sourcepath: handle user-written package objects

Turns out we never handled this properly before.

Author: smarter

compiler/src/dotty/tools/dotc/ast/Desugar.scala

@@ -804,6 +804,26 @@ object desugar {
     flatTree(cdef1 :: companions ::: implicitWrappers)
   }.reporting(i"desugared: $result", Printers.desugar)
 
+  /** Expand
+   *
+   *    package object name { body }
+   *
+   *  to:
+   *
+   *    package name {
+   *      object `package` { body }
+   *    }
+   */
+  def packageModuleDef(mdef: ModuleDef)(implicit ctx: Context): Tree =
+    val impl = mdef.impl
+    val mods = mdef.mods
+    val moduleName = normalizeName(mdef, impl).asTermName
+    if (mods.is(Package))
+      PackageDef(Ident(moduleName),
+        cpy.ModuleDef(mdef)(nme.PACKAGE, impl).withMods(mods &~ Package) :: Nil)
+    else
+      mdef
+
   /** Expand
    *
    *    object name extends parents { self => body }
@@ -854,7 +874,7 @@ object desugar {
       ctx.warning(em"${hl("final")} modifier is redundant for objects", flagSourcePos(Final))
 
     if (mods.is(Package))
-      PackageDef(Ident(moduleName), cpy.ModuleDef(mdef)(nme.PACKAGE, impl).withMods(mods &~ Package) :: Nil)
+      packageModuleDef(mdef)
     else if (isEnumCase) {
       typeParamIsReferenced(enumClass.typeParams, Nil, Nil, impl.parents)
         // used to check there are no illegal references to enum's type parameters in parents

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

@@ -139,6 +139,8 @@ object SymbolLoaders {
         def simpleDesugar(tree: Tree): Tree = tree match
           case tree: PackageDef =>
             desugar.packageDef(tree)
+          case tree: ModuleDef =>
+            desugar.packageModuleDef(tree)
           case _ =>
             tree
 

tests/pos-special/sourcepath/outer/nested2/package.scala

@@ -0,0 +1,5 @@
+package outer
+
+package object nested2 {
+  val x: Int = 1
+}

tests/pos-special/sourcepath/outer/pkg.scala

@@ -0,0 +1,5 @@
+package outer
+
+object pkg {
+  val y: Int = nested2.x
+}