[backport] Allow lazy vals without await in the initializer

We were incorrectly typechecking the `ClassDef` of the state machine
in the macro in a way that discarded the resulting trees, and only
kept around the symbol.

The led to the the macro engine retypechecking
that node, which somehow led to duplicated lazy val initiaializer
`DefDef`-s in the template, which manifest as a `VerifyError`.

This commit:

  - rescues the typechecked `ClassDef` node from the eager
    typechecking by the macro
  - loosens the restriction on lazy vals in async blocks. They are
    still prohibited if they contain an await on the RHS
  - Adds a test that shows evalution is indeed lazy.

(cherry picked from commit cc4587b1985519f7049d0feb0783d8e22c10f792)

Conflicts:
	src/main/scala/scala/async/internal/AsyncAnalysis.scala
	src/main/scala/scala/async/internal/AsyncTransform.scala

1 files changed, 7 insertions, 3 deletions

diff --git a/src/main/scala/scala/async/internal/AsyncTransform.scala b/src/main/scala/scala/async/internal/AsyncTransform.scala
index ca53ff1..beb828d 100644
--- a/src/main/scala/scala/async/internal/AsyncTransform.scala
+++ b/src/main/scala/scala/async/internal/AsyncTransform.scala
@@ -52,11 +52,10 @@ trait AsyncTransform {
       }
 
       val tryToUnit = appliedType(definitions.FunctionClass(1), futureSystemOps.tryType[Any], typeOf[Unit])
-      val template = Template(List(tryToUnit, typeOf[() => Unit]).map(TypeTree(_)), emptyValDef, body)
+      val template = Template(List(tryToUnit, typeOf[() => Unit]).map(TypeTree(_)), emptyValDef, body).setType(NoType)
 
       val t = ClassDef(NoMods, name.stateMachineT, Nil, template)
-      callSiteTyper.typedPos(macroPos)(Block(t :: Nil, Literal(Constant(()))))
-      t
+      typecheckClassDef(t)
     }
 
     val stateMachineClass = stateMachine.symbol
@@ -218,4 +217,9 @@ trait AsyncTransform {
     }
     result
   }
+
+  def typecheckClassDef(cd: ClassDef): ClassDef = {
+    val Block(cd1 :: Nil, _) = callSiteTyper.typedPos(macroPos)(Block(cd :: Nil, Literal(Constant(()))))
+    cd1.asInstanceOf[ClassDef]
+  }
 }