adds a testcase for HTML comments in the middle of a block and a twea…

…k to src/document.c that recognizes them as tags to copy over literally

src/document.c

@@ -402,9 +402,23 @@ tag_length(uint8_t *data, size_t size, hoedown_autolink_type *autolink)
 	/* a valid tag can't be shorter than 3 chars */
 	if (size < 3) return 0;
 
-	/* begins with a '<' optionally followed by '/', followed by letter or number */
 	if (data[0] != '<') return 0;
-	i = (data[1] == '/') ? 2 : 1;
+
+        /* HTML comment, laxist form */
+        if (size > 5 && data[1] == '!' && data[2] == '-' && data[3] == '-') {
+		i = 5;
+
+		while (i < size && !(data[i - 2] == '-' && data[i - 1] == '-' && data[i] == '>'))
+			i++;
+
+		i++;
+
+		if (i <= size)
+			return i;
+        }
+
+	/* begins with a '<' optionally followed by '/', followed by letter or number */
+        i = (data[1] == '/') ? 2 : 1;
 
 	if (!isalnum(data[i]))
 		return 0;

src/html_smartypants.c

@@ -314,7 +314,7 @@ smartypants_cb__ltag(hoedown_buffer *ob, struct smartypants_data *smrt, uint8_t
 	size_t tag, i = 0;
 
 	/* This is a comment. Copy everything verbatim until --> or EOF is seen. */
-	if (i + 4 < size && memcmp(text, "<!--", 4) == 0) {
+	if (i + 4 < size && memcmp(text + i, "<!--", 4) == 0) {
 		i += 4;
 		while (i + 3 < size && memcmp(text + i, "-->",  3) != 0)
 			i++;

test/Tests/CommentsInMiddleOfLine.html

@@ -0,0 +1,6 @@
+<p>It would be super-keen to be able to use <a href=
+"https://github.com/google/moe">MOE</a> directives in Markdown.</p>
+<!-- HTML comments work at the start of a block -->
+<p>But I'd <!-- MOE:begin_strip -->really, really
+<!-- MOE:end_strip -->
+like to be able to use them in the middle of a line.</p>

test/Tests/CommentsInMiddleOfLine.text

@@ -0,0 +1,8 @@
+It would be super-keen to be able to use [MOE](https://github.com/google/moe)
+directives in Markdown.
+
+<!-- HTML comments work at the start of a block -->
+
+But I'd <!-- MOE:begin_strip -->really, really <!-- MOE:end_strip -->
+like to be able to use them in the middle of a line.
+

test/config.json

@@ -97,6 +97,10 @@
             "output": "Tests/Formatting in Table of Contents.html",
             "flags": ["--html-toc", "-t", "3"]
         },
+        {
+            "input": "Tests/CommentsInMiddleOfLine.text",
+            "output": "Tests/CommentsInMiddleOfLine.html"
+        },
         {
             "input": "Tests/Math.text",
             "output": "Tests/Math.html",