diff options
| -rw-r--r-- | src/compiler/scala/tools/nsc/typechecker/Macros.scala | 64 | ||||
| -rw-r--r-- | test/files/run/t5923a/Macros_1.scala | 42 | ||||
| -rw-r--r-- | test/files/run/t5923c.check | 1 | ||||
| -rw-r--r-- | test/files/run/t5923c/Macros_1.scala | 39 | ||||
| -rw-r--r-- | test/files/run/t5923c/Test_2.scala | 12 | ||||
| -rw-r--r-- | test/files/run/t5923d.check | 0 | ||||
| -rw-r--r-- | test/files/run/t5923d/Macros_1.scala | 9 | ||||
| -rw-r--r-- | test/files/run/t5923d/Test_2.scala | 7 |
8 files changed, 160 insertions, 14 deletions
diff --git a/src/compiler/scala/tools/nsc/typechecker/Macros.scala b/src/compiler/scala/tools/nsc/typechecker/Macros.scala index 6b9537e27d..b3675d6a82 100644 --- a/src/compiler/scala/tools/nsc/typechecker/Macros.scala +++ b/src/compiler/scala/tools/nsc/typechecker/Macros.scala @@ -589,18 +589,23 @@ trait Macros extends FastTrack with MacroRuntimes with Traces with Helpers { /** Expands a term macro used in apply role as `M(2)(3)` in `val x = M(2)(3)`. * @see MacroExpander */ - def macroExpandApply(typer: Typer, expandee: Tree, mode: Mode, pt: Type) = { + def macroExpandApply(typer: Typer, expandee: Tree, mode: Mode, pt: Type): Tree = { object expander extends TermMacroExpander(APPLY_ROLE, typer, expandee, mode, pt) { override def onSuccess(expanded: Tree) = { // prematurely annotate the tree with a macro expansion attachment // so that adapt called indirectly by typer.typed knows that it needs to apply the existential fixup linkExpandeeAndExpanded(expandee, expanded) - var expectedTpe = expandee.tpe - if (isNullaryInvocation(expandee)) expectedTpe = expectedTpe.finalResultType + // approximation is necessary for whitebox macros to guide type inference + // read more in the comments for onDelayed below + def approximate(tp: Type) = { + val undetparams = tp collect { case tp if tp.typeSymbol.isTypeParameter => tp.typeSymbol } + deriveTypeWithWildcards(undetparams)(tp) + } + val macroPtApprox = approximate(if (isNullaryInvocation(expandee)) expandee.tpe.finalResultType else expandee.tpe) // `macroExpandApply` is called from `adapt`, where implicit conversions are disabled // therefore we need to re-enable the conversions back temporarily - if (macroDebugVerbose) println(s"typecheck #1 (against expectedTpe = $expectedTpe): $expanded") - val expanded1 = typer.context.withImplicitsEnabled(typer.typed(expanded, mode, expectedTpe)) + if (macroDebugVerbose) println(s"typecheck #1 (against macroPtApprox = $macroPtApprox): $expanded") + val expanded1 = typer.context.withImplicitsEnabled(typer.typed(expanded, mode, macroPtApprox)) if (expanded1.isErrorTyped) { if (macroDebugVerbose) println(s"typecheck #1 has failed: ${typer.context.reportBuffer.errors}") expanded1 @@ -612,6 +617,8 @@ trait Macros extends FastTrack with MacroRuntimes with Traces with Helpers { } } override def onDelayed(delayed: Tree) = { + // =========== THE SITUATION =========== + // // If we've been delayed (i.e. bailed out of the expansion because of undetermined type params present in the expandee), // then there are two possible situations we're in: // 1) We're in POLYmode, when the typer tests the waters wrt type inference @@ -627,12 +634,43 @@ trait Macros extends FastTrack with MacroRuntimes with Traces with Helpers { // the undetermined type params. Therefore we need to do something ourselves or otherwise this // expandee will forever remaing not expanded (see SI-5692). A traditional way out of this conundrum // is to call `instantiate` and let the inferencer try to find the way out. It works for simple cases, - // but sometimes, if the inferencer lacks information, it will be forced to approximate. This prevents - // an important class of macros, fundep materializers, from working, which I perceive is a problem we need to solve. - // For details see SI-7470. + // but sometimes, if the inferencer lacks information, it will be forced to approximate. + // + // =========== THE PROBLEM =========== + // + // Consider the following example (thanks, Miles!): + // + // Iso represents an isomorphism between two datatypes: + // 1) An arbitrary one (e.g. a random case class) + // 2) A uniform representation for all datatypes (e.g. an HList) + // + // trait Iso[T, U] { + // def to(t : T) : U + // def from(u : U) : T + // } + // implicit def materializeIso[T, U]: Iso[T, U] = macro ??? + // + // case class Foo(i: Int, s: String, b: Boolean) + // def foo[C, L](c: C)(implicit iso: Iso[C, L]): L = iso.to(c) + // foo(Foo(23, "foo", true)) + // + // In the snippet above, even though we know that there's