Unfork one file, and prepare for unforking more

[gnprice]

This is a first step toward zulip/zulip-mobile#4242.

Most of this is one-time stuff; just the one commit "Unfork one module, fenced_code." represents what we'll repeat for each successive file.

After this file, emoji.js is ready for similar treatment. Then when more files are ready from the web side, we can act on those in turn.

/cc @showell

[gnprice]

(In addition to this repo's own tests, I've tested these changes manually in the mobile app, using yarn link. Once this is merged, I'll publish zulip-markdown-parser to NPM and then bump the version referred to in zulip-mobile's package.json.)

[chrisbobbe]

Great! See one comment, below; otherwise, this looks good.

I also tested this PR by setting zulip-markdown-parser to gnprice/zulip-markdown-parser#pr-unfork-1 in package.json and running yarn, and all seems to work fine.

[chrisbobbe]

Hmm, I'm still getting the following error when we start using code from @zulip/shared in the next commit:

 FAIL  __tests__/preview-tests.js
  ● Test suite failed to run

    Jest encountered an unexpected token

    This usually means that you are trying to import a file which Jest cannot parse, e.g. it's not plain JavaScript.

    By default, if Jest sees a Babel config, it will use that to transform your files, ignoring "node_modules".

    Here's what you can do:
     • To have some of your "node_modules" files transformed, you can specify a custom "transformIgnorePatterns" in your config.
     • If you need a custom transformation specify a "transform" option in your config.
     • If you simply want to mock your non-JS modules (e.g. binary assets) you can stub them out with the "moduleNameMapper" config option.

    You'll find more details and examples of these config options in the docs:
    https://jestjs.io/docs/en/configuration.html

    Details:

    /Users/chrisbobbe/dev/zulip-markdown-parser/node_modules/@zulip/shared/js/fenced_code.js:1
    import katex from "katex";
    ^^^^^^

    SyntaxError: Cannot use import statement outside a module

      14 | const marked = require('./marked');
      15 | const hash_util = require('./hash_util');
    > 16 | const fenced_code = require('@zulip/shared/js/fenced_code.js');
         |                     ^
      17 | const emoji = require('./emoji');
      18 | var emoji_codes = require('./emoji_codes');
      19 | const katex = require('katex');

      at Runtime._execModule (node_modules/jest-runtime/build/index.js:1179:56)
      at Object.<anonymous> (markdown.js:16:21)
      at Object.<anonymous> (parseMarkdown.js:1:18)
      at Object.<anonymous> (__tests__/preview-tests.js:3:23)

[chrisbobbe]

It goes away when I apply the following to jest.config.js (like we do in zulip-mobile):

+ const transformModulesWhitelist = ['@zulip/shared'];
+
+ const transformIgnorePattern = `node_modules/(?!${transformModulesWhitelist.join('|')})`;
+
  module.exports = {
    transform: {
      '.\\.js$': 'babel-jest',
    },
+   transformIgnorePatterns: [transformIgnorePattern],
  };

[chrisbobbe]

From the first item in that error's list of possible solutions—

     • To have some of your "node_modules" files transformed, you can specify a custom "transformIgnorePatterns" in your config.

—it seems like anything in node_modules won't be transformed by default.

[chrisbobbe]

Ah, I just noticed another thing, @gnprice: the author field on these commits has an email address that differs from the @zulip.com one you use for zulip-mobile (in case you wanted to change that). 🙂