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WojciechMazurWojciechMazur
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Check user defined PolyFunction refinements
`PolyFunction` must be refined with an `apply` method that has a single parameter list with no by-name nor varargs parameters. It may optionally have type parameters. Some of these restrictions could be lifted later, but for now these features are not properly handled by the compiler. Fixes #8299 Fixes #18302 [Cherry-picked e5ca0c4][modified]
1 parent e056b2e commit 82ff24f

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

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@@ -1157,6 +1157,17 @@ class Definitions {
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if tpe.refinedName == nme.apply && tpe.parent.derivesFrom(defn.PolyFunctionClass) =>
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Some(mt)
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case _ => None
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def isValidPolyFunctionInfo(info: Type)(using Context): Boolean =
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def isValidMethodType(info: Type) = info match
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case info: MethodType =>
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!info.resType.isInstanceOf[MethodOrPoly] && // Has only one parameter list
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!info.isVarArgsMethod &&
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!info.paramInfos.exists(_.isInstanceOf[ExprType]) // No by-name parameters
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case _ => false
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info match
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case info: PolyType => isValidMethodType(info.resType)
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case _ => isValidMethodType(info)
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}
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object ErasedFunctionOf {

‎compiler/src/dotty/tools/dotc/transform/PostTyper.scala

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@@ -375,13 +375,15 @@ class PostTyper extends MacroTransform with IdentityDenotTransformer { thisPhase
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case tree: ValDef =>
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registerIfHasMacroAnnotations(tree)
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checkErasedDef(tree)
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Checking.checkPolyFunctionType(tree.tpt)
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val tree1 = cpy.ValDef(tree)(rhs = normalizeErasedRhs(tree.rhs, tree.symbol))
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if tree1.removeAttachment(desugar.UntupledParam).isDefined then
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checkStableSelection(tree.rhs)
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processValOrDefDef(super.transform(tree1))
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case tree: DefDef =>
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registerIfHasMacroAnnotations(tree)
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checkErasedDef(tree)
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Checking.checkPolyFunctionType(tree.tpt)
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annotateContextResults(tree)
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val tree1 = cpy.DefDef(tree)(rhs = normalizeErasedRhs(tree.rhs, tree.symbol))
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processValOrDefDef(superAcc.wrapDefDef(tree1)(super.transform(tree1).asInstanceOf[DefDef]))
@@ -483,6 +485,9 @@ class PostTyper extends MacroTransform with IdentityDenotTransformer { thisPhase
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)
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case Block(_, Closure(_, _, tpt)) if ExpandSAMs.needsWrapperClass(tpt.tpe) =>
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superAcc.withInvalidCurrentClass(super.transform(tree))
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case tree: RefinedTypeTree =>
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Checking.checkPolyFunctionType(tree)
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super.transform(tree)
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case _: Quote =>
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ctx.compilationUnit.needsStaging = true
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super.transform(tree)

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

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@@ -804,6 +804,31 @@ object Checking {
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else Feature.checkExperimentalFeature("features", imp.srcPos)
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case _ =>
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end checkExperimentalImports
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/** Checks that PolyFunction only have valid refinements.
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*
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* It only supports `apply` methods with one parameter list and optional type arguments.
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*/
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def checkPolyFunctionType(tree: Tree)(using Context): Unit = new TreeTraverser {
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def traverse(tree: Tree)(using Context): Unit = tree match
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case tree: RefinedTypeTree if tree.tpe.derivesFrom(defn.PolyFunctionClass) =>
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if tree.refinements.isEmpty then
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reportNoRefinements(tree.srcPos)
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tree.refinements.foreach {
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case refinement: DefDef if refinement.name != nme.apply =>
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report.error("PolyFunction only supports apply method refinements", refinement.srcPos)
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case refinement: DefDef if !defn.PolyFunctionOf.isValidPolyFunctionInfo(refinement.tpe.widen) =>
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report.error("Implementation restriction: PolyFunction apply must have exactly one parameter list and optionally type arguments. No by-name nor varags are allowed.", refinement.srcPos)
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case _ =>
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}
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case _: RefTree if tree.symbol == defn.PolyFunctionClass =>
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reportNoRefinements(tree.srcPos)
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case _ =>
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traverseChildren(tree)
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def reportNoRefinements(pos: SrcPos) =
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report.error("PolyFunction subtypes must refine the apply method", pos)
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}.traverse(tree)
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}
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trait Checking {

‎tests/neg/i18302b.check

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-- Error: tests/neg/i18302b.scala:3:32 ---------------------------------------------------------------------------------
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3 |def polyFun: PolyFunction { def apply(x: Int)(y: Int): Int } = // error
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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|Implementation restriction: PolyFunction apply must have exactly one parameter list and optionally type arguments. No by-name nor varags are allowed.

