feat(literalMidWordUnderscores): add support for GFM literal midword underscores

Github Flavored Markdown does not parse underscores in the middle of a word as emphasis/bold.
This commit adds this feature to showdown through an option called "literalMidWordUnderscores".

Related to #164

src/converter.js

@@ -22,11 +22,7 @@ showdown.Converter = function (converterOptions) {
        * @private
        * @type {{}}
        */
-      options = {
+      options = {},
-        omitExtraWLInCodeBlocks: false,
-        prefixHeaderId:          false,
-        noHeaderId:              false
-      },
 
       /**
        * Language extensions used by this converter

src/showdown.js

@@ -12,7 +12,8 @@ var showdown = {},
       noHeaderId:                false,
       headerLevelStart:          1,
       parseImgDimensions:        false,
-      simplifiedAutoLink:      false
+      simplifiedAutoLink:        false,
+      literalMidWordUnderscores: false
     },
     globalOptions = JSON.parse(JSON.stringify(defaultOptions)); //clone default options out of laziness =P
 

src/subParsers/italicsAndBold.js

@@ -1,9 +1,19 @@
-showdown.subParser('italicsAndBold', function (text) {
+showdown.subParser('italicsAndBold', function (text, options) {
   'use strict';
+
+  if (options.literalMidWordUnderscores) {
+    //underscores
+    // Since we are consuming a \s character, we need to add it
+    text = text.replace(/(\s)__(?=\S)([^]+?)__(?=\s)/g, '$1<strong>$2</strong>');
+    text = text.replace(/(\s)_(?=\S)([^]+?)_(?=\s)/g, '$1<em>$2</em>');
+    //asterisks
+    text = text.replace(/\*\*(?=\S)([^]+?)\*\*/g, '<strong>$1</strong>');
+    text = text.replace(/\*(?=\S)([^]+?)\*/g, '<em>$1</em>');
+
+  } else {
     // <strong> must go first:
     text = text.replace(/(\*\*|__)(?=\S)([^\r]*?\S[*_]*)\1/g, '<strong>$2</strong>');
-
     text = text.replace(/(\*|_)(?=\S)([^\r]*?\S)\1/g, '<em>$2</em>');
-
+  }
   return text;
 });

test/features/#164.2.disallow_underscore_emphasis_mid_word.html

@@ -0,0 +1,11 @@
+<p>this is a sentence_with_mid underscores</p>
+
+<p>this is a sentence with just_one underscore</p>
+
+<p>this <em>should be parsed</em> as emphasis</p>
+
+<p>this is double__underscore__mid word</p>
+
+<p>this has just__one double underscore</p>
+
+<p>this <strong>should be parsed</strong> as bold</p>

test/features/#164.2.disallow_underscore_emphasis_mid_word.md

@@ -0,0 +1,11 @@
+this is a sentence_with_mid underscores
+
+this is a sentence with just_one underscore
+
+this _should be parsed_ as emphasis
+
+this is double__underscore__mid word
+
+this has just__one double underscore
+
+this __should be parsed__ as bold

test/node/showdown.js

@@ -23,7 +23,8 @@ describe('showdown.options', function () {
         noHeaderId:                false,
         headerLevelStart:          1,
         parseImgDimensions:        false,
-        simplifiedAutoLink:      false
+        simplifiedAutoLink:        false,
+        literalMidWordUnderscores: false
       };
       expect(showdown.getDefaultOptions()).to.be.eql(opts);
     });

test/node/testsuite.features.js

@@ -16,6 +16,8 @@ describe('makeHtml() features testsuite', function () {
       converter = new showdown.Converter({headerLevelStart: 3});
     } else if (testsuite[i].name === '#164.1.simple_autolink') {
       converter = new showdown.Converter({simplifiedAutoLink: true});
+    } else if (testsuite[i].name === '#164.2.disallow_underscore_emphasis_mid_word') {
+      converter = new showdown.Converter({literalMidWordUnderscores: true});
     } else {
       converter = new showdown.Converter();
     }