Enhance the link plugin to handle external links.

The following ways to create a link are supported now:
[[url]]
[[text|url]]
url can be one of the following:
- an internal wikilink: will be handled as before
- any other kind of URL, including mailto: proper links will be created:
  <a href="url">url</a>
  <a href="url">text</a>
- an email address:
  <a href="mailto:url">url</a>
  <a href="mailto:url">text</a>

IkiWiki/Plugin/link.pm

@@ -7,6 +7,9 @@ use IkiWiki 3.00;
 
 my $link_regexp;
 
+my $email_regexp = qr/^(?:[a-z0-9!#$%&'*+\/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+\/=?^_`{|}~-]+)*|"(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21\x23-\x5b\x5d-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])*")@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?|\[(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?|[a-z0-9-]*[a-z0-9]:(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21-\x5a\x53-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])+)\])$/i; 
+my $url_regexp = qr/^(?:[^:]+:\/\/|mailto:).*/i;
+
 sub import {
 	hook(type => "getsetup", id => "link", call => \&getsetup);
 	hook(type => "checkconfig", id => "link", call => \&checkconfig);
@@ -57,10 +60,44 @@ sub checkconfig () {
 			)?                      # optional
 
 			\]\]                    # end of link
-		}x,
+		}x;
 	}
 }
 
+sub is_externallink ($$) {
+	my $page = shift;
+	my $url = shift;
+	if ($url =~ /$email_regexp/) {
+		# url looks like an email address, so we assume it
+		# is supposed to be an external link if there is no
+		# page with that name.
+		$url =~ s/#.*//;
+		return (! (bestlink($page, linkpage($url))))
+	}
+	return ($url =~ /$url_regexp/)
+}
+
+sub externallink ($;@) {
+	my $url = shift;
+	my $pagetitle = shift;
+
+	# build pagetitle
+	if (!($pagetitle)) {
+		$pagetitle = $url;
+		# use only the email address as title for mailto: urls
+		if ($pagetitle =~ /^mailto:.*/) {
+			$pagetitle =~ s/^mailto:([^?]+).*/$1/;
+		}
+	}
+
+	# handle email-addresses (without mailto:):
+	if ($url =~ /$email_regexp/) {
+		$url = "mailto:" . $url;
+	}
+
+	return "<a href=\"$url\">$pagetitle</a>";
+}
+
 sub linkify (@) {
 	my %params=@_;
 	my $page=$params{page};
@@ -70,10 +107,14 @@ sub linkify (@) {
 		defined $2
 			? ( $1 
 				? "[[$2|$3".($4 ? "#$4" : "")."]]" 
+				: is_externallink($page, $3 . ($4 ? "#$4" : ""))
+					? externallink("$3" . ($4 ? "#$4" : ""), $2)
 					: htmllink($page, $destpage, linkpage($3),
 						anchor => $4, linktext => pagetitle($2)))
 			: ( $1 
 				? "[[$3".($4 ? "#$4" : "")."]]"
+				: is_externallink($page, $3 . ($4 ? "#$4" : ""))
+					? externallink("$3" . ($4 ? "#$4" : ""))
 					: htmllink($page, $destpage, linkpage($3),
 						anchor => $4))
 	}eg;
@@ -87,8 +128,10 @@ sub scan (@) {
 	my $content=$params{content};
 
 	while ($content =~ /(?<!\\)$link_regexp/g) {
+		if (! is_externallink($page, $2 . ($3 ? "#$3" : ""))) {
 			add_link($page, linkpage($2));
 		}
+	}
 }
 
 sub renamepage (@) {
@@ -98,6 +141,7 @@ sub renamepage (@) {
 	my $new=$params{newpage};
 
 	$params{content} =~ s{(?<!\\)$link_regexp}{
+		if (! is_externallink($page, $2 . ($3 ? "#$3" : ""))) {
 			my $linktext=$2;
 			my $link=$linktext;
 			if (bestlink($page, linkpage($linktext)) eq $old) {
@@ -116,6 +160,7 @@ sub renamepage (@) {
 			defined $1
 				? ( "[[$1|$link".($3 ? "#$3" : "")."]]" )
 				: ( "[[$link".   ($3 ? "#$3" : "")."]]" )
+		}
 	}eg;
 
 	return $params{content};

doc/plugins/link.mdwn

@@ -1,4 +1,4 @@
 [[!template id=plugin name=link core=1 author="[[Joey]]"]]
 [[!tag type/link]]
 
-This plugin implements standard [[WikiLinks|ikiwiki/wikilink]].
+This plugin implements standard [[WikiLinks|ikiwiki/wikilink]] and links to [[external pages|http://www.debian.org]].