upgrade to HTML::TreeBuilder 5 to get weak references

This might break people's code on really old Perls.

Closes #251

Changes

@@ -4,6 +4,10 @@ Revision history for WWW::Mechanize
     [DOCUMENTATION]
     - Fix broken Pod
 
+    [ENHANCEMENTS]
+    - Upgrade to HTML::TreeBuilder version 5 to get support for weak references in
+      HTML::Element (GH#251) (Julien Fiegehenn)
+
 1.89      2018-10-18 19:13:34Z
     [ENHANCEMENTS]
     - Add support to find_image() and find_all_images() via 'id'

dist.ini

@@ -23,6 +23,7 @@ dir = bin
 
 [Prereqs / RuntimeRequires]
 perl = 5.006
+Scalar::Util = 1.14
 
 [Prereqs / TestRequires]
 CGI = 4.32

lib/WWW/Mechanize.pm

@@ -748,9 +748,9 @@ are passed to I<content()>:
 =item I<< $mech->content( format => 'text' ) >>
 
 Returns a text-only version of the page, with all HTML markup
-stripped. This feature requires I<HTML::TreeBuilder> to be installed,
-or a fatal error will be thrown. This works only if the contents are
-HTML.
+stripped. This feature requires I<HTML::TreeBuilder> version 5 or higher
+to be installed, or a fatal error will be thrown. This works only if
+the contents are HTML.
 
 =item I<< $mech->content( base_href => [$base_href|undef] ) >>
 
@@ -822,7 +822,7 @@ sub content {
 =head2 $mech->text()
 
 Returns the text of the current HTML content.  If the content isn't
-HTML, $mech will die.
+HTML, C<$mech> will die.
 
 The text is extracted by parsing the content, and then the extracted
 text is cached, so don't worry about performance of calling this
@@ -834,13 +834,16 @@ sub text {
     my $self = shift;
 
     if ( not defined $self->{text} ) {
-        require HTML::TreeBuilder;
+        unless ( exists $INC{'HTML::TreeBuilder'} ) {
+            require HTML::TreeBuilder;
+            HTML::TreeBuilder->VERSION(5);
+            HTML::TreeBuilder->import('-weak');
+        }
         my $tree = HTML::TreeBuilder->new();
         $tree->parse( $self->content );
         $tree->eof();
         $tree->elementify(); # just for safety
         $self->{text} = $tree->as_text();
-        $tree->delete;
     }
 
     return $self->{text};

t/content.t

@@ -40,8 +40,8 @@ $mech->update_html($html);
 =cut
 
 SKIP: {
-    eval 'use HTML::TreeBuilder';
-    skip 'HTML::TreeBuilder not installed', 2 if $@;
+    eval 'use HTML::TreeBuilder 5';
+    skip 'HTML::TreeBuilder version 5 not installed', 2 if $@;
 
     my $text = $mech->content(format => 'text');
     like( $text, qr/Fine/, 'Found Fine' );