Add fenced comment block support (%%%)

src/block.ts

@@ -50,6 +50,7 @@ const pattNextBarOrTicks = pattern("[^`|\\r\\n]*(?:[|]|`+)");
 const pattCaptionStart = pattern("\\^[ \\t]+");
 const pattFootnoteStart = pattern("\\[\\^([^\\]]+)\\]:[ \\t\\r\\n]");
 const pattThematicBreak = pattern("[-*][ \t]*[-*][ \\t]*[-*][-* \\t]*\\r?\\n");
+const pattCommentFence = pattern("(%%%%*)[ \\t]*\\r?\\n");
 const pattDivFence = pattern("(::::*)[ \\t]*\\r?\\n");
 const pattDivFenceStart = pattern("(::::*)[ \\t]*");
 const pattDivFenceEnd = pattern("([\\w_-]*)[ \\t]*\\r?\\n");
@@ -626,6 +627,50 @@ class EventParser {
         }
       },
 
+      {
+        name: "fenced_comment",
+        type: ContentType.Block,
+        content: ContentType.Text,
+        continue: (container) => {
+          const m = this.find(container.extra.closePattern);
+          if (m) {
+            container.extra.endFenceStartpos = m.startpos;
+            container.extra.endFenceEndpos = m.startpos + m.captures[0].length - 1;
+            this.pos = m.endpos;
+            this.finishedLine = true;
+            return false;
+          } else {
+            return true;
+          }
+        },
+        open: (spec) => {
+          const m = this.find(pattCommentFence);
+          if (m) {
+            const border = m.captures[0];
+            const closePattern = pattern("(" + border +
+                              "%*)[ \\t]*[\\r\\n]");
+            this.addContainer(new Container(spec, { closePattern: closePattern }));
+            this.addMatch(m.startpos, m.startpos + border.length - 1,
+              "+comment");
+            this.pos = m.endpos;
+            this.finishedLine = true;
+            return true;
+          } else {
+            return false;
+          }
+        },
+        close: () => {
+          const container = this.containers.pop();
+          if (!container) return;
+          const sp = container.extra.endFenceStartpos || this.pos;
+          const ep = container.extra.endFenceEndpos || this.pos;
+          this.addMatch(sp, ep, "-comment");
+          if (sp === ep) {
+            this.warn(new Warning("Unclosed comment block", this.pos));
+          }
+        }
+      },
+
       {
         name: "fenced_div",
         type: ContentType.Block,

src/functional.spec.ts

@@ -11,6 +11,7 @@ const testfiles = [
   "symb.test",
   "emphasis.test",
   "escapes.test",
+  "fenced_comments.test",
   "fenced_divs.test",
   "footnotes.test",
   "headings.test",

src/parse.ts

@@ -1075,6 +1075,18 @@ const parse = function(input: string, options: ParseOptions = {}): Doc {
           input.substring(startpos, endpos + 1);
       },
 
+      ["+comment"]: (suffixes, startpos, endpos, pos) => {
+        pushContainer(pos);
+        context = Context.Verbatim;
+      },
+
+      ["-comment"]: (suffixes, startpos, endpos, pos) => {
+        popContainer(pos);
+        // Discard content - comments are not rendered
+        context = Context.Normal;
+        accumulatedText = "";
+      },
+
       ["+code_block"]: (suffixes, startpos, endpos, pos) => {
         pushContainer(pos);
         context = Context.Verbatim;

test/fenced_comments.test

@@ -0,0 +1,54 @@
+Basic fenced comment:
+
+```
+Before.
+
+%%%
+This is a comment.
+%%%
+
+After.
+.
+<p>Before.</p>
+<p>After.</p>
+```
+
+Fenced comment with blank lines:
+
+```
+%%%
+First line.
+
+Second line.
+%%%
+.
+```
+
+Fenced comment with longer fence:
+
+```
+%%%%
+%%% not the end
+still inside
+%%%%
+.
+```
+
+Closing fence must match length:
+
+```
+%%%%
+comment
+%%%
+still comment
+%%%%
+.
+```
+
+Unclosed fenced comment consumes rest of document:
+
+```
+%%%
+This comment never closes.
+.
+```