feat(requireSpaceBeforeHeadingText): option to make space between `#` and header text mandatory

Credit: @nikz [Nik Wakelin](https://github.com/nikz)

Closes #277

README.md

@@ -288,6 +288,8 @@ var defaultOptions = showdown.getDefaultOptions();
    wrapped in two</p>
    ```
 
+ * **requireSpaceBeforeHeadingText**: (boolean) [default false] Makes adding a space between `#` and the header text mandatory (since v1.5.3)
+ 
 ## Flavors
 
 You can also use flavors or presets to set the correct options automatically, so that showdown behaves like popular markdown flavors.

dist/showdown.js

@@ -92,6 +92,11 @@ function getDefaultOpts(simple) {
       defaultValue: false,
       description: 'Parses simple line breaks as <br> (GFM Style)',
       type: 'boolean'
+    },
+    requireSpaceBeforeHeadingText: {
+      defaultValue: false,
+      description: 'Makes adding a space between `#` and the header text mandatory (GFM Style)',
+      type: 'boolean'
     }
   };
   if (simple === false) {
@@ -128,7 +133,8 @@ var showdown = {},
         ghCodeBlocks:                         true,
         tasklists:                            true,
         disableForced4SpacesIndentedSublists: true,
-        simpleLineBreaks:                     true
+        simpleLineBreaks:                     true,
+        requireSpaceBeforeHeadingText:        true
       },
       vanilla: getDefaultOpts(true)
     };
@@ -1802,7 +1808,9 @@ showdown.subParser('headers', function (text, options, globals) {
   //  ...
   //  ###### Header 6
   //
-  text = text.replace(/^(#{1,6})[ \t]*(.+?)[ \t]*#*\n+/gm, function (wholeMatch, m1, m2) {
+  var atxStyle = (options.requireSpaceBeforeHeadingText) ? /^(#{1,6})[ \t]+(.+?)[ \t]*#*\n+/gm : /^(#{1,6})[ \t]*(.+?)[ \t]*#*\n+/gm;
+
+  text = text.replace(atxStyle, function (wholeMatch, m1, m2) {
     var span = showdown.subParser('spanGamut')(m2, options, globals),
         hID = (options.noHeaderId) ? '' : ' id="' + headerId(m2) + '"',
         hLevel = headerLevelStart - 1 + m1.length,

src/options.js

@@ -90,6 +90,11 @@ function getDefaultOpts(simple) {
       defaultValue: false,
       description: 'Parses simple line breaks as <br> (GFM Style)',
       type: 'boolean'
+    },
+    requireSpaceBeforeHeadingText: {
+      defaultValue: false,
+      description: 'Makes adding a space between `#` and the header text mandatory (GFM Style)',
+      type: 'boolean'
     }
   };
   if (simple === false) {

src/showdown.js

@@ -20,7 +20,8 @@ var showdown = {},
         ghCodeBlocks:                         true,
         tasklists:                            true,
         disableForced4SpacesIndentedSublists: true,
-        simpleLineBreaks:                     true
+        simpleLineBreaks:                     true,
+        requireSpaceBeforeHeadingText:        true
       },
       vanilla: getDefaultOpts(true)
     };

src/subParsers/headers.js

@@ -40,7 +40,9 @@ showdown.subParser('headers', function (text, options, globals) {
   //  ...
   //  ###### Header 6
   //
-  text = text.replace(/^(#{1,6})[ \t]*(.+?)[ \t]*#*\n+/gm, function (wholeMatch, m1, m2) {
+  var atxStyle = (options.requireSpaceBeforeHeadingText) ? /^(#{1,6})[ \t]+(.+?)[ \t]*#*\n+/gm : /^(#{1,6})[ \t]*(.+?)[ \t]*#*\n+/gm;
+
+  text = text.replace(atxStyle, function (wholeMatch, m1, m2) {
     var span = showdown.subParser('spanGamut')(m2, options, globals),
         hID = (options.noHeaderId) ? '' : ' id="' + headerId(m2) + '"',
         hLevel = headerLevelStart - 1 + m1.length,

test/features/requireSpaceBeforeHeadingText.html

@@ -0,0 +1,2 @@
+<h1 id="header">header</h1>
+<p>#header</p>

test/features/requireSpaceBeforeHeadingText.md

@@ -0,0 +1,3 @@
+# header
+
+#header

test/node/testsuite.features.js

@@ -39,6 +39,8 @@ describe('makeHtml() features testsuite', function () {
       converter = new showdown.Converter({simpleLineBreaks: true});
     } else if (testsuite[i].name === 'excludeTrailingPunctuationFromURLs-option') {
       converter = new showdown.Converter({simplifiedAutoLink: true, excludeTrailingPunctuationFromURLs: true});
+    } else if (testsuite[i].name === 'requireSpaceBeforeHeadingText') {
+      converter = new showdown.Converter({requireSpaceBeforeHeadingText: true});
     } else {
       converter = new showdown.Converter();
     }