Remove by-name restriction for case copy

src/compiler/scala/tools/nsc/typechecker/Unapplies.scala

@@ -28,7 +28,7 @@ trait Unapplies extends ast.TreeDSL {
   import global._
   import definitions._
   import CODE.{ CASE => _, _ }
-  import treeInfo.{ isRepeatedParamType, isByNameParamType }
+  import treeInfo.isRepeatedParamType
 
   private def unapplyParamName = nme.x_0
   private def caseMods         = Modifiers(SYNTHETIC | CASE)
@@ -265,10 +265,9 @@ trait Unapplies extends ast.TreeDSL {
    * ClassDef of the case class.
    */
   def caseClassCopyMeth(cdef: ClassDef): Option[DefDef] = {
-    def isDisallowed(vd: ValDef) = isRepeatedParamType(vd.tpt) || isByNameParamType(vd.tpt)
     val classParamss  = constrParamss(cdef)
 
-    if (cdef.symbol.hasAbstractFlag || mexists(classParamss)(isDisallowed)) None
+    if (cdef.symbol.hasAbstractFlag || mexists(classParamss)(isRepeatedParamType)) None
     else {
       def makeCopyParam(vd: ValDef, putDefault: Boolean) = {
         val rhs = if (putDefault) toIdent(vd) else EmptyTree

test/files/run/t7879.check

@@ -0,0 +1,25 @@
+
+scala> case class C(i: Int)(j: => Int) { def sum = i + j }
+class C
+
+scala> def z = 27.tap(println)
+def z: Int
+
+scala> val c = C(42)(z)
+val c: C = C(42)
+
+scala> c.sum
+27
+val res0: Int = 69
+
+scala> def y = 28.tap(println)
+def y: Int
+
+scala> c.copy()(y)
+val res1: C = C(42)
+
+scala> c.copy()(y).sum
+28
+val res2: Int = 70
+
+scala> :quit

test/files/run/t7879.scala

@@ -0,0 +1,6 @@
+
+import scala.tools.partest.SessionTest
+
+object Test extends SessionTest {
+  override def extraSettings = "-Yimports:java.lang,scala,scala.Predef,scala.util.chaining"
+}