Make members of the empty package invisible from inside other packages

Fixes #13114

Author: odersky

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -153,19 +153,28 @@ class Typer extends Namer
       if !suppressErrors then report.error(msg, pos)
 
     /** A symbol qualifies if it really exists and is not a package class.
-     *  In addition, if we are in a constructor of a pattern, we ignore all definitions
-     *  which are methods and not accessors (note: if we don't do that
-     *  case x :: xs in class List would return the :: method).
-     *
      *  Package classes are part of their parent's scope, because otherwise
      *  we could not reload them via `_.member`. On the other hand, accessing a
      *  package as a type from source is always an error.
+
+     *  In addition:
+     *    - if we are in a constructor of a pattern, we ignore all definitions
+     *      which are methods and not accessors (note: if we don't do that
+     *      case x :: xs in class List would return the :: method).
+     *    - Members of the empty package can be accessed only from within the empty package.
+     *      Note: it would be cleaner to never nest package definitions in empty package definitions,
+     *      but then we'd have to give up the fiction that a compilation unit consists of
+     *      a single tree (because a source file may have both toplevel classes which go
+     *      into the empty package and package definitions, which would have to stay outside).
+     *      Since the concept of a single tree per compilation unit is known to many
+     *      tools, we did not want to take that step.
      */
     def qualifies(denot: Denotation): Boolean =
       reallyExists(denot)
       && (!pt.isInstanceOf[UnapplySelectionProto]
           || denot.hasAltWith(sd => !sd.symbol.is(Method, butNot = Accessor)))
       && !denot.symbol.is(PackageClass)
+      && (!denot.symbol.maybeOwner.isEmptyPackage || ctx.owner.enclosingPackageClass.isEmptyPackage)
 
     /** Find the denotation of enclosing `name` in given context `ctx`.
      *  @param previous    A denotation that was found in a more deeply nested scope,

language-server/test/dotty/tools/languageserver/CompletionTest.scala

@@ -547,7 +547,8 @@ class CompletionTest {
   }
 
   @Test def completeFromPackageObjectWithInheritance: Unit = {
-    code"""trait Foo[A] { def xxxx(a: A) = a }
+    code"""package test
+          |trait Foo[A] { def xxxx(a: A) = a }
           |package object foo extends Foo[Int] {}
           |object Test {
           |  foo.xx$m1

tests/neg/i13114/A.scala

@@ -0,0 +1,3 @@
+def f = 42
+
+class C

tests/neg/i13114/B.scala

@@ -0,0 +1,7 @@
+class D2 extends C
+
+package p {
+  class D extends C  // error: not found
+
+  @main def test = println(new D)
+}

tests/neg/implicit-package-object.scala

@@ -1,6 +1,9 @@
-trait ToString[A] {
-  def print(a: A): Unit
-}
+package toString:
+  trait ToString[A] {
+    def print(a: A): Unit
+  }
+
+import toString._
 
 package A {
   case class AA(text: String)

tests/pos/i0239.scala

@@ -1,3 +1,5 @@
+package i0239
+
 package p {
   class C[A] {
     implicit def foo: M[A] = ???

tests/pos/i5978.scala

@@ -1,3 +1,4 @@
+package test
 import scala.language.implicitConversions
 
 opaque type Position[Buffer] = Int

tests/pos/pos_valueclasses/t5953.scala

@@ -1,3 +1,5 @@
+package t5953
+
 trait CBF[-F, -A, +C]
 trait GenTraversable[+A]
 trait Traversable[+A] extends GenTraversable[A]

tests/run-staging/i4730.scala

@@ -1,24 +1,21 @@
 import scala.quoted.*
 import scala.quoted.staging.*
 
-object Test {
+
+package i4730:
   given Compiler = Compiler.make(getClass.getClassLoader)
   def ret(using Quotes): Expr[Int => Int] = '{ (x: Int) =>
     ${
       val z = run('{x + 1}) // throws scala.quoted.runtime.impl.ScopeException =>
       Expr(z)
     }
   }
-  def main(args: Array[String]): Unit = {
-    scala.mytest.myTest()
-  }
-}
 
 package scala {
   package mytest {
     def myTest()(using Compiler) = {
       try {
-        run(Test.ret).apply(10)
+        run(i4730.ret).apply(10)
         throw new Exception
       } catch {
         case ex: Exception if ex.getClass.getName == "scala.quoted.runtime.impl.ScopeException" =>
@@ -27,3 +24,9 @@ package scala {
     }
   }
 }
+object Test {
+  import i4730.given
+  def main(args: Array[String]): Unit = {
+    scala.mytest.myTest()
+  }
+}

tests/run-staging/i6992/Macro_1.scala

@@ -2,19 +2,20 @@
 import scala.quoted.*
 import scala.quoted.staging.*
 
+package macros:
 
-object macros {
-  inline def mcr(x: => Any): Any = ${mcrImpl('x)}
+  object macros {
+    inline def mcr(x: => Any): Any = ${mcrImpl('x)}
 
-  class Foo { val x = 10 }
+    class Foo { val x = 10 }
 
-  def mcrImpl(body: Expr[Any])(using ctx: Quotes): Expr[Any] =
-    MyTest.mcrImpl(body)
-}
+    def mcrImpl(body: Expr[Any])(using ctx: Quotes): Expr[Any] =
+      MyTest.mcrImpl(body)
+  }
 
 package scala {
   object MyTest {
-    import macros.*
+    import macros.macros.*
 
    given Compiler = Compiler.make(getClass.getClassLoader)
 

tests/run-staging/i6992/Test_2.scala

@@ -1,4 +1,4 @@
-import macros.*
+import macros.macros.*
 
 object Test {
   val foo = new Foo