implementing Martin's suggestions for tcpoly

- prefixString in SingleType suppresses scala.Predef prefixes
- (sym.isPredefModule) better handling of double defs of `_' in type
- params (now in enterInScope in Namers) introduced HKmode to indicate
- we're typing a higher-kinded type, instead of reusing POLYmode |
- TAPPmode

- Typers.typedTypeConstructor does not normalize the result anymore -- now in GenICode
          generatedType = toTypeKind(tpt.tpe.normalize)

5 files changed, 30 insertions, 20 deletions

diff --git a/src/compiler/scala/tools/nsc/backend/icode/GenICode.scala b/src/compiler/scala/tools/nsc/backend/icode/GenICode.scala
index 1cb38f79e1..0a2e024a57 100644
--- a/src/compiler/scala/tools/nsc/backend/icode/GenICode.scala
+++ b/src/compiler/scala/tools/nsc/backend/icode/GenICode.scala
@@ -624,7 +624,7 @@ abstract class GenICode extends SubComponent  {
           assert(ctor.isClassConstructor,
                  "'new' call to non-constructor: " + tree)
 
-          generatedType = toTypeKind(tpt.tpe)
+          generatedType = toTypeKind(tpt.tpe.normalize) // @M: because typedTypeConstructor doesn't normalize anymore
           assert(generatedType.isReferenceType || generatedType.isArrayType,
                  "Non reference type cannot be instantiated: " + generatedType)
 
diff --git a/src/compiler/scala/tools/nsc/symtab/Symbols.scala b/src/compiler/scala/tools/nsc/symtab/Symbols.scala
index 63c502db84..e9b62f1b99 100644
--- a/src/compiler/scala/tools/nsc/symtab/Symbols.scala
+++ b/src/compiler/scala/tools/nsc/symtab/Symbols.scala
@@ -209,6 +209,7 @@ trait Symbols requires SymbolTable {
     final def isRootPackage = isPackage && name == nme.ROOTPKG
     final def isEmptyPackage = isPackage && name == nme.EMPTY_PACKAGE_NAME
     final def isEmptyPackageClass = isPackageClass && name == nme.EMPTY_PACKAGE_NAME.toTypeName
+    final def isPredefModule = isModule && name == nme.Predef
     def isDeprecated =
       attributes exists (attr => attr.atp.symbol == DeprecatedAttr)
 
@@ -1120,12 +1121,7 @@ trait Symbols requires SymbolTable {
    *  of this class. Classes are instances of a subclass.
    */
   class TypeSymbol(initOwner: Symbol, initPos: PositionType, initName: Name)
-  extends Symbol(initOwner, initPos,
-// @M type params with name "_" implicitly get unique name @M TODO: the name generation is a bit hacky...
-                 if(initName.length==1 && initName(0)=='_') // faster equality test than first converting to string
-                   newTypeName("_$" + (ids+1))
-                 else initName) {
-    override def nameString: String = if(name.startsWith("_$")) "_"+idString else super.nameString // @M: undo underscore-mangling
+  extends Symbol(initOwner, initPos, initName) {
     override def isType = true
     privateWithin = NoSymbol
     private var tyconCache: Type = null
diff --git a/src/compiler/scala/tools/nsc/symtab/Types.scala b/src/compiler/scala/tools/nsc/symtab/Types.scala
index c27cf02811..71c97bef15 100644
--- a/src/compiler/scala/tools/nsc/symtab/Types.scala
+++ b/src/compiler/scala/tools/nsc/symtab/Types.scala
@@ -670,7 +670,7 @@ trait Types requires SymbolTable {
     override def symbol = sym
     override def prefix: Type = pre
     override def prefixString: String =
-      if ((sym.isEmptyPackage || sym.isInterpreterWrapper) && !settings.debug.value) ""
+      if ((sym.isEmptyPackage || sym.isInterpreterWrapper || sym.isPredefModule) && !settings.debug.value) ""
       else pre.prefixString + sym.nameString + "."
   }
 
