An old patch on pattern matcher exhaustivity.

Simplifies the implementation a bit.

6 files changed, 50 insertions, 47 deletions

diff --git a/src/compiler/scala/tools/nsc/matching/MatchSupport.scala b/src/compiler/scala/tools/nsc/matching/MatchSupport.scala
index 5e46960d04..371f4bc4d8 100644
--- a/src/compiler/scala/tools/nsc/matching/MatchSupport.scala
+++ b/src/compiler/scala/tools/nsc/matching/MatchSupport.scala
@@ -115,6 +115,10 @@ trait MatchSupport extends ast.TreeDSL { self: ParallelMatching =>
       println(fmt.format(xs: _*) + " == " + x)
       x
     }
+    private[nsc] def debugging[T](fmt: String, xs: Any*)(x: T): T = {
+      if (settings.debug.value) printing(fmt, xs: _*)(x)
+      else x
+    }
 
     def indent(s: Any) = s.toString() split "\n" map ("  " + _) mkString "\n"
     def indentAll(s: Seq[Any]) = s map ("  " + _.toString() + "\n") mkString
diff --git a/src/compiler/scala/tools/nsc/matching/Matrix.scala b/src/compiler/scala/tools/nsc/matching/Matrix.scala
index d81f05cd51..e1ff88557e 100644
--- a/src/compiler/scala/tools/nsc/matching/Matrix.scala
+++ b/src/compiler/scala/tools/nsc/matching/Matrix.scala
@@ -198,6 +198,10 @@ trait Matrix extends MatrixAdditions {
     class PatternVar(val lhs: Symbol, val rhs: Tree, val checked: Boolean) {
       def sym = lhs
       def tpe = lhs.tpe
+      if (checked)
+        lhs resetFlag NO_EXHAUSTIVE
+      else
+        lhs setFlag NO_EXHAUSTIVE
 
       // See #1427 for an example of a crash which occurs unless we retype:
       // in that instance there is an existential in the pattern.
@@ -207,11 +211,6 @@ trait Matrix extends MatrixAdditions {
       override def toString() = "%s: %s = %s".format(lhs, tpe, rhs)
     }
 
-    /** Sets the rhs to EmptyTree, which makes the valDef ignored in Scrutinee.
-     */
-    def specialVar(lhs: Symbol, checked: Boolean) =
-      new PatternVar(lhs, EmptyTree, checked)
-
     /** Given a tree, creates a new synthetic variable of the same type
      *  and assigns the tree to it.
      */
diff --git a/src/compiler/scala/tools/nsc/matching/MatrixAdditions.scala b/src/compiler/scala/tools/nsc/matching/MatrixAdditions.scala
index 24d3c38e74..e72a0007a0 100644
--- a/src/compiler/scala/tools/nsc/matching/MatrixAdditions.scala
+++ b/src/compiler/scala/tools/nsc/matching/MatrixAdditions.scala
@@ -131,23 +131,11 @@ trait MatrixAdditions extends ast.TreeDSL {
 
       import Flags.{ MUTABLE, ABSTRACT, SEALED }
 
-      private case class Combo(index: Int, sym: Symbol) {
-        val isBaseClass = sym.tpe.baseClasses.toSet
-
-        // is this combination covered by the given pattern?
-        def isCovered(p: Pattern) = {
-          def coversSym = isBaseClass(decodedEqualsType(p.tpe).typeSymbol)
-
-          cond(p.tree) {
-            case _: UnApply | _: ArrayValue => true
-            case x                          => p.isDefault || coversSym
-          }
-        }
-      }
+      private case class Combo(index: Int, sym: Symbol) { }
 
       /* True if the patterns in 'row' cover the given type symbol combination, and has no guard. */
       private def rowCoversCombo(row: Row, combos: List[Combo]) =
-        row.guard.isEmpty && (combos forall (c => c isCovered row.pats(c.index)))
+        row.guard.isEmpty && combos.forall(c => row.pats(c.index) covers c.sym)
 
       private def requiresExhaustive(sym: Symbol) = {
          (sym.isMutable) &&                 // indicates that have not yet checked exhaustivity
diff --git a/src/compiler/scala/tools/nsc/matching/ParallelMatching.scala b/src/compiler/scala/tools/nsc/matching/ParallelMatching.scala
index 9d4c9b4411..1285e29d4a 100644
--- a/src/compiler/scala/tools/nsc/matching/ParallelMatching.scala
+++ b/src/compiler/scala/tools/nsc/matching/ParallelMatching.scala
@@ -745,7 +745,7 @@ trait ParallelMatching extends ast.TreeDSL
           (others.head :: _column.tail, make(_tvars, _rows))
 
         def mix() = {
-          val newScrut = new Scrutinee(specialVar(_pv.sym, _pv.checked))
+          val newScrut = new Scrutinee(new PatternVar(_pv.sym, EmptyTree, _pv.checked))
           PatternMatch(newScrut, _ncol) mkRule _nrep
         }
       }
diff --git a/src/compiler/scala/tools/nsc/matching/PatternBindings.scala b/src/compiler/scala/tools/nsc/matching/PatternBindings.scala
index 5dd7d8f3ee..56297f0195 100644
--- a/src/compiler/scala/tools/nsc/matching/PatternBindings.scala
+++ b/src/compiler/scala/tools/nsc/matching/PatternBindings.scala
@@ -19,9 +19,10 @@ trait PatternBindings extends ast.TreeDSL
   import Debug._
 
