X-Git-Url: https://perl5.git.perl.org/perl5.git/blobdiff_plain/b7569deb825abe0814411c06d6990b49bb917a6d..12578451ab3883e1692ecd2814459f3e9f083028:/lib/feature.pm

diff --git a/lib/feature.pm b/lib/feature.pm
index 1517c1f..37e571f 100644
--- a/lib/feature.pm
+++ b/lib/feature.pm
@@ -1,31 +1,49 @@
+# -*- buffer-read-only: t -*-
+# !!!!!!!   DO NOT EDIT THIS FILE   !!!!!!!
+# This file is built by regen/feature.pl.
+# Any changes made here will be lost!
+
 package feature;
 
-our $VERSION = '1.16';
+our $VERSION = '1.28';
 
-# (feature name) => (internal name, used in %^H)
-my %feature = (
+our %feature = (
+    fc              => 'feature_fc',
+    say             => 'feature_say',
+    state           => 'feature_state',
     switch          => 'feature_switch',
-    say             => "feature_say",
-    state           => "feature_state",
-    unicode_strings => "feature_unicode",
+    evalbytes       => 'feature_evalbytes',
+    array_base      => 'feature_arybase',
+    current_sub     => 'feature___SUB__',
+    unicode_eval    => 'feature_unieval',
+    unicode_strings => 'feature_unicode',
+);
+
+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)],
 );
 
+$feature_bundle{"5.12"} = $feature_bundle{"5.11"};
+$feature_bundle{"5.13"} = $feature_bundle{"5.11"};
+$feature_bundle{"5.14"} = $feature_bundle{"5.11"};
+$feature_bundle{"5.16"} = $feature_bundle{"5.15"};
+$feature_bundle{"5.17"} = $feature_bundle{"5.15"};
+$feature_bundle{"5.18"} = $feature_bundle{"5.15"};
+$feature_bundle{"5.9.5"} = $feature_bundle{"5.10"};
+
+our $hint_shift   = 26;
+our $hint_mask    = 0x1c000000;
+our @hint_bundles = qw( default 5.10 5.11 5.15 );
+
 # This gets set (for now) in $^H as well as in %^H,
 # for runtime speed of the uc/lc/ucfirst/lcfirst functions.
 # See HINT_UNI_8_BIT in perl.h.
 our $hint_uni8bit = 0x00000800;
 
-# NB. the latest bundle must be loaded by the -E switch (see toke.c)
-
-my %feature_bundle = (
-    "5.10" => [qw(switch say state)],
-    "5.11" => [qw(switch say state unicode_strings)],
-    "5.12" => [qw(switch say state unicode_strings)],
-);
-
-# special case
-$feature_bundle{"5.9.5"} = $feature_bundle{"5.10"};
-
 # TODO:
 # - think about versioned features (use feature switch => 2)
 
@@ -35,24 +53,28 @@ feature - Perl pragma to enable new features
 
 =head1 SYNOPSIS
 
-    use feature qw(switch say);
+    use feature qw(say switch);
     given ($foo) {
-	when (1)	  { say "\$foo == 1" }
-	when ([2,3])	  { say "\$foo == 2 || \$foo == 3" }
-	when (/^a[bc]d$/) { say "\$foo eq 'abd' || \$foo eq 'acd'" }
-	when ($_ > 100)   { say "\$foo > 100" }
-	default		  { say "None of the above" }
+        when (1)          { say "\$foo == 1" }
+        when ([2,3])      { say "\$foo == 2 || \$foo == 3" }
+        when (/^a[bc]d$/) { say "\$foo eq 'abd' || \$foo eq 'acd'" }
+        when ($_ > 100)   { say "\$foo > 100" }
+        default           { say "None of the above" }
     }
 
     use feature ':5.10'; # loads all features available in perl 5.10
 
+    use v5.10;           # implicitly loads :5.10 feature bundle
+
 =head1 DESCRIPTION
 
 It is usually impossible to add new syntax to Perl without breaking
-some existing programs. This pragma provides a way to minimize that
+some existing programs.  This pragma provides a way to minimize that
 risk. New syntactic constructs, or new semantic meanings to older
 constructs, can be enabled by C<use feature 'foo'>, and will be parsed
-only when the appropriate feature pragma is in scope.
+only when the appropriate feature pragma is in scope.  (Nevertheless, the
+C<CORE::> prefix provides access to all Perl keywords, regardless of this
+pragma.)
 
