fix(markdown) Images with empty alt or links with empty text

CHANGES.md

@@ -2,6 +2,7 @@
 
 Grammars:
 
+- fix(markdown) Images with empty alt or links with empty text (#3233) [Josh Goebel][]
 - fix(python) identifiers starting with underscore not highlighted (#3221) [Antoine Lambert][]
 - enh(clojure) added `edn` alias (#3213) [Stel Abrego][]
 - enh(elixir) much improved regular expression sigil support (#3207) [Josh Goebel][]

src/languages/markdown.js

@@ -105,12 +105,16 @@ export default function(hljs) {
       },
       // whatever else, lower relevance (might not be a link at all)
       {
-        begin: /\[.+?\]\(.*?\)/,
+        begin: /\[.*?\]\(.*?\)/,
         relevance: 0
       }
     ],
     returnBegin: true,
     contains: [
+      {
+        // empty strings for alt or link text
+        match: /\[(?=\])/
+      },
       {
         className: 'string',
         relevance: 0,

test/markup/markdown/links.expect.txt

@@ -0,0 +1,4 @@
+![](<span class="hljs-link">https://example.com</span>)
+[](<span class="hljs-link">https://example.com</span>)
+![<span class="hljs-string">alt</span>](<span class="hljs-link">https://example.com</span>)
+[<span class="hljs-string">text</span>](<span class="hljs-link">https://example.com</span>)

test/markup/markdown/links.txt

@@ -0,0 +1,4 @@
+![](https://example.com)
+[](https://example.com)
+![alt](https://example.com)
+[text](https://example.com)