TypeTree is usage of simple name

Author: som-snytt

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

@@ -118,6 +118,9 @@ class CheckUnused private (phaseMode: CheckUnused.PhaseMode, suffix: String, _ke
   override def transformTypeTree(tree: TypeTree)(using Context): tree.type =
     tree.tpe match
     case AnnotatedType(_, annot) => transformAllDeep(annot.tree)
+    case tpt if tpt.typeSymbol.exists =>
+      preparing:
+        ud.registerUsed(tpt.typeSymbol, Some(tpt.typeSymbol.name), tree = tree) // usage was a simple name
     case _ =>
     tree
 
@@ -405,6 +408,7 @@ object CheckUnused:
         !languageImport(imp.expr).nonEmpty
           && !imp.isGeneratedByEnum
           && !isTransparentAndInline(imp)
+          && !doNotRegisterPrefix(imp.expr.tpe.typeSymbol)
           && peekScopeType != ScopeType.ReplWrapper // #18383 Do not report top-level import's in the repl as unused
       then
         val qualTpe = imp.expr.tpe

tests/warn/i19657.scala

@@ -88,3 +88,28 @@ import scala.annotation.meta.*
 object Alias {
   type A = Deprecated @param
 }
+
+// avoid reporting on runtime (nothing to do with transparent inline)
+import scala.runtime.EnumValue
+
+trait Lime
+
+enum Color(val rgb: Int):
+  case Red   extends Color(0xFF0000) with EnumValue
+  case Green extends Color(0x00FF00) with Lime
+  case Blue  extends Color(0x0000FF)
+
+object prefixes:
+  class C:
+    object N:
+      type U
+  object Test:
+    val c: C = ???
+    def k2: c.N.U = ???
+    import c.N.*
+    def k3: U = ??? // TypeTree if not a select
+  object Alt:
+    val c: C = ???
+    import c.N
+    def k4: N.U = ???
+end prefixes