fix(prefixHeaderId): make prefixHeaderId string be parsed along the generated id

If an invalid prefix was passed (a string with spaces, for instance),
the string would be added as is. This ould generate invalid ids.
Also, this makes `prefixHeaderId` option play nicely with `ghCompatibleHeaderId`, since they will
follow the same escaping rules when both options are enabled.

src/subParsers/headers.js

@@ -3,8 +3,7 @@ showdown.subParser('headers', function (text, options, globals) {
 
   text = globals.converter._dispatch('headers.before', text, options, globals);
 
-  var prefixHeader = options.prefixHeaderId,
-      headerLevelStart = (isNaN(parseInt(options.headerLevelStart))) ? 1 : parseInt(options.headerLevelStart),
+  var headerLevelStart = (isNaN(parseInt(options.headerLevelStart))) ? 1 : parseInt(options.headerLevelStart),
       ghHeaderId = options.ghCompatibleHeaderId,
 
   // Set text-style headers:
@@ -53,10 +52,18 @@ showdown.subParser('headers', function (text, options, globals) {
   });
 
   function headerId (m) {
-    var title, escapedId;
+    var title;
+    // Prefix id to prevent causing inadvertent pre-existing style matches.
+    if (showdown.helper.isString(options.prefixHeaderId)) {
+      title = options.prefixHeaderId + m;
+    } else if (options.prefixHeaderId === true) {
+      title = 'section ' + m;
+    } else {
+      title = m;
+    }
 
     if (ghHeaderId) {
-      escapedId = m
+      title = title
         .replace(/ /g, '-')
         // replace previously escaped chars (&, ¨ and $)
         .replace(/&/g, '')
@@ -67,23 +74,15 @@ showdown.subParser('headers', function (text, options, globals) {
         .replace(/[&+$,\/:;=?@"#{}|^¨~\[\]`\\*)(%.!'<>]/g, '')
         .toLowerCase();
     } else {
-      escapedId = m.replace(/[^\w]/g, '').toLowerCase();
+      title = title
+        .replace(/[^\w]/g, '')
+        .toLowerCase();
     }
 
-    if (globals.hashLinkCounts[escapedId]) {
-      title = escapedId + '-' + (globals.hashLinkCounts[escapedId]++);
+    if (globals.hashLinkCounts[title]) {
+      title = title + '-' + (globals.hashLinkCounts[title]++);
     } else {
-      title = escapedId;
-      globals.hashLinkCounts[escapedId] = 1;
-    }
-
-    // Prefix id to prevent causing inadvertent pre-existing style matches.
-    if (prefixHeader === true) {
-      prefixHeader = 'section';
-    }
-
-    if (showdown.helper.isString(prefixHeader)) {
-      return prefixHeader + title;
+      globals.hashLinkCounts[title] = 1;
     }
     return title;
   }

test/features/prefixHeaderId-simple.html

@@ -0,0 +1 @@
+<h1 id="sectionfooheader">foo header</h1>

test/features/prefixHeaderId-simple.md

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

test/features/prefixHeaderId-string-and-ghCompatibleHeaderId.html

@@ -0,0 +1 @@
+<h1 id="my-prefix-foo-header">foo header</h1>

test/features/prefixHeaderId-string-and-ghCompatibleHeaderId.md

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

test/features/prefixHeaderId-string-and-ghCompatibleHeaderId2.html

@@ -0,0 +1 @@
+<h1 id="my-prefix-foo-header">foo header</h1>

test/features/prefixHeaderId-string-and-ghCompatibleHeaderId2.md

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

test/features/prefixHeaderId-string.html

@@ -0,0 +1 @@
+<h1 id="myprefixfooheader">foo header</h1>

test/features/prefixHeaderId-string.md

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

test/node/testsuite.features.js

@@ -61,6 +61,14 @@ describe('makeHtml() features testsuite', function () {
       converter = new showdown.Converter({encodeEmails: false, simplifiedAutoLink: true});
     } else if (testsuite[i].name === '#331.allow-escaping-of-tilde') {
       converter = new showdown.Converter({strikethrough: true});
+    } else if (testsuite[i].name === 'prefixHeaderId-simple') {
+      converter = new showdown.Converter({prefixHeaderId: true});
+    } else if (testsuite[i].name === 'prefixHeaderId-string') {
+      converter = new showdown.Converter({prefixHeaderId: 'my-prefix-'});
+    } else if (testsuite[i].name === 'prefixHeaderId-string-and-ghCompatibleHeaderId') {
+      converter = new showdown.Converter({prefixHeaderId: 'my-prefix-', ghCompatibleHeaderId: true});
+    } else if (testsuite[i].name === 'prefixHeaderId-string-and-ghCompatibleHeaderId2') {
+      converter = new showdown.Converter({prefixHeaderId: 'my prefix ', ghCompatibleHeaderId: true});
     } else {
       converter = new showdown.Converter();
     }