   /** EqualsPattern **/
-  def isEquals(tpe: Type)             = cond(tpe) { case TypeRef(_, EqualsPatternClass, _) => true }
+  def isEquals(tpe: Type)             = tpe.typeSymbol == EqualsPatternClass
   def mkEqualsRef(tpe: Type)          = typeRef(NoPrefix, EqualsPatternClass, List(tpe))
-  def decodedEqualsType(tpe: Type)    = condOpt(tpe) { case TypeRef(_, EqualsPatternClass, List(arg)) => arg } getOrElse (tpe)
+  def decodedEqualsType(tpe: Type)    =
+    if (tpe.typeSymbol == EqualsPatternClass) tpe.typeArgs.head else tpe
 
   // A subtype test which creates fresh existentials for type
   // parameters on the right hand side.
diff --git a/src/compiler/scala/tools/nsc/matching/Patterns.scala b/src/compiler/scala/tools/nsc/matching/Patterns.scala
index 18409cfffe..a6d8556db3 100644
--- a/src/compiler/scala/tools/nsc/matching/Patterns.scala
+++ b/src/compiler/scala/tools/nsc/matching/Patterns.scala
@@ -26,19 +26,6 @@ trait Patterns extends ast.TreeDSL {
   type PatternMatch       = MatchMatrix#PatternMatch
   private type PatternVar = MatrixContext#PatternVar
 
-  // private def unapplyArgs(x: Any) = x match {
-  //   case UnApply(Apply(TypeApply(_, targs), args), _) => (targs map (_.symbol), args map (_.symbol))
-  //   case _                                            => (Nil, Nil)
-  // }
-  //
-  // private def unapplyCall(x: Any) = x match {
-  //   case UnApply(t, _)  => treeInfo.methPart(t).symbol
-  //   case _              => NoSymbol
-  // }
-
-  private lazy val dummyMethod =
-    NoSymbol.newTermSymbol(newTermName("matching$dummy"))
-
   // Fresh patterns
   def emptyPatterns(i: Int): List[Pattern] = List.fill(i)(NoPattern)
   def emptyTrees(i: Int): List[Tree] = List.fill(i)(EmptyTree)
@@ -56,13 +43,14 @@ trait Patterns extends ast.TreeDSL {
   case class VariablePattern(tree: Ident) extends NamePattern {
     lazy val Ident(name) = tree
     require(isVarPattern(tree) && name != nme.WILDCARD)
-
+    override def covers(sym: Symbol) = true
     override def description = "%s".format(name)
   }
 
   // 8.1.1 (b)
   case class WildcardPattern() extends Pattern {
-    def tree = EmptyTree
+    val tree = EmptyTree
+    override def covers(sym: Symbol) = true
     override def isDefault = true
     override def description = "_"
   }
@@ -71,6 +59,8 @@ trait Patterns extends ast.TreeDSL {
   case class TypedPattern(tree: Typed) extends Pattern {
     lazy val Typed(expr, tpt) = tree
 
+    override def covers(sym: Symbol) = newMatchesPattern(sym, tpt.tpe)
+    override def sufficientType = tpt.tpe
     override def subpatternsForVars: List[Pattern] = List(Pattern(expr))
     override def simplify(pv: PatternVar) = Pattern(expr) match {
       case ExtractorPattern(ua) if pv.sym.tpe <:< tpt.tpe => this rebindTo expr
@@ -115,6 +105,7 @@ trait Patterns extends ast.TreeDSL {
         }
     }
 
+    override def covers(sym: Symbol) = newMatchesPattern(sym, sufficientType)
     override def simplify(pv: PatternVar) = this.rebindToObjectCheck()
     override def description = backticked match {
       case Some(s)  => "this." + s
@@ -133,13 +124,15 @@ trait Patterns extends ast.TreeDSL {
   case class ObjectPattern(tree: Apply) extends ApplyPattern {  // NamePattern?
     require(!fn.isType && isModule)
 
+    override def covers(sym: Symbol) = newMatchesPattern(sym, sufficientType)
     override def sufficientType = tpe.narrow
     override def simplify(pv: PatternVar) = this.rebindToObjectCheck()
     override def description = "Obj(%s)".format(fn)
   }
   // 8.1.4 (e)
   case class SimpleIdPattern(tree: Ident) extends NamePattern {
-    lazy val Ident(name) = tree
+    val Ident(name) = tree
+    override def covers(sym: Symbol) = newMatchesPattern(sym, tpe.narrow)
     override def description = "Id(%s)".format(name)
   }
 
