Add missing and double symbol checking to TreeChecker

TreeChecker now tests that a symbol does not have two definitions that define it,
and that every reference to a symbol owner by a term is in the scope of a definition
of that symbol.

Both tests fail on several files for pattern matcher.

Author: odersky

src/dotty/tools/dotc/ast/tpd.scala

@@ -9,6 +9,7 @@ import SymDenotations._, Symbols._, StdNames._, Annotations._, Trees._, Symbols.
 import Denotations._, Decorators._
 import config.Printers._
 import typer.Mode
+import collection.mutable
 import typer.ErrorReporting._
 
 import scala.annotation.tailrec
@@ -620,6 +621,12 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
       }
       acc(false, tree)
     }
+
+    def filterSubTrees(f: Tree => Boolean): List[Tree] = {
+      val buf = new mutable.ListBuffer[Tree]
+      foreachSubTree { tree => if (f(tree)) buf += tree }
+      buf.toList
+    }
   }
 
   implicit class ListOfTreeDecorator(val xs: List[tpd.Tree]) extends AnyVal {

src/dotty/tools/dotc/core/Decorators.scala

@@ -100,6 +100,11 @@ object Decorators {
         else x1 :: xs1
       }
 
+    def foldRightBN[U](z: => U)(op: (T, => U) => U): U = xs match {
+      case Nil => z
+      case x :: xs1 => op(x, xs1.foldRightBN(z)(op))
+    }
+
     final def hasSameLengthAs[U](ys: List[U]): Boolean = {
       @tailrec def loop(xs: List[T], ys: List[U]): Boolean =
         if (xs.isEmpty) ys.isEmpty

src/dotty/tools/dotc/transform/TreeChecker.scala

@@ -20,6 +20,7 @@ import reporting.ThrowingReporter
 import ast.Trees._
 import ast.{tpd, untpd}
 import util.SourcePosition
+import collection.mutable
 import ProtoTypes._
 import java.lang.AssertionError
 
@@ -57,6 +58,32 @@ class TreeChecker {
   }
 
   class Checker(phasesToCheck: Seq[Phase]) extends ReTyper {
+
+    val definedSyms = new mutable.HashSet[Symbol]
+
+    def withDefinedSym[T](tree: untpd.Tree)(op: => T)(implicit ctx: Context): T = {
+      if (tree.isDef) {
+        //assert(!definedSyms.contains(tree.symbol), i"doubly defined symbol: ${tree.symbol}in $tree")
+        definedSyms += tree.symbol
+        //println(i"defined: ${tree.symbol}")
+        val res = op
+        definedSyms -= tree.symbol
+        //println(i"undefined: ${tree.symbol}")
+        res
+      }
+      else op
+    }
+
+    def withDefinedSyms[T](trees: List[untpd.Tree])(op: => T)(implicit ctx: Context) =
+      trees.foldRightBN(op)(withDefinedSym(_)(_))
+
+    def withDefinedSymss[T](vparamss: List[List[untpd.ValDef]])(op: => T)(implicit ctx: Context): T =
+      vparamss.foldRightBN(op)(withDefinedSyms(_)(_))
+
+    def assertDefined(tree: untpd.Tree)(implicit ctx: Context) =
+      if (tree.symbol.maybeOwner.isTerm)
+        ()//assert(definedSyms contains tree.symbol, i"undefined symbol ${tree.symbol}")
+
     override def typed(tree: untpd.Tree, pt: Type)(implicit ctx: Context) = {
       val res = tree match {
         case _: untpd.UnApply =>
@@ -88,7 +115,8 @@ class TreeChecker {
 
     override def typedIdent(tree: untpd.Ident, pt: Type)(implicit ctx: Context): Tree = {
       assert(tree.isTerm || !ctx.isAfterTyper, tree.show + " at " + ctx.phase)
-      assert(tree.isType || !needsSelect(tree.tpe), i"bad type ${tree.tpe} for $tree")
+      assert(tree.isType || !needsSelect(tree.tpe), i"bad type ${tree.tpe} for $tree # ${tree.uniqueId}")
+      assertDefined(tree)
       super.typedIdent(tree, pt)
     }
 
