scalameta code generator JS module

[drom]

I am constructing my scalameta AST object in JS, then I want to call some JS package to serialize Sacala string. Can someone help me with NPM module that would do that?
Here is an example of such a project for JS : https://github.com/estools/escodegen

[olafurpg]

Thank you for reporting! Can you elaborate on what APIs you are currently using and give an example of what is missing? The JavaScript facade is defined here

https://github.com/scalameta/scalameta/blob/7c5c020cc0ff9b97d9029b315fb8659590236a2c/scalameta/parsers/js/src/main/scala/scala/meta/parsers/JSFacade.scala

We could add more methods to the facade and publish a new npm update.

cc/ @gabro

[drom]

In my current flow I use scalameta-parsers NPM package and can call parser to construct AST:

const scalametaParsers = require('scalameta-parsers');

const a = '1 + 2';

const b = scalametaParsers.parseStat.call({}, a);
/* =>
{
  type: "Term.ApplyInfix", pos: {start: 0, end: 7},
  lhs: {
    type: "Lit.Int", pos: {start: 1, end: 2},
    value: 1, syntax: "1"
  },
  op: {
    type: "Term.Name", pos: {start: 3, end: 4},
    value: "+"
  },
  targs: [],
  args: [
    {
      type: "Lit.Int", pos: {start: 5, end: 6},
      value: 2, syntax: "2"
    }
  ]
}
*/

I wish there is some other NPM package that I can use to perform the inverse transformation from AST to text:

const codegen = require('scalameta-codegen');

const c = codegen(b);
// => 1 + 2

[olafurpg]

@drom do you make transformations on the AST before calling codegen?

[drom]

Typically I programmatically construct new AST and sometimes make transformations of AST from JavaScript.

[olafurpg]

Thanks for the explanation. I estimate it requires some effort work to map from the JavaScript object into scala.meta.Tree, it would be a large pattern match that looks something like this

def tree(obj: js.Dynamic): Tree = obj.`type` match {
  case "Term.ApplyInfix" => Term.ApplyInfix(tree(obj.lhs), tree(obj.op), tree(obj.targs), tree(obj.args))
  // ...
}

Some work is needed to make sure everything compiles.

Is this something you would be interested in contributing? I'm afraid it's probably not a project that will be prioritized in the near future.

[olafurpg]

Another approach could be to expose public methods to contruct scala.meta.Tree instances, for example

@JSExport()
def applyInfix(lhs: Term, op: Term.Name, targs: List[Type.Arg], args: List[Term]): Term.ApplyInfix = ...

This might be easier to compile than the large pattern match.

[drom]

Thank you @olafurpg for clarification. I have started writing AST serializer in JavaScript https://github.com/sifive/scala-codegen . That seems pretty straightforward if I could figure out full list of AST node types.