Fix #2395: Check if the scala or dotty libraries are missing

compiler/src/dotty/tools/dotc/MissingCoreLibraryException.scala

@@ -0,0 +1,9 @@
+package dotty.tools.dotc
+
+import dotty.tools.FatalError
+
+class MissingCoreLibraryException(rootPackage: String) extends FatalError(
+  s"""Could not find package $rootPackage from compiler core libraries.
+     |Make sure the compiler core libraries are on the classpath.
+   """.stripMargin
+)

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -212,7 +212,7 @@ class Definitions {
    *  in `scalaShadowing` so they don't clash with the same-named `scala`
    *  members at runtime.
    */
-  lazy val ScalaShadowingPackageVal = ctx.requiredPackage("scalaShadowing")
+  lazy val ScalaShadowingPackageVal = ctx.requiredPackage(nme.scalaShadowing)
   lazy val ScalaShadowingPackageClass = ScalaShadowingPackageVal.moduleClass.asClass
 
   /** Note: We cannot have same named methods defined in Object and Any (and AnyVal, for that matter)

compiler/src/dotty/tools/dotc/core/Denotations.scala

@@ -1192,14 +1192,23 @@ object Denotations {
     def staticRef(path: Name, generateStubs: Boolean = true, isPackage: Boolean = false)(implicit ctx: Context): Denotation = {
       def select(prefix: Denotation, selector: Name): Denotation = {
         val owner = prefix.disambiguate(_.info.isParameterless)
+        def isPackageFromCoreLibMissing: Boolean = {
+          owner.symbol == defn.RootClass &&
+          (
+            selector == nme.scala_ || // if the scala package is missing, the stdlib must be missing
+            selector == nme.scalaShadowing // if the scalaShadowing package is missing, the dotty library must be missing
+          )
+        }
         if (owner.exists) {
           val result = if (isPackage) owner.info.decl(selector) else owner.info.member(selector)
           if (result.exists) result
           else {
             val alt =
               if (generateStubs) missingHook(owner.symbol.moduleClass, selector)
               else NoSymbol
-            if (alt.exists) alt.denot else MissingRef(owner, selector)
+            if (alt.exists) alt.denot
+            else if (isPackageFromCoreLibMissing) throw new MissingCoreLibraryException(selector.toString)
+            else MissingRef(owner, selector)
           }
         }
         else owner

compiler/src/dotty/tools/dotc/core/StdNames.scala

@@ -491,6 +491,7 @@ object StdNames {
     val runtimeMirror: N        = "runtimeMirror"
     val sameElements: N         = "sameElements"
     val scala_ : N              = "scala"
+    val scalaShadowing : N      = "scalaShadowing"
     val selectDynamic: N        = "selectDynamic"
     val selectDynamicMethod: N  = "selectDynamicMethod"
     val selectOverloadedMethod: N = "selectOverloadedMethod"

compiler/test/dotty/tools/dotc/MissingCoreLibTests.scala

@@ -0,0 +1,34 @@
+package dotty
+package tools
+package dotc
+
+import org.junit.{ Test, AfterClass }
+
+import vulpix.{ ParallelTesting, SummaryReport, SummaryReporting, TestConfiguration }
+
+import scala.concurrent.duration._
+
+class MissingCoreLibTests extends ParallelTesting {
+  import MissingCoreLibTests._
+  import TestConfiguration._
+
+  // Test suite configuration --------------------------------------------------
+
+  def maxDuration = 30.seconds
+  def numberOfSlaves = 5
+  def safeMode = Properties.testsSafeMode
+  def isInteractive = SummaryReport.isInteractive
+  def testFilter = Properties.testsFilter
+
+  @Test def missingDottyLib: Unit = {
+    val classPath = mkClassPath(Jars.dottyCompiler :: Jars.dottyInterfaces :: Jars.dottyExtras) // missing Jars.dottyLib
+    val options = noCheckOptions ++ checkOptions ++ yCheckOptions ++ classPath
+    compileFile("../tests/neg/nolib/Foo.scala", options).checkExpectedErrors()
+  }
+
+}
+
+object MissingCoreLibTests {
+  implicit val summaryReport: SummaryReporting = new SummaryReport
+  @AfterClass def cleanup(): Unit = summaryReport.echoSummary()
+}

compiler/test/dotty/tools/vulpix/TestConfiguration.scala

@@ -23,8 +23,10 @@ object TestConfiguration {
     "-Yforce-sbt-phases"
   )
 
-  val classPath = {
-    val paths = Jars.dottyTestDeps map { p =>
+  val classPath = mkClassPath(Jars.dottyTestDeps)
+
+  def mkClassPath(deps: List[String]): Array[String] = {
+    val paths = deps map { p =>
       val file = new java.io.File(p)
       assert(
         file.exists,
@@ -50,7 +52,7 @@ object TestConfiguration {
     Array("-classpath", paths)
   }
 
-  private val yCheckOptions = Array("-Ycheck:tailrec,resolveSuper,erasure,mixin,getClass,restoreScopes,labelDef")
+  val yCheckOptions = Array("-Ycheck:tailrec,resolveSuper,erasure,mixin,getClass,restoreScopes,labelDef")
 
   val defaultUnoptimised = noCheckOptions ++ checkOptions ++ yCheckOptions ++ classPath
   val defaultOptimised = defaultUnoptimised :+ "-optimise"

tests/neg/nolib/Foo.scala

@@ -0,0 +1,2 @@
+// nopos-error
+class Foo