fix: use already imported package aliases for auto import

Author: kasiaMarek

presentation-compiler/src/main/dotty/tools/pc/AutoImports.scala

@@ -269,7 +269,14 @@ object AutoImports:
     private def importName(sym: Symbol): String =
       if indexedContext.importContext.toplevelClashes(sym) then
         s"_root_.${sym.fullNameBackticked(false)}"
-      else sym.fullNameBackticked(false)
+      else
+        sym.ownersIterator.zipWithIndex.foldLeft((List.empty[String], false)) { case ((acc, isDone), (sym, idx)) =>
+          if(isDone || sym.isEmptyPackage || sym.isRoot) (acc, true)
+          else indexedContext.rename(sym) match
+            case Some(renamed) => (renamed :: acc, true)
+            case None if !sym.isPackageObject => (sym.nameBackticked(false) :: acc, false)
+            case None => (acc, false)
+        }._1.mkString(".")
   end AutoImportsGenerator
 
   private def autoImportPosition(

presentation-compiler/test/dotty/tools/pc/tests/edit/AutoImportsSuite.scala

@@ -436,6 +436,19 @@ class AutoImportsSuite extends BaseAutoImportsSuite:
          |""".stripMargin
     )
 
+  @Test def `use-packages-in-scope` =
+    checkEdit(
+      """|import scala.collection.mutable as mut
+         |
+         |val l = <<ListBuffer>>(2)
+         |""".stripMargin,
+      """|import scala.collection.mutable as mut
+         |import mut.ListBuffer
+         |
+         |val l = ListBuffer(2)
+         |""".stripMargin
+    )
+
   private def ammoniteWrapper(code: String): String =
     // Vaguely looks like a scala file that Ammonite generates
     // from a sc file.