a fundep going from T to U + // (in a sense that a datatype's uniform representation is unambiguously determined by the datatype, + // e.g. for Foo it will be Int :: String :: Boolean :: HNil), there's no way to convey this information + // to the typechecker. Therefore the typechecker will infer Nothing for L, which is hardly what we want. + // + // =========== THE SOLUTION =========== + // + // To give materializers a chance to say their word before vanilla inference kicks in, + // we infer as much as possible (e.g. in the example above even though L is hopeless, C still can be inferred to Foo) + // and then trigger macro expansion with the undetermined type parameters still there. + // Thanks to that the materializer can take a look at what's going on and react accordingly. val shouldInstantiate = typer.context.undetparams.nonEmpty && !mode.inPolyMode - if (shouldInstantiate) typer.instantiatePossiblyExpectingUnit(delayed, mode, pt) - else delayed + if (shouldInstantiate) { + forced += delayed + typer.infer.inferExprInstance(delayed, typer.context.extractUndetparams(), pt, keepNothings = false) + macroExpandApply(typer, delayed, mode, pt) + } else delayed } } expander(expandee) @@ -750,10 +788,12 @@ trait Macros extends FastTrack with MacroRuntimes with Traces with Helpers { * 2) undetparams (sym.isTypeParameter && !sym.isSkolem) */ var hasPendingMacroExpansions = false + private val forced = perRunCaches.newWeakSet[Tree] private val delayed = perRunCaches.newWeakMap[Tree, scala.collection.mutable.Set[Int]]() private def isDelayed(expandee: Tree) = delayed contains expandee private def calculateUndetparams(expandee: Tree): scala.collection.mutable.Set[Int] = - delayed.get(expandee).getOrElse { + if (forced(expandee)) scala.collection.mutable.Set[Int]() + else delayed.getOrElse(expandee, { val calculated = scala.collection.mutable.Set[Symbol]() expandee foreach (sub => { def traverse(sym: Symbol) = if (sym != null && (undetparams contains sym.id)) calculated += sym @@ -762,7 +802,7 @@ trait Macros extends FastTrack with MacroRuntimes with Traces with Helpers { }) macroLogVerbose("calculateUndetparams: %s".format(calculated)) calculated map (_.id) - } + }) private val undetparams = perRunCaches.newSet[Int]() def notifyUndetparamsAdded(newUndets: List[Symbol]): Unit = { undetparams ++= newUndets map (_.id) diff --git a/test/files/run/t5923a/Macros_1.scala b/test/files/run/t5923a/Macros_1.scala index 6d21362c4d..97076eb102 100644 --- a/test/files/run/t5923a/Macros_1.scala +++ b/test/files/run/t5923a/Macros_1.scala @@ -7,8 +7,46 @@ object C { } object Macros { - def impl[T: c.WeakTypeTag](c: Context) = { + def impl[T](c: Context)(ttag: c.WeakTypeTag[T]) = { import c.universe._ - reify(C[T](c.literal(weakTypeOf[T].toString).splice)) + val ttag0 = ttag; + { + // When we're expanding implicitly[C[Nothing]], the type inferencer will see + // that foo[T] returns C[T] and that we request an implicit of type C[Nothing]. + // + // Then the type inferencer will try to match C[T] against C[Nothing] and infer everything it can infer + // from that match, but not more (e.g. if we were returning Iso[T, U] and the type we were looking at was Iso[Foo, L], + // we wouldn't want U to be auto-inferred to Nothing, as it usually happens with normal methods, + // but would rather want it to remain unknown, so that our macro could take a stab at inferring it: + // see the comments in this commit for more information). + // + // Equipped with common sense, in our case of C[T] and C[Nothing] we would expect T to be inferred as Nothing, and then we + // would expect T in the corresponding macro invocation to be Nothing. Unfortunately it is not that simple. + // + // Internally the type inferencer uses Nothing as a dummy value, which stands for "don't know how to + // infer this type parameter". In the Iso example, matching Iso[T, U] against Iso[Foo, L] would result in + // T being inferred as Foo and U being inferred as Nothing (!!). Then the type inferencer will think: + // "Aha! U ended up being Nothing. This means that I failed to infer it, + // therefore the result of my work is: T -> Foo, U -> still unknown". + // + // That's all very good and works very well until Nothing is a genuine result of type inference, + // as in our original example of inferring T in C[T] from C[Nothing]. In that case, the inferencer becomes confused + // and here in the macro implementation we get weakTypeOf[T] equal to some dummy type carrying a type parameter + // instead of Nothing. + // + // This eccentric behavior of the type inferencer