From 2c4889e295bb6faa2278ac16f2fd9ab77e6d1706 Mon Sep 17 00:00:00 2001
From: Guillaume Martres <smarter@ubuntu.com>
Date: Wed, 29 May 2024 14:31:52 +0200
Subject: [PATCH] Allow `apply` adaptation on Selectable with Fields

Just like when using a regular Selectable with refinements, this change allows:

    fromFlds.xs(0)

to be expanded to:

    fromFlds.xs.apply(0)
---
 .../src/dotty/tools/dotc/typer/Typer.scala    |  4 +--
 tests/neg/named-tuple-selectable.scala        | 29 +++++++++++++++++++
 tests/pos/named-tuple-selectable.scala        | 29 +++++++++++++++++++
 3 files changed, 60 insertions(+), 2 deletions(-)
 create mode 100644 tests/neg/named-tuple-selectable.scala
 create mode 100644 tests/pos/named-tuple-selectable.scala

diff --git a/compiler/src/dotty/tools/dotc/typer/Typer.scala b/compiler/src/dotty/tools/dotc/typer/Typer.scala
index e44da20814dd..24d28aa8b4e6 100644
--- a/compiler/src/dotty/tools/dotc/typer/Typer.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Typer.scala
@@ -821,10 +821,10 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
 
     // Otherwise, if the qualifier derives from class Selectable,
     // and the selector name matches one of the element of the `Fields` type member,
-    // and the selector is neither applied nor assigned to,
+    // and the selector is not assigned to,
     // expand to a typed dynamic dispatch using selectDynamic wrapped in a cast
     if qual.tpe.derivesFrom(defn.SelectableClass) && !isDynamicExpansion(tree)
-        && !pt.isInstanceOf[FunOrPolyProto] && pt != LhsProto
+        && 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
diff --git a/tests/neg/named-tuple-selectable.scala b/tests/neg/named-tuple-selectable.scala
new file mode 100644
index 000000000000..5cf7e68654ef
--- /dev/null
+++ b/tests/neg/named-tuple-selectable.scala
@@ -0,0 +1,29 @@
+import scala.language.experimental.namedTuples
+
+class FromFields extends Selectable:
+  type Fields = (i: Int)
+  def selectDynamic(key: String) =
+    List(1, 2, 3)
+
+trait FromRefs extends Selectable:
+  def selectDynamic(key: String) =
+    List(1, 2, 3)
+
+def test(
+    fromFlds: FromFields,
+    fromRefs: FromRefs { val i: Int }
+): Unit =
+  fromFlds.i(0) // error
+  fromRefs.i(0) // error
+
+  fromFlds.i.apply(0) // error
+  fromRefs.i.apply(0) // error
+
+  fromFlds.i[Int](List(1)) // error
+  fromRefs.i[Int](List(1)) // error
+
+  fromFlds.i(List(1)) // error
+  fromRefs.i(List(1)) // error
+
+  fromFlds.i.apply(List(1)) // error
+  fromRefs.i.apply(List(1)) // error
diff --git a/tests/pos/named-tuple-selectable.scala b/tests/pos/named-tuple-selectable.scala
new file mode 100644
index 000000000000..be5f0400e58c
--- /dev/null
+++ b/tests/pos/named-tuple-selectable.scala
@@ -0,0 +1,29 @@
+import scala.language.experimental.namedTuples
+
+class FromFields extends Selectable:
+  type Fields = (xs: List[Int], poly: [T] => (x: List[T]) => Option[T])
+  def selectDynamic(key: String) =
+    List(1, 2, 3)
+
+trait FromRefs extends Selectable:
+  def selectDynamic(key: String) =
+    List(1, 2, 3)
+
+def test(
+    fromFlds: FromFields,
+    fromRefs: FromRefs { val xs: List[Int]; val poly: [T] => (x: List[T]) => Option[T] }
+): Unit =
+  fromFlds.xs(0)
+  fromRefs.xs(0)
+
+  fromFlds.xs.apply(0)
+  fromRefs.xs.apply(0)
+
+  fromFlds.poly[Int](List(1)): Option[Int]
+  fromRefs.poly[Int](List(1)): Option[Int]
+
+  fromFlds.poly(List(1))
+  fromRefs.poly(List(1))
+
+  fromFlds.poly.apply(List(1))
+  fromRefs.poly.apply(List(1))