Follow GFM spec on EM and STRONG delimiters

src/Lexer.js

@@ -319,9 +319,29 @@ module.exports = class Lexer {
   /**
    * Lexing/Compiling
    */
-  inlineTokens(src, tokens = [], inLink = false, inRawBlock = false) {
+  inlineTokens(src, tokens = [], inLink = false, inRawBlock = false, prevChar = '') {
     let token;
 
+    // String with links masked to avoid interference with em and strong
+    let maskedSrc = src;
+    let match;
+
+    // Mask out reflinks
+    if (this.tokens.links) {
+      const links = Object.keys(this.tokens.links);
+      if (links.length > 0) {
+        while ((match = this.tokenizer.rules.inline.reflinkSearch.exec(maskedSrc)) != null) {
+          if (links.includes(match[0].slice(match[0].lastIndexOf('[') + 1, -1))) {
+            maskedSrc = maskedSrc.slice(0, match.index) + '[' + 'a'.repeat(match[0].length - 2) + ']' + maskedSrc.slice(this.tokenizer.rules.inline.reflinkSearch.lastIndex);
+          }
+        }
+      }
+    }
+    // Mask out other blocks
+    while ((match = this.tokenizer.rules.inline.blockSkip.exec(maskedSrc)) != null) {
+      maskedSrc = maskedSrc.slice(0, match.index) + '[' + 'a'.repeat(match[0].length - 2) + ']' + maskedSrc.slice(this.tokenizer.rules.inline.blockSkip.lastIndex);
+    }
+
     while (src) {
       // escape
       if (token = this.tokenizer.escape(src)) {
@@ -360,15 +380,15 @@ module.exports = class Lexer {
       }
 
       // strong
-      if (token = this.tokenizer.strong(src)) {
+      if (token = this.tokenizer.strong(src, maskedSrc, prevChar)) {
         src = src.substring(token.raw.length);
         token.tokens = this.inlineTokens(token.text, [], inLink, inRawBlock);
         tokens.push(token);
         continue;
       }
 
       // em
-      if (token = this.tokenizer.em(src)) {
+      if (token = this.tokenizer.em(src, maskedSrc, prevChar)) {
         src = src.substring(token.raw.length);
         token.tokens = this.inlineTokens(token.text, [], inLink, inRawBlock);
         tokens.push(token);
@@ -414,6 +434,7 @@ module.exports = class Lexer {
       // text
       if (token = this.tokenizer.inlineText(src, inRawBlock, smartypants)) {
         src = src.substring(token.raw.length);
+        prevChar = token.raw.slice(-1);
         tokens.push(token);
         continue;
       }

src/Tokenizer.js

@@ -489,25 +489,49 @@ module.exports = class Tokenizer {
     }
   }
 
-  strong(src) {
-    const cap = this.rules.inline.strong.exec(src);
-    if (cap) {
-      return {
-        type: 'strong',
-        raw: cap[0],
-        text: cap[4] || cap[3] || cap[2] || cap[1]
-      };
+  strong(src, maskedSrc, prevChar = '') {
+    let match = this.rules.inline.strong.start.exec(src);
+
+    if (match && (!match[1] || (match[1] && (prevChar === '' || this.rules.inline.punctuation.exec(prevChar))))) {
+      maskedSrc = maskedSrc.slice(-1 * src.length);
+      const endReg = match[0] === '**' ? this.rules.inline.strong.endAst : this.rules.inline.strong.endUnd;
+
+      endReg.lastIndex = 0;
+
+      let cap;
+      while ((match = endReg.exec(maskedSrc)) != null) {
+        cap = this.rules.inline.strong.middle.exec(maskedSrc.slice(0, match.index + 3));
+        if (cap) {
+          return {
+            type: 'strong',
+            raw: src.slice(0, cap[0].length),
+            text: src.slice(2, cap[0].length - 2)
+          };
+        }
+      }
     }
   }
 