 =head2 Lexical effect
 
@@ -68,7 +90,7 @@ from that point to the end of the enclosing block.
 
 =head2 C<no feature>
 
-Features can also be turned off by using C<no feature "foo">. This too
+Features can also be turned off by using C<no feature "foo">.  This too
 has lexical effect.
 
     use feature 'say';
@@ -79,72 +101,194 @@ has lexical effect.
     }
     say "Yet it is here.";
 
-C<no feature> with no features specified will turn off all features.
-
-=head2 The 'switch' feature
-
-C<use feature 'switch'> tells the compiler to enable the Perl 6
-given/when construct.
+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'>.
 
-See L<perlsyn/"Switch statements"> for details.
+=head1 AVAILABLE FEATURES
 
 =head2 The 'say' feature
 
-C<use feature 'say'> tells the compiler to enable the Perl 6
+C<use feature 'say'> tells the compiler to enable the Perl 6 style
 C<say> function.
 
 See L<perlfunc/say> for details.
 
-=head2 the 'state' feature
+This feature is available starting with Perl 5.10.
+
+=head2 The 'state' feature
 
 C<use feature 'state'> tells the compiler to enable C<state>
 variables.
 
 See L<perlsub/"Persistent Private Variables"> for details.
 
-=head2 the 'unicode_strings' feature
+This feature is available starting with Perl 5.10.
+
+=head2 The 'switch' feature
+
+C<use feature 'switch'> tells the compiler to enable the Perl 6
+given/when construct.
+
+See L<perlsyn/"Switch Statements"> for details.
+
+This feature is available starting with Perl 5.10.
+
+=head2 The 'unicode_strings' feature
+
+C<use feature 'unicode_strings'> tells the compiler to use Unicode semantics
+in all string operations executed within its scope (unless they are also
+within the scope of either C<use locale> or C<use bytes>).  The same applies
+to all regular expressions compiled within the scope, even if executed outside
+it.
+
+C<no feature 'unicode_strings'> tells the compiler to use the traditional
+Perl semantics wherein the native character set semantics is used unless it is
+clear to Perl that Unicode is desired.  This can lead to some surprises
+when the behavior suddenly changes.  (See
+L<perlunicode/The "Unicode Bug"> for details.)  For this reason, if you are
+potentially using Unicode in your program, the
+C<use feature 'unicode_strings'> subpragma is B<strongly> recommended.
+
+This feature is available starting with Perl 5.12; was almost fully
+implemented in Perl 5.14; and extended in Perl 5.16 to cover C<quotemeta>.
+
+=head2 The 'unicode_eval' and 'evalbytes' features
+
+Under the C<unicode_eval> feature, Perl's C<eval> function, when passed a
+string, will evaluate it as a string of characters, ignoring any
+C<use utf8> declarations.  C<use utf8> exists to declare the encoding of
+the script, which only makes sense for a stream of bytes, not a string of
+characters.  Source filters are forbidden, as they also really only make
+sense on strings of bytes.  Any attempt to activate a source filter will
+result in an error.
+
+The C<evalbytes> feature enables the C<evalbytes> keyword, which evaluates
+the argument passed to it as a string of bytes.  It dies if the string
+contains any characters outside the 8-bit range.  Source filters work
+within C<evalbytes>: they apply to the contents of the string being
+evaluated.
+
+Together, these two features are intended to replace the historical C<eval>
+function, which has (at least) two bugs in it, that cannot easily be fixed
+without breaking existing programs:
+
+=over
+
+=item *
+
+C<eval> behaves differently depending on the internal encoding of the
+string, sometimes treating its argument as a string of bytes, and sometimes
+as a string of characters.
+
+=item *
+
+Source filters activated within C<eval> leak out into whichever I<file>
+scope is currently being compiled.  To give an example with the CPAN module
+L<Semi::Semicolons>:
+
+    BEGIN { eval "use Semi::Semicolons;  # not filtered here " }
+    # filtered here!
+
+C<evalbytes> fixes that to work the way one would expect:
 
