Remove by-name restriction for case copy

src/compiler/scala/tools/nsc/Global.scala

@@ -1188,6 +1188,7 @@ class Global(var currentSettings: Settings, reporter0: Reporter)
       import s.XsourceFeatures.contains
       def caseApplyCopyAccess    = isScala3 && contains(o.caseApplyCopyAccess)
       def caseCompanionFunction  = isScala3 && contains(o.caseCompanionFunction)
+      def caseCopyByName         = isScala3 && contains(o.caseCopyByName)
       def inferOverride          = isScala3 && contains(o.inferOverride)
       def any2StringAdd          = isScala3 && contains(o.any2StringAdd)
       def unicodeEscapesRaw      = isScala3 && contains(o.unicodeEscapesRaw)

src/compiler/scala/tools/nsc/settings/ScalaSettings.scala

@@ -125,8 +125,8 @@ trait ScalaSettings extends StandardScalaSettings with Warnings { _: MutableSett
   val sourceReader       = StringSetting       ("-Xsource-reader", "classname", "Specify a custom method for reading source files.", "")
   val reporter           = StringSetting       ("-Xreporter", "classname", "Specify a custom subclass of FilteringReporter for compiler messages.", "scala.tools.nsc.reporters.ConsoleReporter")
   private val XsourceHelp =
-    sm"""|-Xsource:3 is for migrating a codebase, -Xsource-features can be added for
-         |cross-building to adopt certain Scala 3 behavior.
+    sm"""|-Xsource:3 is for migrating a codebase. -Xsource-features can be added for
+         |cross-building to adopt certain Scala 3 behaviors.
          |
          |See also "Scala 2 with -Xsource:3" on docs.scala-lang.org.
          |
@@ -169,9 +169,10 @@ trait ScalaSettings extends StandardScalaSettings with Warnings { _: MutableSett
   // buffet of features available under -Xsource:3
   object sourceFeatures extends MultiChoiceEnumeration {
     // Changes affecting binary encoding
-    val caseApplyCopyAccess = Choice("case-apply-copy-access", "Constructor modifiers are used for apply / copy methods of case classes. [bin]")
+    val caseApplyCopyAccess    = Choice("case-apply-copy-access", "Constructor modifiers are used for apply / copy methods of case classes. [bin]")
     val caseCompanionFunction  = Choice("case-companion-function", "Synthetic case companion objects no longer extend FunctionN. [bin]")
-    val inferOverride = Choice("infer-override", "Inferred type of member uses type of overridden member. [bin]")
+    val caseCopyByName         = Choice("case-copy-by-name", "Synthesize case copy method with by-name parameters. [bin]")
+    val inferOverride          = Choice("infer-override", "Inferred type of member uses type of overridden member. [bin]")
 
     // Other semantic changes
     val any2StringAdd          = Choice("any2stringadd", "Implicit `any2stringadd` is never inferred.")
@@ -203,10 +204,11 @@ trait ScalaSettings extends StandardScalaSettings with Warnings { _: MutableSett
     helpText = Some(
       sm"""Enable Scala 3 features under -Xsource:3.
           |
-          |Instead of `-Xsource-features:_`, it is recommended to enable specific features, for
-          |example `-Xsource-features:v2.13.14,-case-companion-function` (-x to exclude x).
-          |This way, new semantic changes in future Scala versions are not silently adopted;
-          |new features can be enabled after auditing the corresponding migration warnings.
+          |Instead of `-Xsource-features:_`, it is recommended to enable individual features.
+          |Features can also be removed from a feature group by prefixing with `-`;
+          |for example, `-Xsource-features:v2.13.14,-case-companion-function`.
+          |Listing features explicitly ensures new semantic changes in future Scala versions are
+          |not silently adopted; new features can be enabled after auditing migration warnings.
           |
           |`-Xsource:3-cross` is a shorthand for `-Xsource:3 -Xsource-features:_`.
           |

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

@@ -27,8 +27,8 @@ trait Unapplies extends ast.TreeDSL {
 
   import global._
   import definitions._
-  import CODE.{ CASE => _, _ }
-  import treeInfo.{ isRepeatedParamType, isByNameParamType }
+  import CODE.{CASE => _, _}
+  import treeInfo.{isByNameParamType, isRepeatedParamType}
 
   private def unapplyParamName = nme.x_0
   private def caseMods         = Modifiers(SYNTHETIC | CASE)
@@ -265,26 +265,24 @@ 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
-    else {
+    val classParamss = constrParamss(cdef)
+    def warn() = runReporting.warning(cdef.namePos, "case `copy` method is allowed to have by-name parameters under Scala 3 (or with -Xsource-features:case-copy-by-name)", Scala3Migration, cdef.symbol)
+    def isDisallowed(vd: ValDef) = isRepeatedParamType(vd.tpt) || isByNameParamType(vd.tpt).tap(if (_) warn())
+    def copyOK = currentRun.sourceFeatures.caseCopyByName || !mexists(classParamss)(isDisallowed)
+    def synthesizeCopy = {
       def makeCopyParam(vd: ValDef, putDefault: Boolean) = {
         val rhs = if (putDefault) toIdent(vd) else EmptyTree
         val flags = PARAM | (vd.mods.flags & IMPLICIT) | (if (putDefault) DEFAULTPARAM else 0)
         // empty tpt: see comment above
         val tpt = atPos(vd.pos.focus)(TypeTree() setOriginal vd.tpt)
         treeCopy.ValDef(vd, Modifiers(flags), vd.name, tpt, rhs)
       }
-
       val tparams = constrTparamsInvariant(cdef)
       val paramss = classParamss match {
         case Nil => Nil
         case ps :: pss =>
           ps.map(makeCopyParam(_, putDefault = true)) :: mmap(pss)(makeCopyParam(_, putDefault = false))
       }
-
       val classTpe = classType(cdef, tparams)
       val argss = mmap(paramss)(toIdent)
       val body: Tree = New(classTpe, argss)
@@ -301,10 +299,10 @@ trait Unapplies extends ast.TreeDSL {
           }
         }
         else synth
-      val copyDefDef = atPos(cdef.pos.focus)(
+      atPos(cdef.pos.focus)(
         DefDef(copyMods, nme.copy, tparams, paramss, TypeTree(), body)
       )
-      Some(copyDefDef)
     }
+    if (!cdef.symbol.hasAbstractFlag && copyOK) Some(synthesizeCopy) else None
   }
 }

test/files/neg/t7879.check

@@ -0,0 +1,6 @@
+t7879.scala:2: error: case `copy` method is allowed to have by-name parameters under Scala 3 (or with -Xsource-features:case-copy-by-name)
+Scala 3 migration messages are issued as errors under -Xsource:3. Use -Wconf or @nowarn to demote them to warnings or suppress.
+Applicable -Wconf / @nowarn filters for this fatal warning: msg=<part of the message>, cat=scala3-migration, site=C
+case class C(i: Int)(j: => Int)(k: => Int) { def sum = i + j + k }
+           ^
+1 error

test/files/neg/t7879.scala

@@ -0,0 +1,2 @@
+//> using options -Xsource:3
+case class C(i: Int)(j: => Int)(k: => Int) { def sum = i + j + k }

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 -Xsource:3 -Xsource-features:case-copy-by-name"
+}