-  em(src) {
-    const cap = this.rules.inline.em.exec(src);
-    if (cap) {
-      return {
-        type: 'em',
-        raw: cap[0],
-        text: cap[6] || cap[5] || cap[4] || cap[3] || cap[2] || cap[1]
-      };
+  em(src, maskedSrc, prevChar = '') {
+    let match = this.rules.inline.em.start.exec(src);
+
+    if (match && (!match[1] || (match[1] && (prevChar === '' || this.rules.inline.punctuation.exec(prevChar))))) {
+      maskedSrc = maskedSrc.slice(-1 * src.length);
+      const endReg = match[0] === '*' ? this.rules.inline.em.endAst : this.rules.inline.em.endUnd;
+
+      endReg.lastIndex = 0;
+
+      let cap;
+      while ((match = endReg.exec(maskedSrc)) != null) {
+        cap = this.rules.inline.em.middle.exec(maskedSrc.slice(0, match.index + 2));
+        if (cap) {
+          return {
+            type: 'em',
+            raw: src.slice(0, cap[0].length),
+            text: src.slice(1, cap[0].length - 1)
+          };
+        }
+      }
     }
   }
 

src/rules.js

@@ -168,19 +168,74 @@ const inline = {
   link: /^!?\[(label)\]\(\s*(href)(?:\s+(title))?\s*\)/,
   reflink: /^!?\[(label)\]\[(?!\s*\])((?:\\[\[\]]?|[^\[\]\\])+)\]/,
   nolink: /^!?\[(?!\s*\])((?:\[[^\[\]]*\]|\\[\[\]]|[^\[\]])*)\](?:\[\])?/,
-  strong: /^__([^\s_])__(?!_)|^\*\*([^\s*])\*\*(?!\*)|^__([^\s][\s\S]*?[^\s])__(?!_)|^\*\*([^\s][\s\S]*?[^\s])\*\*(?!\*)/,
-  em: /^_([^\s_])_(?!_)|^_([^\s_<][\s\S]*?[^\s_])_(?!_|[^\s,punctuation])|^_([^\s_<][\s\S]*?[^\s])_(?!_|[^\s,punctuation])|^\*([^\s*<\[])\*(?!\*)|^\*([^\s<"][\s\S]*?[^\s\[\*])\*(?![\]`punctuation])|^\*([^\s*"<\[][\s\S]*[^\s])\*(?!\*)/,
+  reflinkSearch: 'reflink|nolink(?!\\()',
+  strong: {
+    start: /^(?:(\*\*(?=[*punctuation]))|\*\*)(?![\s])|__/, // (1) returns if starts w/ punctuation
+    middle: /^\*\*(?:(?:(?!overlapSkip)(?:[^*]|\\\*)|overlapSkip)|\*(?:(?!overlapSkip)(?:[^*]|\\\*)|overlapSkip)*?\*)+?\*\*$|^__(?![\s])((?:(?:(?!overlapSkip)(?:[^_]|\\_)|overlapSkip)|_(?:(?!overlapSkip)(?:[^_]|\\_)|overlapSkip)*?_)+?)__$/,
+    endAst: /[^punctuation\s]\*\*(?!\*)|[punctuation]\*\*(?!\*)(?:(?=[punctuation\s]|$))/, // last char can't be punct, or final * must also be followed by punct (or endline)
+    endUnd: /[^\s]__(?!_)(?:(?=[punctuation\s])|$)/ // last char can't be a space, and final _ must preceed punct or \s (or endline)
+  },
+  em: {
+    start: /^(?:(\*(?=[punctuation]))|\*)(?![*\s])|_/, // (1) returns if starts w/ punctuation
+    middle: /^\*(?:(?:(?!overlapSkip)(?:[^*]|\\\*)|overlapSkip)|\*(?:(?!overlapSkip)(?:[^*]|\\\*)|overlapSkip)*?\*)+?\*$|^_(?![_\s])(?:(?:(?!overlapSkip)(?:[^_]|\\_)|overlapSkip)|_(?:(?!overlapSkip)(?:[^_]|\\_)|overlapSkip)*?_)+?_$/,
+    endAst: /[^punctuation\s]\*(?!\*)|[punctuation]\*(?!\*)(?:(?=[punctuation\s]|$))/, // last char can't be punct, or final * must also be followed by punct (or endline)
+    endUnd: /[^\s]_(?!_)(?:(?=[punctuation\s])|$)/ // last char can't be a space, and final _ must preceed punct or \s (or endline)
+  },
   code: /^(`+)([^`]|[^`][\s\S]*?[^`])\1(?!`)/,
   br: /^( {2,}|\\)\n(?!\s*$)/,
   del: noopTest,
-  text: /^(`+|[^`])(?:[\s\S]*?(?:(?=[\\<!\[`*]|\b_|$)|[^ ](?= {2,}\n))|(?= {2,}\n))/
+  text: /^(`+|[^`])(?:[\s\S]*?(?:(?=[\\<!\[`*]|\b_|$)|[^ ](?= {2,}\n))|(?= {2,}\n))/,
+  punctuation: /^([\s*punctuation])/
 };
 
