From 661c602630e72f7a9a81e6f21ca5cd6946a9618f Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Mon, 12 Mar 2007 11:13:41 +0000
Subject: Fixed David Pollacks stack overflow problem.

---
 src/compiler/scala/tools/nsc/symtab/Types.scala    | 28 +++++++++++++++++++++-
 .../scala/tools/nsc/typechecker/Infer.scala        |  4 ++--
 .../scala/tools/nsc/typechecker/Typers.scala       | 18 +++++++-------
 3 files changed, 39 insertions(+), 11 deletions(-)

diff --git a/src/compiler/scala/tools/nsc/symtab/Types.scala b/src/compiler/scala/tools/nsc/symtab/Types.scala
index c359d166d9..9ddd8df4a7 100644
--- a/src/compiler/scala/tools/nsc/symtab/Types.scala
+++ b/src/compiler/scala/tools/nsc/symtab/Types.scala
@@ -261,6 +261,10 @@ trait Types requires SymbolTable {
     def contains(sym: Symbol): boolean =
       new ContainsTraverser(sym).traverse(this).result
 
+    /** Does this type contain a reference to this type */
+    def containsTp(tp: Type): boolean =
+      new ContainsTypeTraverser(tp).traverse(this).result
+
     /** Is this type a subtype of that type? */
     def <:<(that: Type): boolean = {
       if (util.Statistics.enabled) subtypeCount = subtypeCount + 1
@@ -1201,6 +1205,7 @@ trait Types requires SymbolTable {
    *  Not used after phase `typer'.
    */
   case class TypeVar(origin: Type, constr: TypeConstraint) extends Type {
+    //constr.self = this //DEBUG
     override def symbol = origin.symbol
     override def toString(): String =
       if (constr.inst eq null) "<null " + origin + ">"
@@ -1520,10 +1525,19 @@ trait Types requires SymbolTable {
   /** A class expressing upper and lower bounds constraints
    *  for type variables, as well as their instantiations */
   class TypeConstraint(lo: List[Type], hi: List[Type]) {
+    //var self: Type = _ //DEBUG
     def this() = this(List(), List())
     var lobounds: List[Type] = lo
     var hibounds: List[Type] = hi
-    var inst: Type = NoType
+    private var inst: Type = NoType
+/* debug
+    private var _inst: Type = NoType
+    def inst = _inst
+    def inst_=(tp: Type) {
+      assert(tp == null || !(tp containsTp self), tp)
+      _inst = tp
+    }
+*/
 
     def instantiate(tp: Type): boolean =
       if (lobounds.forall(.<:<(tp)) && hibounds.forall(tp.<:<)) {
@@ -1835,6 +1849,18 @@ trait Types requires SymbolTable {
     }
   }
 
+  /** A map to implement the <code>contains</code> method */
+  class ContainsTypeTraverser(t: Type) extends TypeTraverser {
+    var result = false
+    def traverse(tp: Type): ContainsTypeTraverser = {
+      if (!result) {
+        if (tp eq t) result = true
+        else mapOver(tp)
+      }
+      this
+    }
+  }
+
   /** A map to implement the <code>contains</code> method */
   object ErroneousTraverser extends TypeTraverser {
     var result: boolean = _
diff --git a/src/compiler/scala/tools/nsc/typechecker/Infer.scala b/src/compiler/scala/tools/nsc/typechecker/Infer.scala
index ed1e1a04d0..c184a62784 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Infer.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Infer.scala
@@ -140,8 +140,8 @@ trait Infer requires Analyzer {
         val up = if (variance != CONTRAVARIANT) upper else !upper
         tvar.constr.inst = null
         val bound: Type = if (up) tparam.info.bounds.hi else tparam.info.bounds.lo
-        //Console.println("solveOne0 "+tvar+" "+config+" "+bound);//DEBUG
-        var cyclic = false
+        // Console.println("solveOne0 "+tvar+" "+config+" "+bound);//DEBUG
+        var cyclic = bound contains tparam
         for (val (tvar2, (tparam2, variance2)) <- config) {
           if (tparam2 != tparam &&
               ((bound contains tparam2) ||
diff --git a/src/compiler/scala/tools/nsc/typechecker/Typers.scala b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
index cfd18731b2..431d21f5f8 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Typers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
@@ -1871,14 +1871,16 @@ trait Typers requires Analyzer {
           // update `pre' to be `sym's prefix type in case it is an imported member,
           // and compute value of:
 
-          // imported symbols take precedence over package-owned symbols in different
-          // compilation units
-          if (defSym.exists && impSym.exists &&
-              defSym.owner.isPackageClass &&
-              (!currentRun.compiles(defSym) ||
-               (context.unit ne null) && defSym.sourceFile != context.unit.source.file))
-            defSym = NoSymbol
-
+          if (defSym.exists && impSym.exists) {
+            // imported symbols take precedence over package-owned symbols in different
+            // compilation units. Defined symbols take precedence over errenous imports.
+            if (defSym.owner.isPackageClass &&
+                (!currentRun.compiles(defSym) ||
+                 (context.unit ne null) && defSym.sourceFile != context.unit.source.file))
+              defSym = NoSymbol
+            else if (impSym.isError)
+              impSym = NoSymbol
+          }
           if (defSym.exists) {
             if (impSym.exists)
               ambiguousError(
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