mdwn: Don't mangle <style> into <elyts> under some circumstances

We can ask libdiscount not to elide <style> blocks, which means we
don't have to work around them.

IkiWiki/Plugin/mdwn.pm

@@ -82,10 +82,15 @@ sub htmlize (@) {
 					# Workaround for discount's eliding
 					# of <style> blocks.
 					# https://rt.cpan.org/Ticket/Display.html?id=74016
-					$t=~s/<style/<elyts/ig;
-					my $r=Text::Markdown::Discount::markdown($t, $flags);
-					$r=~s/<elyts/<style/ig;
-					return $r;
+					if (Text::Markdown::Discount->can("MKD_NOSTYLE")) {
+						$flags |= Text::Markdown::Discount::MKD_NOSTYLE();
+					}
+					else {
+						# This is correct for the libmarkdown.so.2 ABI
+						$flags |= 0x00400000;
+					}
+
+					return Text::Markdown::Discount::markdown($t, $flags);
 				}
 			}
 		}

debian/changelog

@@ -7,6 +7,7 @@ ikiwiki (3.20170112) UNRELEASED; urgency=medium
     misconfigured nginx servers, and in general treat sessions with
     a set-but-empty name as if they were not signed in.
   * When the CGI fails, print the error to stderr, not "Died"
+  * mdwn: Don't mangle <style> into <elyts> under some circumstances
 
  -- Simon McVittie <smcv@debian.org>  Sun, 14 May 2017 15:34:52 +0100
 

doc/bugs/escaped_style_tag_becomes_elyts.mdwn

@@ -28,3 +28,7 @@ discuss style markup several times. The first couple of times I saw this happen,
 I thought it was some sort of misguided anti-cross-site-scripting filter...
 
 --[[smcv]]
+
+> [[Fixed|done]] by passing the `MKD_NOSTYLE` flag to Discount instead.
+> Unfortunately this isn't bound by [[!cpan Text::Markdown::Discount]] yet,
+> so for now I'm hard-coding its numeric value. --[[smcv]]