Don't want to chase NPEs around for the rest of...

Don't want to chase NPEs around for the rest of my life. Created
"NoCompilationUnit" and "NoSourceFile" objects to represent not-present
versions of these items. Seems a lot better than null. References
SI-4859, got past NPE only to uncover the actual problem. No review.

1 files changed, 8 insertions, 9 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Contexts.scala b/src/compiler/scala/tools/nsc/typechecker/Contexts.scala
index 96b27b58ae..44c28cf2f5 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Contexts.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Contexts.scala
@@ -21,6 +21,7 @@ trait Contexts { self: Analyzer =>
   val NoContext = new Context {
     override def implicitss: List[List[ImplicitInfo]] = List()
     outer = this
+    override def toString = "NoContext"
   }
   NoContext.enclClass = NoContext
   NoContext.enclMethod = NoContext
@@ -89,7 +90,7 @@ trait Contexts { self: Analyzer =>
   }
 
   class Context private[typechecker] {
-    var unit: CompilationUnit = _
+    var unit: CompilationUnit = NoCompilationUnit
     var tree: Tree = _                      // Tree associated with this context
     var owner: Symbol = NoSymbol            // The current owner
     var scope: Scope = _                    // The current scope
@@ -164,12 +165,11 @@ trait Contexts { self: Analyzer =>
      */
     def make(unit: CompilationUnit, tree: Tree, owner: Symbol,
              scope: Scope, imports: List[ImportInfo]): Context = {
-      val c = new Context
-      c.unit = unit
-      c.tree = tree
+      val c   = new Context
+      c.unit  = unit
+      c.tree  = tree
       c.owner = owner
       c.scope = scope
-
       c.outer = this
 
       tree match {
@@ -203,6 +203,7 @@ trait Contexts { self: Analyzer =>
       c.retyping = this.retyping
       c.openImplicits = this.openImplicits
       registerContext(c.asInstanceOf[analyzer.Context])
+      debuglog("Created context: " + this + " ==> " + c)
       c
     }
 
@@ -364,11 +365,9 @@ trait Contexts { self: Analyzer =>
     def nextEnclosing(p: Context => Boolean): Context =
       if (this == NoContext || p(this)) this else outer.nextEnclosing(p)
 
-    override def toString = (
-      if (this == NoContext) "NoContext"
-      else "Context(%s@%s scope=%s)".format(owner.fullName, tree.getClass.getName split "[.$]" last, scope.##)
+    override def toString = "Context(%s@%s unit=%s scope=%s)".format(
+      owner.fullName, tree.shortClass, unit, scope.##
     )
-
     /** Is `sub` a subclass of `base` or a companion object of such a subclass?
      */
     def isSubClassOrCompanion(sub: Symbol, base: Symbol) =