@@ -163,6 +156,11 @@ trait Patterns extends ast.TreeDSL {
       if (args.isEmpty) this rebindToEmpty tree.tpe
       else this
 
+    override def covers(sym: Symbol) = {
+      debugging("[constructor] Does " + this + " cover " + sym + " ? ") {
+        sym.tpe.typeSymbol == this.tpe.typeSymbol
+      }
+    }
     override def description = {
       if (isColonColon) "%s :: %s".format(Pattern(args(0)), Pattern(args(1)))
       else "%s(%s)".format(name, toPats(args).mkString(", "))
@@ -175,17 +173,12 @@ trait Patterns extends ast.TreeDSL {
 
   // 8.1.7 / 8.1.8 (unapply and unapplySeq calls)
   case class ExtractorPattern(tree: UnApply) extends UnapplyPattern {
-    override def simplify(pv: PatternVar) = {
-      if (pv.sym hasFlag NO_EXHAUSTIVE) ()
-      else {
-        TRACE("Setting NO_EXHAUSTIVE on " + pv.sym + " due to extractor " + tree)
-        pv.sym setFlag NO_EXHAUSTIVE
-      }
+    private def uaTyped = Typed(tree, TypeTree(arg.tpe)) setType arg.tpe
 
+    override def simplify(pv: PatternVar) = {
       if (pv.tpe <:< arg.tpe) this
       else this rebindTo uaTyped
     }
-
     override def description = "Unapply(%s => %s)".format(necessaryType, resTypesString)
   }
 
@@ -208,6 +201,7 @@ trait Patterns extends ast.TreeDSL {
     private def listFolder(hd: Tree, tl: Tree): Tree = unbind(hd) match {
       case t @ Star(_) => moveBindings(hd, WILD(t.tpe))
       case _           =>
+        val dummyMethod = NoSymbol.newTermSymbol(newTermName("matching$dummy"))
         val consType    = MethodType(dummyMethod newSyntheticValueParams List(packedType, listRef), consRef)
 
         Apply(TypeTree(consType), List(hd, tl)) setType consRef
@@ -376,7 +370,7 @@ trait Patterns extends ast.TreeDSL {
       case _: This if isVariableName(name)  => Some("`%s`".format(name))
       case _                                => None
     }
-
+    override def covers(sym: Symbol) = newMatchesPattern(sym, tree.tpe)
     protected def getPathSegments(t: Tree): List[Name] = t match {
       case Select(q, name)  => name :: getPathSegments(q)
       case Apply(f, Nil)    => getPathSegments(f)
@@ -395,7 +389,13 @@ trait Patterns extends ast.TreeDSL {
     lazy val UnApply(unfn, args) = tree
     lazy val Apply(fn, _) = unfn
     lazy val MethodType(List(arg, _*), _) = fn.tpe
-    protected def uaTyped = Typed(tree, TypeTree(arg.tpe)) setType arg.tpe
+    
+    // Covers if the symbol matches the unapply method's argument type,
+    // and the return type of the unapply is Some.
+    override def covers(sym: Symbol) = newMatchesPattern(sym, arg.tpe)
+    
+    // TODO: for alwaysCovers:
+    //   fn.tpe.finalResultType.typeSymbol == SomeClass
 
     override def necessaryType = arg.tpe
     override def subpatternsForVars = args match {
@@ -419,6 +419,7 @@ trait Patterns extends ast.TreeDSL {
       else emptyPatterns(sufficientType.typeSymbol.caseFieldAccessors.size)
 
     def isConstructorPattern = fn.isType
+    override def covers(sym: Symbol) = newMatchesPattern(sym, fn.tpe)
   }
 
   sealed abstract class Pattern extends PatternBindingLogic {
@@ -443,6 +444,15 @@ trait Patterns extends ast.TreeDSL {
     // the subpatterns for this pattern (at the moment, that means constructor arguments)
     def subpatterns(pm: MatchMatrix#PatternMatch): List[Pattern] = pm.dummies
 
+    // if this pattern should be considered to cover the given symbol
+    def covers(sym: Symbol): Boolean = newMatchesPattern(sym, sufficientType)
+    def newMatchesPattern(sym: Symbol, pattp: Type) = {
+      debugging("[" + kindString + "] Does " + pattp + " cover " + sym + " ? ") {
+        (sym.isModuleClass && (sym.tpe.typeSymbol eq pattp.typeSymbol)) ||
+        (sym.tpe.baseTypeSeq exists (_ matchesPattern pattp))
+      }
+    }
+    
     def    sym  = tree.symbol
     def    tpe  = tree.tpe
     def isEmpty = tree.isEmpty
@@ -475,6 +485,7 @@ trait Patterns extends ast.TreeDSL {
     final override def toString = description
 
     def toTypeString() = "%s <: x <: %s".format(necessaryType, sufficientType)
+    def kindString = ""
   }
 
   /*** Extractors ***/