Parser: Fix crash if no href given to anchor or link tag (#780)

MarkBind crashes if no href is given to an anchor or link tag, as it
tries to rewrite a non-existent URL.

Let's introduce an extra check for the href attribute. Only if the
href attribute is present, do we proceed to rewrite URL to their
absolute paths.

Author: sijie123

src/lib/markbind/src/parser.js

@@ -387,7 +387,7 @@ Parser.prototype._preprocess = function (node, context, config) {
         element.attribs.src = utils.ensurePosix(resultPath);
       }
     } else if (['a', 'link'].includes(element.name)) {
-      if (!isUrl && !isAbsolutePath) {
+      if (!isUrl && !isAbsolutePath && hasHref) {
         const resultPath = path.join('{{hostBaseUrl}}', path.relative(config.rootPath, filePath));
         element.attribs.href = utils.ensurePosix(resultPath);
       }

test/functional/test_site/expected/index.html

@@ -479,8 +479,11 @@ <h2 id="feature-list">Feature list<a class="fa fa-anchor" href="#feature-list"><
               <pic src="/test_site/sub_site/images/I'm not allowed to use my favorite tool.png"></pic>
               <pic src="https://dummyimage.com/600x400/000/fff"></pic>
             </p>
-            <p>Anchor link:
-              <a href="https://dummyimage.com/600x400/000/fff">External Image</a></p>
+            <p>Anchor:
+              <a href="https://dummyimage.com/600x400/000/fff">External Image</a>
+              <a href="/test_site/sub_site/images/I'm not allowed to use my favorite tool.png">Link to picture</a>
+              <a id="namedAnchor">Named Anchor</a>
+              <a>Anchor with no attributes</a></p>
           </div>
           <h1 id="trimmed-include">Trimmed include<a class="fa fa-anchor" href="#trimmed-include"></a></h1>
           <h2 id="fragment-with-leading-spaces-and-newline"><span>Fragment with leading spaces and newline</span><a class="fa fa-anchor" href="#fragment-with-leading-spaces-and-newline"></a></h2>

test/functional/test_site/expected/sub_site/testReuse._include_.html

@@ -14,5 +14,8 @@
   <pic src="/test_site/sub_site/images/I'm not allowed to use my favorite tool.png"></pic>
   <pic src="https://dummyimage.com/600x400/000/fff"></pic>
 </p>
-<p>Anchor link:
-  <a href="https://dummyimage.com/600x400/000/fff">External Image</a></p>
+<p>Anchor:
+  <a href="https://dummyimage.com/600x400/000/fff">External Image</a>
+  <a href="/test_site/sub_site/images/I'm not allowed to use my favorite tool.png">Link to picture</a>
+  <a id="namedAnchor">Named Anchor</a>
+  <a>Anchor with no attributes</a></p>

test/functional/test_site/sub_site/testReuse.md

@@ -19,5 +19,8 @@ PIC tags:
 <pic src="{{baseUrl}}/images/I'm not allowed to use my favorite tool.png"></pic>
 <pic src="https://dummyimage.com/600x400/000/fff"></pic>
 
-Anchor link:
-<a href="https://dummyimage.com/600x400/000/fff">External Image</a>
+Anchor:
+<a href="https://dummyimage.com/600x400/000/fff">External Image</a>
+<a href="{{baseUrl}}/images/I'm not allowed to use my favorite tool.png">Link to picture</a>
+<a id="namedAnchor">Named Anchor</a>
+<a>Anchor with no attributes</a>