SI-10097 Error if no non-implicit case class param

Case class must have a non-implicit param list.

Error early, error often.

Also update spec to say that class implicitly gets
a non-implicit parameter section if it doesn't
have one, and that a case class must have one.

10 files changed, 42 insertions, 23 deletions

diff --git a/spec/05-classes-and-objects.md b/spec/05-classes-and-objects.md
index 75620f57d4..6738c7a5b7 100644
--- a/spec/05-classes-and-objects.md
+++ b/spec/05-classes-and-objects.md
@@ -709,7 +709,7 @@ Here,
     value parameter may not form part of the types of any of the parent classes or members of the class template $t$.
     It is illegal to define two formal value parameters with the same name.
 
-    If no formal parameter sections are given, an empty parameter section `()` is assumed.
+    If a class has no formal parameter section that is not implicit, an empty parameter section `()` is assumed.
 
     If a formal parameter declaration $x: T$ is preceded by a `val`
     or `var` keyword, an accessor (getter) [definition](04-basic-declarations-and-definitions.html#variable-declarations-and-definitions)
@@ -842,12 +842,13 @@ TmplDef  ::=  ‘case’ ‘class’ ClassDef
 If a class definition is prefixed with `case`, the class is said
 to be a _case class_.
 
-The formal parameters in the first parameter section of a case class
-are called _elements_; they are treated
-specially. First, the value of such a parameter can be extracted as a
+A case class is required to have a parameter section that is not implicit.
+The formal parameters in the first parameter section 
+are called _elements_ and are treated specially.
+First, the value of such a parameter can be extracted as a
 field of a constructor pattern. Second, a `val` prefix is
-implicitly added to such a parameter, unless the parameter carries
-already a `val` or `var` modifier. Hence, an accessor
+implicitly added to such a parameter, unless the parameter already carries
+a `val` or `var` modifier. Hence, an accessor
 definition for the parameter is [generated](#class-definitions).
 
 A case class definition of `$c$[$\mathit{tps}\,$]($\mathit{ps}_1\,$)$\ldots$($\mathit{ps}_n$)` with type
diff --git a/src/compiler/scala/tools/nsc/ast/parser/Parsers.scala b/src/compiler/scala/tools/nsc/ast/parser/Parsers.scala
index cf66e0a7dc..a511d753c1 100644
--- a/src/compiler/scala/tools/nsc/ast/parser/Parsers.scala
+++ b/src/compiler/scala/tools/nsc/ast/parser/Parsers.scala
@@ -2238,6 +2238,8 @@ self =>
     def paramClauses(owner: Name, contextBounds: List[Tree], ofCaseClass: Boolean): List[List[ValDef]] = {
       var implicitmod = 0
       var caseParam = ofCaseClass
+      val vds = new ListBuffer[List[ValDef]]
+      val start = in.offset
       def paramClause(): List[ValDef] = {
         if (in.token == RPAREN)
           return Nil
@@ -2248,12 +2250,7 @@ self =>
         }
         commaSeparated(param(owner, implicitmod, caseParam  ))
       }
-      val vds = new ListBuffer[List[ValDef]]
-      val start = in.offset
       newLineOptWhenFollowedBy(LPAREN)
-      if (ofCaseClass && in.token != LPAREN)
-        syntaxError(in.lastOffset, "case classes without a parameter list are not allowed;\n"+
-                                   "use either case objects or case classes with an explicit `()' as a parameter list.")
       while (implicitmod == 0 && in.token == LPAREN) {
         in.nextToken()
         vds += paramClause()
@@ -2261,6 +2258,14 @@ self =>
         caseParam = false
         newLineOptWhenFollowedBy(LPAREN)
       }
+      if (ofCaseClass) {
+        if (vds.isEmpty)
+          syntaxError(in.lastOffset, 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 ${
+                                         owner.encoded}()${ vds.map(vs => "(...)").mkString }'")
+      }
       val result = vds.toList
       if (owner == nme.CONSTRUCTOR && (result.isEmpty || (result.head take 1 exists (_.mods.isImplicit)))) {
         in.token match {
diff --git a/src/reflect/scala/reflect/internal/Printers.scala b/src/reflect/scala/reflect/internal/Printers.scala
index 9602a2859b..bb352e9d31 100644
--- a/src/reflect/scala/reflect/internal/Printers.scala
+++ b/src/reflect/scala/reflect/internal/Printers.scala
@@ -775,7 +775,7 @@ trait Printers extends api.Printers { self: SymbolTable =>
             }
             // constructor's params processing (don't print single empty constructor param list)
             vparamss match {
-              case Nil | List(Nil) if (!mods.isCase && !ctorMods.hasFlag(AccessFlags)) =>
+              case Nil | List(Nil) if !mods.isCase && !ctorMods.hasFlag(AccessFlags) =>
               case _ => vparamss foreach printConstrParams
             }
             parents
diff --git a/src/reflect/scala/reflect/internal/ReificationSupport.scala b/src/reflect/scala/reflect/internal/ReificationSupport.scala
index 026438e421..1b2be64654 100644
--- a/src/reflect/scala/reflect/internal/ReificationSupport.scala
+++ b/src/reflect/scala/reflect/internal/ReificationSupport.scala
@@ -266,7 +266,7 @@ trait ReificationSupport { self: SymbolTable =>
     }
 
