Fix #2266: Do not replace constant type lazy vals with constant.

Author: nicolasstucki

compiler/src/dotty/tools/dotc/ast/TreeInfo.scala

@@ -427,7 +427,7 @@ trait TypedTreeInfo extends TreeInfo[Type] { self: Trees.Instance[Type] =>
   def constToLiteral(tree: Tree)(implicit ctx: Context): Tree = {
     val tree1 = ConstFold(tree)
     tree1.tpe.widenTermRefExpr match {
-      case ConstantType(value) if isIdempotentExpr(tree1) => Literal(value)
+      case ConstantType(value) if isIdempotentExpr(tree1) && !tree1.symbol.is(Lazy) => Literal(value)
       case _ => tree1
     }
   }

tests/run/inline-constant-lazy-val.check

@@ -0,0 +1,2 @@
+X
+Y

tests/run/inline-constant-lazy-val.scala

@@ -0,0 +1,10 @@
+
+object Test {
+  lazy val x: true = { println("X"); true }
+
+  def main(args: Array[String]): Unit = {
+    lazy val y: true = { println("Y"); true }
+    x
+    y
+  }
+}