benjamn/recast

JavaScript syntax tree transformer, nondestructive pretty-printer, and automatic source map generator

Ben Newman

@benjamn

it's all about your productivity :)

Jeroen Engels

@jfmengels

Well, I spent a few evenings on this, where I kept thinking in the "jscodeshift box", not outside the box

Ok, off to bed. Thanks a lot @benjamn, and I'll let you know how it goes ;)

Ben Newman

@benjamn

good luck & take care!

Jeroen Engels

@jfmengels

Hey!
I'm off to bed, but just wanted to let you know that my (second) PR for the lodash docs has been merged lodash/lodash#1963.
Original core docs: https://github.com/lodash/lodash/blob/4.3.0/doc/README.md
Generated fp docs: https://gist.github.com/jfmengels/6b973b69c491375117dc#_pullatindexes-array (scroll a little bit down)
Have a good one ;)

Benjamin Tan

@bnjmnt4n

Hi @benjamn I sent in a few PRs recently, wonder if you've seen them?

demetriusnunes

@demetriusnunes

hi guys, wonder if you could help me. I'm just starting with codemods, and I wonder how could use it to instrument my code, ie, add logging statements at the beginning of each function. has anyone done that?

Brendan Annable

@BrendanAnnable

Buzzing in here!

Any thoughts on adding jsdoc/closure compiler annotations support? Or adding some plugin architecture for externally adding support?

My goal is to use recast as a general programmatic refactoring tool, but I need it to refactor the typing information along with it.

There is a parser here https://github.com/hegemonic/catharsis but it does not appear to support codegen.

jsdoc also has an internal parser that you can't really access properly, but again no codegen either.

Ben Newman

@benjamn

@BrendanAnnable is there an AST specification for that parser? And, at a minimum, does it generate AST nodes that have .loc.{start,end} information?

Brendan Annable

@BrendanAnnable

@benjamn So that parser only parses the typing information, so I doubt it would have .loc information. i.e. if you have a comment e.g. /** @type {Array<SomeFancyType>} */ it won't actually parse the entire comment, just the Array<SomeFancyType> part.

I only briefly looked into it though

jsdoc have their own "regex parser" infront of it https://github.com/jsdoc3/jsdoc/blob/master/lib/jsdoc/doclet.js#L110

Matheus Fernandes

@matheuss

Hi guys! I'm reading a file that have this array:
plugins: [],
With recast, I'm adding to elements and then saving the file. Turns out that recast does this:
plugins: ["hyperpanic", "hypercwd"],
Any change that I could print this?

plugins: [
   "hyperpanic",
   "hypercwd"
],

Brendan Annable

@BrendanAnnable

Recast doesn't have the ability to print according to a style guide.

There was a github issue requesting such a feature.

Matheus Fernandes

@matheuss

😔

Thanks!

Ari Porad

@ariporad

Hi All, quick question: Is there a way to use scope to eliminate unused variables? For example, if I have this:

function () {
  var x = 5;
  doFoo(123);
};

I want to convert it to:

function () {
  // Notice: No `x`
  doFoo(123);
}

Thanks!

Brendan Annable

@BrendanAnnable

@ariporad Maybe collect two pieces of information in a single traversal and analze after. e.g. Collect each declared Identifier and its associated scope, and also collect all used variables and their associated scope (using scope.lookup) and then compare the two for disparities.

Ari Porad

@ariporad

Ok, thanks!

Brendan Annable

@BrendanAnnable

@benjamn Is there any plans for scope.js to support defaulted function params? It currently treats them as global variables.

(ast-types)

Lucas Bento

@lucasbento

Do I have to enable something for recast to parse async/await?

I'm not finding anything about it on the repository

Ben Newman

@benjamn

@BrendanAnnable that's definitely an oversight/bug, and I'd be happy to review a pull request!

@lucasbento try recast.parse(source, { parser: <any object with a .parse method> })

Lucas Bento

@lucasbento

@benjamn: thank you, I fixed it by using babylon parser

sorry I forgot to mention that here

Ben Newman

@benjamn

np, glad you figured it out

Lucas Bento

@lucasbento

@benjamn: ;)

Brendan Annable

@BrendanAnnable

@benjamn looks like the File type does not a filename? It is somehow possible to add an optional filename to it?

maybe taking the sourceFileName from the options given to recast.parse?

Brendan Annable

@BrendanAnnable

My use case that I have no way of tracking the filename when performing AST transformations (which may include filename changes). I could track it with external state, but that would be sucky. Especially when there is a perfect File node which could store it directly within the AST itself.

Brendan Annable

@BrendanAnnable

Oh man, it was a 2 line change to ast-types and a 1 line change to recast and works perfectly for my use case. I'll create the PRs, hopefully there isn't an issue.

Brendan Annable

@BrendanAnnable

PRs in benjamn/ast-types#200 benjamn/recast#354

Saveliy Baranov

@concubicycle

Hey

Can this lib preserve comments when pretty printing?

Mitermayer Reis

@mitermayer

I am working on a project that would update/adds new comments to the AST to be printed.

What is the recommended way to do that ?
Can I achieve this using recast/lib/comments?

Ben Newman

@benjamn

@mitermayer In an AST produced by recast.parse, comments are exposed as a .comments property on nodes

each comment object has boolean .leading and .trailing properties, indicating the comment's relationship to the node

you can create new comment objects with require("recast").types.builders.block("comment text") or .line("comment text")

most nodes in the AST won't have a .comments array attached to them, because they don't have any comments

so you might have to create the array if you're adding new comments for the first time

and of course any modifications to existing comments will be picked up by recast.print (only the comment will change unless you modify the AST in other ways)

Ben Newman

@benjamn

the recast/lib/comments module probably won't be helpful to you, as that logic is mostly about attaching comments to nodes during recast.parse and printing them in recast.print

Mitermayer Reis

@mitermayer

Thanks @benjamn for the detailed response.

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