Fix to catch non-parse katex errors

Closes GH-82.

Author: wooorm

packages/rehype-katex/index.js

@@ -56,6 +56,25 @@ export default function rehypeKatex(options) {
 
         file[fn](error.message, element.position, origin)
 
+        // KaTeX can handle `ParseError` itself, but not others.
+        // Generate similar markup if this is an other error.
+        // See: <https://github.com/KaTeX/KaTeX/blob/5dc7af0/docs/error.md>.
+        if (error.name !== 'ParseError') {
+          element.children = [
+            {
+              type: 'element',
+              tagName: 'span',
+              properties: {
+                className: ['katex-error'],
+                title: String(error),
+                style: 'color:' + (settings.errorColor || '#cc0000')
+              },
+              children: [{type: 'text', value}]
+            }
+          ]
+          return
+        }
+
         result = katex.renderToString(
           value,
           assign({}, settings, {

packages/rehype-katex/test.js

@@ -214,5 +214,24 @@ test('rehype-katex', (t) => {
     'should support comments'
   )
 
+  t.deepEqual(
+    unified()
+      .use(rehypeParse, {fragment: true})
+      .use(rehypeKatex)
+      .use(rehypeStringify)
+      .processSync(
+        '<span class="math-display">\\begin{split}\n\\end{{split}}\n</span>'
+      )
+      .toString(),
+    unified()
+      .use(rehypeParse, {fragment: true})
+      .use(rehypeStringify)
+      .processSync(
+        '<span class="math-display"><span class="katex-error" title="Error: Expected node of type textord, but got node of type ordgroup" style="color:#cc0000">\\begin{split}\n\\end{{split}}\n</span></span>'
+      )
+      .toString(),
+    'should not crash on non-parse errors'
+  )
+
   t.end()
 })