SI-10097 Adapt unless -Xsource:2.13

For 2.12 migration, insert missing case class param section,
strip caseaccessor from implicit paramsection,
and deprecate the adaptation.

Author: som-snytt

src/compiler/scala/tools/nsc/ast/parser/Parsers.scala

@@ -2262,11 +2262,20 @@ self =>
       }
       if (ofCaseClass) {
         if (vds.isEmpty)
-          syntaxError(in.lastOffset, s"case classes must have a parameter list; try 'case class ${owner.encoded
+          syntaxError(start, s"case classes must have a parameter list; try 'case class ${owner.encoded
                                          }()' or 'case object ${owner.encoded}'")
-        else if (vds.head.nonEmpty && vds.head.head.mods.isImplicit)
-          syntaxError(in.lastOffset, s"case classes must have a non-implicit parameter list; try 'case class ${
+        else if (vds.head.nonEmpty && vds.head.head.mods.isImplicit) {
+          if (settings.isScala213)
+            syntaxError(start, s"case classes must have a non-implicit parameter list; try 'case class ${
                                          owner.encoded}()${ vds.map(vs => "(...)").mkString }'")
+          else {
+            deprecationWarning(start, s"case classes should have a non-implicit parameter list; adapting to 'case class ${
+                                         owner.encoded}()${ vds.map(vs => "(...)").mkString }'", "2.12.2")
+            vds.insert(0, List.empty[ValDef])
+            vds(1) = vds(1).map(vd => copyValDef(vd)(mods = vd.mods & ~Flags.CASEACCESSOR))
+            if (implicitSection != -1) implicitSection += 1
+          }
+        }
       }
       if (implicitSection != -1 && implicitSection != vds.length - 1)
         syntaxError(implicitOffset, "an implicit parameter section must be last")

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

@@ -84,7 +84,10 @@ trait ScalaSettings extends AbsScalaSettings
    * though this helper.
    */
   def isScala211: Boolean = source.value >= ScalaVersion("2.11.0")
-  def isScala212: Boolean = source.value >= ScalaVersion("2.12.0")
+  private[this] val version212 = ScalaVersion("2.12.0")
+  def isScala212: Boolean = source.value >= version212
+  private[this] val version213 = ScalaVersion("2.13.0")
+  def isScala213: Boolean = source.value >= version213
 
   /**
    * -X "Advanced" settings

test/files/neg/t10097.check

@@ -1,9 +1,9 @@
 t10097.scala:2: error: case classes must have a non-implicit parameter list; try 'case class C()(...)'
 case class C(implicit val c: Int)
-                                 ^
+            ^
 t10097.scala:4: error: case classes must have a non-implicit parameter list; try 'case class D()(...)(...)'
 case class D(implicit c: Int)(s: String)
-                                        ^
+            ^
 t10097.scala:4: error: an implicit parameter section must be last
 case class D(implicit c: Int)(s: String)
              ^

test/files/neg/t10097.flags

@@ -0,0 +1 @@
+-Xfuture

test/files/neg/t10097b.check

@@ -0,0 +1,6 @@
+t10097b.scala:2: warning: case classes should have a non-implicit parameter list; adapting to 'case class C()(...)'
+case class C(implicit val c: Int)
+            ^
+error: No warnings can be incurred under -Xfatal-warnings.
+one warning found
+one error found

test/files/neg/t10097b.flags

@@ -0,0 +1 @@
+-deprecation -Xfatal-warnings

test/files/neg/t10097b.scala

@@ -0,0 +1,3 @@
+
+case class C(implicit val c: Int)
+

test/files/run/t10097.check

@@ -0,0 +1,3 @@
+t10097.scala:2: warning: case classes should have a non-implicit parameter list; adapting to 'case class C()(...)'
+case class C(implicit c: Int)
+            ^

test/files/run/t10097.flags

@@ -0,0 +1 @@
+-deprecation

test/files/run/t10097.scala

@@ -0,0 +1,6 @@
+
+case class C(implicit c: Int)
+
+object Test extends App {
+  assert(C()(42).productArity == 0)
+}