Ability to emit TypeScript from syntax tree

[ctaggart]

Now that #5595 has landed, it has me excited that it may soon be possible to emit TypeScript. Is it now possible with the 2.1 nightly? If not, please consider this a feature request. It would open the door for a lot of cool code generation.

Related issues:

• 2015-01-08 Building a TypeScript Syntax Tree with source from another language (F#) #1514 Building a TypeScript Syntax Tree with source from another language (F#)
• 2015-04-20 How do you do a straight TS emit? #1651 How do you do a straight TS emit?
• 2016-02-22 TypeScript code generation from the Language Service #3241 TypeScript code generation from the Language Service

[RyanCavanaugh]

Depending on what you're doing, https://github.com/RyanCavanaugh/dts-dom may be a useful alternative

[stephanos]

@ctaggart hey there, you seem to have a pretty good grasp on the whole emitting functionality. I was just curious if you could tell me what exactly I need to watch out for in order to be able to read a .ts file, parse it, add some nodes and emit it to a new .ts file. Thanks :)

(background: I would love to be able to build the TypeScript version of my Babel plugin https://github.com/stephanos/babel-plugin-immutable-record)

[ctaggart]

@stephanos, it has been possible to do everything you are asking by using the compiler api for a while, except emit the .ts file. If it is indeed possible now, I don't know how to do it. I too would like it to be possible, which is why I opened this issue. I recommend adding a 👍 above if you would like to see support added.

[stephanos]

@ctaggart thanks for your reply :) I'm now focusing on emitting .js until this issue is resolved. I managed to get started on this today and got as far as parsing the .ts and navigating through the AST nodes. But now I'm stuck: How do I create a new node (e.g. a variable declaration) and add it to an array of statements? I'd appreciate if you could share any insights or point me in the right direction. Thank you. (sorry for hijacking this issue :-/ - should I post this somewhere else?)

[ivogabe]

Would you accept a pull request on this? I'd propose a new function emit(file: SourceFile, transformers: Transformer[] = nullTransformers, newLine = "\n"): string in emitter.ts and exposing the functions in factory.ts. Since factory.ts contains a lot of helpers, I guess that should be placed in a namespace like ts.factory (instead of exposing it under ts).

[ivogabe]

I played a bit with it, and I created PR #11561.

[morlay]

We really need something like babel-types & babel-generator

Sometimes, we need to generate code by specs like json-schema, swagger.

There is a cool tool TSTypeInfo to do this.

However, Hope typescript could provide these features.

[ctaggart]

Now that TypeScript 2.1 has been released where ya'll are now rewriting the emit pipeline to use tree transforms, is this something that may be enabled soon. I brought up this issue at both @DanielRosenwasser's presentation and a Q&A with @ahejlsberg at the Microsoft MVP conference in November.

thanks,
Squeaky Wheel

[DanielRosenwasser]

Hey @ctaggart! #11561 was the most recent PR regarding this, but we want to do some cleanup on the API. See @mhegazy's comment at #11561 (comment).

TL;DR: pretty-printing a synthesized tree is planned for the 2.2 timeframe.

[ctaggart]

Now that #13940 has been merged to master, this may actually be possible now, right? @rbuckton