Fix #9295: Avoid recursive Dynamics conversion

Avoid trying to apply `Dynamic` transformation on `apply` with a qualifier that already has
a been handled by the `Dynamic` transformation.

Author: nicolasstucki

compiler/src/dotty/tools/dotc/typer/TypeAssigner.scala

@@ -142,7 +142,8 @@ trait TypeAssigner {
     val mbr = qualType.findMember(name, pre)
     if (reallyExists(mbr))
       qualType.select(name, mbr)
-    else if (qualType.derivesFrom(defn.DynamicClass) && name.isTermName && !Dynamic.isDynamicMethod(name))
+    else if (qualType.derivesFrom(defn.DynamicClass) && name.isTermName && !Dynamic.isDynamicMethod(name) &&
+        !(name == nme.apply && tree.span.isSynthetic && Dynamic.isDynamicMethod(qual1.symbol.name)))
       TryDynamicCallType
     else if (qualType.isErroneous || name.toTermName == nme.ERROR)
       UnspecifiedErrorType

tests/neg/i9295a.scala

@@ -0,0 +1,9 @@
+import scala.language.dynamics
+
+class Foo extends Dynamic {
+  def applyDynamic(arg: Any): Foo = ???
+}
+object F {
+  val foo = new Foo
+  def baz = foo.blah(43) // error: method applyDynamic in class Foo does not take more parameters
+}

tests/neg/i9295b.scala

@@ -0,0 +1,14 @@
+import scala.language.dynamics
+
+class Foo extends Dynamic {
+  def applyDynamic(arg: Any): Bar = ???
+}
+class Bar extends Dynamic {
+  def applyDynamic(arg: Any)(x: Int): Int = ???
+}
+object F {
+  val foo = new Foo
+  def baz = foo.blah(43) // error: method applyDynamic in class Foo does not take more parameters
+  def qux = foo.blah.blah(43) // error: value selectDynamic is not a member of Foo
+  def quxx = foo.blah().blah(43) // error: method applyDynamic in class Foo does not take more parameters
+}

tests/pos/i9295.scala

@@ -0,0 +1,12 @@
+import scala.language.dynamics
+
+class Foo extends Dynamic {
+  def applyDynamic(name: String)(): Bar = ???
+}
+
+class Bar extends Dynamic {
+  def applyDynamic(name: String)(x: Int) = ???
+}
+
+val foo = new Foo
+def baz = foo.blah().apply(42)