[PATCH 5/6] hlmod: support "```$LANG" blocks in text

[Eric Wong <e@80x24.org>]

This is compatible with Markdown; but we still keep the WYSIWYG
nature of plain-text with this.  This is only intended for use
with our documentation.  Enabling any type of Markdown support
for emails can lead to incompatibilities or interopability
problems with alternative implementations.
---
 lib/PublicInbox/HlMod.pm | 21 ++++++++++++++++++++-
 t/hl_mod.t               | 20 ++++++++++++++++++++
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/lib/PublicInbox/HlMod.pm b/lib/PublicInbox/HlMod.pm
index 014d82f..36e3110 100644
--- a/lib/PublicInbox/HlMod.pm
+++ b/lib/PublicInbox/HlMod.pm
@@ -16,7 +16,7 @@ package PublicInbox::HlMod;
 use strict;
 use warnings;
 use highlight; # SWIG-generated stuff
-use PublicInbox::Hval qw(src_escape);
+use PublicInbox::Hval qw(src_escape ascii_html);
 my $hl;
 
 sub _parse_filetypes ($) {
@@ -127,4 +127,23 @@ sub do_hl_lang {
 	\$out;
 }
 
+# Highlight text, but support Markdown "```$LANG" notation
+# while preserving WYSIWYG of plain-text documentation.
+# This is NOT to be enabled by default or encouraged for parsing
+# emails, since it is NOT stable and can lead to standards
+# proliferation of email.
+sub do_hl_text {
+	my ($self, $str) = @_;
+
+	$$str = join('', map {
+		if (/\A(``` ?)(\w+)\s*?\n(.+)(^```\s*)\z/sm) {
+			my ($pfx, $lang, $code, $post) = ($1, $2, $3, $4);
+			my $hl = do_hl_lang($self, \$code, $lang) || \$code;
+			$pfx . $lang . "\n" . $$hl . $post;
+		} else {
+			ascii_html($_);
+		}
+	} split(/(^``` ?\w+\s*?\n.+?^```\s*$)/sm, $$str));
+}
+
 1;
diff --git a/t/hl_mod.t b/t/hl_mod.t
index f2eb5f9..84a4b57 100644
--- a/t/hl_mod.t
+++ b/t/hl_mod.t
@@ -40,4 +40,24 @@ my $orig = $str;
 	}
 }
 
+if ('experimental, only for help text') {
+	my $tmp = <<'EOF';
+:>
+```perl
+my $foo = 1 & 2;
+```
+:<
+EOF
+	$hls->do_hl_text(\$tmp);
+	my @hl = split(/^/m, $tmp);
+	is($hl[0], ":&gt;\n", 'first line escaped');
+	is($hl[1], "```perl\n", '2nd line preserved');
+	like($hl[2], qr/<span\b/, 'code highlighted');
+	like($hl[2], qr/&amp;/, 'ampersand escaped');
+	is($hl[3], "```\n", '4th line preserved');
+	is($hl[4], ":&lt;\n", '5th line escaped');
+	is(scalar(@hl), 5, 'no extra line');
+
+}
+
 done_testing;
-- 
EW