scalameta/scalameta

Library to read, analyze, transform and generate Scala programs

Roman Janusz

@ghik

I swear I'll end up writing my own parser at some point...

Ólafur Páll Geirsson

@olafurpg

@ghik what's your use-case?

the parser in the Scala compiler does decent error recovery

Roman Janusz

@ghik

Well, a programming language, to be honest... but a simple one, for very specific, company-internal use case. I wanted to use a small subset of Scala.

Yes, scalac parser does that well, but it loses a lot of information

Lossless parsing is one of the selling points of scalameta

Ólafur Páll Geirsson

@olafurpg

If you're doing a new programming language then I think it's totally reasonable to write your own parser

even if it's only a subset of Scala

btw, the dotty parser doesn't loose as much information as the scalac parser

Roman Janusz

@ghik

That's interesting, how public/reusable its API is?

Ólafur Páll Geirsson

@olafurpg

there is also a nice parser in https://github.com/twitter/rsc/ that you could base off

Roman Janusz

@ghik

I'd be fine if I could just fork some existing parser and modify it to my needs

Ólafur Páll Geirsson

@olafurpg

I think you can consider all dotty compiler apis as private

Roman Janusz

@ghik

Oh yeah I forgot about rsc, thanks

Ólafur Páll Geirsson

@olafurpg

best approach is probably to copy-paste and adapt

so find the code you understand the best and feel most comfortable changing

I BTW found the link to the tolerant-php-parser in https://github.com/scalameta/scalameta/issues/1170#issuecomment-403751263 interesting

Roman Janusz

@ghik

I'll look into it, thanks for help and all the references!

Ólafur Páll Geirsson

@olafurpg

One somewhat interesting observation I found while working on diagnostics in Metals is that it seems to be totally fine to publish only a single syntax error

it's usually the first syntax error that's most helpful in tracking down the problem, if the parser recovers from the first error and continues to publish 10 more syntax errors then it makes it harder to track the source of the error

Roman Janusz

@ghik

yeah but even that single syntax error prevents the parser from returning an actual tree that could be used for things like completion

Ólafur Páll Geirsson

@olafurpg

so Metals actually runs the Scalameta parser on every keystroke even if it has no parser recovery and publishes at most a single syntax error

the thing is that you wouldn't be able to implement completions anyways with the impartial scalameta tree

for completions you need a typechecker

Roman Janusz

@ghik

scala presentation compiler has no problem with that

it can typecheck on best-effort manner

Ólafur Páll Geirsson

@olafurpg

yeah, we use the presentation compiler with completions and it's working pretty great in my experience

Roman Janusz

@ghik

yes I'm also using it in my "current version" of this "programming language"

but lossy parsing is really biting me

Ólafur Páll Geirsson

@olafurpg

the desugared scalac trees simplify a lot of semantic analysis

Roman Janusz

@ghik

the thing that i hoped for is scalameta for syntactic analysis and presentation compiler for potential typechecking and completion

presentation compiler unfortunately has a lot of limitations

for example: it doesn't handle scala.Dynamic well

Ólafur Páll Geirsson

@olafurpg

we have an mtags module in metals that adds several feature improvements to the scala presentation compiler APIs, including support for Dynamic

the dynamic fixes could be upstreamed into the compiler, but other improvements include for example auto-importing symbols that are in the workspace but not in scope

the public API is based on lsp4j types https://github.com/scalameta/metals/blob/master/mtags-interfaces/src/main/java/scala/meta/pc/PresentationCompiler.java

we do several syntactic analyses using the scalameta parser such as code folding and document outlines

but they only run on valid source code, in between that we adjust positions based on token edit distance between the last successful parse and the current dirty buffer

Kiko

@kikofernandez

Hi there. I was wondering if there is any way to get transform a semanticdb class into its pretty printed form, so that I can get interesting information from semantic db and use the AST facilities of scalameta

Ólafur Páll Geirsson

@olafurpg

@kikofernandez the scalafix apis combine the Scalameta ast and SemanticDB

Kiko

@kikofernandez

right, so I have to go for scalafix them. Thanks

I am really new into Scala and Scalameta et al. Is there any way I can use Scalafix to generate code (not visible to the developer) that gets compiled?

Anthony Garo

@agaro1121

Hi everyone, I want to match on imports that start with a specific string.
What’s the best way to do that?
something like:

case importer"scala.$eref.{..$importeesnel}" =>
      println(eref)
      println(importeesnel)
      println()

mohnishkodnani

@mohnishkodnani

Hi,
I am trying to create a service , where given certain parameters, you create code for a new usecase. I have a scala.meta.Type from parsing the case class() extends ... with ... > i want to use that scala.meta.Type with reflection to find all the methods I have to override and generate them ? Is there a way to do this ?

Ólafur Páll Geirsson

@olafurpg

@mohnishkodnani a scala.meta.Type represents only the syntax tree of that source code, it has no knowledge about the type or the supermethods to implement so this is not possible I'm afraid.

Gabriele Petronella

@gabro

is anyone experiencing this issue with spurious unused warnings when using quasiquotes as a pattern?

def f(m: Decl.Def): List[scala.meta.Type] =
    m.decltpe.collect {
      case t"$_[$tpe]" => tpe
    }

This yields two unused warnings, one for each $

Soren

@srnb_gitlab

What's the status on Scala Meta for Native 0.3.9/2.11 and JS 1.0.0-M8/2.12-2.13?

Brent Gracey

@myFree

Hi all;

Is there a plugin which can generate SemanticDb files for a Java project?

From https://scalameta.org/docs/semanticdb/guide.html#example
SemanticDB producers provide full Scala support and partial Java support

Is this support only for when a Scala project calls to Java files?

Thanks

mtes3

@mtes3

Hello.
I tried to move from scala-macros to meta.
But I still do not understand the next things:
meta v4.2.0 is library for analyze scala code (read file -> transform to tokens, ans so on)
but meta contain inline definition for make macros, is it right? and for macro purposes I should use 1.8.0 + meta/paradise compiler plugin, is it correct?
thanks in advance

Gabriele Petronella

@gabro

@mtes3 scalameta macros is a dead unmaintained project, that won’t be published for Scala 2.13. You should stick with macro paradise, which has been moved into the compiler under a flag

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