repl-tooling

REPL-Tooling Clients

Chlorine, Clover and Clematis are all implementations of the same library: REPL-Tooling. In this post I will show you how to create a new implementation of it in a way that’s completely disconnected from any editors, so you can grasp the general concepts.

Suppose I want to do an implementation for an editor that doesn’t run JavaScript – so it’ll connect by some kind of socket. In this example I’m going to use WebSockets because… why not?

We’re going to create a shadow-cljs node project and add repl-tooling as a dependency. We will also had some more dependencies: mostly ws for websockets and the same react libraries that we use for reagent (react, create-react-class and react-dom) – repl-tooling still needs reagent, and probably in the future I will split it into two different libraries (one for the REPL handling and other for the visual rendering part). This supposedly is not to much of a problem because ClojureScript compiler will probably remove these parts in the dead code elimination process anyway. So, our package.json file will just be like this:

{
  "name": "ws-repl",
  "devDependencies": {
    "shadow-cljs": "^2.8.83"
  },
  "dependencies": {
    "create-react-class": "^15.6.3",
    "install": "^0.13.0",
    "react": "^16.12.0",
    "react-dom": "^16.12.0",
    "ws": "^7.2.1"
  }
}

And our shadow-cljs.edn file:

{:source-paths ["src"]

 :dependencies [[repl-tooling "0.4.0"]]
 :builds {:node {:output-to "index.js"
                 :target :node-script
                 :main ws-repl.core/main}}}

The first step is when someone connects to the WebSocket. Then, we’ll just create a connection to the client, and send a list of supported commands – for now, is just the “connect” command:
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By Maurício Szabo, ago

Putting REPL-Tooling to test – VSCode!

Sometimes you make some tooling because you want to use it; sometimes, to experiment; and sometimes to test the waters.

The last tooling in that I did was one of these cases – now there’s a port of Chlorine to Visual Studio Code called Clover!

Now, when I started the project I imagined that VSCode would not have all the features that I have in Atom, nor all the APIs that I want to use – for example I didn’t have any hope of having the inline results in this version.

The thing is, I wasn’t expecting it to be so bad! To begin with, the API: is not really that bad documented, but compared to the Atom, it is incredibly weak. The first thing is that they expect you to use TypeScript so there’s little to no documentation on how to represent objects in pure JavaScript; for example in some cases you can use pure objects, on others you have to instantiate a TypeScript class in the JavaScript code. Also, there are multiple parts of the documentation when they just give you the type signatures and little (or even no) explanation (and let’s make a little detour here: what’s the deal with some people that use static types, that they expect you to understand how any API work just by showing the types of the functions?).

The second part is that VSCode expects you to fit your plug-in infrastructure on what they offer – so, some functionalities will land on the “peek definition” API, others on “Code Lens” and so on. The problem is that they don’t explain what’s a “code lens” for example nor give you any screenshots of the functionality in action – mostly the documentation is some code examples in GitHub repositories so you have to download, install the example extension on your machine and then run it to simply understand how something works.

The second hard part is that you can’t test the API in the devtools – in fact the devtools is almost useless because when you have an error, the stacktrace will point you to a minified JS code in the VSCode internal API. Also, some exception messages are completely obscure and some log errors on the devtools but things work fine on the editor. Well, to summarize: it’s completely useless to depend on the errors.

But the worst part, at least for REPL-Tooling, is that you can’t change the UI of VSCode in any way – and this means no pop-ups, no new elements, no console in the editor, nothing – the only way you have that you can extend the visual components is by implementing a webview – and by webview I am not saying an “electrom webview” when you can access all the Node.JS APIs – I am saying a simple web page when you have to pass your data to and from the editor using JSON. And and that’s all there is – no Date, no JavaScript classes and, of course no Clojure objects.
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By Maurício Szabo, ago

Complex testing – the saga

While I’m developing Chlorine, sometimes I need to test multiple specific implementations of lots of really complicated stuff like REPL state, connection, async stuff (as the project is ClojureScript on Node.JS, all I/O treatment is via callbacks) and the complicated nature of rendering multiple different object types on Atom editor. I had multiple regression errors, then I’ve created some “acceptance” tests (these open up a real Atom editor and evaluate commands on it). The problem with these tests should be obvious: they are slow, and I mean REALLY SLOW, and they need a real Atom editor, lots of setups, and because Atom is not really predictable on its actions (sometimes you connect REPL and it changes the focus on the editor) there are lots of unnecessary interactions on the editor just to have less false-negatives.

Now, as I told before, I’m developing Chlorine together with REPL-Tooling, a library that should contain all tooling for any editor capable of running Javascript to run a port or Chlorine. There’s still too much on Chlorine that relies on internal Atom APIs (for example, detection of the beginning and end of forms is one, detection of namespace’s forms is other) but time is passing and more and more is being moved to REPL-Tooling, and as soon as the detection of forms is on REPL-Tooling (and is stable) there should be possible to port most Clojure parts to REPL-Tooling, and then I can think on how to refactor the ClojureScript part, test it, and then Chlorine will be a very easy project to port. Also, as a proof-of-concept there’s Clematis for NeoVIM (it’s still on the very beginning and nothing much happened after I wrote about it here), and also an “electron fake editor” that I’m using as test.

Wait, What?
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By Maurício Szabo, ago