feature: add support for highlighting syntax in Markdown previews

Author: marcusrbrown

extension.js

@@ -0,0 +1,87 @@
+/* eslint-disable global-require */
+const packageJson = require('./package.json');
+
+const get = (obj, path, defaultValue) => {
+    const lookup = !(obj === null || obj === undefined) ? obj[path] : undefined;
+    if (lookup !== undefined) {
+        return lookup;
+    }
+    const result = String.prototype.split
+        .call(path, /[,.[\]]+?/)
+        .filter(Boolean)
+        .reduce(
+            (res, key) => (!(res === null || res === undefined) ? res[key] : undefined),
+            obj
+        );
+    return result === undefined || result === obj ? defaultValue : result;
+};
+
+const languageId = get(packageJson, 'contributes.languages[0].id', 'textproto').toLowerCase();
+const aliases = []
+    .concat(get(packageJson, 'contributes.languages[0].aliases'))
+    .map((x) => x.toLowerCase())
+    .filter((x) => x !== languageId);
+const languageTest = new RegExp(`(${languageId}|${aliases.join('|')})`, 'i');
+
+/** @type LanguageFn */
+const textproto = (hljs) => {
+    /** @type Mode */
+    const HERE_DOCS = {
+        begin: /<<\s*(?=[A-Z_a-z]+)/,
+        starts: {
+            contains: [
+                hljs.END_SAME_AS_BEGIN({
+                    begin: /([A-Z_a-z]+)/,
+                    end: /([A-Z_a-z]+)/,
+                    className: 'string',
+                }),
+            ],
+        },
+    };
+    return {
+        name: 'Protocol Buffer Text Format',
+        aliases,
+        contains: [
+            hljs.QUOTE_STRING_MODE,
+            hljs.NUMBER_MODE,
+            hljs.HASH_COMMENT_MODE,
+            {
+                className: 'object',
+                begin: /{/,
+                end: /}/,
+                contains: [
+                    hljs.QUOTE_STRING_MODE,
+                    hljs.NUMBER_MODE,
+                    hljs.HASH_COMMENT_MODE,
+                    HERE_DOCS,
+                ],
+            },
+            HERE_DOCS,
+        ],
+    };
+};
+
+module.exports.activate = () => ({
+    extendMarkdownIt(md) {
+        const hljs = require('highlight.js/lib/core');
+        const { highlight } = md.options;
+        md.use(require('markdown-it-highlightjs/core'), {
+            hljs,
+            register: {
+                textproto,
+            },
+        });
+        // eslint-disable-next-line no-param-reassign
+        md.options.highlight = (code, lang) => {
+            if (lang && lang.match(languageTest)) {
+                try {
+                    return `<div>${hljs.highlight(lang, code, true).value}</div>`;
+                } catch (error) {
+                    /* empty */
+                }
+            }
+            return highlight(code, lang);
+        };
+        return md;
+    },
+});