SI-6829, SI-6788, NPEs during erroneous compilation.

Have to intercept trees which have a null type due to errors
before they leave the warm confines of 'def typed' because from
that point everything assumes tree.tpe != null.

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

@@ -5264,7 +5264,7 @@ trait Typers extends Modes with Adaptations with Tags {
 
       def typedDocDef(docdef: DocDef) = {
         if (forScaladoc && (sym ne null) && (sym ne NoSymbol)) {
-          val comment = docdef.comment          
+          val comment = docdef.comment
           docComments(sym) = comment
           comment.defineVariables(sym)
           val typer1 = newTyper(context.makeNewScope(tree, context.owner))
@@ -5595,12 +5595,18 @@ trait Typers extends Modes with Adaptations with Tags {
               "context.owner"    -> context.owner
             )
           )
-          val tree1 = typed1(tree, mode, dropExistential(pt))
+          typed1(tree, mode, dropExistential(pt))
+        }
+        // Can happen during erroneous compilation - error(s) have been
+        // reported, but we need to avoid causing an NPE with this tree
+        if (tree1.tpe eq null)
+          return setError(tree)
+
+        if (!alreadyTyped) {
           printTyping("typed %s: %s%s".format(
             ptTree(tree1), tree1.tpe,
             if (isSingleType(tree1.tpe)) " with underlying "+tree1.tpe.widen else "")
           )
-          tree1
         }
 
         tree1.tpe = addAnnotations(tree1, tree1.tpe)

test/files/neg/t6788.check

@@ -0,0 +1,5 @@
+t6788.scala:6: error: not found: value foo
+Error occurred in an application involving default arguments.
+  s.copy(b = foo)
+             ^
+one error found

test/files/neg/t6788.scala

@@ -0,0 +1,7 @@
+case class B[T](b: T, a: List[Int]) // need two args, B must be polymorphic
+
+class A {
+  var s: B[Int] = _ // has to be a var
+
+  s.copy(b = foo)
+}

test/files/neg/t6829.check

@@ -0,0 +1,36 @@
+t6829.scala:35: error: type mismatch;
+ found   : AgentSimulation.this.state.type (with underlying type G#State)
+ required: _10.State
+    lazy val actions: Map[G#Agent,G#Action] = agents.map(a => a -> a.chooseAction(state)).toMap
+                                                                                  ^
+t6829.scala:45: error: trait AgentSimulation takes type parameters
+                                               pastHistory: List[G#State] = Nil) extends AgentSimulation
+                                                                                         ^
+t6829.scala:47: error: class LearningSimulation takes type parameters
+    lazy val step: LearningSimulation = {
+                   ^
+t6829.scala:49: error: not found: value actions
+        val (s,a,s2) = (state,actions(agent),nextState)
+                              ^
+t6829.scala:49: error: not found: value nextState
+        val (s,a,s2) = (state,actions(agent),nextState)
+                                             ^
+t6829.scala:50: error: type mismatch;
+ found   : s.type (with underlying type Any)
+ required: _54.State where val _54: G
+        val r = rewards(agent).r(s,a,s2)
+                                 ^
+t6829.scala:51: error: type mismatch;
+ found   : s.type (with underlying type Any)
+ required: _51.State
+        agent.learn(s,a,s2,r): G#Agent
+                    ^
+t6829.scala:53: error: not found: value nextState
+Error occurred in an application involving default arguments.
+      copy(agents = updatedAgents, state = nextState, pastHistory = currentHistory)
+                                           ^
+t6829.scala:53: error: not found: value currentHistory
+Error occurred in an application involving default arguments.
+      copy(agents = updatedAgents, state = nextState, pastHistory = currentHistory)
+                                                                    ^
+9 errors found

test/files/neg/t6829.scala

@@ -0,0 +1,64 @@
+package bugs
+
+/**
+  * Created with IntelliJ IDEA.
+  * User: arya
+  * Date: 12/18/12
+  * Time: 4:17 PM
+  * To change this template use File | Settings | File Templates.
+  */
+object currenttype2 {
+
+   type Reward = Double
+
+   trait AbstractAgent[State,Action] {
+     type A = AbstractAgent[State,Action]
+     def chooseAction(s: State): Action
+     def startEpisode: A = this
+     def learn(s1: State, a: Action, s2: State, r: Reward): A
+   }
+
+   case class RewardFunction[State,Action](r: (State,Action,State) => Reward)
+
+  trait Rules[G<:GameDomain] {
+    def simulate(state: G#State, agentActions: List[(G#Agent,G#Action)]): G#State
+  }
+
+  trait AgentSimulation[G<:GameDomain] {
+    val agents: List[G#Agent]
+    val state: G#State
+    val rewards: Map[G#Agent,G#Rewards]
+    val rules: Rules[G]
+    val pastHistory: List[G#State]
+    lazy val currentHistory = state :: pastHistory
+
+    lazy val actions: Map[G#Agent,G#Action] = agents.map(a => a -> a.chooseAction(state)).toMap
+    lazy val nextState: G#State = rules.simulate(state, actions.toList)
+
+    def step: AgentSimulation[G]
+  }
+
+  case class LearningSimulation[G<:GameDomain](agents: List[G#Agent],
+                                               state: G#State,
+                                               rewards: Map[G#Agent,G#Rewards],
+                                               rules: Rules[G],
+                                               pastHistory: List[G#State] = Nil) extends AgentSimulation
+  {
+    lazy val step: LearningSimulation = {
+      val updatedAgents: List[G#Agent] = agents map { agent =>
+        val (s,a,s2) = (state,actions(agent),nextState)
+        val r = rewards(agent).r(s,a,s2)
+        agent.learn(s,a,s2,r): G#Agent
+      }
+      copy(agents = updatedAgents, state = nextState, pastHistory = currentHistory)
+    }
+  }
+
+   trait GameDomain {
+     domain =>
+     type State
+     type Action
+     type Agent = AbstractAgent[State, Action] // agent supertype
+     type Rewards = RewardFunction[State,Action]
+   }
+ }