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smartersmarter
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Disallow extending PolyFunction in user code (#18920)
The `PolyFunction` trait should only be used for compiler generated encoded lambdas. Any other use case that was allowed before was accidental. In the future, we might consider supporting these if there is a good use case. This would probably require a SIP. Fixes #10075
2 parents 052bce4 + 63b31ac commit 00e9e6b

20 files changed

+99
-17
lines changed

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

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@@ -370,6 +370,7 @@ class PostTyper extends MacroTransform with InfoTransformer { thisPhase =>
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val callTrace = ref(call.symbol)(using ctx.withSource(pos.source)).withSpan(pos.span)
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cpy.Inlined(tree)(callTrace, transformSub(bindings), transform(expansion)(using inlineContext(tree)))
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case templ: Template =>
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Checking.checkPolyFunctionExtension(templ)
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withNoCheckNews(templ.parents.flatMap(newPart)) {
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forwardParamAccessors(templ)
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synthMbr.addSyntheticMembers(

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

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@@ -845,6 +845,14 @@ object Checking {
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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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/** Check that users do not extend the `PolyFunction` trait.
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* We only allow compiler generated `PolyFunction`s.
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*/
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def checkPolyFunctionExtension(templ: Template)(using Context): Unit =
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templ.parents.find(_.tpe.derivesFrom(defn.PolyFunctionClass)) match
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case Some(parent) => report.error(s"`PolyFunction` marker trait is reserved for compiler generated refinements", parent.srcPos)
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case None =>
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}
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trait Checking {

‎tests/run/erased-15.scala‎ renamed to ‎tests/neg/erased-15.scala‎

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@@ -12,7 +12,7 @@ object Test {
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}
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}
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class Foo extends PolyFunction {
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class Foo extends PolyFunction { // error
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def apply(erased x: Int): Int = {
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println("Foo.apply")
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‎tests/neg/i10075.check‎

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-- Error: tests/neg/i10075.scala:8:24 ----------------------------------------------------------------------------------
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8 |trait PolyTrait extends PolyFunction // error
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| ^^^^^^^^^^^^
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| `PolyFunction` marker trait is reserved for compiler generated refinements
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-- Error: tests/neg/i10075.scala:10:24 ---------------------------------------------------------------------------------
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10 |class PolyClass extends PolyTrait { // error
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| ^^^^^^^^^
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| `PolyFunction` marker trait is reserved for compiler generated refinements
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-- Error: tests/neg/i10075.scala:14:26 ---------------------------------------------------------------------------------
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14 |object PolyObject extends PolyFunction // error
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| ^^^^^^^^^^^^
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| `PolyFunction` marker trait is reserved for compiler generated refinements
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-- Error: tests/neg/i10075.scala:2:14 ----------------------------------------------------------------------------------
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2 |val foo = new PolyFunction { } // error
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| ^^^^^^^^^^^^
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| `PolyFunction` marker trait is reserved for compiler generated refinements
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-- Error: tests/neg/i10075.scala:3:14 ----------------------------------------------------------------------------------
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3 |val bar = new PolyFunction { def bar = 23 } // error
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| ^^^^^^^^^^^^
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| `PolyFunction` marker trait is reserved for compiler generated refinements
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-- Error: tests/neg/i10075.scala:4:14 ----------------------------------------------------------------------------------
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4 |val baz = new PolyFunction { def apply = 23 } // error
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| ^^^^^^^^^^^^
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| `PolyFunction` marker trait is reserved for compiler generated refinements
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-- Error: tests/neg/i10075.scala:5:14 ----------------------------------------------------------------------------------
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5 |val qux = new PolyFunction { def apply[T] = 47 } // error
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| ^^^^^^^^^^^^
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| `PolyFunction` marker trait is reserved for compiler generated refinements
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-- Error: tests/neg/i10075.scala:6:15 ----------------------------------------------------------------------------------
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6 |val quxx = new PolyFunction { def apply[T](x: T): T = x } // error
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| ^^^^^^^^^^^^
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| `PolyFunction` marker trait is reserved for compiler generated refinements

‎tests/neg/i10075.scala‎

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@@ -0,0 +1,14 @@
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val poly = [T] => (x: T) => x
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val foo = new PolyFunction { } // error
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val bar = new PolyFunction { def bar = 23 } // error
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val baz = new PolyFunction { def apply = 23 } // error
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val qux = new PolyFunction { def apply[T] = 47 } // error
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val quxx = new PolyFunction { def apply[T](x: T): T = x } // error
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trait PolyTrait extends PolyFunction // error
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class PolyClass extends PolyTrait { // error
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def apply[T](x: T): T = x
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}
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object PolyObject extends PolyFunction // error

‎tests/neg/i10369.scala‎

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type Upgrade[T] = T match
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case Int => Double
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case Char => String
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case Boolean => Boolean
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val upgrade: [t] => t => Upgrade[t] = new PolyFunction: // error
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def apply[T](x: T): Upgrade[T] = x match
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case x: Int => x.toDouble
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case x: Char => x.toString
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case x: Boolean => !x

‎tests/pos/i18302a.scala‎ renamed to ‎tests/neg/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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new PolyFunction { def apply(x: Int): Int = x + 1 } // error

‎tests/neg/i18302b.check‎

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@@ -2,3 +2,7 @@
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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.
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-- Error: tests/neg/i18302b.scala:4:6 ----------------------------------------------------------------------------------
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4 | new PolyFunction: // error
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| ^^^^^^^^^^^^
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| `PolyFunction` marker trait is reserved for compiler generated refinements

‎tests/neg/i18302b.scala‎

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@@ -1,5 +1,5 @@
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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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new PolyFunction: // error
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def apply(x: Int)(y: Int): Int = x + y

‎tests/neg/i18302c.check‎

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@@ -2,3 +2,7 @@
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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
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-- Error: tests/neg/i18302c.scala:5:6 ----------------------------------------------------------------------------------
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5 | new PolyFunction { def foo(x: Int): Int = x + 1 } // error
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| ^^^^^^^^^^^^
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| `PolyFunction` marker trait is reserved for compiler generated refinements

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