Fix incorrect level recalculation in text_collapse

close #466

lib/rules_block/state_block.js

@@ -111,9 +111,9 @@ StateBlock.prototype.push = function (type, tag, nesting) {
   var token = new Token(type, tag, nesting);
   token.block = true;
 
-  if (nesting < 0) { this.level--; }
+  if (nesting < 0) this.level--; // closing tag
   token.level = this.level;
-  if (nesting > 0) { this.level++; }
+  if (nesting > 0) this.level++; // opening tag
 
   this.tokens.push(token);
   return token;

lib/rules_inline/state_inline.js

@@ -50,9 +50,9 @@ StateInline.prototype.push = function (type, tag, nesting) {
 
   var token = new Token(type, tag, nesting);
 
-  if (nesting < 0) { this.level--; }
+  if (nesting < 0) this.level--; // closing tag
   token.level = this.level;
-  if (nesting > 0) { this.level++; }
+  if (nesting > 0) this.level++; // opening tag
 
   this.pendingLevel = this.level;
   this.tokens.push(token);

lib/rules_inline/text_collapse.js

@@ -1,4 +1,10 @@
-// Merge adjacent text nodes into one, and re-calculate all token levels
+// Clean up tokens after emphasis and strikethrough postprocessing:
+// merge adjacent text nodes into one and re-calculate all token levels
+//
+// This is necessary because initially emphasis delimiter markers (*, _, ~)
+// are treated as their own separate text tokens. Then emphasis rule either
+// leaves them as text (needed to merge with adjacent text) or turns them
+// into opening/closing tags (which messes up levels inside).
 //
 'use strict';
 
@@ -10,9 +16,11 @@ module.exports = function text_collapse(state) {
       max = state.tokens.length;
 
   for (curr = last = 0; curr < max; curr++) {
-    // re-calculate levels
-    level += tokens[curr].nesting;
+    // re-calculate levels after emphasis/strikethrough turns some text nodes
+    // into opening/closing tags
+    if (tokens[curr].nesting < 0) level--; // closing tag
     tokens[curr].level = level;
+    if (tokens[curr].nesting > 0) level++; // opening tag
 
     if (tokens[curr].type === 'text' &&
         curr + 1 < max &&