Relative path to source file in sourcemap is broken sometimes

[glmars]

I found stable reproduction (see example project https://github.com/glmars/scalajs-wrongsourcemap)

Steps to reproduce

1. run sbt clean fastOptJS first time
2. check generated source map file ./target/scala-2.11/scalajs-wrongsourcemap-fastopt.js.map, there is such path to source file:

   "../src/main/scala/ru/lmars/bundler/Application.scala"
   

   this is wrong path!
3. run sbt clean fastOptJS second time
4. path to source file will be different:

   "../../src/main/scala/ru/lmars/bundler/Application.scala"
   

   and this is right path!
5. delete directory ./target/scala-2.11
6. run sbt clean fastOptJS
7. source file path in .map file is broken again!

I ran into this bug many times when my file manager holds some directories inside target and sbt clean couldn't delete them (but successfully deletes ./target/scala-2.11).

[sjrd]

Thanks for the report. I can indeed reproduce this. The reliable way to reproduce it is to start sbt (or reload it) at a time when the target/scala-2.11 directory does not exist. This happens because of this line:

scala-js/sbt-plugin/src/main/scala/org/scalajs/sbtplugin/ScalaJSPluginInternal.scala

Line 211 in 7245687

Some((artifactPath in key).value.getParentFile.toURI())

It is incorrect because getParentFile will return a path without a trailing /. Then, .toURI fixes it with a trailing / but only if the file already exists and is a directory. Since this line of code is evaluated at the time sbt is loaded, it will do the wrong thing if target/scala-2.11 does not exist at that time.

The fix is to ensure that there is a trailing / in the URI in all cases.

[sjrd]

In fact, there is an even better way: don't use getParentFile at all. Relativizing URIs is perfectly capable of relativizing against a file rather than a directory. This is even more correct, since the browser will then resolve the relative URI based on the file URI, not its parent directory.

[sjrd]

@glmars Workaround that you can use right now:

scalaJSLinkerConfig := {
  val fastOptJSURI = (artifactPath in (Compile, fastOptJS)).value.toURI
  scalaJSLinkerConfig.value.withRelativizeSourceMapBase(Some(fastOptJSURI))
}

In fact, you'll have to do that in 1.x anyway, because relativeSourceMaps does not exist there, replaced by scalaJSLinkerConfig.

[sjrd]

Fixed in 4d8f39a.

[glmars]

@sjrd, thank you for your attention even to such a minor (for someone) bug.