From 4c58507151ccb4a358acec068fb309ade8652dbf Mon Sep 17 00:00:00 2001
From: Som Snytt <som.snytt@gmail.com>
Date: Mon, 6 Jan 2025 15:22:30 -0800
Subject: [PATCH] Original of literal

---
 .../tools/dotc/transform/CheckUnused.scala    |  9 ++++--
 .../src/dotty/tools/dotc/typer/Typer.scala    | 21 ++++++------
 tests/warn/i17318.scala                       | 32 +++++++++++++++++++
 3 files changed, 49 insertions(+), 13 deletions(-)
 create mode 100644 tests/warn/i17318.scala

diff --git a/compiler/src/dotty/tools/dotc/transform/CheckUnused.scala b/compiler/src/dotty/tools/dotc/transform/CheckUnused.scala
index 755bf5fd5b76..a5893d3fb030 100644
--- a/compiler/src/dotty/tools/dotc/transform/CheckUnused.scala
+++ b/compiler/src/dotty/tools/dotc/transform/CheckUnused.scala
@@ -16,7 +16,7 @@ import dotty.tools.dotc.report
 import dotty.tools.dotc.reporting.{CodeAction, UnusedSymbol}
 import dotty.tools.dotc.rewrites.Rewrites
 import dotty.tools.dotc.transform.MegaPhase.MiniPhase
-import dotty.tools.dotc.typer.ImportInfo
+import dotty.tools.dotc.typer.{ImportInfo, Typer}
 import dotty.tools.dotc.util.{Property, Spans, SrcPos}, Spans.Span
 import dotty.tools.dotc.util.Chars.{isLineBreakChar, isWhitespace}
 import dotty.tools.dotc.util.chaining.*
@@ -40,9 +40,8 @@ class CheckUnused private (phaseMode: PhaseMode, suffix: String) extends MiniPha
   override def isRunnable(using Context): Boolean = super.isRunnable && ctx.settings.WunusedHas.any && !ctx.isJava
 
   override def prepareForUnit(tree: Tree)(using Context): Context =
-    val infos = tree.getAttachment(refInfosKey).getOrElse {
+    val infos = tree.getAttachment(refInfosKey).getOrElse:
       RefInfos().tap(tree.withAttachment(refInfosKey, _))
-    }
     ctx.fresh.setProperty(refInfosKey, infos)
   override def transformUnit(tree: Tree)(using Context): tree.type =
     if phaseMode == PhaseMode.Report then
@@ -68,6 +67,10 @@ class CheckUnused private (phaseMode: PhaseMode, suffix: String) extends MiniPha
       refUsage(tree.symbol)
     tree
 
+  override def transformLiteral(tree: Literal)(using Context): tree.type =
+    tree.getAttachment(Typer.AdaptedTree).foreach(transformAllDeep)
+    tree
+
   override def prepareForCaseDef(tree: CaseDef)(using Context): Context =
     nowarner.traverse(tree.pat)
     ctx
diff --git a/compiler/src/dotty/tools/dotc/typer/Typer.scala b/compiler/src/dotty/tools/dotc/typer/Typer.scala
index 8e3a77b41efd..0f1d6e638e80 100644
--- a/compiler/src/dotty/tools/dotc/typer/Typer.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Typer.scala
@@ -84,6 +84,9 @@ object Typer {
   /** Indicates that an expression is explicitly ascribed to [[Unit]] type. */
   val AscribedToUnit = new Property.StickyKey[Unit]
 
+  /** Tree adaptation lost fidelity; this attachment preserves the original tree. */
+  val AdaptedTree = new Property.StickyKey[tpd.Tree]
+
   /** An attachment on a Select node with an `apply` field indicating that the `apply`
    *  was inserted by the Typer.
    */
@@ -4565,16 +4568,14 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
     }
 
     /** Adapt an expression of constant type to a different constant type `tpe`. */
-    def adaptConstant(tree: Tree, tpe: ConstantType): Tree = {
-      def lit = Literal(tpe.value).withSpan(tree.span)
-      tree match {
-        case Literal(c) => lit
-        case tree @ Block(stats, expr) => tpd.cpy.Block(tree)(stats, adaptConstant(expr, tpe))
-        case tree =>
-          if (isIdempotentExpr(tree)) lit // See discussion in phase Literalize why we demand isIdempotentExpr
-          else Block(tree :: Nil, lit)
-      }
-    }
+    def adaptConstant(tree: Tree, tpe: ConstantType): Tree =
+      def lit = Literal(tpe.value).withSpan(tree.span).withAttachment(AdaptedTree, tree)
+      tree match
+      case Literal(_) => lit
+      case tree @ Block(stats, expr) => tpd.cpy.Block(tree)(stats, adaptConstant(expr, tpe))
+      case tree =>
+        if isIdempotentExpr(tree) then lit // See discussion in phase FirstTransform why we demand isIdempotentExpr
+        else Block(tree :: Nil, lit)
 
     def toSAM(tree: Tree, samParent: Type): Tree = tree match {
       case tree: Block => tpd.cpy.Block(tree)(tree.stats, toSAM(tree.expr, samParent))
diff --git a/tests/warn/i17318.scala b/tests/warn/i17318.scala
new file mode 100644
index 000000000000..2a534bdb396c
--- /dev/null
+++ b/tests/warn/i17318.scala
@@ -0,0 +1,32 @@
+
+//> using options -Wunused:all
+
+object events {
+  final val PollOut = 0x002
+  transparent inline def POLLIN = 0x001
+}
+
+def withShort(v: Short): Unit = ???
+def withInt(v: Int): Unit = ???
+
+def usage() = 
+  import events.POLLIN // reports unused
+  def v: Short = POLLIN
+  println(v)
+
+def usage2() = 
+  import events.POLLIN // reports unused
+  withShort(POLLIN)
+
+def usage3() =
+  import events.POLLIN // does not report unused
+  withInt(POLLIN) 
+
+def usage4() = 
+  import events.POLLIN // reports unused
+  withShort(POLLIN)
+
+def value = 42
+def withDouble(v: Double): Unit = ???
+def usage5() = withDouble(value)
+def usage6() = withShort(events.POLLIN)