     // undo gen.mkTemplate
-    protected object UnMkTemplate {
+    protected class UnMkTemplate(isCaseClass: Boolean) {
       def unapply(templ: Template): Option[(List[Tree], ValDef, Modifiers, List[List[ValDef]], List[Tree], List[Tree])] = {
         val Template(parents, selfType, _) = templ
         val tbody = treeInfo.untypecheckedTemplBody(templ)
@@ -296,8 +296,9 @@ trait ReificationSupport { self: SymbolTable =>
             result(ctorMods, Nil, edefs, body)
           else {
             // undo conversion from (implicit ... ) to ()(implicit ... ) when it's the only parameter section
+            // except that case classes require the explicit leading empty parameter list
             val vparamssRestoredImplicits = ctorVparamss match {
-              case Nil :: (tail @ ((head :: _) :: _)) if head.mods.isImplicit => tail
+              case Nil :: (tail @ ((head :: _) :: _)) if head.mods.isImplicit && !isCaseClass => tail
               case other => other
             }
             // undo flag modifications by merging flag info from constructor args and fieldDefs
@@ -314,7 +315,9 @@ trait ReificationSupport { self: SymbolTable =>
           }
         }
       }
+      def asCase = new UnMkTemplate(isCaseClass = true)
     }
+    protected object UnMkTemplate extends UnMkTemplate(isCaseClass = false)
 
     protected def mkSelfType(tree: Tree) = tree match {
       case vd: ValDef =>
@@ -346,9 +349,11 @@ trait ReificationSupport { self: SymbolTable =>
 
