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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

Diff for: ‎compiler/src/dotty/tools/dotc/transform/PostTyper.scala

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Original file line numberDiff line numberDiff line change
@@ -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(

Diff for: ‎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 {

Diff for: ‎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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Diff for: ‎tests/neg/i10075.check

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@@ -0,0 +1,32 @@
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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

Diff for: ‎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

Diff for: ‎tests/neg/i10369.scala

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@@ -0,0 +1,10 @@
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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

Diff for: ‎tests/pos/i18302a.scala renamed to ‎tests/neg/i18302a.scala

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@@ -1,4 +1,4 @@
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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

Diff for: ‎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

Diff for: ‎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

Diff for: ‎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

Diff for: ‎tests/neg/i18302c.scala

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Original file line numberDiff line numberDiff line change
@@ -2,4 +2,4 @@ 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 }
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new PolyFunction { def foo(x: Int): Int = x + 1 } // error

Diff for: ‎tests/neg/i18302d.check

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@@ -2,3 +2,7 @@
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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.
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-- Error: tests/neg/i18302d.scala:2:6 ----------------------------------------------------------------------------------
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2 | new PolyFunction { def apply: Int = 1 } // error
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| ^^^^^^^^^^^^
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| `PolyFunction` marker trait is reserved for compiler generated refinements

Diff for: ‎tests/neg/i18302d.scala

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@@ -1,2 +1,2 @@
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def polyFun: PolyFunction { def apply: Int } = // error
2-
new PolyFunction { def apply: Int = 1 }
2+
new PolyFunction { def apply: Int = 1 } // error

Diff for: ‎tests/neg/i18302e.check

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@@ -2,6 +2,10 @@
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1 |def polyFun: PolyFunction { } = // error
33
| ^^^^^^^^^^^^^^^^^
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| PolyFunction subtypes must refine the apply method
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-- Error: tests/neg/i18302e.scala:2:6 ----------------------------------------------------------------------------------
6+
2 | new PolyFunction { } // error
7+
| ^^^^^^^^^^^^
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| `PolyFunction` marker trait is reserved for compiler generated refinements
59
-- Error: tests/neg/i18302e.scala:4:15 ---------------------------------------------------------------------------------
610
4 |def polyFun(f: PolyFunction { }) = () // error
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| ^^^^^^^^^^^^^^^^^

Diff for: ‎tests/neg/i18302e.scala

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@@ -1,4 +1,4 @@
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def polyFun: PolyFunction { } = // error
2-
new PolyFunction { }
2+
new PolyFunction { } // error
33

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

Diff for: ‎tests/neg/i18302f.check

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@@ -2,6 +2,10 @@
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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:2:6 ----------------------------------------------------------------------------------
6+
2 | new PolyFunction { } // error
7+
| ^^^^^^^^^^^^
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| `PolyFunction` marker trait is reserved for compiler generated refinements
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-- Error: tests/neg/i18302f.scala:4:16 ---------------------------------------------------------------------------------
610
4 |def polyFun2(a: PolyFunction) = () // error
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| ^^^^^^^^^^^^
@@ -10,3 +14,7 @@
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6 |val polyFun3: 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:7:6 ----------------------------------------------------------------------------------
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7 | new PolyFunction { } // error
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| ^^^^^^^^^^^^
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| `PolyFunction` marker trait is reserved for compiler generated refinements

Diff for: ‎tests/neg/i18302f.scala

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@@ -1,7 +1,7 @@
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def polyFun: PolyFunction = // error
2-
new PolyFunction { }
2+
new PolyFunction { } // error
33

44
def polyFun2(a: PolyFunction) = () // error
55

66
val polyFun3: PolyFunction = // error
7-
new PolyFunction { }
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new PolyFunction { } // error

Diff for: ‎tests/neg/i18302j.scala

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@@ -1,5 +1,5 @@
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def polyFunByName: PolyFunction { def apply(thunk: => Int): Int } = // error
2-
new PolyFunction { def apply(thunk: => Int): Int = 1 }
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new PolyFunction { def apply(thunk: => Int): Int = 1 } // error
33

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def polyFunVarArgs: PolyFunction { def apply(args: Int*): Int } = // error
5-
new PolyFunction { def apply(thunk: Int*): Int = 1 }
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new PolyFunction { def apply(thunk: Int*): Int = 1 } // error

Diff for: ‎tests/pos/i10369.scala

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@@ -3,12 +3,6 @@ type Upgrade[T] = T match
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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:
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def apply[T](x: T): Upgrade[T] = x match
8-
case x: Int => x.toDouble
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case x: Char => x.toString
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case x: Boolean => !x
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val upgrade2: [t] => t => Upgrade[t] = [t] => (x: t) => x match
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case x: Int => x.toDouble
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case x: Char => x.toString

Diff for: ‎tests/run/erased-15.check

-1
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