Markdown.pl: avoid list nesting confusion

With this source:

    * A

      * B

      C

    D

    * E

      * F

      G

    * H

      I

The parser was getting confused about where each unordered list
actually ended when nesting the processed inner list inside the
outer list.

Address this by:

  1) Giving "```" style code blocks their own hash just in case to
     make sure they can never collide with html blocks.

  2) Temporarily (the indentation gets removed before final output)
     indent nested list tags by the current list nesting level to
     ensure there's no confusion about where each list/sublist
     starts and ends.

  3) Make sure the list closing tag is followed by two newlines
     rather than one to avoid potentially not applying markup to
     the immediately following line.

Since a few patterns had minor adjustments for these changes, those
patterns also had a few unnecessarily capturing groups changed to
non-capturing groups in the hope that some miniscule performance
gain can be squeezed out with the change.

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>

Markdown.pl

@@ -75,6 +75,7 @@ my %g_titles;
 my %g_anchors;
 my %g_anchors_id;
 my %g_block_ids;
+my %g_code_block_ids;
 my %g_html_blocks;
 my %g_code_blocks;
 my %opt;
@@ -88,9 +89,10 @@ my %opt;
 # else, it's prefixed with a control character and suffixed with another
 # both of which are not allowed by the XML standard or Unicode.
 sub block_id {
-    $_[1] ?
-    "\2".refaddr(\$g_perm_block_ids{$_[0]})."\3" :
-    "\5".refaddr(\$g_block_ids{$_[0]})."\6";
+    $_[1] or return "\5".refaddr(\$g_block_ids{$_[0]})."\6";
+    $_[1] == 1 and return "\2".refaddr(\$g_perm_block_ids{$_[0]})."\3";
+    $_[1] == 2 and return "\25".refaddr(\$g_code_block_ids{$_[0]})."\26";
+    die "programmer error: bad block_id type $_[1]";
 }
 
 # Regex to match balanced [brackets]. See Friedl's
@@ -439,6 +441,7 @@ sub Markdown {
     %g_titles = ();
     %g_anchors = ();
     %g_block_ids = ();
+    %g_code_block_ids = ();
     %g_html_blocks = ();
     %g_code_blocks = ();
     $g_list_level = 0;
@@ -470,8 +473,11 @@ sub Markdown {
 
     $text = _RunBlockGamut($text, 1);
 
+    # Remove indentation markers
+    $text =~ s/\027+//gs;
+
     # Unhashify code blocks
-    $text =~ s/(\005\d+\006)/$g_code_blocks{$1}/g;
+    $text =~ s/(\025\d+\026)/$g_code_blocks{$1}/g;
 
     $text = _UnescapeSpecialChars($text);
 
@@ -578,6 +584,7 @@ BEGIN {
 sub _HashHTMLBlocks {
     my $text = shift;
     my $less_than_indent = $opt{indent_width} - 1;
+    my $idt = "\027" x $g_list_level;
 
     # Hashify HTML blocks:
     # We only want to do this for block-level HTML tags, such as headers,
@@ -600,10 +607,11 @@ sub _HashHTMLBlocks {
     $text =~ s{
 		(			# save in $1
 		    ^			# start of line (with /m)
-		    <($block_tags_a)	# start tag = $2
+		    ((?:\Q$idt\E)?)	# optional lead in = $2
+		    <($block_tags_a)	# start tag = $3
 		    \b			# word break
-		    (.*\n)*?		# any number of lines, minimally matching
-		    </\2>		# the matching end tag
+		    (?:.*\n)*?		# any number of lines, minimally matching
+		    \2</\3>		# the matching end tag
 		    [ ]*		# trailing spaces
 		    (?=\n+|\Z) # followed by a newline or end of document
 		)
@@ -620,9 +628,10 @@ sub _HashHTMLBlocks {
     $text =~ s{
 		(			# save in $1
 		    ^			# start of line (with /m)
+		    (?:\Q$idt\E)?	# optional lead in
 		    <($block_tags_b)	# start tag = $2
 		    \b			# word break
-		    (.*\n)*?		# any number of lines, minimally matching
+		    (?:.*\n)*?		# any number of lines, minimally matching
 		    .*</\2>		# the matching end tag
 		    [ ]*		# trailing spaces
 		    (?=\n+|\Z) # followed by a newline or end of document
@@ -642,9 +651,9 @@ sub _HashHTMLBlocks {
 		)
 		(			# save in $1
 		    [ ]{0,$less_than_indent}
-		    <(hr)		# start tag = $2
+		    <(?:hr)		# start tag
 		    \b			# word break
-		    ([^<>])*?		#
+		    (?:[^<>])*?		#
 		    /?>			# the matching end tag
 		    [ ]*
 		    (?=\n{2,}|\Z)	# followed by a blank line or end of document
@@ -1422,7 +1431,8 @@ sub _DoLists {
 		    $list_att .= " start=\"$first_marker_num\"" unless $first_marker_num == 1;
 		}
 	}
-	$result = "<$list_type$list_att$list_class>\n$list_incr" . $result . "</$list_type>\n";
+	my $idt = "\027" x $g_list_level;
+	$result = "$idt<$list_type$list_att$list_class>\n$list_incr" . $result . "$idt</$list_type>\n\n";
 	$result;
     };
 
@@ -1513,6 +1523,7 @@ sub _ProcessListItems {
     # starting cardinal number; e.g. "1." or "a.".
 
     $g_list_level++;
+    my $idt = "\027" x $g_list_level;
     my $marker_kind = $list_type eq "ul" ? $marker_ul : $marker_ol;
     my $first_marker;
     my $first_marker_type;
@@ -1639,12 +1650,12 @@ sub _ProcessListItems {
 	}
 
 	# Append to $result
-	$result .= "$incr<li$liatt>" . $checkbox . $item . "</li>\n";
+	$result .= "$incr$idt<li$liatt>" . $checkbox . $item . "$idt</li>\n";
     }
     if ($fancy) {
 	# remove "incrlevel=$g_list_level " parts
 	$result =~ s{<span incrlevel=$g_list_level class="$opt{style_prefix}ol-incr((?:-\d{1,2})?)">}
-	    {<span class="$opt{style_prefix}ol-incr$1">}g;
+	    {$idt<span class="$opt{style_prefix}ol-incr$1">}g;
     } else {
 	# remove the $g_list_level incr spans entirely
 	$result =~ s{<span incrlevel=$g_list_level class="$opt{style_prefix}ol-incr(?:-\d{1,2})?"></span>\n}{}g;
@@ -1687,7 +1698,7 @@ sub _DoCodeBlocks {
 
 	    my $result = "<div class=\"$opt{style_prefix}code\"><pre style=\"display:none\"></pre><pre><code>"
 		. $codeblock . "\n</code></pre></div>";
-	    my $key = block_id($result);
+	    my $key = block_id($result, 2);
 	    $g_code_blocks{$key} = $result;
 	    "\n\n" . $key . "\n\n";
 	}egmx;