From 0dad1c5bb12e4852ff5e418ebe7d63f8dac88882 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Patryk=20Zieli=C5=84ski?= <patrykzielinskiti@gmail.com>
Date: Fri, 12 Dec 2025 13:28:19 +0100
Subject: [PATCH] fix incorrect XRay hint

---
 .../dotty/tools/pc/PcInlayHintsProvider.scala |  7 ++--
 .../pc/tests/inlayHints/InlayHintsSuite.scala | 36 +++++++++++++++++++
 2 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/presentation-compiler/src/main/dotty/tools/pc/PcInlayHintsProvider.scala b/presentation-compiler/src/main/dotty/tools/pc/PcInlayHintsProvider.scala
index fe46419fe577..46b9cf3f4e3b 100644
--- a/presentation-compiler/src/main/dotty/tools/pc/PcInlayHintsProvider.scala
+++ b/presentation-compiler/src/main/dotty/tools/pc/PcInlayHintsProvider.scala
@@ -529,7 +529,7 @@ object XRayModeHint:
         case apply @ Apply(inner, _)
             if !apply.span.isZeroExtent && inner.sourcePos.exists && !isParentOnSameLine &&
             !isParentApply && endsInSimpleSelect(apply) && isEndOfLine(tree.sourcePos) =>
-          Some((apply.tpe.widen.deepDealiasAndSimplify, tree.sourcePos))
+          Some((apply.tpe.widen.finalResultType.deepDealiasAndSimplify, tree.sourcePos))
         /*
         innerTree
          .select
@@ -537,7 +537,10 @@ object XRayModeHint:
         case select @ Select(innerTree, _)
             if !select.span.isZeroExtent && innerTree.sourcePos.exists &&
             !isParentOnSameLine && !isParentApply && isEndOfLine(tree.sourcePos) =>
-          Some((select.tpe.widen.deepDealiasAndSimplify, tree.sourcePos))
+          val tpe = parent match
+            case Some(ta: TypeApply) => ta.tpe
+            case _ => select.tpe
+          Some((tpe.widen.finalResultType.deepDealiasAndSimplify, tree.sourcePos))
         case _ => None
     else None
 
diff --git a/presentation-compiler/test/dotty/tools/pc/tests/inlayHints/InlayHintsSuite.scala b/presentation-compiler/test/dotty/tools/pc/tests/inlayHints/InlayHintsSuite.scala
index 555287a96837..4f5a593c10e4 100644
--- a/presentation-compiler/test/dotty/tools/pc/tests/inlayHints/InlayHintsSuite.scala
+++ b/presentation-compiler/test/dotty/tools/pc/tests/inlayHints/InlayHintsSuite.scala
@@ -1687,4 +1687,40 @@ class InlayHintsSuite extends BaseInlayHintsSuite {
          |}
          |""".stripMargin
     )
+
+  @Test def `xray-metals-i8021` =
+    check(
+      """|object Main:
+         |
+         |  case class Order(id: String, amount: BigDecimal)
+         |  case class User(name: String, orders: List[Order])
+         |
+         |  val users = List(
+         |    User("Alice", List(Order("A1", 100), Order("A2", 50))),
+         |    User("Bob", List(Order("B1", 200)))
+         |  )
+         |
+         |  val total = users
+         |    .filter(_.name.startsWith("A"))
+         |    .flatMap(_.orders)
+         |    .map(_.amount)
+         |    .sum
+         |""".stripMargin,
+      """|object Main:
+         |
+         |  case class Order(id: String, amount: BigDecimal)
+         |  case class User(name: String, orders: List[Order])
+         |
+         |  val users/*: List<<scala/collection/immutable/List#>>[User<<(4:13)>>]*/ = List/*[User<<(4:13)>>]*/(
+         |    /*elems = */User(/*name = */"Alice", /*orders = */List/*[Order<<(3:13)>>]*/(/*elems = */Order(/*id = */"A1", /*int2bigDecimal<<scala/math/BigDecimal.int2bigDecimal().>>(*//*amount = */100/*)*/), Order(/*id = */"A2", /*int2bigDecimal<<scala/math/BigDecimal.int2bigDecimal().>>(*//*amount = */50/*)*/))),
+         |    User(/*name = */"Bob", /*orders = */List/*[Order<<(3:13)>>]*/(/*elems = */Order(/*id = */"B1", /*int2bigDecimal<<scala/math/BigDecimal.int2bigDecimal().>>(*//*amount = */200/*)*/)))
+         |  )
+         |
+         |  val total/*: BigDecimal<<scala/math/BigDecimal#>>*/ = users
+         |    .filter(/*p = */_.name.startsWith("A"))/*: List<<scala/collection/immutable/List#>>[User<<(4:13)>>]*/
+         |    .flatMap/*[Order<<(3:13)>>]*/(/*f = */_.orders)/*             : List<<scala/collection/immutable/List#>>[Order<<(3:13)>>]*/
+         |    .map/*[BigDecimal<<scala/math/BigDecimal#>>]*/(/*f = */_.amount)/*                 : List<<scala/collection/immutable/List#>>[BigDecimal<<scala/math/BigDecimal#>>]*/
+         |    .sum/*[BigDecimal<<scala/math/BigDecimal#>>]*//*(using BigDecimalIsFractional<<scala/math/Numeric.BigDecimalIsFractional.>>)*//*                           : BigDecimal<<scala/math/BigDecimal#>>*/
+         |""".stripMargin
+    )
 }