Wunused: Only use type treverser for checking refinements in refined type trees

closes lampepfl#17631

Author: KacperFKorban

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

@@ -229,15 +229,15 @@ class CheckUnused private (phaseMode: CheckUnused.PhaseMode, suffix: String, _ke
           pushInBlockTemplatePackageDef(tree)
           traverseChildren(tree)(using newCtx)
           popOutBlockTemplatePackageDef()
-        case t:tpd.ValDef =>
+        case t: tpd.ValDef =>
           prepareForValDef(t)
           traverseChildren(tree)(using newCtx)
           transformValDef(t)
-        case t:tpd.DefDef =>
+        case t: tpd.DefDef =>
           prepareForDefDef(t)
           traverseChildren(tree)(using newCtx)
           transformDefDef(t)
-        case t:tpd.TypeDef =>
+        case t: tpd.TypeDef =>
           prepareForTypeDef(t)
           traverseChildren(tree)(using newCtx)
           transformTypeDef(t)
@@ -248,6 +248,10 @@ class CheckUnused private (phaseMode: CheckUnused.PhaseMode, suffix: String, _ke
           prepareForAssign(t)
           traverseChildren(tree)
         case _: tpd.InferredTypeTree =>
+        case t@tpd.RefinedTypeTree(tpt, refinements) =>
+          //! DIFFERS FROM MINIPHASE
+          typeTraverser(unusedDataApply).traverse(t.tpe)
+          traverse(tpt)(using newCtx)
         case t@tpd.TypeTree() =>
           //! DIFFERS FROM MINIPHASE
           typeTraverser(unusedDataApply).traverse(t.tpe)

tests/pos-special/fatal-warnings/i17631.scala

@@ -0,0 +1,34 @@
+// scalac: -Wunused:all
+
+object foo {
+  type Bar
+}
+
+import foo.Bar
+
+def Test = {
+
+  type Person = { val name: String }
+
+  def good: Person = ???
+  def bad1: { val name: String } = ???
+  def bad2 = (good: { val name: String })
+  def justIs: { val bar: Bar } = ???
+  (bad1, bad2, justIs)
+}
+
+class Record(elems: (String, Any)*) extends Selectable:
+  private val fields = elems.toMap
+  def selectDynamic(name: String): Any = fields(name)
+
+object Main {
+
+  type Person = Record { val name: String; val age: Int }
+
+  locally {
+    def good: Person = ???
+    def bad1: Record { val name: String; val age: Int } = ???
+    def bad2 = (good: Record { val name: String; val age: Int })
+    (bad1, bad2)
+  }
+}