Fix GFM Example 116

Only code fences made from backticks cannot have other backticks in the same line. Fences with tildes can have both tildes and backticks. This allows the tilde case to work correctly.

Also test for detection of these fences as they break or do not break paragraphs.

src/rules.js

@@ -10,7 +10,7 @@ const {
 const block = {
   newline: /^\n+/,
   code: /^( {4}[^\n]+\n*)+/,
-  fences: /^ {0,3}(`{3,}|~{3,})([^`~\n]*)\n(?:|([\s\S]*?)\n)(?: {0,3}\1[~`]* *(?:\n+|$)|$)/,
+  fences: /^ {0,3}(`{3,}(?=[^`\n]*\n)|~{3,})([^\n]*)\n(?:|([\s\S]*?)\n)(?: {0,3}\1[~`]* *(?:\n+|$)|$)/,
   hr: /^ {0,3}((?:- *){3,}|(?:_ *){3,}|(?:\* *){3,})(?:\n+|$)/,
   heading: /^ {0,3}(#{1,6}) +([^\n]*?)(?: +#+)? *(?:\n+|$)/,
   blockquote: /^( {0,3}> ?(paragraph|[^\n]*)(?:\n|$))+/,
@@ -72,7 +72,7 @@ block.paragraph = edit(block._paragraph)
   .replace('heading', ' {0,3}#{1,6} +')
   .replace('|lheading', '') // setex headings don't interrupt commonmark paragraphs
   .replace('blockquote', ' {0,3}>')
-  .replace('fences', ' {0,3}(?:`{3,}|~{3,})[^`\\n]*\\n')
+  .replace('fences', ' {0,3}(?:`{3,}(?=[^`\\n]*\\n)|~{3,})[^\\n]*\\n')
   .replace('list', ' {0,3}(?:[*+-]|1[.)]) ') // only lists starting from 1 can interrupt
   .replace('html', '</?(?:tag)(?: +|\\n|/?>)|<(?:script|pre|style|!--)')
   .replace('tag', block._tag) // pars can be interrupted by type (6) html blocks

test/specs/commonmark/commonmark.0.29.json

@@ -930,8 +930,7 @@
     "example": 116,
     "start_line": 1996,
     "end_line": 2003,
-    "section": "Fenced code blocks",
-    "shouldFail": true
+    "section": "Fenced code blocks"
   },
   {
     "markdown": "```\n``` aaa\n```\n",

test/specs/gfm/commonmark.0.29.json

@@ -930,8 +930,7 @@
     "example": 116,
     "start_line": 1996,
     "end_line": 2003,
-    "section": "Fenced code blocks",
-    "shouldFail": true
+    "section": "Fenced code blocks"
   },
   {
     "markdown": "```\n``` aaa\n```\n",

test/specs/new/fences_breaking_paragraphs.html

@@ -0,0 +1,14 @@
+<p>A paragraph</p>
+<pre><code class="language-A">Here is code in
+backtick fences</code></pre>
+<p>B paragraph</p>
+<pre><code class="language-B">Here is code in
+tilde fences</code></pre>
+<p>C paragraph</p>
+<pre><code class="language-`C~">Alternative
+tilde fences</code></pre>
+<p>D paragraph ```~D` Invalid use of backtick fences</p>
+<pre><code>
+This will be read as
+part of a codeblock
+that ends with the file</code></pre>

test/specs/new/fences_breaking_paragraphs.md

@@ -0,0 +1,27 @@
+A paragraph
+```A
+Here is code in
+backtick fences
+```
+
+B paragraph
+~~~B
+Here is code in
+tilde fences
+~~~
+
+C paragraph
+~~~`C~
+Alternative
+tilde fences
+~~~
+
+D paragraph
+```~D`
+Invalid use of
+backtick fences
+```
+
+This will be read as
+part of a codeblock
+that ends with the file