Make Scala.js usable for people #9637

sjrd · 2020-08-25T15:34:11Z

This PR contains a series of polishing commits that make the Scala.js support in Dotty usable for people using Dotty in their projects. After this PR, if someone adds the ScalaJSPlugin to a project, and the build has the sbt-dotty plugin, that project will be correctly configured to use Dotty with the Scala.js support.

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sbt-dotty/src/dotty/tools/sbtplugin/DottyPlugin.scala

sjrd · 2020-08-25T15:39:13Z

sbt-dotty/src/dotty/tools/sbtplugin/DottyPlugin.scala

@@ -169,6 +170,12 @@ object DottyPlugin extends AutoPlugin {
  override def projectSettings: Seq[Setting[_]] = {
    Seq(
      isDotty := scalaVersion.value.startsWith("0.") || scalaVersion.value.startsWith("3."),
+      isDottyJS := {


The way this works basically assumes that the settings of ScalaJSPlugin will be applied before those of DottyPlugin. It seems to be the case in the tests I did, perhaps because ScalaJSPlugin is explicitly enabled, while DottyPlugin is triggered. However, I could not find an authoritative source on the topic.

I have an alternative implementation in mind, that would not have that assumption: it would be to have another DottyJSPlugin, that would be auto-triggered by the presence of DottyPlugin and ScalaJSPlugin. That plugin would be guaranteed to have its settings be applied after both of them, by the documented rules. However, that would require sbt-dotty to depend on sbt-scalajs to be able to refer to ScalaJSPlugin.

Hopefully in the not-too-distant future sbt-dotty will be obsoleted by sbt supporting dotty natively, so we need to plan for that too

When that happens, the Scala.js-Dotty combination will have to be handled by sbt-scalajs. Currently though, since apparently DottyPlugin gets applied after ScalaJSPlugin, there's nothing sbt-scalajs can do, AFAICT.

When that happens, the Scala.js-Dotty combination will have to be handled by sbt-scalajs.

OK, can you add a comment mentioning this around here?

smarter · 2020-08-25T21:29:01Z

sbt-dotty/src/dotty/tools/sbtplugin/DottyPlugin.scala

@@ -169,6 +170,12 @@ object DottyPlugin extends AutoPlugin {
  override def projectSettings: Seq[Setting[_]] = {
    Seq(
      isDotty := scalaVersion.value.startsWith("0.") || scalaVersion.value.startsWith("3."),
+      isDottyJS := {


When that happens, the Scala.js-Dotty combination will have to be handled by sbt-scalajs.

OK, can you add a comment mentioning this around here?

smarter · 2020-08-25T21:32:01Z

@anatoliykmetyuk To publish a new version of sbt-dotty we just need to push a tag sbt-dotty-v0.4.2, right?

gzm0

Is there anything specific you want me to review here? This seems to be mostly dotty build and library setup plumbing. I have no clue about these :-/

So there is nothing that looks wrong, but I also cannot really gauge if anything is right.

sjrd · 2020-08-26T13:44:33Z

@gzm0 It was mostly about the last commit, which are changes to sbt-dotty that interact with sbt-scalajs in non-obvious ways.

gzm0 · 2020-08-26T13:52:18Z

sbt-dotty/src/dotty/tools/sbtplugin/DottyPlugin.scala

+                moduleID.name == "scalajs-library" || moduleID.name == "scalajs-compiler"
+              )
+            }
+            // Apply withDottyCompat to the dependency on scalajs-test-bridge


I assume this applies transitively to scalajs-test-interface?

Yes, because the dependency on scalajs-test-interface will be lookup up in its POM file. And in the POM file, this has already been hard-wired to scalajs-test-interface_2.13.

In addition to remove the `-bootstrapped` suffix, we must also remove the `js` suffix.

…ate. So that it gets published together with the rest of the distribution.

This allows `withDottyCompat` to work for Scala.js dependencies, for example.

This also implies changes in the build for JS projects, since they will now get the configuration for JS from `DottyPlugin`.

anatoliykmetyuk · 2020-08-27T11:26:15Z

@anatoliykmetyuk To publish a new version of sbt-dotty we just need to push a tag sbt-dotty-v0.4.2, right?

Yes, publishing SBT plugin is done by tagging.

sjrd requested review from smarter and anatoliykmetyuk August 25, 2020 15:34

sjrd assigned smarter and anatoliykmetyuk Aug 25, 2020

dottybot reviewed Aug 25, 2020

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smarter reviewed Aug 25, 2020

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sbt-dotty/src/dotty/tools/sbtplugin/DottyPlugin.scala Show resolved Hide resolved

sjrd commented Aug 25, 2020

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sjrd force-pushed the make-sjs-usable-for-people branch 4 times, most recently from 4414a9d to a6ff937 Compare August 25, 2020 19:07

sjrd requested a review from gzm0 August 25, 2020 21:28

smarter approved these changes Aug 25, 2020

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sjrd force-pushed the make-sjs-usable-for-people branch 3 times, most recently from c5d9b7c to 14c1478 Compare August 26, 2020 12:38

gzm0 reviewed Aug 26, 2020

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gzm0 approved these changes Aug 26, 2020

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sjrd added 4 commits August 27, 2020 10:51

Correctly configure the module name of bootstrapped JS artifacts.

9a2247f

In addition to remove the `-bootstrapped` suffix, we must also remove the `js` suffix.

Add dotty-library-bootstrappedJS in the dotty-bootstrapped aggreg…

80b1fd3

…ate. So that it gets published together with the rest of the distribution.

Handle the prefix and suffix of CrossVersions in withDottyCompat.

2b6417b

This allows `withDottyCompat` to work for Scala.js dependencies, for example.

Have sbt-dotty correctly configure Scala.js projects.

0a7d9dc

This also implies changes in the build for JS projects, since they will now get the configuration for JS from `DottyPlugin`.

sjrd force-pushed the make-sjs-usable-for-people branch from 14c1478 to 0a7d9dc Compare August 27, 2020 08:51

sjrd mentioned this pull request Aug 27, 2020

Release Dotty 0.27.0-RC1 and 0.26.0 #9651

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42 tasks

smarter merged commit 539dd06 into scala:master Aug 27, 2020

sjrd deleted the make-sjs-usable-for-people branch August 27, 2020 11:11

sjrd mentioned this pull request Aug 27, 2020

Add 0.27.0-RC1 release article #9653

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Make Scala.js usable for people #9637

Make Scala.js usable for people #9637

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anatoliykmetyuk commented Aug 27, 2020

Make Scala.js usable for people #9637

Make Scala.js usable for people #9637

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anatoliykmetyuk commented Aug 27, 2020