Fail more gracefully on > 22 case class paramet...

Fail more gracefully on > 22 case class parameters. Closes #3631, no
review.

3 files changed, 19 insertions, 9 deletions

diff --git a/src/compiler/scala/tools/nsc/ast/TreeInfo.scala b/src/compiler/scala/tools/nsc/ast/TreeInfo.scala
index f21b1b20ff..46ddf7b24b 100644
--- a/src/compiler/scala/tools/nsc/ast/TreeInfo.scala
+++ b/src/compiler/scala/tools/nsc/ast/TreeInfo.scala
@@ -151,6 +151,12 @@ abstract class TreeInfo {
     case _ :: stats1 => firstConstructor(stats1)
   }
 
+  /** The arguments to the first constructor in `stats'. */
+  def firstConstructorArgs(stats: List[Tree]): List[Tree] = firstConstructor(stats) match {
+    case DefDef(_, _, _, args :: _, _, _) => args
+    case _                                => Nil
+  }
+
   /** The value definitions marked PRESUPER in this statement sequence */
   def preSuperFields(stats: List[Tree]): List[ValDef] =
     for (vdef @ ValDef(mods, _, _, _) <- stats if mods hasFlag PRESUPER) yield vdef
diff --git a/src/compiler/scala/tools/nsc/typechecker/Namers.scala b/src/compiler/scala/tools/nsc/typechecker/Namers.scala
index d56b8ed944..2123a00550 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Namers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Namers.scala
@@ -287,13 +287,11 @@ trait Namers { self: Analyzer =>
      *  class definition tree.
      *  @return the companion object symbol.
      */
-    def ensureCompanionObject(tree: ClassDef, creator: => Tree): Symbol = {
-      val m: Symbol = context.scope.lookup(tree.name.toTermName).filter(! _.isSourceMethod)
-      if (m.isModule && inCurrentScope(m) && currentRun.compiles(m)) m
-      else
-        /*util.trace("enter synthetic companion object for "+currentRun.compiles(m)+":")*/(
-        enterSyntheticSym(creator))
-    }
+     def ensureCompanionObject(tree: ClassDef, creator: => Tree): Symbol = {
+       val m: Symbol = context.scope.lookup(tree.name.toTermName).filter(! _.isSourceMethod)
+       if (m.isModule && inCurrentScope(m) && currentRun.compiles(m)) m
+       else enterSyntheticSym(creator)
+     }
 
     private def enterSymFinishWith(tree: Tree, tparams: List[TypeDef]) {
       val sym = tree.symbol
@@ -350,6 +348,9 @@ trait Namers { self: Analyzer =>
             tree.symbol = enterClassSymbol(tree)
             finishWith(tparams)
             if (mods.isCase) {
+              if (treeInfo.firstConstructorArgs(impl.body).size > MaxFunctionArity)
+                context.error(tree.pos, "Implementation restriction: case classes cannot have more than " + MaxFunctionArity + " parameters.")
+
               val m = ensureCompanionObject(tree, caseModuleDef(tree))
               caseClassOfModuleClass(m.moduleClass) = tree
             }
diff --git a/src/compiler/scala/tools/nsc/typechecker/Unapplies.scala b/src/compiler/scala/tools/nsc/typechecker/Unapplies.scala
index c3631f0d05..735cb4a3c4 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Unapplies.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Unapplies.scala
@@ -133,8 +133,11 @@ trait Unapplies extends ast.TreeDSL
   /** The module corresponding to a case class; overrides toString to show the module's name
    */
   def caseModuleDef(cdef: ClassDef): ModuleDef = {
-    def inheritFromFun = !(cdef.mods hasFlag ABSTRACT) && cdef.tparams.isEmpty && constrParamss(cdef).length == 1
-    def createFun      = gen.scalaFunctionConstr(constrParamss(cdef).head map (_.tpt), toIdent(cdef), abstractFun = true)
+    // > MaxFunctionArity is caught in Namers, but for nice error reporting instead of
+    // an abrupt crash we trim the list here.
+    def primaries      = constrParamss(cdef).head take MaxFunctionArity map (_.tpt)
+    def inheritFromFun = !cdef.mods.isAbstract && cdef.tparams.isEmpty && constrParamss(cdef).length == 1
+    def createFun      = gen.scalaFunctionConstr(primaries, toIdent(cdef), abstractFun = true)
     def parents        = if (inheritFromFun) List(createFun) else Nil
     def toString       = DefDef(
       Modifiers(OVERRIDE | FINAL),