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Merge pull request scala#7364 from dotty-staging/fix-6570-1
Fix scala#6570: Don't reduce match types with empty scrutinies
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,33 @@ | ||
| import scala.Tuple._ | ||
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| trait Trait1 | ||
| trait Trait2 | ||
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| case class Box[+T](t: T) | ||
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| type N[x] = x match { | ||
| case Box[String] => Trait1 | ||
| case Box[Int] => Trait2 | ||
| } | ||
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| trait Cov[+T] | ||
| type M[t] = t match { | ||
| case Cov[x] => N[x] | ||
| } | ||
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| trait Root[A] { | ||
| def thing: M[A] | ||
| } | ||
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| class Asploder extends Root[Cov[Box[Int & String]]] { | ||
| def thing = new Trait1 {} // error | ||
| } | ||
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| object Main { | ||
| def foo[T <: Cov[Box[Int]]](c: Root[T]): Trait2 = c.thing | ||
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| def explode = foo(new Asploder) | ||
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| def main(args: Array[String]): Unit = | ||
| explode | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,109 @@ | ||
| object Base { | ||
| trait Trait1 | ||
| trait Trait2 | ||
| type N[t] = t match { | ||
| case String => Trait1 | ||
| case Int => Trait2 | ||
| } | ||
| } | ||
| import Base._ | ||
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| object UpperBoundParametricVariant { | ||
| trait Cov[+T] | ||
| type M[t] = t match { | ||
| case Cov[x] => N[x] | ||
| } | ||
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| trait Root[A] { | ||
| def thing: M[A] | ||
| } | ||
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| trait Child[A <: Cov[Int]] extends Root[A] | ||
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| // we reduce `M[T]` to `Trait2`, even though we cannot be certain of that | ||
| def foo[T <: Cov[Int]](c: Child[T]): Trait2 = c.thing | ||
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| class Asploder extends Child[Cov[String & Int]] { | ||
| def thing = new Trait1 {} // error | ||
| } | ||
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| def explode = foo(new Asploder) // ClassCastException | ||
| } | ||
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| object InheritanceVariant { | ||
| // allows binding a variable to the UB of a type member | ||
| type Trick[a] = { type A <: a } | ||
| type M[t] = t match { case Trick[a] => N[a] } | ||
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| trait Root { | ||
| type B | ||
| def thing: M[B] | ||
| } | ||
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| trait Child extends Root { type B <: { type A <: Int } } | ||
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| def foo(c: Child): Trait2 = c.thing | ||
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| class Asploder extends Child { | ||
| type B = { type A = String & Int } | ||
| def thing = new Trait1 {} // error | ||
| } | ||
| } | ||
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| object ThisTypeVariant { | ||
| type Trick[a] = { type A <: a } | ||
| type M[t] = t match { case Trick[a] => N[a] } | ||
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| trait Root { | ||
| def thing: M[this.type] | ||
| } | ||
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| trait Child extends Root { type A <: Int } | ||
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| def foo(c: Child): Trait2 = c.thing | ||
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| class Asploder extends Child { | ||
| type A = String & Int | ||
| def thing = new Trait1 {} // error | ||
| } | ||
| } | ||
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| object ParametricVariant { | ||
| type Trick[a] = { type A <: a } | ||
| type M[t] = t match { case Trick[a] => N[a] } | ||
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| trait Root[B] { | ||
| def thing: M[B] | ||
| } | ||
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| trait Child[B <: { type A <: Int }] extends Root[B] | ||
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| def foo[T <: { type A <: Int }](c: Child[T]): Trait2 = c.thing | ||
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| class Asploder extends Child[{ type A = String & Int }] { | ||
| def thing = new Trait1 {} // error | ||
| } | ||
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| def explode = foo(new Asploder) | ||
| } | ||
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| object UpperBoundVariant { | ||
| trait Cov[+T] | ||
| type M[t] = t match { case Cov[t] => N[t] } | ||
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| trait Root { | ||
| type A | ||
| def thing: M[A] | ||
| } | ||
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| trait Child extends Root { type A <: Cov[Int] } | ||
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| def foo(c: Child): Trait2 = c.thing | ||
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| class Asploder extends Child { | ||
| type A = Cov[String & Int] | ||
| def thing = new Trait1 {} // error | ||
| } | ||
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| def explode = foo(new Asploder) | ||
| } |
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