Stack trace filenames are different when running from SBT

[armanbilge]

Cats Effect isn't strictly necessary for a minimization, but here it helps demonstrate how this issue affects published source maps.

// build.sbt
scalaVersion := "2.13.7"
scalaJSUseMainModuleInitializer := true
libraryDependencies += "org.typelevel" %%% "cats-effect" % "3.2.9"
enablePlugins(ScalaJSPlugin)

// project/plugins.sbt
addSbtPlugin("org.scala-js" % "sbt-scalajs" % "1.7.1")

// src/main/scala/Example.scala
import cats.effect.{IO, IOApp}

object Example extends IOApp.Simple {
  override def run: IO[Unit] = IO.raiseError(new Throwable("Boom!"))
}

Running within sbt I get:

java.lang.Throwable: Boom!
    at $c_LExample$.run__Lcats_effect_IO (/workspace/example/target/scala-2.13/example-fastopt/file:/workspace/example/src/main/scala/Example.scala:4:46)
    at $f_Lcats_effect_IOApp__main__AT__V (/workspace/example/target/scala-2.13/example-fastopt/https:/raw.githubusercontent.com/typelevel/cats-effect/v3.2.9/core/js/src/main/scala/cats/effect/IOApp.scala:267:55)
    at $s_LExample__main__AT__V (/workspace/example/target/scala-2.13/example-fastopt/file:/workspace/example/src/main/scala/Example.scala:3:8)
    at /workspace/example/target/scala-2.13/example-fastopt/main.js:43393:1
    at /workspace/example/target/scala-2.13/example-fastopt/main.js:43394:4
    at Script.runInThisContext (node:vm:129:12)
    at Object.runInThisContext (node:vm:305:38)
    at [stdin]:8:25
    at Script.runInThisContext (node:vm:129:12)
    at Object.runInThisContext (node:vm:305:38)

Notice how the filenames are prepended with my workspace and also the URL has lost a slash. If I run directly with node --enable-source-maps I get:

<ref *1> /workspace/example/src/main/scala/Example.scala:4
  override def run: IO[Unit] = IO.raiseError(new Throwable("Boom!"))
                                             ^

java.lang.Throwable: Boom!
    at $c_LExample$.run__Lcats_effect_IO (/workspace/example/src/main/scala/Example.scala:4:46)
    at null.$f_Lcats_effect_IOApp__main__AT__V (https://raw.githubusercontent.com/typelevel/cats-effect/v3.2.9/core/js/src/main/scala/cats/effect/IOApp.scala:267:55)
    at null.$s_LExample__main__AT__V (/workspace/example/src/main/scala/Example.scala:3:8)
    at Object.<anonymous> (/workspace/example/target/scala-2.13/example-fastopt/main.js:43393:1)
    at Object.<anonymous> (/workspace/example/target/scala-2.13/example-fastopt/main.js:43394:4)
    at Module._compile (node:internal/modules/cjs/loader:1101:14)
    at Object.Module._extensions..js (node:internal/modules/cjs/loader:1153:10)
    at Module.load (node:internal/modules/cjs/loader:981:32)
    at Function.Module._load (node:internal/modules/cjs/loader:822:12)
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:81:12) {
  jl_Throwable__f_s: 'Boom!',
  jl_Throwable__f_e: null,
  jl_Throwable__f_enableSuppression: true,
  jl_Throwable__f_writableStackTrace: true,
  jl_Throwable__f_stackTraceStateInternal: [Circular *1],
  jl_Throwable__f_stackTrace: null,
  jl_Throwable__f_suppressed: null
}

[sjrd]

I did not know that Node.js had introduced their own --enable-source-maps. It might be useful to investigate if we can use it instead of source-map-support.

You can do so today even from sbt with

jsEnv := new org.scalajs.jsenv.nodejs.NodeJSEnv(
  org.scalajs.jsenv.nodejs.NodeJSEnv.Config()
    .withSourceMap(false).withArgs(List("--enable-source-maps")))

[armanbilge]

Oh, I didn't realize you were using something else? AFAIK --enable-source-maps still requires source-map-support to be installed.

Edit: scratch that, I've just been confused by these two different source maps features :)

[armanbilge]

Hmm, I tried your suggestion of .withSourceMap(false).withArgs(List("--enable-source-maps")) in typelevel/cats-effect#2582 but it doesn't seem to work.

[gzm0]

Note that inside NodeJSEnv we execute scripts using the vm module. So that might make the result different.

[armanbilge]

Thanks. Not sure if the native sourcemaps work with the vm module:

• VM: Add source mapping support nodejs/node#8042

They recommend using the V8 stack trace API to customize it, which I assume is what you might already be doing in NodeJSEnv?

[gzm0]

Nope :)

scala-js-js-envs/nodejs-env/src/main/scala/org/scalajs/jsenv/nodejs/NodeJSEnv.scala

Lines 104 to 107 in 01b0e95

	require('vm').runInThisContext(
	require('fs').readFileSync($pathJS, { encoding: "utf-8" }),
	{ filename: $pathJS, displayErrors: true }
	)

[armanbilge]

Hmm. Maybe require('source-map-support').install() is doing something magical 😆

[gzm0]

It more feels like the path mangling / unmangling is broken. Maybe it assumes that we give it a relative path in fileName and then just concatenates things... 🤷

[armanbilge]

Oh, for sure. I was disappointed that this workaround didn't work:

jsEnv := new org.scalajs.jsenv.nodejs.NodeJSEnv(
  org.scalajs.jsenv.nodejs.NodeJSEnv.Config()
    .withSourceMap(false).withArgs(List("--enable-source-maps")))

It might have to do with the VM thing.

[gzm0]

I'm having a more detailed look at this. For starters, I'm going to transfer this to https://github.com/scala-js/scala-js-js-envs, because the issue is almost certainly there. Also, we need to test things there anyways :)

[gzm0]

Well... So it seems this is a known issue (since 2015):

evanw/node-source-map-support#84

Now, the question is why it works in the case you pass a single file.

[armanbilge]

Thanks for looking into this!

The case where it works, it's not using the source-map-support package. It's using Node.js builtin source map implementation. It would be amazing if you could switch the env to use that instead, so we don't have to install the npm package everywhere :)

[gzm0]

OK, I can reproduce this on node 14 onward (node 12 seems to have the same issue with the --enable-source-map flag).

[gzm0]

What I have found out so far:

• We could probably replace our entire source map machinery with simply a flag (if we require node >= 12.12.0 which is acceptable IMO).
• However, it will not work on Script inputs due to VM: Add source mapping support nodejs/node#8042 (with the current implementation). tl;dr: vm.runInThisContext does not support source maps.
• ATM I do not understand JS contexts sufficiently well to know what our alternatives are (if any).

@sjrd, any thoughts you have would be appreciated.