Set up local Codesandbox development environment

This guide walks through setting up a local Codesandbox repository and integrating it with a local GitLab instance. Codesandbox is used to power the Web IDE's Live Preview feature. Having a local Codesandbox setup is useful for debugging upstream issues or creating upstream contributions like this one.

Initial setup

Before using Codesandbox with your local GitLab instance, you must:

Enable HTTPS on your GDK. Codesandbox uses Service Workers that require https. Follow the GDK NGINX configuration instructions to enable HTTPS for GDK.
Clone the codesandbox-client project locally. If you plan on contributing upstream, you might want to fork and clone first.
(Optional) Use correct python and nodejs versions. Otherwise, yarn may fail to install or build some packages. If you're using asdf you can run the following commands:
```
asdf local nodejs 10.14.2
asdf local python 2.7.18
```
Run the following commands in the codesandbox-client project checkout:
```
# This might be necessary for the `prepublishOnly` job that is run later
yarn global add lerna

# Install packages
yarn
```
You can run yarn build:clean to clean up the build assets.

Use local GitLab instance with local Codesandbox

GitLab integrates with two parts of Codesandbox:

An NPM package called smooshpack (called sandpack in the codesandbox-client project). This exposes an entrypoint for us to kick off Codesandbox's bundler.
A server that houses Codesandbox assets for bundling and previewing. This is hosted on a separate server for security.

Each time you want to run GitLab and Codesandbox together, you need to perform the steps in the following sections.

Use local `smooshpack` for GitLab

GitLab usually satisfies its smooshpack dependency with a remote module, but we want to use a locally-built module. To build and use a local smooshpack module:

In the codesandbox-client project directory, run:
```
cd standalone-packages/sandpack
yarn link

# (Optional) you might want to start a development build
yarn run start
```
Now, in the GitLab project, you can run yarn link "smooshpack". yarn looks for smooshpack on disk as opposed to the one hosted remotely.

In the gitlab project directory, run:

# Remove and reinstall node_modules just to be safe
rm -rf node_modules
yarn install

# Use the "smooshpack" package on disk
yarn link "smooshpack"

Fix possible GDK webpack problem

webpack in GDK can fail to find packages inside a linked package. This step can help you avoid webpack breaking with messages saying that it can't resolve packages from smooshpack/dist/sandpack.es5.js.

In the codesandbox-client project directory, run:

cd standalone-packages

mkdir node_modules
ln -s $PATH_TO_LOCAL_GITLAB/node_modules/core-js ./node_modules/core-js

Start building codesandbox app assets

In the codesandbox-client project directory:

cd packages/app

yarn start:sandpack-sandbox

Create HTTPS proxy for Codesandbox `sandpack` assets

Because we need https, we need to create a proxy to the webpack server. We can use http-server, which can do this proxying out of the box:

npx http-server --proxy http://localhost:3000 -S -C $PATH_TO_CERT_PEM -K $PATH_TO_KEY_PEM -p 8044 -d false

Update `bundler_url` setting in GitLab

We need to update our application_setting_implementation.rb to point to the server that hosts the Codesandbox sandpack assets. For instance, if these assets are hosted by a server at https://sandpack.local:8044:

diff --git a/app/models/application_setting_implementation.rb b/app/models/application_setting_implementation.rb
index 6eed627b502..1824669e881 100644
--- a/app/models/application_setting_implementation.rb
+++ b/app/models/application_setting_implementation.rb
@@ -391,7 +391,7 @@ def static_objects_external_storage_enabled?
   # This will eventually be configurable
   # https://gitlab.com/gitlab-org/gitlab/issues/208161
   def web_ide_clientside_preview_bundler_url
-    'https://sandbox-prod.gitlab-static.net'
+    'https://sandpack.local:8044'
   end

   private

NOTE: You can apply this patch by copying it to your clipboard and running pbpaste | git apply.

You'll might want to restart the GitLab Rails server after making this change:

gdk restart rails-web