@@ -117,6 +145,22 @@ class TreeChecker {
       super.typedClassDef(cdef, cls)
     }
 
+    override def typedDefDef(ddef: untpd.DefDef, sym: Symbol)(implicit ctx: Context) =
+      withDefinedSyms(ddef.tparams) {
+        withDefinedSymss(ddef.vparamss) {
+          super.typedDefDef(ddef, sym)
+        }
+      }
+
+    override def typedCase(tree: untpd.CaseDef, pt: Type, selType: Type, gadtSyms: Set[Symbol])(implicit ctx: Context): CaseDef = {
+      withDefinedSyms(tree.pat.asInstanceOf[tpd.Tree].filterSubTrees(_.isInstanceOf[ast.Trees.Bind[_]])) {
+        super.typedCase(tree, pt, selType, gadtSyms)
+      }
+    }
+
+    override def typedBlock(tree: untpd.Block, pt: Type)(implicit ctx: Context) =
+      withDefinedSyms(tree.stats) { super.typedBlock(tree, pt) }
+
     /** Check that all defined symbols have legal owners.
      *  An owner is legal if it is either the same as the context's owner
      *  or there's an owner chain of valdefs starting at the context's owner and

src/dotty/tools/dotc/typer/Typer.scala

@@ -610,29 +610,29 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
           accu(Set.empty, selType)
         }
 
-        def typedCase(tree: untpd.CaseDef): CaseDef = track("typedCase") {
-          def caseRest(pat: Tree)(implicit ctx: Context) = {
-            gadtSyms foreach (_.resetGADTFlexType)
-            pat foreachSubTree {
-              case b: Bind =>
-                if (ctx.scope.lookup(b.name) == NoSymbol) ctx.enter(b.symbol)
-                else ctx.error(d"duplicate pattern variable: ${b.name}", b.pos)
-              case _ =>
-            }
-            val guard1 = typedExpr(tree.guard, defn.BooleanType)
-            val body1 = typedExpr(tree.body, pt)
-            assignType(cpy.CaseDef(tree)(pat, guard1, body1), body1)
-          }
-          val doCase: () => CaseDef =
-            () => caseRest(typedPattern(tree.pat, selType))(ctx.fresh.setNewScope)
-          (doCase /: gadtSyms)((op, tsym) => tsym.withGADTFlexType(op))()
-        }
-
-        val cases1 = tree.cases mapconserve typedCase
+        val cases1 = tree.cases mapconserve (typedCase(_, pt, selType, gadtSyms))
         assignType(cpy.Match(tree)(sel1, cases1), cases1)
     }
   }
 
+  def typedCase(tree: untpd.CaseDef, pt: Type, selType: Type, gadtSyms: Set[Symbol])(implicit ctx: Context): CaseDef = track("typedCase") {
+    def caseRest(pat: Tree)(implicit ctx: Context) = {
+      gadtSyms foreach (_.resetGADTFlexType)
+      pat foreachSubTree {
+        case b: Bind =>
+          if (ctx.scope.lookup(b.name) == NoSymbol) ctx.enter(b.symbol)
+          else ctx.error(d"duplicate pattern variable: ${b.name}", b.pos)
+        case _ =>
+      }
+      val guard1 = typedExpr(tree.guard, defn.BooleanType)
+      val body1 = typedExpr(tree.body, pt)
+      assignType(cpy.CaseDef(tree)(pat, guard1, body1), body1)
+    }
+    val doCase: () => CaseDef =
+      () => caseRest(typedPattern(tree.pat, selType))(ctx.fresh.setNewScope)
+    (doCase /: gadtSyms)((op, tsym) => tsym.withGADTFlexType(op))()
+  }
+
   def typedReturn(tree: untpd.Return)(implicit ctx: Context): Return = track("typedReturn") {
     def returnProto(owner: Symbol) =
       if (owner.isConstructor) defn.UnitType else owner.info.finalResultType