is a long-standing problem in scalac, + // so the best one can do for now until it's fixed is to work around, manually converting + // suspicious T's into Nothings. Of course, this means that we would have to approximate, + // because there's no way to know whether having T here stands for a failed attempt to infer Nothing + // or for a failed attempt to infer anything, but at least we're in full control of making the best + // of this sad situation. + implicit def ttag: WeakTypeTag[T] = { + val tpe = ttag0.tpe + val sym = tpe.typeSymbol.asType + if (sym.isParameter && !sym.isSkolem) TypeTag.Nothing.asInstanceOf[TypeTag[T]] + else ttag0 + } + reify(C[T](c.literal(weakTypeOf[T].toString).splice)) + } } }
\ No newline at end of file diff --git a/test/files/run/t5923c.check b/test/files/run/t5923c.check new file mode 100644 index 0000000000..bed7429108 --- /dev/null +++ b/test/files/run/t5923c.check @@ -0,0 +1 @@ +(23,foo,true) diff --git a/test/files/run/t5923c/Macros_1.scala b/test/files/run/t5923c/Macros_1.scala new file mode 100644 index 0000000000..0b7a3399e2 --- /dev/null +++ b/test/files/run/t5923c/Macros_1.scala @@ -0,0 +1,39 @@ +import language.experimental.macros +import scala.reflect.macros.Context + +trait Iso[T, U] { + def to(t : T) : U + // def from(u : U) : T +} + +object Iso { + implicit def materializeIso[T, U]: Iso[T, U] = macro impl[T, U] + def impl[T: c.WeakTypeTag, U: c.WeakTypeTag](c: Context): c.Expr[Iso[T, U]] = { + import c.universe._ + import definitions._ + import Flag._ + + val sym = c.weakTypeOf[T].typeSymbol + if (!sym.isClass || !sym.asClass.isCaseClass) c.abort(c.enclosingPosition, s"$sym is not a case class") + val fields = sym.typeSignature.declarations.toList.collect{ case x: TermSymbol if x.isVal && x.isCaseAccessor => x } + + def mkTpt() = { + val core = Ident(TupleClass(fields.length) orElse UnitClass) + if (fields.length == 0) core + else AppliedTypeTree(core, fields map (f => TypeTree(f.typeSignature))) + } + + def mkFrom() = { + if (fields.length == 0) Literal(Constant(Unit)) + else Apply(Ident(newTermName("Tuple" + fields.length)), fields map (f => Select(Ident(newTermName("f")), newTermName(f.name.toString.trim)))) + } + + val evidenceClass = ClassDef(Modifiers(FINAL), newTypeName("$anon"), List(), Template( + List(AppliedTypeTree(Ident(newTypeName("Iso")), List(Ident(sym), mkTpt()))), + emptyValDef, + List( + DefDef(Modifiers(), nme.CONSTRUCTOR, List(), List(List()), TypeTree(), Block(List(Apply(Select(Super(This(tpnme.EMPTY), tpnme.EMPTY), nme.CONSTRUCTOR), List())), Literal(Constant(())))), + DefDef(Modifiers(), newTermName("to"), List(), List(List(ValDef(Modifiers(PARAM), newTermName("f"), Ident(sym), EmptyTree))), TypeTree(), mkFrom())))) + c.Expr[Iso[T, U]](Block(List(evidenceClass), Apply(Select(New(Ident(newTypeName("$anon"))), nme.CONSTRUCTOR), List()))) + } +} diff --git a/test/files/run/t5923c/Test_2.scala b/test/files/run/t5923c/Test_2.scala new file mode 100644 index 0000000000..a00f4ed7db --- /dev/null +++ b/test/files/run/t5923c/Test_2.scala @@ -0,0 +1,12 @@ +// see the comments for macroExpandApply.onDelayed for an explanation of what's tested here +object Test extends App { + case class Foo(i: Int, s: String, b: Boolean) + def foo[C, L](c: C)(implicit iso: Iso[C, L]): L = iso.to(c) + + { + val equiv = foo(Foo(23, "foo", true)) + def typed[T](t: => T) {} + typed[(Int, String, Boolean)](equiv) + println(equiv) + } +}
\ No newline at end of file diff --git a/test/files/run/t5923d.check b/test/files/run/t5923d.check new file mode 100644 index 0000000000..e69de29bb2 --- /dev/null +++ b/test/files/run/t5923d.check diff --git a/test/files/run/t5923d/Macros_1.scala b/test/files/run/t5923d/Macros_1.scala new file mode 100644 index 0000000000..f32d1af704 --- /dev/null +++ b/test/files/run/t5923d/Macros_1.scala @@ -0,0 +1,9 @@ +import scala.language.experimental.macros +import scala.reflect.macros.Context + +trait MappedRow +trait RowMapper[T <: MappedRow] +object RowMapper { + implicit def mapper[T <: MappedRow]: RowMapper[T] = macro impl[T] + def impl[T <: MappedRow : c.WeakTypeTag](c: Context) = c.universe.reify(new RowMapper[T]{}) +}
\ No newline at end of file diff --git a/test/files/run/t5923d/Test_2.scala b/test/files/run/t5923d/Test_2.scala new file mode 100644 index 0000000000..6be10227c2 --- /dev/null +++ b/test/files/run/t5923d/Test_2.scala @@ -0,0 +1,7 @@ +class RowA extends MappedRow +class RowB extends MappedRow + +object Test extends App { + implicitly[RowMapper[RowA]] + implicitly[RowMapper[RowB]] +}
\ No newline at end of file |