From 2808f3d7b04867626081e21538faa13f570b6d3a Mon Sep 17 00:00:00 2001
From: odersky <odersky@gmail.com>
Date: Wed, 15 Mar 2023 13:41:31 +0100
Subject: [PATCH] Also allow structural dispatch on Dynamic

Given
```scala
trait Sel extends Dynamic

extension (s: Sel)
  def selectDynamic(name: String) = ???
```
the following worked:
```scala
val sel = new Sel {}
val foo = sel.foo
```
but the following didn't:
```scala
val sel2 = (new Sel {}).asInstanceOf[Sel{ def foo: String }]
val foo2 = sel2.foo
```
The problem was that we recognized a structural dispatch and then required
the qualifier to be an instance of `Selectable`. But in fact, `Dynamic`
works just as well, and the mechanism is the same. It's just that
`Dynamic` is less type safe then `Selectable`.
---
 compiler/src/dotty/tools/dotc/typer/Dynamic.scala |  2 +-
 tests/pos/i17100a.scala                           | 12 ++++++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)
 create mode 100644 tests/pos/i17100a.scala

diff --git a/compiler/src/dotty/tools/dotc/typer/Dynamic.scala b/compiler/src/dotty/tools/dotc/typer/Dynamic.scala
index 1513872cf47a..717966923708 100644
--- a/compiler/src/dotty/tools/dotc/typer/Dynamic.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Dynamic.scala
@@ -181,7 +181,7 @@ trait Dynamic {
     val vargss = termArgss(tree)
 
     def structuralCall(selectorName: TermName, classOfs: => List[Tree]) = {
-      val selectable = adapt(qual, defn.SelectableClass.typeRef)
+      val selectable = adapt(qual, defn.SelectableClass.typeRef | defn.DynamicClass.typeRef)
 
       // ($qual: Selectable).$selectorName("$name")
       val base =
diff --git a/tests/pos/i17100a.scala b/tests/pos/i17100a.scala
new file mode 100644
index 000000000000..abf74c80a4f5
--- /dev/null
+++ b/tests/pos/i17100a.scala
@@ -0,0 +1,12 @@
+
+import scala.language.dynamics
+trait Sel extends Dynamic
+
+extension (s: Sel)
+  def selectDynamic(name: String) = ???
+
+val sel = new Sel {}
+val foo = sel.foo
+val sel2 = (new Sel {}).asInstanceOf[Sel{ def foo: String }]
+val foo2 = sel2.foo
+