Respect @unchecked annotation

Author: liufengyun

compiler/src/dotty/tools/dotc/transform/init/Potentials.scala

@@ -140,6 +140,8 @@ object Potentials {
 
   def (ps: Potentials) select (symbol: Symbol, source: Tree)(implicit ctx: Context): Summary =
     ps.foldLeft(Summary.empty) { case ((pots, effs), pot) =>
+      // max potential length
+      // TODO: it can be specified on a project basis via compiler options
       if (pot.size > 2)
         (pots, effs + Leak(pot)(source))
       else if (symbol.isConstructor)

compiler/src/dotty/tools/dotc/transform/init/Summarization.scala

@@ -100,7 +100,8 @@ object Summarization {
         }
 
       case Typed(expr, tpt) =>
-        analyze(expr)
+        if (tpt.tpe.hasAnnotation(defn.UncheckedAnnot)) Summary.empty
+        else analyze(expr)
 
       case NamedArg(name, arg) =>
         analyze(arg)

tests/init/neg/lazylist2.scala

@@ -7,7 +7,7 @@ trait LazyList[+A] {
 }
 
 object LazyList {
-  inline implicit def toHelper[A](l: => LazyList[A]): Helper[A] = new Helper(l)
+  implicit def toHelper[A](l: => LazyList[A]): Helper[A] = new Helper(l)
   final class Helper[A](l: => LazyList[A]) {
     def #:: [B >: A](elem: => B): LazyList[B] = new LazyList[B] {
       override def isEmpty: Boolean = false
@@ -21,7 +21,7 @@ import LazyList._
 
 final class Test1 {
   lazy val a: LazyList[Int] = 5 #:: b
-  val b: LazyList[Int] = 10 #:: a
+  lazy val b: LazyList[Int] = 10 #:: a
 
   a.head // ok
   b.head // ok
@@ -33,11 +33,11 @@ final class Test1 {
 final class Test2 {
   lazy val a: LazyList[Int] = 5 #:: b
   lazy val b: LazyList[Int] = 10 #:: 30 #:: c
-  val c: LazyList[Int] = 20 #:: a
+  lazy val c: LazyList[Int] = 20 #:: a
 }
 
 final class Test3 {
-  val a: LazyList[Int] = n #:: a
+  val a: LazyList[Int] = n #:: (a: @unchecked)
   a.head
   val n: Int = 20    // error
 }