-Z]+\z/;
+    $keyword_count++;
+    my $rand = rand;
+    use feature sprintf(":%vd", $^V); # need to use the latest, to make
+    local *$word = sub { $rand };     # sure we test all keywords properly
+    subs->import($word);
+    local $_; # to avoid strange side effects when tests fail
+    is eval qq{$word()}, $rand, "$word under 'overrides' feature";
+  }
+}
+
+close $kh or die "$0 cannot close $keywords_file: $!";
+
+
+my $more_tests = 26;
 
 #
 # This file tries to test builtin override using CORE::GLOBAL
@@ -123,3 +152,7 @@ BEGIN { *OverridenPop::pop = sub { ::is( $_[0][0], "ok" ) }; }
     };
     is $@, '';
 }
+
+
+is curr_test, $more_tests+$keyword_count+1, 'right number of tests';
+done_testing;
diff --git a/toke.c b/toke.c
index aaeff85a27..7690529af1 100644
--- a/toke.c
+++ b/toke.c
@@ -6459,7 +6459,8 @@ Perl_yylex(pTHX)
 	    TOKEN(LABEL);
 	}
 
-	if (tmp < 0) {			/* second-class keyword? */
+	if (tmp < 0			/* second-class keyword? */
+	  || FEATURE_IS_ENABLED("overrides")) {
 	    GV *ogv = NULL;	/* override (winner) */
 	    GV *hgv = NULL;	/* hidden (loser) */
 	    if (PL_expect != XOPERATOR && (*s != ':' || s[1] != ':')) {
@@ -6493,7 +6494,7 @@ Perl_yylex(pTHX)
 		tmp = 0;		/* any sub overrides "weak" keyword */
 	    }
 	    else {			/* no override */
-		tmp = -tmp;
+		if (tmp < 0) tmp = -tmp;
 		if (tmp == KEY_dump) {
 		    Perl_ck_warner(aTHX_ packWARN(WARN_MISC),
 				   "dump() better written as CORE::dump()");
-- 
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