Synthesize ValueOf[Unit] for a name designator

Fixes #12510

Author: nicolasstucki

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

@@ -160,13 +160,12 @@ class Synthesizer(typer: Typer)(using @constructorOnly c: Context):
 
     def success(t: Tree) =
       New(defn.ValueOfClass.typeRef.appliedTo(t.tpe), t :: Nil).withSpan(span)
-
     formal.argInfos match
       case arg :: Nil =>
         fullyDefinedType(arg.dealias, "ValueOf argument", span).normalized match
           case ConstantType(c: Constant) =>
             success(Literal(c))
-          case TypeRef(_, sym) if sym == defn.UnitClass =>
+          case tp: TypeRef if tp.isRef(defn.UnitClass) =>
             success(Literal(Constant(())))
           case n: TermRef =>
             success(ref(n))

tests/pos-macros/i12510/Macro_1.scala

@@ -0,0 +1,11 @@
+object M {
+  import scala.quoted.*
+
+  inline def valueOfUnit: ValueOf[Unit] =
+    ${ _valueOfUnit }
+
+  def _valueOfUnit(using Quotes): Expr[ValueOf[Unit]] = {
+    import quotes.reflect.*
+    Expr.summon[ValueOf[Unit]] getOrElse sys.error("Not found")
+  }
+}

tests/pos-macros/i12510/Test_2.scala

@@ -0,0 +1,4 @@
+object T {
+  val ok = summon[ValueOf[Unit]]
+  val ko = M.valueOfUnit
+}