diff --git a/src/compiler/scala/tools/nsc/typechecker/Namers.scala b/src/compiler/scala/tools/nsc/typechecker/Namers.scala
index fb3e7931cc..4bbd881cb5 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Namers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Namers.scala
@@ -126,7 +126,8 @@ trait Namers requires Analyzer {
         if ((prev ne null) && prev.owner == context.scope &&
             (!prev.sym.isSourceMethod ||
              nme.isSetterName(sym.name) ||
-             sym.owner.isPackageClass)) {
+             sym.owner.isPackageClass) &&
+             !(sym.owner.isTypeParameter && sym.name.length==1 && sym.name(0)=='_')) { //@M: allow repeated use of `_' for higher-order type params
            doubleDefError(sym.pos, prev.sym)
            sym setInfo ErrorType
         } else context.scope enter sym
diff --git a/src/compiler/scala/tools/nsc/typechecker/Typers.scala b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
index e52fc84523..7534df9bbb 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Typers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
@@ -123,6 +123,12 @@ trait Typers requires Analyzer {
   /** The mode <code>ALTmode</code> is set when we are under a pattern alternative */
   val ALTmode       = 0x2000
 
+  /** The mode <code>HKmode</code> is set when we are typing a higher-kinded type
+   * adapt should then check kind-arity based on the prototypical type's kind arity
+   * type arguments should not be inferred
+   */
+  val HKmode        = 0x4000 // @M: could also use POLYmode | TAPPmode
+
   private val stickyModes: int  = EXPRmode | PATTERNmode | TYPEmode | CONSTmode | ALTmode
 
