Backport "Fix false positive in WUnused for renamed path-dependent im…

…ports (2)" to LTS (#20637)

Backports #18617 to the LTS branch.

PR submitted by the release tooling.
[skip ci]

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

@@ -337,7 +337,7 @@ object CheckUnused:
    * - usage
    */
   private class UnusedData:
-    import collection.mutable.{Set => MutSet, Map => MutMap, Stack => MutStack}
+    import collection.mutable.{Set => MutSet, Map => MutMap, Stack => MutStack, ListBuffer => MutList}
     import UnusedData.*
 
     /** The current scope during the tree traversal */
@@ -346,7 +346,7 @@ object CheckUnused:
     var unusedAggregate: Option[UnusedResult] = None
 
     /* IMPORTS */
-    private val impInScope = MutStack(MutSet[tpd.Import]())
+    private val impInScope = MutStack(MutList[tpd.Import]())
     /**
      * We store the symbol along with their accessibility without import.
      * Accessibility to their definition in outer context/scope
@@ -449,7 +449,7 @@ object CheckUnused:
     def pushScope(newScopeType: ScopeType): Unit =
       // unused imports :
       currScopeType.push(newScopeType)
-      impInScope.push(MutSet())
+      impInScope.push(MutList())
       usedInScope.push(MutSet())
 
     def registerSetVar(sym: Symbol): Unit =

tests/pos/i18366.scala

@@ -0,0 +1,10 @@
+//> using options -Xfatal-warnings -Wunused:all
+
+trait Builder {
+  def foo(): Unit
+}
+
+def repro =
+  val builder: Builder = ???
+  import builder.{foo => bar}
+  bar()