Experimental feature to alias a package

Author: retronym

src/compiler/scala/tools/nsc/settings/ScalaSettings.scala

@@ -265,6 +265,7 @@ trait ScalaSettings extends StandardScalaSettings with Warnings { _: MutableSett
   val YpickleWrite = StringSetting("-Ypickle-write", "directory|jar", "destination for generated .sig files containing type signatures.", "", None).internalOnly()
   val YpickleWriteApiOnly = BooleanSetting("-Ypickle-write-api-only", "Exclude private members (other than those material to subclass compilation, such as private trait vals) from generated .sig files containing type signatures.").internalOnly()
   val YtrackDependencies = BooleanSetting("-Ytrack-dependencies", "Record references to in unit.depends. Deprecated feature that supports SBT 0.13 with incOptions.withNameHashing(false) only.", default = true)
+  val YaliasPackage = MultiStringSetting("-Yalias-package", "alias.name=underlying.name", "Alias package")
 
   sealed abstract class CachePolicy(val name: String, val help: String)
   object CachePolicy {

src/compiler/scala/tools/nsc/transform/Erasure.scala

@@ -746,7 +746,7 @@ abstract class Erasure extends InfoTransform
             } else if (isMethodTypeWithEmptyParams(qual1.tpe)) { // see also adaptToType in TypeAdapter
               assert(qual1.symbol.isStable, qual1.symbol)
               adaptMember(selectFrom(applyMethodWithEmptyParams(qual1)))
-            } else if (!qual1.isInstanceOf[Super] && (!isJvmAccessible(qual1.tpe.typeSymbol, context) || !qual1.tpe.typeSymbol.isSubClass(tree.symbol.owner))) {
+            } else if (!tree.symbol.isTopLevel && !qual1.isInstanceOf[Super] && (!isJvmAccessible(qual1.tpe.typeSymbol, context) || !qual1.tpe.typeSymbol.isSubClass(tree.symbol.owner))) {
               // A selection requires a cast:
               //   - In `(foo: Option[String]).get.trim`, the qualifier has type `Object`. We cast
               //     to the owner of `trim` (`String`), unless the owner is a non-accessible Java

src/compiler/scala/tools/nsc/typechecker/Analyzer.scala

@@ -44,6 +44,19 @@ trait Analyzer extends AnyRef
       override val checkable = false
       override def keepsTypeParams = false
 
+      override def run(): Unit = {
+        val aliases: List[String] = settings.YaliasPackage.value
+        aliases.foreach {
+          alias =>
+            alias.split('=').toList match {
+              case a :: b :: Nil =>
+                processPackageAliases(a, b)
+              case _             =>
+                globalError(s"Cannot parse value for ${settings.YaliasPackage}: $alias")
+            }
+        }
+        super.run()
+      }
       def apply(unit: CompilationUnit) {
         newNamer(rootContext(unit)).enterSym(unit.body)
       }

src/compiler/scala/tools/nsc/typechecker/Contexts.scala

@@ -1016,6 +1016,8 @@ trait Contexts { self: Analyzer =>
         else if (mt1 =:= mt2 && name.isTypeName && imp1Symbol.isMonomorphicType && imp2Symbol.isMonomorphicType) {
           log(s"Suppressing ambiguous import: $mt1 =:= $mt2 && $imp1Symbol and $imp2Symbol are equivalent")
           Some(imp1)
+        } else if (imp1Symbol == imp2Symbol && imp1Symbol.owner.isTopLevel) {
+          Some(imp1)
         }
         else {
           log(s"Import is genuinely ambiguous:\n  " + characterize)
@@ -1145,7 +1147,10 @@ trait Contexts { self: Analyzer =>
         else sym match {
           case NoSymbol if inaccessible ne null => inaccessible
           case NoSymbol                         => LookupNotFound
-          case _                                => LookupSucceeded(qual, sym)
+          case _                                =>
+            if (qual.symbol != null && qual.symbol.isPackage && qual.symbol.moduleClass != sym.owner)
+              qual.setSymbol(sym.owner.sourceModule)
+            LookupSucceeded(qual, sym)
         }
       )
       def finishDefSym(sym: Symbol, pre0: Type): NameLookup =

src/compiler/scala/tools/nsc/typechecker/Namers.scala

@@ -53,6 +53,48 @@ trait Namers extends MethodSynthesis {
     case _                 => false
   }
 
+  def processPackageAliases(package1: String, package2: String): Unit = {
+    class Pack(sym: Symbol) {
+      val packageClassSym: Symbol = sym.moduleClass
+      val declsList = packageClassSym.info.decls.toList
+      val (packDecls, nonPackDecls) = declsList.partition(_.hasPackageFlag)
+      val packDeclNames = packDecls.map(_.name).toSet
+      def enter(sym: Symbol): Unit = {
+        val scope = packageClassSym.info.decls
+        if (scope.lookupSymbolEntry(sym) == null) {
+          scope.enter(sym)
+        }
+      }
+    }
+    def smoosh(p1: Pack, p2: Pack): Unit = {
+      p2.nonPackDecls.foreach(p1.enter(_))
+
+      val sharedNames = p1.packDeclNames.intersect(p2.packDeclNames)
+      p1.packDecls.foreach { p1Decl =>
+        p2.packDecls.find(_.name == p1Decl.name) match {
+          case None =>
+          case Some(p2Decl) =>
+            smoosh(new Pack(p1Decl), new Pack(p2Decl))
+        }
+      }
+      p2.packDecls.foreach { p2Decl =>
+        if (sharedNames.contains(p2Decl.name)) {
+          val p1Decl = p1.packDecls.find(_.name == p2Decl.name).get
+          smoosh(new Pack(p1Decl), new Pack(p2Decl))
+        } else {
+          val dummySelect        = Select(gen.mkAttributedRef(p1.packageClassSym.sourceModule), p2Decl.name)
+          val p2DeclClone = newNamer(NoContext.make(EmptyTree, RootClass)).createPackageSymbol(NoPosition, dummySelect)
+          p1.enter(p2DeclClone)
+        }
+      }
+    }
+    val package1Sym = rootMirror.getPackageIfDefined(package1)
+    val package2Sym = rootMirror.getPackageIfDefined(package2)
+    // for now require both packages to be defined
+    if (package1Sym != NoSymbol && package2Sym != NoSymbol)
+      smoosh(new Pack(package1Sym), new Pack(package2Sym))
+  }
+
   private class NormalNamer(context: Context) extends Namer(context)
   def newNamer(context: Context): Namer = new NormalNamer(context)
 
