Tweak scanDelims algorithm

- explicitly set nextChar and lastChar to 0x20 at the begin/end of line

 - `_` between punctuation characters can now close an emphasis, see:
   https://github.com/jgm/commonmark.js/issues/12#issuecomment-77421682

 - `"` between punctuation characters can now be a closed quote
   in smartquotes rule.

lib/rules_core/smartquotes.js

@@ -50,17 +50,15 @@ function process_inlines(tokens, state) {
       pos = t.index + 1;
       isSingle = (t[0] === "'");
 
-      lastChar = t.index - 1 >= 0 ? text.charCodeAt(t.index - 1) : -1;
-      nextChar = pos < max ? text.charCodeAt(pos) : -1;
+      // treat begin/end of the line as a whitespace
+      lastChar = t.index - 1 >= 0 ? text.charCodeAt(t.index - 1) : 0x20;
+      nextChar = pos < max ? text.charCodeAt(pos) : 0x20;
 
-      isLastPunctChar = lastChar >= 0 &&
-        (isMdAsciiPunct(lastChar) || isPunctChar(String.fromCharCode(lastChar)));
-      isNextPunctChar = nextChar >= 0 &&
-        (isMdAsciiPunct(nextChar) || isPunctChar(String.fromCharCode(nextChar)));
+      isLastPunctChar = isMdAsciiPunct(lastChar) || isPunctChar(String.fromCharCode(lastChar));
+      isNextPunctChar = isMdAsciiPunct(nextChar) || isPunctChar(String.fromCharCode(nextChar));
 
-      // begin/end of the line counts as a whitespace too
-      isLastWhiteSpace = lastChar < 0 || isWhiteSpace(lastChar);
-      isNextWhiteSpace = nextChar < 0 || isWhiteSpace(nextChar);
+      isLastWhiteSpace = isWhiteSpace(lastChar);
+      isNextWhiteSpace = isWhiteSpace(nextChar);
 
       if (isNextWhiteSpace) {
         canOpen = false;
@@ -87,7 +85,8 @@ function process_inlines(tokens, state) {
 
       if (canOpen && canClose) {
         // treat this as the middle of the word
-        canOpen = canClose = false;
+        canOpen = false;
+        canClose = isNextPunctChar;
       }
 
       if (!canOpen && !canClose) {

lib/rules_inline/emphasis.js

@@ -19,7 +19,8 @@ function scanDelims(state, start) {
       max = state.posMax,
       marker = state.src.charCodeAt(start);
 
-  lastChar = start > 0 ? state.src.charCodeAt(start - 1) : -1;
+  // treat beginning of the line as a whitespace
+  lastChar = start > 0 ? state.src.charCodeAt(start - 1) : 0x20;
 
   while (pos < max && state.src.charCodeAt(pos) === marker) { pos++; }
 
@@ -29,16 +30,14 @@ function scanDelims(state, start) {
 
   count = pos - start;
 
-  nextChar = pos < max ? state.src.charCodeAt(pos) : -1;
+  // treat end of the line as a whitespace
+  nextChar = pos < max ? state.src.charCodeAt(pos) : 0x20;
 
-  isLastPunctChar = lastChar >= 0 &&
-    (isMdAsciiPunct(lastChar) || isPunctChar(String.fromCharCode(lastChar)));
-  isNextPunctChar = nextChar >= 0 &&
-    (isMdAsciiPunct(nextChar) || isPunctChar(String.fromCharCode(nextChar)));
+  isLastPunctChar = isMdAsciiPunct(lastChar) || isPunctChar(String.fromCharCode(lastChar));
+  isNextPunctChar = isMdAsciiPunct(nextChar) || isPunctChar(String.fromCharCode(nextChar));
 
-  // begin/end of the line counts as a whitespace too
-  isLastWhiteSpace = lastChar < 0 || isWhiteSpace(lastChar);
-  isNextWhiteSpace = nextChar < 0 || isWhiteSpace(nextChar);
+  isLastWhiteSpace = isWhiteSpace(lastChar);
+  isNextWhiteSpace = isWhiteSpace(nextChar);
 
   if (isNextWhiteSpace) {
     can_open = false;
@@ -59,7 +58,8 @@ function scanDelims(state, start) {
   if (marker === 0x5F /* _ */) {
     if (can_open && can_close) {
       // "_" inside a word can neither open nor close an emphasis
-      can_open = can_close = false;
+      can_open = false;
+      can_close = isNextPunctChar;
     }
   }
 

lib/rules_inline/strikethrough.js

@@ -19,7 +19,8 @@ function scanDelims(state, start) {
       max = state.posMax,
       marker = state.src.charCodeAt(start);
 
-  lastChar = start > 0 ? state.src.charCodeAt(start - 1) : -1;
+  // treat beginning of the line as a whitespace
+  lastChar = start > 0 ? state.src.charCodeAt(start - 1) : 0x20;
 
   while (pos < max && state.src.charCodeAt(pos) === marker) { pos++; }
 
@@ -29,16 +30,14 @@ function scanDelims(state, start) {
 
   count = pos - start;
 
-  nextChar = pos < max ? state.src.charCodeAt(pos) : -1;
+  // treat end of the line as a whitespace
+  nextChar = pos < max ? state.src.charCodeAt(pos) : 0x20;
 
-  isLastPunctChar = lastChar >= 0 &&
-    (isMdAsciiPunct(lastChar) || isPunctChar(String.fromCharCode(lastChar)));
-  isNextPunctChar = nextChar >= 0 &&
-    (isMdAsciiPunct(nextChar) || isPunctChar(String.fromCharCode(nextChar)));
+  isLastPunctChar = isMdAsciiPunct(lastChar) || isPunctChar(String.fromCharCode(lastChar));
+  isNextPunctChar = isMdAsciiPunct(nextChar) || isPunctChar(String.fromCharCode(nextChar));
 
-  // begin/end of the line counts as a whitespace too
-  isLastWhiteSpace = lastChar < 0 || isWhiteSpace(lastChar);
-  isNextWhiteSpace = nextChar < 0 || isWhiteSpace(nextChar);
+  isLastWhiteSpace = isWhiteSpace(lastChar);
+  isNextWhiteSpace = isWhiteSpace(nextChar);
 
   if (isNextWhiteSpace) {
     can_open = false;

test/fixtures/markdown-it/commonmark_extras.txt

@@ -61,6 +61,14 @@ just a funny little fence
 </code></pre>
 .
 
+Underscore between punctuation chars should be able to close emphasis.
+
+.
+_(hai)_.
+.
+<p><em>(hai)</em>.</p>
+.
+
 
 Coverage. Directive can terminate paragraph.
 .

test/fixtures/markdown-it/smartquotes.txt

@@ -82,3 +82,11 @@ users' stuff
 .
 <p>users’ stuff</p>
 .
+
+Quotes between punctuation chars:
+
+.
+"(hai)".
+.
+<p>“(hai)”.</p>
+.