‎tests/neg/i18302b.scala

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def test = polyFun(1)(2)
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def polyFun: PolyFunction { def apply(x: Int)(y: Int): Int } = // error
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new PolyFunction:
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def apply(x: Int)(y: Int): Int = x + y

‎tests/neg/i18302c.check

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-- Error: tests/neg/i18302c.scala:4:32 ---------------------------------------------------------------------------------
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4 |def polyFun: PolyFunction { def foo(x: Int): Int } = // error
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| ^^^^^^^^^^^^^^^^^^^^
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| PolyFunction only supports apply method refinements

‎tests/neg/i18302c.scala

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import scala.reflect.Selectable.reflectiveSelectable
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def test = polyFun.foo(1)
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def polyFun: PolyFunction { def foo(x: Int): Int } = // error
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new PolyFunction { def foo(x: Int): Int = x + 1 }

‎tests/neg/i18302d.check

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-- Error: tests/neg/i18302d.scala:1:32 ---------------------------------------------------------------------------------
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1 |def polyFun: PolyFunction { def apply: Int } = // error
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| ^^^^^^^^^^^^^^
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|Implementation restriction: PolyFunction apply must have exactly one parameter list and optionally type arguments. No by-name nor varags are allowed.

‎tests/neg/i18302d.scala

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def polyFun: PolyFunction { def apply: Int } = // error
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new PolyFunction { def apply: Int = 1 }

‎tests/neg/i18302e.check

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-- Error: tests/neg/i18302e.scala:1:13 ---------------------------------------------------------------------------------
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1 |def polyFun: PolyFunction { } = // error
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| ^^^^^^^^^^^^^^^^^
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| PolyFunction subtypes must refine the apply method
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-- Error: tests/neg/i18302e.scala:4:15 ---------------------------------------------------------------------------------
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4 |def polyFun(f: PolyFunction { }) = () // error
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| ^^^^^^^^^^^^^^^^^
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| PolyFunction subtypes must refine the apply method

‎tests/neg/i18302e.scala

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def polyFun: PolyFunction { } = // error
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new PolyFunction { }
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def polyFun(f: PolyFunction { }) = () // error

‎tests/neg/i18302f.check

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-- Error: tests/neg/i18302f.scala:1:13 ---------------------------------------------------------------------------------
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1 |def polyFun: PolyFunction = // error
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| ^^^^^^^^^^^^
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| PolyFunction subtypes must refine the apply method
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-- Error: tests/neg/i18302f.scala:4:16 ---------------------------------------------------------------------------------
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4 |def polyFun2(a: PolyFunction) = () // error
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| ^^^^^^^^^^^^
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| PolyFunction subtypes must refine the apply method
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-- Error: tests/neg/i18302f.scala:6:14 ---------------------------------------------------------------------------------
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6 |val polyFun3: PolyFunction = // error
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| ^^^^^^^^^^^^
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| PolyFunction subtypes must refine the apply method

‎tests/neg/i18302f.scala

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def polyFun: PolyFunction = // error
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new PolyFunction { }
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def polyFun2(a: PolyFunction) = () // error
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val polyFun3: PolyFunction = // error
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new PolyFunction { }

‎tests/neg/i18302i.scala

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def polyFun1: Option[PolyFunction] = ??? // error
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def polyFun2: PolyFunction & Any = ??? // error
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def polyFun3: Any & PolyFunction = ??? // error
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def polyFun4: PolyFunction | Any = ??? // error
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def polyFun5: Any | PolyFunction = ??? // error
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def polyFun6(a: Any | PolyFunction) = ??? // error

‎tests/neg/i18302j.scala

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def polyFunByName: PolyFunction { def apply(thunk: => Int): Int } = // error
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new PolyFunction { def apply(thunk: => Int): Int = 1 }
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def polyFunVarArgs: PolyFunction { def apply(args: Int*): Int } = // error
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new PolyFunction { def apply(thunk: Int*): Int = 1 }

‎tests/neg/i8299.scala

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package example
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object Main {
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def main(a: Array[String]): Unit = {
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val p: PolyFunction = // error: PolyFunction subtypes must refine the apply method
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[A] => (xs: List[A]) => xs.headOption
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}
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}

‎tests/pos/i18302a.scala

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def test = polyFun(1)
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def polyFun: PolyFunction { def apply(x: Int): Int } =
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new PolyFunction { def apply(x: Int): Int = x + 1 }

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