@@ -362,7 +404,6 @@ trait Namers extends MethodSynthesis {
         case Select(qual: RefTree, _) => createPackageSymbol(pos, qual).moduleClass
       }
       val existing = pkgOwner.info.decls.lookup(pid.name)
-
       if (existing.hasPackageFlag && pkgOwner == existing.owner)
         existing
       else {

src/compiler/scala/tools/nsc/typechecker/Typers.scala

@@ -571,13 +571,18 @@ trait Typers extends Adaptations with Tags with TypersTracking with PatternTyper
           }
         }
         val qual = typedQualifier { atPos(tree.pos.makeTransparent) {
+          def packageObject =
+            if (!sym.isOverloaded && sym.owner.isModuleClass) sym.owner.sourceModule // historical optimization, perhaps no longer needed
+            else pre.typeSymbol.packageObject
           tree match {
             case Ident(_) =>
-              val packageObject =
-                if (!sym.isOverloaded && sym.owner.isModuleClass) sym.owner.sourceModule // historical optimization, perhaps no longer needed
-                else pre.typeSymbol.packageObject
               Ident(packageObject)
-            case Select(qual, _) => Select(qual, nme.PACKAGEkw)
+            case Select(qual, _) =>
+              if (qual.symbol != sym.owner.owner) {
+                Ident(packageObject)
+              } else {
+                Select(qual, nme.PACKAGEkw)
+              }
             case SelectFromTypeTree(qual, _) => Select(qual, nme.PACKAGEkw)
           }
         }}

src/reflect/scala/reflect/internal/Symbols.scala

@@ -2647,8 +2647,8 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
         else if (isAnonymousClass)               ("anonymous class",      "anonymous class", "AC")
         else if (isRefinementClass)              ("refinement class",     "",                "RC")
         else if (isJavaAnnotation)               ("Java annotation",      "Java annotation", "JANN")
-        else if (isJavaEnum
-            || companion.isJavaEnum)             ("Java enumeration",     "Java enum",       "JENUM")
+//        else if (isJavaEnum
+//            || companion.isJavaEnum)             ("Java enumeration",     "Java enum",       "JENUM")
         else if (isJava && isModule)             ("Java module",          "class",           "JMOD")
         else if (isJava && isModuleClass)        ("Java module class",    "class",           "JMODC")
         else if (isModule)                       ("module",               "object",          "MOD")

test/junit/scala/tools/nsc/PackageSmoosherTest.scala

@@ -0,0 +1,101 @@
+package scala.tools.nsc
+
+import java.nio.file.Files
+
+object PackageSmoosherTest {
+  def main(args: Array[String]): Unit = {
+    val g = new Global(new Settings)
+    g.settings.usejavacp.value = true
+    import g._
+    val tmpDir = Files.createTempDirectory("test-classes-")
+
+    val code =
+      s"""
+     package o {
+       package platform {
+         package a {
+           class A
+           object `package` {}
+           object SomeObject
+         }
+         object `package` {
+           implicit def foo: a.A = null
+         }
+         object SomeObject
+       }
+       package prime {
+         package b {
+           class B
+         }
+         package a {
+           class A2
+         }
+         package q {
+            class Query
+         }
+         class Query
+       }
+       }
+       """
+
+    def compile(enabled: Boolean)(code: String) = {
+      settings.Xprint.value = List("all")
+      settings.outdir.value = tmpDir.toAbsolutePath.toString
+      if (enabled)
+        settings.YaliasPackage.value = "o.prime=o.platform" :: Nil
+      reporter.reset()
+      val r = new Run
+      r.compileSources(newSourceFile(code) :: Nil)
+      assert(!reporter.hasErrors)
+    }
+
+    compile(enabled = false)(code)
+    compile(enabled = true)(
+      """
+        | package client {
+        |   object Client {
+        |     new o.platform.a.A
+        |     new o.prime.a.A
+        |     o.prime.SomeObject
+        |     o.prime.a.SomeObject
+        |   }
+        | }
+        |""".stripMargin)
+    compile(enabled = true)(
+      """
+        |import o.platform._
+        |import o.prime._
+        |class Test {
+        |  foo
+        |  implicitly[o.platform.a.A]
+        |}
+        |""".stripMargin)
+    compile(enabled = true)(
+      """
+        |package o.platform.bt
+        |object `package` {
+        |}
+        |object O1
+        |trait T1
+        |""".stripMargin
+    )
+    compile(enabled = true)(
+      """
+        |package o.prime.bt
+        |
+        |class C2
+        |""".stripMargin
+    )
+
+    compile(enabled = true)(
+      """
+        |import o.platform._
+        |import o.prime.q._
+        |
+        |class Test extends Query {
+        |
+        |}
+        |""".stripMargin
+      )
+  }
+}