-C<use feature 'unicode_strings'> tells the compiler to treat
-all strings outside of C<use locale> and C<use bytes> as Unicode. It is
-available starting with Perl 5.11.3.
+    use feature "evalbytes";
+    BEGIN { evalbytes "use Semi::Semicolons;  # filtered " }
+    # not filtered
 
-See L<perlunicode/The "Unicode Bug"> for details.
+=back
+
+These two features are available starting with Perl 5.16.
+
+=head2 The 'current_sub' feature
+
+This provides the C<__SUB__> token that returns a reference to the current
+subroutine or C<undef> outside of a subroutine.
+
+This feature is available starting with Perl 5.16.
+
+=head2 The 'array_base' feature
+
+This feature supports the legacy C<$[> variable.  See L<perlvar/$[> and
+L<arybase>.  It is on by default but disabled under C<use v5.16> (see
+L</IMPLICIT LOADING>, below).
+
+This feature is available under this name starting with Perl 5.16.  In
+previous versions, it was simply on all the time, and this pragma knew
+nothing about it.
+
+=head2 The 'fc' feature
+
+C<use feature 'fc'> tells the compiler to enable the C<fc> function,
+which implements Unicode casefolding.
+
+See L<perlfunc/fc> for details.
+
+This feature is available from Perl 5.16 onwards.
 
 =head1 FEATURE BUNDLES
 
-It's possible to load a whole slew of features in one go, using
-a I<feature bundle>. The name of a feature bundle is prefixed with
-a colon, to distinguish it from an actual feature. At present, the
-only feature bundle is C<use feature ":5.10"> which is equivalent
-to C<use feature qw(switch say state)>.
+It's possible to load multiple features together, using
+a I<feature bundle>.  The name of a feature bundle is prefixed with
+a colon, to distinguish it from an actual feature.
+
+  use feature ":5.10";
+
+The following feature bundles are available:
+
+  bundle    features included
+  --------- -----------------
+  :default  array_base
+
+  :5.10     say state switch array_base
+
+  :5.12     say state switch unicode_strings array_base
+
+  :5.14     say state switch unicode_strings array_base
+
+  :5.16     say state switch unicode_strings
+            unicode_eval evalbytes current_sub fc
+
+  :5.18     say state switch unicode_strings
+            unicode_eval evalbytes current_sub fc
+
+The C<:default> bundle represents the feature set that is enabled before
+any C<use feature> or C<no feature> declaration.
 
-Specifying sub-versions such as the C<0> in C<5.10.0> in feature bundles has
-no effect: feature bundles are guaranteed to be the same for all sub-versions.
+Specifying sub-versions such as the C<0> in C<5.14.0> in feature bundles has
+no effect.  Feature bundles are guaranteed to be the same for all sub-versions.
+
+  use feature ":5.14.0";    # same as ":5.14"
+  use feature ":5.14.1";    # same as ":5.14"
 
 =head1 IMPLICIT LOADING
 
-There are two ways to load the C<feature> pragma implicitly :
+Instead of loading feature bundles by name, it is easier to let Perl do
+implicit loading of a feature bundle for you.
+
+There are two ways to load the C<feature> pragma implicitly:
 
 =over 4
 
 =item *
 
-By using the C<-E> switch on the command-line instead of C<-e>. It enables
-all available features in the main compilation unit (that is, the one-liner.)
+By using the C<-E> switch on the Perl command-line instead of C<-e>.
+That will enable the feature bundle for that version of Perl in the
+main compilation unit (that is, the one-liner that follows C<-E>).
 
 =item *
 
-By requiring explicitly a minimal Perl version number for your program, with
-the C<use VERSION> construct, and when the version is higher than or equal to
-5.10.0. That is,
+By explicitly requiring a minimum Perl version number for your program, with
+the C<use VERSION> construct.  That is,
 
-    use 5.10.0;
+    use v5.10.0;
 
 will do an implicit
 
+    no feature ':all';
     use feature ':5.10';
 
-and so on. Note how the trailing sub-version is automatically stripped from the
+and so on.  Note how the trailing sub-version
+is automatically stripped from the
 version.
 
