Merge pull request #2528 from abeln/java-packages

Fix #2456: eliminate syntactic references to Java packages

Author: DarkDimius

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

@@ -48,7 +48,8 @@ class Compiler {
       List(new sbt.ExtractAPI),     // Sends a representation of the API of classes to sbt via callbacks
       List(new Pickler),            // Generate TASTY info
       List(new FirstTransform,      // Some transformations to put trees into a canonical form
-           new CheckReentrant),     // Internal use only: Check that compiled program has no data races involving global vars
+           new CheckReentrant,      // Internal use only: Check that compiled program has no data races involving global vars
+           new ElimJavaPackages),   // Eliminate syntactic references to Java packages
       List(new CheckStatic,         // Check restrictions that apply to @static members
            new CheckPhantomCast,    // Checks that no Phantom types in are in casts
            new ElimRepeated,        // Rewrite vararg parameters and arguments

compiler/src/dotty/tools/dotc/transform/ElimJavaPackages.scala

@@ -0,0 +1,46 @@
+package dotty.tools.dotc.transform
+
+import dotty.tools.dotc.ast.tpd._
+import dotty.tools.dotc.core.Contexts.Context
+import dotty.tools.dotc.core.Flags._
+import dotty.tools.dotc.core.Types.{Type, TypeRef}
+import dotty.tools.dotc.transform.TreeTransforms.{MiniPhaseTransform, TransformerInfo}
+
+/**
+  * Eliminates syntactic references to Java packages, so that there's no chance
+  * they accidentally end up in the backend.
+  */
+class ElimJavaPackages extends MiniPhaseTransform {
+
+  override def phaseName: String = "elimJavaPackages"
+
+  override def transformSelect(tree: Select)(implicit ctx: Context, info: TransformerInfo): Tree = {
+    if (isJavaPackage(tree)) {
+      assert(tree.tpe.isInstanceOf[TypeRef], s"Expected tree with type TypeRef, but got ${tree.tpe.show}")
+      Ident(tree.tpe.asInstanceOf[TypeRef])
+    } else {
+      tree
+    }
+  }
+
+  override def checkPostCondition(tree: Tree)(implicit ctx: Context): Unit = {
+    tree match {
+      case tree: Select =>
+        assert(!isJavaPackage(tree), s"Unexpected reference to Java package in ${tree.show}")
+      case _ => ()
+    }
+  }
+
+  /**
+    * Is the given tree a syntactic reference to a Java package?
+    */
+  private def isJavaPackage(tree: Select)(implicit ctx: Context): Boolean = {
+    tree.tpe match {
+      case TypeRef(prefix, _) =>
+        val flags = prefix.termSymbol.flags
+        // Testing for each flag separately is more efficient than using FlagConjunction.
+        flags.is(Package) && flags.is(JavaDefined)
+      case _ => false
+    }
+  }
+}