       def unapply(tree: Tree): Option[(Modifiers, TypeName, List[TypeDef], Modifiers, List[List[ValDef]],
                                        List[Tree], List[Tree], ValDef, List[Tree])] = tree match {
-        case ClassDef(mods, name, tparams, UnMkTemplate(parents, selfType, ctorMods, vparamss, earlyDefs, body))
-          if !ctorMods.isTrait && !ctorMods.hasFlag(JAVA) =>
-          Some((mods, name, tparams, ctorMods, vparamss, earlyDefs, parents, selfType, body))
+        case ClassDef(mods, name, tparams, impl) =>
+          val X = if (mods.isCase) UnMkTemplate.asCase else UnMkTemplate
+          val X(parents, selfType, ctorMods, vparamss, earlyDefs, body) = impl
+          if (ctorMods.isTrait || ctorMods.hasFlag(JAVA)) None
+          else Some((mods, name, tparams, ctorMods, vparamss, earlyDefs, parents, selfType, body))
         case _ =>
           None
       }
diff --git a/test/files/neg/quasiquotes-syntax-error-position.check b/test/files/neg/quasiquotes-syntax-error-position.check
index 9fd6ce0417..b12a7d13d6 100644
--- a/test/files/neg/quasiquotes-syntax-error-position.check
+++ b/test/files/neg/quasiquotes-syntax-error-position.check
@@ -16,8 +16,7 @@ quasiquotes-syntax-error-position.scala:9: error: '{' expected but end of quote
 quasiquotes-syntax-error-position.scala:10: error: ';' expected but '@' found.
   q"foo@$a"
        ^
-quasiquotes-syntax-error-position.scala:11: error: case classes without a parameter list are not allowed;
-use either case objects or case classes with an explicit `()' as a parameter list.
+quasiquotes-syntax-error-position.scala:11: error: case classes must have a parameter list; try 'case class A()' or 'case object A'
   q"case class A"
                 ^
 quasiquotes-syntax-error-position.scala:12: error: identifier expected but ']' found.
diff --git a/test/files/neg/t10097.check b/test/files/neg/t10097.check
new file mode 100644
index 0000000000..bb896dffd2
--- /dev/null
+++ b/test/files/neg/t10097.check
@@ -0,0 +1,4 @@
+t10097.scala:2: error: case classes must have a non-implicit parameter list; try 'case class C()(...)'
+case class C(implicit val c: Int)
+                                 ^
+one error found
diff --git a/test/files/neg/t10097.scala b/test/files/neg/t10097.scala
new file mode 100644
index 0000000000..754e105359
--- /dev/null
+++ b/test/files/neg/t10097.scala
@@ -0,0 +1,5 @@
+
+case class C(implicit val c: Int)
+
+// SI-8704
+//case class D(implicit c: Int)(s: String)
diff --git a/test/files/run/patmat-exprs.scala b/test/files/run/patmat-exprs.scala
index 7ca5fd3063..d18df9c714 100644
--- a/test/files/run/patmat-exprs.scala
+++ b/test/files/run/patmat-exprs.scala
@@ -344,13 +344,13 @@ trait Pattern {
   }
 
 
-  case class Zero[T] (implicit num: NumericOps[T]) extends Leaf[T] {
+  case class Zero[T]()(implicit num: NumericOps[T]) extends Leaf[T] {
     def derivative(variable: Var[T]) = Zero[T]
     def eval(f: Any => Any) = num.zero
     override def toString = "0"
   }
 
-  case class One[T] (implicit num: NumericOps[T]) extends Leaf[T] {
+  case class One[T]()(implicit num: NumericOps[T]) extends Leaf[T] {
     def derivative(variable: Var[T]) = Zero[T]
     def eval(f: Any => Any) = num.one
     override def toString = "1"
diff --git a/test/files/run/t5907.scala b/test/files/run/t5907.scala
index a005e9fbd3..81fc43e3f5 100644
--- a/test/files/run/t5907.scala
+++ b/test/files/run/t5907.scala
@@ -86,7 +86,7 @@ object Test extends App {
   }
 }
 
-case class C1(implicit x: Int) {
+case class C1()(implicit x: Int) {
   override def toString = s"c1: $x"
 }
 case class C2()(y: Int) {
diff --git a/test/junit/scala/reflect/internal/PrintersTest.scala b/test/junit/scala/reflect/internal/PrintersTest.scala
index 722062ba21..c7cfe0dfbb 100644
--- a/test/junit/scala/reflect/internal/PrintersTest.scala
+++ b/test/junit/scala/reflect/internal/PrintersTest.scala
@@ -556,7 +556,7 @@ class ClassPrintTest {
 
   @Test def testCaseClassWithParams3 = assertPrintedCode(sm"""
     |{
-    |  case class X(implicit x: scala.Int, s: scala.Predef.String);
+    |  case class X()(implicit x: scala.Int, s: scala.Predef.String);
     |  ()
     |}""")