   private def funMode(mode: int) = mode & (stickyModes | SCCmode) | FUNmode | POLYmode
@@ -541,8 +547,8 @@ trait Typers requires Analyzer {
      *        unapply or unapplySeq method.
      *
      *  (6) Convert all other types to TypeTree nodes.
-     *  (7) When in TYPEmode but not FUNmode, check that types are fully parameterized
-     *      (7.1) @M! when in POLYmode | TAPPmode, check that types have the expected kind
+     *  (7) When in TYPEmode but not FUNmode or HKmode, check that types are fully parameterized
+     *      (7.1) In HKmode, higher-kinded types are allowed, but they must have the expected kind-arity
      *  (8) When in both EXPRmode and FUNmode, add apply method calls to values of object type.
      *  (9) If there are undetermined type variables and not POLYmode, infer expression instance
      *  Then, if tree's type is not a subtype of expected type, try the following adaptations:
@@ -565,6 +571,7 @@ trait Typers requires Analyzer {
       if ((mode & EXPRmode) != 0 && sym == ByNameParamClass) => // (2)
         adapt(tree setType arg, mode, pt)
       case PolyType(tparams, restpe) if ((mode & (TAPPmode | PATTERNmode)) == 0) => // (3)
+        assert((mode & HKmode) == 0) //@M
         val tparams1 = cloneSymbols(tparams)
         val tree1 = if (tree.isType) tree
                     else TypeApply(tree, tparams1 map (tparam =>
@@ -605,15 +612,19 @@ trait Typers requires Analyzer {
         if (tree.isType) {
           if ((mode & FUNmode) != 0) {
             tree
-          } else if (tree.hasSymbol && !tree.symbol.typeParams.isEmpty && (mode & (POLYmode | TAPPmode)) == 0) { // (7)
-            // @M higher-kinded types are allowed in (POLYmode | TAPPmode) -- see (7.1)
+          } else if (tree.hasSymbol && !tree.symbol.typeParams.isEmpty && (mode & HKmode) == 0) { // (7)
+            // @M When not typing a higher-kinded type ((mode & HKmode) == 0), types must be of kind *,
+            // and thus parameterised types must be applied to their type arguments
             errorTree(tree, tree.symbol+" takes type parameters")
             tree setType tree.tpe
-          } else if (tree.hasSymbol && ((mode & (POLYmode | TAPPmode)) == (POLYmode | TAPPmode)) &&             // (7.1) @M: check kind-arity (full checks are done in checkKindBounds in Infer)
+          } else if (tree.hasSymbol && ((mode & HKmode) != 0) && // (7.1) @M: check kind-arity
                      tree.symbol.typeParams.length != pt.typeParams.length &&
-                     !(tree.symbol==AnyClass || tree.symbol==AllClass || pt == WildcardType )) { //@M Any and Nothing are kind-polymorphic
-                       // WildcardType is only used when typing type arguments to an overloaded method, before the overload is resolved
-                       // (or in the case of an error type) -- see case TypeApply in typed1
+                     !(tree.symbol==AnyClass || tree.symbol==AllClass || pt == WildcardType )) {
+              // Check that the actual kind arity (tree.symbol.typeParams.length) conforms to the expected
+              // kind-arity (pt.typeParams.length). Full checks are done in checkKindBounds in Infer.
+              // Note that we treat Any and Nothing as kind-polymorphic.
+              // We can't perform this check when typing type arguments to an overloaded method before the overload is resolved
+              // (or in the case of an error type) -- this is indicated by pt == WildcardType (see case TypeApply in typed1).
               errorTree(tree, tree.symbol+" takes "+reporter.countElementsAsString(tree.symbol.typeParams.length, "type parameter")+
                               ", expected: "+reporter.countAsString(pt.typeParams.length))
               tree setType tree.tpe
@@ -651,6 +662,7 @@ trait Typers requires Analyzer {
                    ((mode & TAPPmode) == 0 || tree.tpe.typeParams.isEmpty) &&
                    member(adaptToName(tree, nme.apply), nme.apply)
                      .filter(m => m.tpe.paramSectionCount > 0) != NoSymbol) { // (8)
+          assert((mode & HKmode) == 0) //@M
           val qual = adaptToName(tree, nme.apply) match {
             case id @ Ident(_) =>
               val pre = if (id.symbol.owner.isPackageClass) id.symbol.owner.thisType
@@ -665,6 +677,7 @@ trait Typers requires Analyzer {
           }
           typed(atPos(tree.pos)(Select(qual, nme.apply)), mode, pt)
         } else if (!context.undetparams.isEmpty && (mode & POLYmode) == 0) { // (9)
+          assert((mode & HKmode) == 0) //@M
           instantiate(tree, mode, pt)
         } else if (tree.tpe <:< pt) {
           tree
@@ -2669,17 +2682,17 @@ trait Typers requires Analyzer {
     /** Types a higher-kinded type tree -- pt denotes the expected kind*/
     def typedHigherKindedType(tree: Tree, pt: Type): Tree =
       if(pt.typeParams.isEmpty) typedType(tree) // kind is known and it's *
-      else withNoGlobalVariance{ typed(tree, POLYmode | TAPPmode, pt) }
+      else withNoGlobalVariance{ typed(tree, HKmode, pt) }
 
     def typedHigherKindedType(tree: Tree): Tree =
-      withNoGlobalVariance{ typed(tree, POLYmode | TAPPmode, WildcardType) }
+      withNoGlobalVariance{ typed(tree, HKmode, WildcardType) }
 
     /** Types a type constructor tree used in a new or supertype */
     def typedTypeConstructor(tree: Tree): Tree = {
       val result = withNoGlobalVariance{ typed(tree, TYPEmode | FUNmode, WildcardType) }
       if (!phase.erasedTypes && result.tpe.isInstanceOf[TypeRef] && !result.tpe.prefix.isStable)
         error(tree.pos, result.tpe.prefix+" is not a legal prefix for a constructor")
-      result setType(result.tpe.normalize) // @MAT remove aliases when instantiating
+      result setType(result.tpe) // @M: no need to normalize here, see GenICode line 627: generatedType = toTypeKind(tpt.tpe.normalize)
     }
 
     def computeType(tree: Tree, pt: Type): Type = {