Update emphasis to match CommonMark 0.19

lib/rules_inline/emphasis.js

@@ -11,11 +11,11 @@ var isMdAsciiPunct = require('../common/utils').isMdAsciiPunct;
 // parse sequence of emphasis markers,
 // "start" should point at a valid marker
 function scanDelims(state, start) {
-  var pos = start, lastChar, nextChar, count,
+  var pos = start, lastChar, nextChar, count, can_open, can_close,
       isLastWhiteSpace, isLastPunctChar,
       isNextWhiteSpace, isNextPunctChar,
-      can_open = true,
-      can_close = true,
+      left_flanking = true,
+      right_flanking = true,
       max = state.posMax,
       marker = state.src.charCodeAt(start);
 
@@ -24,10 +24,6 @@ function scanDelims(state, start) {
 
   while (pos < max && state.src.charCodeAt(pos) === marker) { pos++; }
 
-  if (pos >= max) {
-    can_open = false;
-  }
-
   count = pos - start;
 
   // treat end of the line as a whitespace
@@ -40,27 +36,28 @@ function scanDelims(state, start) {
   isNextWhiteSpace = isWhiteSpace(nextChar);
 
   if (isNextWhiteSpace) {
-    can_open = false;
+    left_flanking = false;
   } else if (isNextPunctChar) {
     if (!(isLastWhiteSpace || isLastPunctChar)) {
-      can_open = false;
+      left_flanking = false;
     }
   }
 
   if (isLastWhiteSpace) {
-    can_close = false;
+    right_flanking = false;
   } else if (isLastPunctChar) {
     if (!(isNextWhiteSpace || isNextPunctChar)) {
-      can_close = false;
+      right_flanking = false;
     }
   }
 
   if (marker === 0x5F /* _ */) {
-    if (can_open && can_close) {
     // "_" inside a word can neither open nor close an emphasis
-      can_open = false;
-      can_close = isNextPunctChar;
-    }
+    can_open  = left_flanking  && (!right_flanking || isLastPunctChar);
+    can_close = right_flanking && (!left_flanking  || isNextPunctChar);
+  } else {
+    can_open  = left_flanking;
+    can_close = right_flanking;
   }
 
   return {