[Encode] decode('alias', $1) goes wild

Dear Porters,

  SUZUKI Norio has reported me an interesting bug in Encode.  See this.

#!
use Encode;
$_ = "eeeee" ;
while (/(e)/g) {
        my $utf = decode('Shift_JIS', $1);
        print "position:",pos,"\n";
}
__END__

This one screws up but decode('shiftjis', $1) does work.  Why?  Evil 
'local $_' in find_alias() in Encode::Alias.  This one has been there 
before I took over the maintenance of Encode for the sake of this;
perldoc Encode::Alias
> As a code reference, e.g.:
> define_alias( sub { return /^iso8859-(\d+)$/i ? "iso-8859-$1" : undef 
> } , '');
>           In this case, $_ will be set to the name that is being
>            looked up and ENCODING is passed to the sub as its
>            first argument.  The example is another way to alias
>            names as used in X11 fonts to the MIME names for the
>            iso-8859-* family.
"my"ing that will breach this example.  here is a sample script to test 
this feature
#!use Encode;
use Encode::Alias;
# $Encode::Alias::DEBUG = 1;
define_alias( sub { return /^isolat-(\d+)$/i ? "iso-8859-$1" : undef } 
, '');
print find_encoding("isolat-1")->name, "\n"; # iso-8859-1
__END__

> > perl t/coderef-alias.pl
> iso-8859-1
> shiftjis
> > perl -Mblib t/coderef-alias.pl
> Can't call method "name" on an undefined value at coderef-alias.pl 
> line 8.
However, this alias-via-coderef feature is hardly ever used and 
decode('alias', $1) ought to be far more common.  So I will change this 
feature if not remove it.
The following patch removes 'local $_' so alias-via-coderef will no 
longer work AS DOCUMENTED.  However, you can still alias-via-coderef as 
follows, which methinks is much cleaner.
define_alias( sub { shift =~ /^isolat-(\d+)$/i ? "iso-8859-$1" : undef 
} );
Dan the Encode Maintainer

P.S.  I still need a little bit more time for $Encode::VERSION++.  My 
load average is too high.  Someone interested in implementing 'use less 
q(time)' ?
--- lib/Encode/Alias.pm 2002/10/06 03:27:02     1.34
+++ lib/Encode/Alias.pm 2003/02/05 18:32:48
@@ -20,38 +20,38 @@
 sub find_alias
 {
     my $class = shift;
-    local $_ = shift;
-    unless (exists $Alias{$_})
+    my $find = shift;
+    unless (exists $Alias{$find})
     {
-        $Alias{$_} = undef; # Recursion guard
+        $Alias{$find} = undef; # Recursion guard
        for (my $i=0; $i < @Alias; $i += 2)
        {
            my $alias = $Alias[$i];
            my $val   = $Alias[$i+1];
            my $new;
-           if (ref($alias) eq 'Regexp' && $_ =~ $alias)
+           if (ref($alias) eq 'Regexp' && $find =~ $alias)
            {
                $DEBUG and warn "eval $val";
                $new = eval $val;
-               # $@ and warn "$val, $@";
+               $DEBUG and $@ and warn "$val, $@";
            }
            elsif (ref($alias) eq 'CODE')
            {
-               $DEBUG and warn "$alias", "->", "($val)";
-               $new = $alias->($val);
+               $DEBUG and warn "$alias", "->", "($find)";
+               $new = $alias->($find);
            }
-           elsif (lc($_) eq lc($alias))
+           elsif (lc($find) eq lc($alias))
            {
                $new = $val;
            }
            if (defined($new))
            {
-               next if $new eq $_; # avoid (direct) recursion on bugs
+               next if $new eq $find; # avoid (direct) recursion on 
bugs
                $DEBUG and warn "$alias, $new";
                my $enc = (ref($new)) ? $new : 
Encode::find_encoding($new);
                if ($enc)
                {
-                   $Alias{$_} = $enc;
+                   $Alias{$find} = $enc;
                    last;
                }
            }
@@ -59,14 +59,14 @@
     }
     if ($DEBUG){
        my $name;
-       if (my $e = $Alias{$_}){
+       if (my $e = $Alias{$find}){
            $name = $e->name;
        }else{
            $name = "";
        }
-       warn "find_alias($class, $_)->name = $name";
+       warn "find_alias($class, $find)->name = $name";
     }
-    return $Alias{$_};
+    return $Alias{$find};
 }

 sub define_alias