mdwn: Don't enable alphabetically labelled ordered lists by default

This avoids misinterpreting initials ("C. S. Lewis was an author"),
the abbreviation for Monsieur ("M. Descartes was a philosopher") and
German page numbering ("S. 42") as ordered lists if they happen to
begin a line.

This only affects the default Discount implementation: Text::Markdown
and Text::MultiMarkdown do not have this feature anyway. A new
mdwn_alpha_list option can be used to restore the old interpretation.

3 files changed, 37 insertions, 0 deletions

diff --git a/IkiWiki/Plugin/mdwn.pm b/IkiWiki/Plugin/mdwn.pm
index e142fec46..9f06c03f2 100644
--- a/IkiWiki/Plugin/mdwn.pm
+++ b/IkiWiki/Plugin/mdwn.pm
@@ -41,10 +41,19 @@ sub getsetup () {
 			safe => 1,
 			rebuild => 1,
 		},
+		mdwn_alpha_lists => {
+			type => "boolean",
+			example => 0,
+			description => "interpret line like 'A. First item' as ordered list when using Discount?",
+			advanced => 1,
+			safe => 1,
+			rebuild => 1,
+		},
 }
 
 sub checkconfig () {
 	$config{mdwn_footnotes} = 1 unless defined $config{mdwn_footnotes};
+	$config{mdwn_alpha_lists} = 0 unless defined $config{mdwn_alpha_lists};
 }
 
 my $markdown_sub;
@@ -101,6 +110,10 @@ sub htmlize (@) {
 						$flags |= Text::Markdown::Discount::MKD_EXTRA_FOOTNOTE();
 					}
 
+					unless ($config{mdwn_alpha_lists}) {
+						$flags |= Text::Markdown::Discount::MKD_NOALPHALIST();
+					}
+
 					# Workaround for discount's eliding
 					# of <style> blocks.
 					# https://rt.cpan.org/Ticket/Display.html?id=74016
diff --git a/debian/changelog b/debian/changelog
index e2a861c3c..455e5981f 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -11,6 +11,10 @@ ikiwiki (3.20170112) UNRELEASED; urgency=medium
   * mdwn: Enable footnotes by default when using the default Discount
     implementation. A new mdwn_footnotes option can be used to disable
     footnotes in MultiMarkdown and Discount.
+  * mdwn: Don't enable alphabetically labelled ordered lists by
+    default when using the default Discount implementation. A new
+    mdwn_alpha_list option can be used to restore the old
+    interpretation.
 
  -- Simon McVittie <smcv@debian.org>  Sun, 14 May 2017 15:34:52 +0100
 
diff --git a/doc/plugins/mdwn.mdwn b/doc/plugins/mdwn.mdwn
index 6b20b7bb0..31123715d 100644
--- a/doc/plugins/mdwn.mdwn
+++ b/doc/plugins/mdwn.mdwn
@@ -7,6 +7,8 @@ It uses the [[ikiwiki/markdown]] minimal markup language.
 This is the standard markup language used by ikiwiki, although some others
 are also available in other plugins.
 
+## Implementations
+
 There are several implementations of markdown support that can be used by
 this plugin. In order of preference:
 
@@ -27,3 +29,21 @@ in the setup file. Note that multimarkdown's metadata and wikilinks
 features are disabled when it's used with ikiwiki. Also note that if the
 `multimarkdown` option is enabled, it takes priority over Discount, which
 might cause formatting that is understood by Discount to be ignored.
+
+
+## Advanced options
+
+* `nodiscount`: If set to 1, Text::Markdown::Discount will not be used
+  even if it is available. The default is to use Discount if available,
+  and this is recommended.
+* `multimarkdown`: If set to 1, Text::MultiMarkdown will be used in
+  preference to Text::Markdown::Discount. The default is to not use
+  MultiMarkdown, and this is recommended.
+* `mdwn_footnotes`: If set to 1, implementations that support it will
+  recognise the PHP Markdown Extra syntax for footnotes. The default
+  is 1.
+* `mdwn_alpha_lists`: If set to 1, Text::Markdown::Discount will
+  accept letters as well as numbers in ordered list markers. The
+  default is 0, to avoid unintended parsing of lines that happen
+  to begin with a letter and a dot, such as "C. S. Lewis was an
+  author" or "M. Descartes was a philosopher".