 // list of punctuation marks from common mark spec
-// without ` and ] to workaround Rule 17 (inline code blocks/links)
-// without , to work around example 393
-inline._punctuation = '!"#$%&\'()*+\\-./:;<=>?@\\[^_{|}~';
-inline.em = edit(inline.em).replace(/punctuation/g, inline._punctuation).getRegex();
+// without * and _ to workaround cases with double emphasis
+inline._punctuation = '!"#$%&\'()+\\-.,/:;<=>?@\\[\\]`^{|}~';
+inline.punctuation = edit(inline.punctuation).replace(/punctuation/g, inline._punctuation).getRegex();
+
+// sequences em should skip over [title](link), `code`, <html>
+inline._blockSkip = '\\[[^\\]]*?\\]\\([^\\)]*?\\)|`[^`]*?`|<[^>]*?>';
+inline._overlapSkip = '__[^_]*?__|\\*\\*\\[^\\*\\]*?\\*\\*';
+
+inline.em.start = edit(inline.em.start)
+  .replace(/punctuation/g, inline._punctuation)
+  .getRegex();
+
+inline.em.middle = edit(inline.em.middle)
+  .replace(/punctuation/g, inline._punctuation)
+  .replace(/overlapSkip/g, inline._overlapSkip)
+  .getRegex();
+
+inline.em.endAst = edit(inline.em.endAst, 'g')
+  .replace(/punctuation/g, inline._punctuation)
+  .getRegex();
+
+inline.em.endUnd = edit(inline.em.endUnd, 'g')
+  .replace(/punctuation/g, inline._punctuation)
+  .getRegex();
+
+inline.strong.start = edit(inline.strong.start)
+  .replace(/punctuation/g, inline._punctuation)
+  .getRegex();
+
+inline.strong.middle = edit(inline.strong.middle)
+  .replace(/punctuation/g, inline._punctuation)
+  .replace(/blockSkip/g, inline._blockSkip)
+  .getRegex();
+
+inline.strong.endAst = edit(inline.strong.endAst, 'g')
+  .replace(/punctuation/g, inline._punctuation)
+  .getRegex();
+
+inline.strong.endUnd = edit(inline.strong.endUnd, 'g')
+  .replace(/punctuation/g, inline._punctuation)
+  .getRegex();
+
+inline.blockSkip = edit(inline._blockSkip, 'g')
+  .getRegex();
+
+inline.overlapSkip = edit(inline._overlapSkip, 'g')
+  .getRegex();
 
 inline._escapes = /\\([!"#$%&'()*+,\-./:;<=>?@\[\]\\^_`{|}~])/g;
 
@@ -212,6 +267,11 @@ inline.reflink = edit(inline.reflink)
   .replace('label', inline._label)
   .getRegex();
 
+inline.reflinkSearch = edit(inline.reflinkSearch, 'g')
+  .replace('reflink', inline.reflink)
+  .replace('nolink', inline.nolink)
+  .getRegex();
+
 /**
  * Normal Inline Grammar
  */
@@ -223,8 +283,18 @@ inline.normal = merge({}, inline);
  */
 
 inline.pedantic = merge({}, inline.normal, {
-  strong: /^__(?=\S)([\s\S]*?\S)__(?!_)|^\*\*(?=\S)([\s\S]*?\S)\*\*(?!\*)/,
-  em: /^_(?=\S)([\s\S]*?\S)_(?!_)|^\*(?=\S)([\s\S]*?\S)\*(?!\*)/,
+  strong: {
+    start: /^__|\*\*/,
+    middle: /^__(?=\S)([\s\S]*?\S)__(?!_)|^\*\*(?=\S)([\s\S]*?\S)\*\*(?!\*)/,
+    endAst: /\*\*(?!\*)/g,
+    endUnd: /__(?!_)/g
+  },
+  em: {
+    start: /^_|\*/,
+    middle: /^()\*(?=\S)([\s\S]*?\S)\*(?!\*)|^_(?=\S)([\s\S]*?\S)_(?!_)/,
+    endAst: /\*(?!\*)/g,
+    endUnd: /_(?!_)/g
+  },
   link: edit(/^!?\[(label)\]\((.*?)\)/)
     .replace('label', inline._label)
     .getRegex(),