`sourcePositionMapper` of sbt doesn't work with `DelegatingReporter` of Dotty

[tototoshi]

Compiler version

3.1.1

Minimized code

project/plugins.sbt

addSbtPlugin("com.typesafe.play" % "sbt-twirl" % "1.6.0-M1")

build.sbt

enablePlugins(SbtTwirl)
scalaVersion := "3.1.1"
crossScalaVersions := Seq("2.13.8", "3.1.1")

libraryDependencies := libraryDependencies.value.map {
  case module if module.name == "twirl-api" =>
    module.cross(CrossVersion.for3Use2_13)
  case module => module
}

src/main/twirl/error.scala.html

<h1>Hello @world</h1>

Output

toshi@/Users/toshi/tmp/twirl-example% sbt ++2.13.8 compile
...
[info] compiling 1 Scala source to /Users/toshi/tmp/twirl-example/target/scala-2.13/classes ...
[error] /Users/toshi/tmp/twirl-example/src/main/twirl/error.scala.html:1:12: not found: value world
[error] <h1>Hello @world</h1>
[error]            ^
[error] one error found
[error] (Compile / compileIncremental) Compilation failed
[error] Total time: 2 s, completed 2022/03/15 22:08:00
toshi@/Users/toshi/tmp/twirl-example% sbt ++3.1.1 compile
...
[info] compiling 1 Scala source to /Users/toshi/tmp/twirl-example/target/scala-3.1.1/classes ...
[error] -- [E006] Not Found Error: /Users/toshi/tmp/twirl-example/target/scala-3.1.1/twirl/main/html/error.template.scala:19:63
[error] 19 |Seq[Any](format.raw/*1.1*/("""<h1>Hello """),_display_(/*1.12*/world),format.raw/*1.17*/("""</h1>
[error]    |                                                               ^^^^^
[error]    |                                                        Not found: world
[error] one error found
[error] one error found
[error] (Compile / compileIncremental) Compilation failed
[error] Total time: 4 s, completed 2022/03/15 22:08:15

Expectation

When we write a template (.scala.html) for playframework/twirl, The template will be converted to a .scala file and compiled as a Scala object. If errors are found, Twirl shows them as template errors using sourcePositionMappers of sbt.
https://github.com/playframework/twirl/blob/2c064e741ff8771c68e6397518fc05cb16d61c67/sbt-twirl/src/main/scala/play/twirl/sbt/SbtTwirl.scala#L79

This works with Scala2 but doesn't work with Scala3. We see error messages directly from Dotty in Scala3.

I think this is because DelegatingReporter of Dotty passes a rendered parameter to xsbti.Reporter.
https://github.com/lampepfl/dotty/blob/d2ebd75a2e63e3dd885e7bad94472931d0bae296/sbt-bridge/src/dotty/tools/xsbt/DelegatingReporter.java#L47

If the rendered parameter is passed, sbt will display the contents of the rendered parameter, and information other than the rendered parameter is ignored. The error information translated by sourcePositionMappers in sbt's ManagedLoggedReporter will also not be displayed.

If I modify the DelegatingReporter so that the rendered parameter is not passed to sbt, it is possible to display the same error message as when compiling with Scala2. However, the message stored in the rendered parameter is from Dotty and contains more detailed error messages, so I feel a bit uncomfortable making it completely invisible. What do you think?

[SethTisue]

I don't feel able to tackle this myself, but I do hope that a volunteer can be found, since it would help Play get onto Scala 3.

[smarter]

It seems that the API provided by zinc in xsbti doesn't expose the sourcePositionMappers stuff, so this will likely require some work on zinc. Alternatively someone could come up with a build-independent way to express source maps (e.g., an annotation that would be interpreted by the compiler). Either way this is likely to be a lot of work that will require significant effort from Someone™.

[smarter]

A temporary hack could be to turn off the use of rendered only if the filename ends with .template.scala and hope that only twirl uses that format...

[smarter]

I've opened sbt/zinc#1074.

[eed3si9n]

I don't feel able to tackle this myself, but I do hope that a volunteer can be found, since it would help Play get onto Scala 3.

I'd be happy to assist anyone who wants to work on Zinc, if Zinc needs updates.

[brbrown25]

I don't feel able to tackle this myself, but I do hope that a volunteer can be found, since it would help Play get onto Scala 3.

I'd be happy to assist anyone who wants to work on Zinc, if Zinc needs updates.

I'm always happy to learn new things and help out, maybe we can find sometime to collaborate together on this :)