Modifying AST and generating source code

[jmthomas]

Forgive my ignorance but I'm trying to use Prism to modify Ruby source (add nodes) and then regenerate the source to be interpreted. I'm using Prism.parse(text) and then implementing a Prism::Visitor to potentially modify the nodes as they are visited. I assume this is possible but I haven't really seen any examples of it. Finally I would like to 'unparse' the AST back into source code.

The Python equivalent is indeed unparse which is where I'm taking many of the ideas. They also have a NodeTransformer which is allowed to modify the nodes in the visit pattern. I don't see equivalents in Prism but perhaps you're always allowed to modify the nodes ... this is Ruby afterall.

Thanks for any help pointing me in the right direction!

[jmthomas]

If it can't be done to generate the source, I don't require the generated source code as long as I can run the modified AST result. Something like eval the modified AST. Not sure if that is possible.

[jmthomas]

@kddnewton Any insights on this?
@Earlopain Any ideas?

[Earlopain]

Not quite sure why you pinged me on this 😅 I guess because I worked on the parser translator here, and RuboCop would need something like this as well in the future. But right now I haven't invested too much time into thinking about how RuboCop would make use of prism without a middleman. No ideas from me, sorry

[jmthomas]

@Earlopain thanks ... I was just looking for advice for someone knowledgeable about Prism to weigh in on whether this was even possible right now.

[mbj]

@jmthomas Evenutally unparser will support prism see:

• Requesting new release #3553
• Add prism parser support mbj/unparser#387
• Using prism translation instead of parser/current at 3.4 mbj/unparser#385

This is done via the translation layer to the parser AST, but I plan to drop to native as soon I do not have to support 3.2 anymore.