Added and corrected existing comments.

Author: dragos

src/compiler/scala/tools/nsc/symtab/Types.scala

@@ -115,7 +115,7 @@ trait Types extends reflect.generic.Types { self: SymbolTable =>
     }
 
     private[Types] def record(tv: TypeVar) = {log = (tv, tv.constr.cloneInternal) :: log}
-    private[nsc] def clear() { log = List() } // TODO: what's the point of this method? -- we roll back the log (using undoTo) in the combinators below anyway, see comments at clear() calls below
+    private[nsc] def clear() { log = List() }
 
     // `block` should not affect constraints on typevars
     def undo[T](block: => T): T = {

src/compiler/scala/tools/nsc/typechecker/Typers.scala

@@ -46,6 +46,9 @@ trait Typers { self: Analyzer =>
     resetImplicits()
     transformed.clear
     superDefs.clear
+    // the log accumulates entries over time, even though it should not (Adriaan, Martin said so).
+    // Lacking a better fix, we clear it here (before the phase is created, meaning for each
+    // compiler run). This is good enough for the resident compiler, which was the most affected.
     undoLog.clear
   }