feat: katex chemical equations support

client/components/editor/editor-markdown.vue

@@ -216,6 +216,7 @@ import mdMark from 'markdown-it-mark'
 import mdFootnote from 'markdown-it-footnote'
 import mdImsize from 'markdown-it-imsize'
 import katex from 'katex'
+import 'katex/dist/contrib/mhchem'
 import twemoji from 'twemoji'
 
 // Prism (Syntax Highlighting)

server/modules/rendering/markdown-katex/renderer.js

 const katex = require('katex')
+const chemParse = require('./mhchem')
 
 /* global WIKI */
 
@@ -8,6 +9,19 @@ const katex = require('katex')
 //
 // Includes code from https://github.com/liradb2000/markdown-it-katex
 
+// Add \ce, \pu, and \tripledash to the KaTeX macros.
+katex.__defineMacro('\\ce', function(context) {
+  return chemParse(context.consumeArgs(1)[0], 'ce')
+})
+katex.__defineMacro('\\pu', function(context) {
+  return chemParse(context.consumeArgs(1)[0], 'pu')
+})
+
+//  Needed for \bond for the ~ forms
+//  Raise by 2.56mu, not 2mu. We're raising a hyphen-minus, U+002D, not
+//  a mathematical minus, U+2212. So we need that extra 0.56.
+katex.__defineMacro('\\tripledash', '{\\vphantom{-}\\raisebox{2.56mu}{$\\mkern2mu' + '\\tiny\\text{-}\\mkern1mu\\text{-}\\mkern1mu\\text{-}\\mkern2mu$}}')
+
 module.exports = {
   init (mdinst, conf) {
     if (conf.useInline) {