From de492fcd0431d41d82fbc10c56b73a8f97f51f5f 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)

---
 compiler/src/dotty/tools/dotc/core/StdNames.scala    |  2 +-
 .../src/dotty/tools/dotc/transform/CheckUnused.scala | 12 +++++++-----
 tests/pos/i18366.scala                               | 10 ++++++++++
 3 files changed, 18 insertions(+), 6 deletions(-)
 create mode 100644 tests/pos/i18366.scala

diff --git a/compiler/src/dotty/tools/dotc/core/StdNames.scala b/compiler/src/dotty/tools/dotc/core/StdNames.scala
index 4fc7ea4185d8..40f8ac2dc252 100644
--- a/compiler/src/dotty/tools/dotc/core/StdNames.scala
+++ b/compiler/src/dotty/tools/dotc/core/StdNames.scala
@@ -53,7 +53,7 @@ object StdNames {
     protected def kw(name: N): N = { kws += name; name }
 
     final val keywords: collection.Set[N] = kws
-  }
+  } 
 
   abstract class ScalaNames[N <: Name] extends DefinedNames[N] {
     protected def encode(s: String): N = fromName(fromString(s).encode)
diff --git a/compiler/src/dotty/tools/dotc/transform/CheckUnused.scala b/compiler/src/dotty/tools/dotc/transform/CheckUnused.scala
index eb3c37622e0d..96c6cb1a9743 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 =
@@ -669,8 +669,10 @@ object CheckUnused:
         val simpleSelections = qual.tpe.member(sym.name).alternatives
         val typeSelections = sels.flatMap(n => qual.tpe.member(n.name.toTypeName).alternatives)
         val termSelections = sels.flatMap(n => qual.tpe.member(n.name.toTermName).alternatives)
+        val sameTermPath = qual.isTerm && sym.exists && sym.owner.isType && qual.tpe.typeSymbol == sym.owner.asType
         val selectionsToDealias = typeSelections ::: termSelections
-        val qualHasSymbol = simpleSelections.map(_.symbol).contains(sym) || (simpleSelections ::: selectionsToDealias).map(_.symbol).map(dealias).contains(dealiasedSym)
+        val renamedSelection = if sameTermPath then sels.find(sel => sel.imported.name == sym.name) else None
+        val qualHasSymbol = simpleSelections.map(_.symbol).contains(sym) || (simpleSelections ::: selectionsToDealias).map(_.symbol).map(dealias).contains(dealiasedSym) || renamedSelection.isDefined
         def selector = sels.find(sel => (sel.name.toTermName == sym.name || sel.name.toTypeName == sym.name) && symName.map(n => n.toTermName == sel.rename).getOrElse(true))
         def dealiasedSelector = if(isDerived) sels.flatMap(sel => selectionsToDealias.map(m => (sel, m.symbol))).collect {
           case (sel, sym) if dealias(sym) == dealiasedSym => sel
@@ -680,7 +682,7 @@ object CheckUnused:
           else None
         def wildcard = sels.find(sel => sel.isWildcard && ((sym.is(Given) == sel.isGiven && sel.bound.isEmpty) || sym.is(Implicit)))
         if qualHasSymbol && (!isAccessible || sym.isRenamedSymbol(symName)) && sym.exists then
-          selector.orElse(dealiasedSelector).orElse(givenSelector).orElse(wildcard) // selector with name or wildcard (or given)
+          selector.orElse(dealiasedSelector).orElse(givenSelector).orElse(wildcard).orElse(renamedSelection) // selector with name or wildcard (or given)
         else
           None
 
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