gatsby-remark-prismjs/highlight-code.js

Adds syntax highlighting to code blocks at build time using PrismJS

"use strict";

const Prism = require(`prismjs`);
const loadPrismLanguage = require(`./load-prism-language`);
const handleDirectives = require(`./directives`);
const escapeHTML = require(`./escape-html`);
const unsupportedLanguages = new Set();
require(`prismjs/components/prism-diff`);
require(`prismjs/plugins/diff-highlight/prism-diff-highlight`);
module.exports = (language, code, additionalEscapeCharacters = {}, lineNumbersHighlight = [], noInlineHighlight = false, diffLanguage = null) => {
  // (Try to) load languages on demand.
  if (!Prism.languages[language]) {
    try {
      loadPrismLanguage(language);
    } catch (e) {
      // Language wasn't loaded so let's bail.
      let message = null;
      switch (language) {
        case `none`:
          return code;
        // Don't escape if set to none.
        case `text`:
          message = noInlineHighlight ? `code block language not specified in markdown.` : `code block or inline code language not specified in markdown.`;
          break;
        default:
          message = `unable to find prism language '${language}' for highlighting.`;
      }
      const lang = language.toLowerCase();
      if (!unsupportedLanguages.has(lang)) {
        console.warn(message, `applying generic code block`);
        unsupportedLanguages.add(lang);
      }
      return escapeHTML(code, additionalEscapeCharacters);
    }
  }

  // (Try to) load diffLanguage on demand.
  if (diffLanguage && !Prism.languages[diffLanguage]) {
    try {
      loadPrismLanguage(diffLanguage);
    } catch (e) {
      const message = `unable to find prism language '${diffLanguage}' for highlighting.`;
      const lang = diffLanguage.toLowerCase();
      if (!unsupportedLanguages.has(lang)) {
        console.warn(message, `applying generic code block`);
        unsupportedLanguages.add(lang);
      }
      // Ignore diffLanguage when it does not exist.
      diffLanguage = null;
    }
  }
  const grammar = Prism.languages[language];
  const highlighted = Prism.highlight(code, grammar, diffLanguage ? `${language}-${diffLanguage}` : language);
  const codeSplits = handleDirectives(highlighted, lineNumbersHighlight);
  let finalCode = ``;
  const lastIdx = codeSplits.length - 1; // Don't add back the new line character after highlighted lines
  // as they need to be display: block and full-width.

  codeSplits.forEach((split, idx) => {
    finalCode += split.highlight ? split.code : `${split.code}${idx == lastIdx ? `` : `\n`}`;
  });
  return finalCode;
};