Fix emphasis algorithm as per 0.30 spec

https://github.com/commonmark/cmark/issues/383

lib/rules_inline/balance_pairs.js

@@ -21,12 +21,14 @@ function processDelimiters(state, delimiters) {
     if (!closer.close) continue;
 
     // Previously calculated lower bounds (previous fails)
-    // for each marker and each delimiter length modulo 3.
+    // for each marker, each delimiter length modulo 3,
+    // and for whether this closer can be an opener;
+    // https://github.com/commonmark/cmark/commit/34250e12ccebdc6372b8b49c44fab57c72443460
     if (!openersBottom.hasOwnProperty(closer.marker)) {
-      openersBottom[closer.marker] = [ -1, -1, -1 ];
+      openersBottom[closer.marker] = [ -1, -1, -1, -1, -1, -1 ];
     }
 
-    minOpenerIdx = openersBottom[closer.marker][closer.length % 3];
+    minOpenerIdx = openersBottom[closer.marker][(closer.open ? 3 : 0) + (closer.length % 3)];
 
     openerIdx = closerIdx - closer.jump - 1;
 
@@ -87,7 +89,7 @@ function processDelimiters(state, delimiters) {
       // See details here:
       // https://github.com/commonmark/cmark/issues/178#issuecomment-270417442
       //
-      openersBottom[closer.marker][(closer.length || 0) % 3] = newMinOpenerIdx;
+      openersBottom[closer.marker][(closer.open ? 3 : 0) + ((closer.length || 0) % 3)] = newMinOpenerIdx;
     }
   }
 }

test/fixtures/markdown-it/commonmark_extras.txt

@@ -1,3 +1,10 @@
+Issue commonmark/cmark#383:
+.
+*****Hello*world****
+.
+<p>**<em><strong>Hello<em>world</em></strong></em></p>
+.
+
 Issue #246.  Double escaping in ALT
 .
 ![&](#)