From 483920640f016c7ccdb31144df7ca602d99297fa Mon Sep 17 00:00:00 2001
From: odersky <odersky@gmail.com>
Date: Thu, 5 Dec 2024 16:45:53 +0100
Subject: [PATCH] Widen singleton types when computing fields from .Fields

Fixes #22018
---
 .../src/dotty/tools/dotc/typer/Typer.scala     |  2 +-
 tests/pos/i22018.scala                         | 18 ++++++++++++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)
 create mode 100644 tests/pos/i22018.scala

diff --git a/compiler/src/dotty/tools/dotc/typer/Typer.scala b/compiler/src/dotty/tools/dotc/typer/Typer.scala
index 6bb5d1ee70ff..1a3f5c2d97c3 100644
--- a/compiler/src/dotty/tools/dotc/typer/Typer.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Typer.scala
@@ -868,7 +868,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
           && pt != LhsProto
       then
         val pre = if !TypeOps.isLegalPrefix(qual.tpe) then SkolemType(qual.tpe) else qual.tpe
-        val fieldsType = pre.select(tpnme.Fields).dealias.simplified
+        val fieldsType = pre.select(tpnme.Fields).widenDealias.simplified
         val fields = fieldsType.namedTupleElementTypes
         typr.println(i"try dyn select $qual, $selName, $fields")
         fields.find(_._1 == selName) match
diff --git a/tests/pos/i22018.scala b/tests/pos/i22018.scala
new file mode 100644
index 000000000000..14f4733732be
--- /dev/null
+++ b/tests/pos/i22018.scala
@@ -0,0 +1,18 @@
+import scala.language.experimental.namedTuples
+
+class SelectableNT[A <: NamedTuple.AnyNamedTuple](val nt: A) extends Selectable:
+  type Fields = A
+  def selectDynamic(x: String) = ???
+
+object Test:
+
+  val a = (name = "foo", age = 1)
+
+  val sa = SelectableNT(a)
+  sa.name   // ok
+
+  type B = a.type
+  val b: B = a
+
+  val sb = SelectableNT(b)
+  sb.name   // fails
\ No newline at end of file