Fix #3538: Better invalidation of typed arguments in FunProtos

compiler/src/dotty/tools/dotc/core/Constraint.scala

@@ -144,4 +144,10 @@ abstract class Constraint extends Showable {
 
   /** Check that constraint only refers to TypeParamRefs bound by itself */
   def checkClosed()(implicit ctx: Context): Unit
+
+  /** Constraint has not yet been retracted from a typer state */
+  def isRetracted: Boolean
+
+  /** Indicate that constraint has been retracted from a typer state */
+  def markRetracted(): Unit
 }

compiler/src/dotty/tools/dotc/core/OrderingConstraint.scala

@@ -570,6 +570,14 @@ class OrderingConstraint(private val boundsMap: ParamBounds,
   private def checkNonCyclic(param: TypeParamRef)(implicit ctx: Context): Unit =
     assert(!isLess(param, param), i"cyclic constraint involving $param in $this")
 
+// ---------- Invalidation -------------------------------------------
+
+  private var retracted = false
+
+  def isRetracted: Boolean = retracted
+
+  def markRetracted(): Unit = retracted = true
+
 // ---------- toText -----------------------------------------------------
 
   override def toText(printer: Printer): Text = {

compiler/src/dotty/tools/dotc/core/TypeComparer.scala

@@ -118,7 +118,7 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
           if (recCount < Config.LogPendingSubTypesThreshold) firstTry(tp1, tp2)
           else monitoredIsSubType(tp1, tp2)
         recCount = recCount - 1
-        if (!result) constraint = saved
+        if (!result) state.resetConstraintTo(saved)
         else if (recCount == 0 && needsGc) {
           state.gc()
           needsGc = false
@@ -129,7 +129,7 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
         case NonFatal(ex) =>
           if (ex.isInstanceOf[AssertionError]) showGoal(tp1, tp2)
           recCount -= 1
-          constraint = saved
+          state.resetConstraintTo(saved)
           successCount = savedSuccessCount
           throw ex
       }

compiler/src/dotty/tools/dotc/core/TyperState.scala

@@ -33,6 +33,12 @@ class TyperState(previous: TyperState /* | Null */) extends DotClass with Showab
     myConstraint = c
   }
 
+  /** Reset constraint to `c` and mark current constraint as retracted if it differs from `c` */
+  def resetConstraintTo(c: Constraint) = {
+    if (c `ne` myConstraint) myConstraint.markRetracted()
+    myConstraint = c
+  }
+
   private val previousConstraint =
     if (previous == null) constraint else previous.constraint
 
@@ -90,8 +96,8 @@ class TyperState(previous: TyperState /* | Null */) extends DotClass with Showab
 
   /** Test using `op`, restoring typerState to previous state afterwards */
   def test[T](op: => T): T = {
-    val savedReporter = myReporter
     val savedConstraint = myConstraint
+    val savedReporter = myReporter
     val savedCommittable = myIsCommittable
     val savedCommitted = isCommitted
     myIsCommittable = false
@@ -105,8 +111,8 @@ class TyperState(previous: TyperState /* | Null */) extends DotClass with Showab
     }
     try op
     finally {
+      resetConstraintTo(savedConstraint)
       myReporter = savedReporter
-      myConstraint = savedConstraint
       myIsCommittable = savedCommittable
       isCommitted = savedCommitted
     }

compiler/src/dotty/tools/dotc/typer/ProtoTypes.scala

@@ -67,7 +67,7 @@ object ProtoTypes {
         case _ =>
           true
       }
-      if (!res) ctx.typerState.constraint = savedConstraint
+      if (!res) ctx.typerState.resetConstraintTo(savedConstraint)
       res
     }
   }
@@ -183,8 +183,8 @@ object ProtoTypes {
     /** A map in which typed arguments can be stored to be later integrated in `typedArgs`. */
     private[this] var myTypedArg: SimpleIdentityMap[untpd.Tree, Tree] = SimpleIdentityMap.Empty
 
-    /** A map recording the typer states in which arguments stored in myTypedArg were typed */
-    private[this] var evalState: SimpleIdentityMap[untpd.Tree, TyperState] = SimpleIdentityMap.Empty
+    /** A map recording the typer states and constraints in which arguments stored in myTypedArg were typed */
+    private[this] var evalState: SimpleIdentityMap[untpd.Tree, (TyperState, Constraint)] = SimpleIdentityMap.Empty
 
     def isMatchedBy(tp: Type)(implicit ctx: Context) =
       typer.isApplicable(tp, Nil, typedArgs, resultType)
@@ -195,17 +195,19 @@ object ProtoTypes {
 
     override def notApplied = WildcardType
 
-    /** Forget the types of any arguments that have been typed producing a constraint in a
-     *  typer state that is not yet committed into the one of the current context `ctx`.
+    /** Forget the types of any arguments that have been typed producing a constraint
+     *    - that is in a typer state that is not yet committed into the one of the current context `ctx`,
+     *    - or that has been retracted from its typestate because oif a failed operation.
      *  This is necessary to avoid "orphan" TypeParamRefs that are referred to from
      *  type variables in the typed arguments, but that are not registered in the
-     *  current constraint. A test case is pos/t1756.scala.
+     *  current constraint. Test cases are pos/t1756.scala and pos/i3538.scala.
      *  @return True if all arguments have types (in particular, no types were forgotten).
      */
     def allArgTypesAreCurrent()(implicit ctx: Context): Boolean = {
-      evalState foreachBinding { (arg, tstate) =>
-        if (tstate.uncommittedAncestor.constraint ne ctx.typerState.constraint) {
-          typr.println(i"need to invalidate $arg / ${myTypedArg(arg)}, ${tstate.constraint}, current = ${ctx.typerState.constraint}")
+      evalState foreachBinding { (arg, tstateConstr) =>
+        if ((tstateConstr._1.uncommittedAncestor.constraint `ne` ctx.typerState.constraint) ||
+            tstateConstr._2.isRetracted) {
+          typr.println(i"need to invalidate $arg / ${myTypedArg(arg)}, ${tstateConstr._2}, current = ${ctx.typerState.constraint}")
           myTypedArg = myTypedArg.remove(arg)
           evalState = evalState.remove(arg)
         }
@@ -219,7 +221,7 @@ object ProtoTypes {
         targ = typerFn(arg)
         if (!ctx.reporter.hasPending) {
           myTypedArg = myTypedArg.updated(arg, targ)
-          evalState = evalState.updated(arg, ctx.typerState)
+          evalState = evalState.updated(arg, (ctx.typerState, ctx.typerState.constraint))
         }
       }
       targ

tests/pos/i3538.scala

@@ -0,0 +1,15 @@
+
+class Inv[T]
+
+class Test {
+  implicit class Wrong(test: Test) {
+    def right: Any = ???
+  }
+  implicit class Right(test: Test) {
+    def right(node: Any): Any = ???
+  }
+
+  def inv[T](x: T): Inv[T] = ???
+
+  (this).right(inv(1))
+}