 But to avoid portability warnings (see L<perlfunc/use>), you may prefer:
@@ -153,79 +297,87 @@ But to avoid portability warnings (see L<perlfunc/use>), you may prefer:
 
 with the same effect.
 
+If the required version is older than Perl 5.10, the ":default" feature
+bundle is automatically loaded instead.
+
 =back
 
 =cut
 
 sub import {
     my $class = shift;
-    if (@_ == 0) {
-	croak("No features specified");
-    }
-    while (@_) {
-	my $name = shift(@_);
-	if (substr($name, 0, 1) eq ":") {
-	    my $v = substr($name, 1);
-	    if (!exists $feature_bundle{$v}) {
-		$v =~ s/^([0-9]+)\.([0-9]+).[0-9]+$/$1.$2/;
-		if (!exists $feature_bundle{$v}) {
-		    unknown_feature_bundle(substr($name, 1));
-		}
-	    }
-	    unshift @_, @{$feature_bundle{$v}};
-	    next;
-	}
-	if (!exists $feature{$name}) {
-	    unknown_feature($name);
-	}
-	$^H{$feature{$name}} = 1;
-        $^H |= $hint_uni8bit if $name eq 'unicode_strings';
+
+    if (!@_) {
+        croak("No features specified");
     }
+
+    __common(1, @_);
 }
 
 sub unimport {
     my $class = shift;
 
-    # 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;
+	$^H &= ~($hint_uni8bit|$hint_mask);
 	return;
     }
 
-    while (@_) {
-	my $name = shift;
-	if (substr($name, 0, 1) eq ":") {
-	    my $v = substr($name, 1);
-	    if (!exists $feature_bundle{$v}) {
-		$v =~ s/^([0-9]+)\.([0-9]+).[0-9]+$/$1.$2/;
-		if (!exists $feature_bundle{$v}) {
-		    unknown_feature_bundle(substr($name, 1));
-		}
-	    }
-	    unshift @_, @{$feature_bundle{$v}};
-	    next;
-	}
-	if (!exists($feature{$name})) {
-	    unknown_feature($name);
+    __common(0, @_);
+}
+
+
+sub __common {
+    my $import = shift;
+    my $bundle_number = $^H & $hint_mask;
+    my $features = $bundle_number != $hint_mask
+	&& $feature_bundle{$hint_bundles[$bundle_number >> $hint_shift]};
+    if ($features) {
+	# Features are enabled implicitly via bundle hints.
+	# Delete any keys that may be left over from last time.
+	delete @^H{ values(%feature) };
+	$^H |= $hint_mask;
+	for (@$features) {
+	    $^H{$feature{$_}} = 1;
+	    $^H |= $hint_uni8bit if $_ eq 'unicode_strings';
 	}
-	else {
-	    delete $^H{$feature{$name}};
+    }
+    while (@_) {
+        my $name = shift;
+        if (substr($name, 0, 1) eq ":") {
+            my $v = substr($name, 1);
+            if (!exists $feature_bundle{$v}) {
+                $v =~ s/^([0-9]+)\.([0-9]+).[0-9]+$/$1.$2/;
+                if (!exists $feature_bundle{$v}) {
+                    unknown_feature_bundle(substr($name, 1));
+                }
+            }
+            unshift @_, @{$feature_bundle{$v}};
+            next;
+        }
+        if (!exists $feature{$name}) {
+            unknown_feature($name);
+        }
+	if ($import) {
+	    $^H{$feature{$name}} = 1;
+	    $^H |= $hint_uni8bit if $name eq 'unicode_strings';
+	} else {
+            delete $^H{$feature{$name}};
             $^H &= ~ $hint_uni8bit if $name eq 'unicode_strings';
-	}
+        }
     }
 }
 
 sub unknown_feature {
     my $feature = shift;
     croak(sprintf('Feature "%s" is not supported by Perl %vd',
-	    $feature, $^V));
+            $feature, $^V));
 }
 
 sub unknown_feature_bundle {
     my $feature = shift;
     croak(sprintf('Feature bundle "%s" is not supported by Perl %vd',
-	    $feature, $^V));
+            $feature, $^V));
 }
 
 sub croak {
@@ -234,3 +386,5 @@ sub croak {
 }
 
 1;
+
+# ex: set ro: