Install the sbt bridge from a binary jar instead of from sources

Normally, the source of the sbt bridge is fetched from
scalaCompilerBridgeSource, compiled, then cached by sbt. Unfortunately
the logic in sbt to do this does not take .java source files into
account, so the previous commit broke our bridge.

Thankfully, it turns out that I have amazing foresight ;). In
sbt/sbt#4332 I added
scalaCompilerBridgeBinaryJar to sbt, which bypasses the whole
bridge compilation and caching logic which is not needed when the bridge
is Java-only and thus binary-compatible across Scala releases. So just
using this setting is enough to make everything work!

Author: smarter

project/Build.scala

@@ -226,17 +226,9 @@ object Build {
     version := dottyVersion,
     scalaVersion := dottyNonBootstrappedVersion,
 
-    // Avoid having to run `dotty-sbt-bridge/publishLocal` before compiling a bootstrapped project
-    scalaCompilerBridgeSource :=
-      (dottyOrganization %% "dotty-sbt-bridge" % dottyVersion)
-      .artifacts(Artifact.sources("dotty-sbt-bridge").withUrl(
-        // We cannot use the `packageSrc` task because a setting cannot depend
-        // on a task. Instead, we make `compile` below depend on the bridge `packageSrc`
-        Some((artifactPath in (`dotty-sbt-bridge`, Compile, packageSrc)).value.toURI.toURL))),
-    compile in Compile := (compile in Compile)
-      .dependsOn(packageSrc in (`dotty-sbt-bridge`, Compile))
-      .dependsOn(compile in (`dotty-sbt-bridge`, Compile))
-      .value,
+    scalaCompilerBridgeBinaryJar := {
+      Some((packageBin in (`dotty-sbt-bridge`, Compile)).value)
+    },
 
     // Use the same name as the non-bootstrapped projects for the artifacts
     moduleName ~= { _.stripSuffix("-bootstrapped") },
@@ -830,12 +822,10 @@ object Build {
       Dependencies.`compiler-interface` % Provided,
       (Dependencies.`zinc-api-info` % Test).withDottyCompat(scalaVersion.value)
     ),
-    // The sources should be published with crossPaths := false since they
-    // need to be compiled by the project using the bridge.
-    crossPaths := false,
 
-    // Don't publish any binaries for the bridge because of the above
-    publishArtifact in (Compile, packageBin) := false,
+    // sources are Java-only, tests are in Scala
+    crossPaths in Compile := false,
+    autoScalaLibrary in Compile := false,
 
     fork in Test := true,
     parallelExecution in Test := false

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

@@ -163,14 +163,21 @@ object DottyPlugin extends AutoPlugin {
           inc
       },
 
-      scalaCompilerBridgeSource := {
-        val scalaBridge = scalaCompilerBridgeSource.value
-        val dottyBridge = (scalaOrganization.value % "dotty-sbt-bridge" % scalaVersion.value).withConfigurations(Some(Configurations.Compile.name)).sources()
-        if (isDotty.value)
-          dottyBridge
-        else
-          scalaBridge
-      },
+      scalaCompilerBridgeBinaryJar := Def.taskDyn {
+        if (isDotty.value) Def.task {
+          val dottyBridgeArtifacts = fetchArtifactsOf("dotty-sbt-bridge", CrossVersion.disabled).value
+          val jars = dottyBridgeArtifacts.filter(art => art.getName.startsWith("dotty-sbt-bridge") && art.getName.endsWith(".jar")).toArray
+          if (jars.size == 0)
+            throw new MessageOnlyException("No jar found for dotty-sbt-bridge")
+          else if (jars.size > 1)
+            throw new MessageOnlyException(s"Multiple jars found for dotty-sbt-bridge: ${jars.toList}")
+          else
+            jars.headOption
+        }
+        else Def.task {
+          None: Option[File]
+        }
+      }.value,
 
       // Needed for RCs publishing
       scalaBinaryVersion := {
@@ -184,7 +191,7 @@ object DottyPlugin extends AutoPlugin {
         val si = scalaInstance.value
         if (isDotty.value) {
           Def.task {
-            val dottydocArtifacts = fetchArtifactsOf("dotty-doc").value
+            val dottydocArtifacts = fetchArtifactsOf("dotty-doc", CrossVersion.binary).value
             val includeArtifact = (f: File) => f.getName.endsWith(".jar")
             val dottydocJars = dottydocArtifacts.filter(includeArtifact).toArray
             val allJars = (si.allJars ++ dottydocJars).distinct
@@ -229,15 +236,15 @@ object DottyPlugin extends AutoPlugin {
     scalacOptions += "-from-tasty"
   ))
 
-  /** Fetch artefacts for scalaOrganization.value %% moduleName % scalaVersion.value */
-  private def fetchArtifactsOf(moduleName: String) = Def.task {
+  /** Fetch artifacts for scalaOrganization.value %% moduleName % scalaVersion.value */
+  private def fetchArtifactsOf(moduleName: String, crossVersion: CrossVersion) = Def.task {
     val dependencyResolution = Keys.dependencyResolution.value
     val log = streams.value.log
     val scalaInfo = scalaModuleInfo.value
     val updateConfiguration = Keys.updateConfiguration.value
     val warningConfiguration = (unresolvedWarningConfiguration in update).value
 
-    val moduleID = (scalaOrganization.value %% moduleName % scalaVersion.value).cross(CrossVersion.binary)
+    val moduleID = (scalaOrganization.value % moduleName % scalaVersion.value).cross(crossVersion)
     val descriptor = dependencyResolution.wrapDependencyInModule(moduleID, scalaInfo)
 
     dependencyResolution.update(descriptor, updateConfiguration, warningConfiguration, log) match {