Map regular function types to impure function types when unpickling

Map regular function types to impure function types when unpickling a class
under -Ycc that was not itself compiled with -Ycc.

Author: odersky

compiler/src/dotty/tools/dotc/cc/CaptureOps.scala

@@ -5,7 +5,7 @@ package cc
 import core.*
 import Types.*, Symbols.*, Contexts.*, Annotations.*
 import ast.{tpd, untpd}
-import Decorators.*
+import Decorators.*, NameOps.*
 import config.Printers.capt
 import util.Property.Key
 import tpd.*
@@ -71,3 +71,17 @@ extension (tp: Type)
       atd.derivedAnnotatedType(parent.stripCapturing, annot)
     case _ =>
       tp
+
+  /** Under -Ycc, map regular function type to impure function type
+   */
+  def adaptFunctionType(using Context): Type = tp match
+    case AppliedType(fn, args)
+    if ctx.settings.Ycc.value && defn.isFunctionClass(fn.typeSymbol) =>
+      val fname = fn.typeSymbol.name
+      defn.FunctionType(
+        fname.functionArity,
+        isContextual = fname.isContextFunction,
+        isErased = fname.isErasedFunction,
+        isImpure = true).appliedTo(args)
+    case _ =>
+      tp

compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala

@@ -31,6 +31,7 @@ import ast.{TreeTypeMap, Trees, tpd, untpd}
 import Trees._
 import Decorators._
 import transform.SymUtils._
+import cc.adaptFunctionType
 
 import dotty.tools.tasty.{TastyBuffer, TastyReader}
 import TastyBuffer._
@@ -87,6 +88,9 @@ class TreeUnpickler(reader: TastyReader,
   /** The root owner tree. See `OwnerTree` class definition. Set by `enterTopLevel`. */
   private var ownerTree: OwnerTree = _
 
+  /** Was unpickled class compiled with -Ycc? */
+  private var wasCaptureChecked: Boolean = false
+
   private def registerSym(addr: Addr, sym: Symbol) =
     symAtAddr(addr) = sym
 
@@ -357,7 +361,7 @@ class TreeUnpickler(reader: TastyReader,
                 // Note that the lambda "rt => ..." is not equivalent to a wildcard closure!
                 // Eta expansion of the latter puts readType() out of the expression.
             case APPLIEDtype =>
-              readType().appliedTo(until(end)(readType()))
+              postProcessFunction(readType().appliedTo(until(end)(readType())))
             case TYPEBOUNDS =>
               val lo = readType()
               if nothingButMods(end) then
@@ -470,6 +474,12 @@ class TreeUnpickler(reader: TastyReader,
     def readTermRef()(using Context): TermRef =
       readType().asInstanceOf[TermRef]
 
+    /** Under -Ycc, map all function types to impure function types,
+     *  unless the unpickled class was also compiled with -Ycc.
+     */
+    private def postProcessFunction(tp: Type)(using Context): Type =
+      if wasCaptureChecked then tp else tp.adaptFunctionType
+
 // ------ Reading definitions -----------------------------------------------------
 
     private def nothingButMods(end: Addr): Boolean =
@@ -605,6 +615,8 @@ class TreeUnpickler(reader: TastyReader,
       }
       registerSym(start, sym)
       if (isClass) {
+        if sym.owner.is(Package) && annots.exists(_.symbol == defn.CaptureCheckedAnnot) then
+          wasCaptureChecked = true
         sym.completer.withDecls(newScope)
         forkAt(templateStart).indexTemplateParams()(using localContext(sym))
       }
@@ -1265,7 +1277,7 @@ class TreeUnpickler(reader: TastyReader,
               val args = until(end)(readTpt())
               val tree = untpd.AppliedTypeTree(tycon, args)
               val ownType = ctx.typeAssigner.processAppliedType(tree, tycon.tpe.safeAppliedTo(args.tpes))
-              tree.withType(ownType)
+              tree.withType(postProcessFunction(ownType))
             case ANNOTATEDtpt =>
               Annotated(readTpt(), readTerm())
             case LAMBDAtpt =>

compiler/src/dotty/tools/dotc/core/unpickleScala2/Scala2Unpickler.scala

@@ -30,6 +30,7 @@ import scala.collection.mutable
 import scala.collection.mutable.ListBuffer
 import scala.annotation.switch
 import reporting._
+import cc.adaptFunctionType
 
 object Scala2Unpickler {
 
@@ -818,7 +819,9 @@ class Scala2Unpickler(bytes: Array[Byte], classRoot: ClassDenotation, moduleClas
           // special-case in erasure, see TypeErasure#eraseInfo.
           OrType(args(0), args(1), soft = false)
         }
-        else if (args.nonEmpty) tycon.safeAppliedTo(EtaExpandIfHK(sym.typeParams, args.map(translateTempPoly)))
+        else if args.nonEmpty then
+          tycon.safeAppliedTo(EtaExpandIfHK(sym.typeParams, args.map(translateTempPoly)))
+            .adaptFunctionType
         else if (sym.typeParams.nonEmpty) tycon.EtaExpand(sym.typeParams)
         else tycon
       case TYPEBOUNDStpe =>

tests/pos-custom-args/captures/capt-separate/Lib_1.scala

@@ -0,0 +1,6 @@
+object Lib:
+  extension [A](xs: Seq[A])
+    def mapp[B](f: A => B): Seq[B] =
+      xs.map(f.asInstanceOf[A -> B])
+
+

tests/pos-custom-args/captures/capt-separate/Test_2.scala

@@ -0,0 +1,15 @@
+import language.experimental.saferExceptions
+import Lib.*
+
+class LimitExceeded extends Exception
+
+val limit = 10e9
+
+def f(x: Double): Double throws LimitExceeded =
+  if x < limit then x * x else throw LimitExceeded()
+
+@main def test(xs: Double*) =
+  try println(xs.mapp(f).sum)
+  catch case ex: LimitExceeded => println("too large")
+
+

tests/pos-custom-args/captures/saferExceptions.scala

@@ -0,0 +1,18 @@
+import language.experimental.saferExceptions
+
+class LimitExceeded extends Exception
+
+val limit = 10e9
+
+extension [A](xs: Seq[A])
+  def mapp[B](f: A => B): Seq[B] =
+    xs.map(f.asInstanceOf[A -> B])
+
+def f(x: Double): Double throws LimitExceeded =
+  if x < limit then x * x else throw LimitExceeded()
+
+@main def test(xs: Double*) =
+  try println(xs.mapp(f).sum + xs.map(f).sum)
+  catch case ex: LimitExceeded => println("too large")
+
+