From db45a20cfa6c11c10a3908f4a63bdb09de95091d Mon Sep 17 00:00:00 2001
From: Szymon Rodziewicz <szymonrodant@gmail.com>
Date: Fri, 29 Sep 2023 12:25:50 +0200
Subject: [PATCH] Fix false positive in WUnused for renamed path-dependent
 imports (attempt 2)

[Cherry-picked cde97d8adbef89111bd20c760edeb5cc2617b5c8]
---
 .../src/dotty/tools/dotc/transform/CheckUnused.scala   |  6 +++---
 tests/pos/i18366.scala                                 | 10 ++++++++++
 2 files changed, 13 insertions(+), 3 deletions(-)
 create mode 100644 tests/pos/i18366.scala

diff --git a/compiler/src/dotty/tools/dotc/transform/CheckUnused.scala b/compiler/src/dotty/tools/dotc/transform/CheckUnused.scala
index 730ef9a32d2e..3b397d8be746 100644
--- a/compiler/src/dotty/tools/dotc/transform/CheckUnused.scala
+++ b/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 =
diff --git a/tests/pos/i18366.scala b/tests/pos/i18366.scala
new file mode 100644
index 000000000000..698510ad13a2
--- /dev/null
+++ b/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()
\ No newline at end of file