Hydra Scala version detection heuristic fallbacks to module SDK versi…

…on. Fix triplequote#37

Our heuristic for extracting the scala version from the scala-compiler jar name
may not work if the scala-compiler jar in the classpath has no version happended
(this for instance can happen when importing an sbt project with the `scalaHome`
setting set to point to a locally installed Scala distribution).

The implemented solution consists in falling back to the module SDK Scala
version if the version cannot be extracted from the scala-compiler jar name.

scala/scala-impl/src/org/jetbrains/plugins/hydra/HydraVersions.scala

@@ -1,10 +1,8 @@
 package org.jetbrains.plugins.hydra
 
 import com.intellij.openapi.diagnostic.Logger
-import org.jetbrains.plugins.scala.project.{ProjectExt, ScalaModule, Version}
 import com.intellij.openapi.project.Project
-
-import scala.collection.breakOut
+import org.jetbrains.plugins.scala.project.{ProjectExt, ScalaModule, ScalaSdk, Version}
 
 /**
   * @author Maris Alexandru
@@ -14,31 +12,50 @@ object HydraVersions {
   val DefaultHydraVersion = "0.9.7"
   private val MinScalaVersion = "2.11.8"
   private val UnsupportedScalaVersion = "2.12.0"
-  private val CompilerRegex = """.*scala-compiler-(\d+\.\d+\.\d+)(-SNAPSHOT)?\.jar""".r
+  private val CompilerJarName = "scala-compiler"
+  private val CompilerVersionRegex = """.*scala-compiler-(\d+\.\d+\.\d+)(-SNAPSHOT)?\.jar""".r
 
   private final val Log: Logger = Logger.getInstance(this.getClass.getName)
 
   def getSupportedScalaVersions(project: Project): Seq[String] = {
     val scalaModules = project.scalaModules
-    // we can't use `module.sdk.compilerVersion` because it assumes the *name* of the Sdk library
-    // matches `SDK-2.12.3` or the like. For the Scala project this is simply called `starr`, so we
-    // need to look inside and retrieve the actual classpath entries
-    val scalaVersionsPerModule: Map[ScalaModule, String] = (for {
+    val module2scalaVersion: Map[ScalaModule, String] = (for {
       module <- scalaModules
-      classpathFile <- module.sdk.compilerClasspath
-      mtch <- CompilerRegex.findFirstMatchIn(classpathFile.getName)
-      scalaVersion = mtch.group(1)
-      if scalaVersion != UnsupportedScalaVersion
-      version = Version(scalaVersion)
-      if version >= Version(MinScalaVersion)
-    } yield module -> version.presentation)(breakOut)
-
-    if (scalaModules.size != scalaVersionsPerModule.size) {
-      // we have some modules that don't have a scala version, we should log it
-      for (module <- scalaModules.filterNot(scalaVersionsPerModule.contains))
-        Log.info(s"Could not retrieve Scala version in module '${module.getName}' with compiler classpath: ${module.sdk.compilerClasspath}")
+      scalaVersion <- findScalaVersionInClasspath(module.sdk)
+    } yield module -> scalaVersion)(collection.breakOut)
+
+    val (supported, unsupported) = module2scalaVersion.foldLeft(Map.empty[ScalaModule, String] -> Map.empty[ScalaModule, String]) { (acc, e) =>
+      val (supported, unsupported) = acc
+      val (module, scalaVersion) = e
+      if (scalaVersion != UnsupportedScalaVersion && Version(scalaVersion) >= Version(MinScalaVersion))
+        (supported + e) -> unsupported
+      else
+        supported -> (unsupported + e)
+    }
+
+    if (unsupported.nonEmpty) {
+      // we have some modules that use a Scala version we don't support
+      for((module, scalaVersion) <- unsupported)
+        Log.info(s"Cannot enable Hydra on module '${module.getName}' because its Scala version ($scalaVersion) is unsupported. The module compiler classpath is: ${module.sdk.compilerClasspath}")
     }
 
-    scalaVersionsPerModule.values.toSeq.distinct
+    supported.values.toList.distinct
+  }
+
+  private def findScalaVersionInClasspath(sdk: ScalaSdk): Option[String] = {
+    // we can't use `module.sdk.compilerVersion` because it assumes the *name* of the Sdk library
+    // matches `SDK-2.12.3` or the like. For the Scala project this is simply called `starr`, so we
+    // need to look inside and retrieve the actual classpath entries
+    val maybeScalaVersion = for {
+      compiler <- sdk.compilerClasspath.find(_.getName.contains(CompilerJarName))
+      matchedJar <- CompilerVersionRegex.findFirstMatchIn(compiler.getName)
+      version <- Option(matchedJar.group(1))
+    } yield version
+
+    // However, if the user has set the scalaHome in his sbt build, then the scala-compiler jar in
+    // the compiler classpath will likely not have the version appended, and hence the above heuristic
+    // for determining the scala version won't work. Therefore, when no version is found, we fallback
+    // to using the SDK compilerVersion.
+    maybeScalaVersion.orElse(sdk.compilerVersion)
   }
 }