8000 Add Regression test for Scala Bug 7131 · scala/scala@39f0192 · GitHub
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Add Regression test for Scala Bug 7131
Scala Bug 7131 reported a compiler crash at the typer phase. Testing recently, that same program no longer crashes the compiler. This commit adds the program in question, to watch for regressions.
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‎test/files/neg/t7131.check

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t7131.scala:21: error: type mismatch;
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found : Iterable[U]
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required: That
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Note: implicit method convertToSimpleMappable is not applicable here because it comes after the application point and it lacks an explicit result type
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x.value.map(f)
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^
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one error found

‎test/files/neg/t7131.flags

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-language:higherKinds -language:reflectiveCalls -language:implicitConversions

‎test/files/neg/t7131.scala

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import collection.generic.CanBuildFrom
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// leaving out the observable part
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trait ObservableValue[-T] {
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def value: T
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}
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object ObservableValue {
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//this works as is
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implicit class SimpleMappable[T](x: ObservableValue[T]) {
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def map[U](f: T => U) = new ObservableValue[U] {
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def value = f(x.value)
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}
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}
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class TraversableMappable[T, Container[X] <: Traversable[X]](x: ObservableValue[Container[T]]) {
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def map[U, That](f: T => U)(implicit bf: CanBuildFrom[Traversable[T], U, That]): ObservableValue[That] = new ObservableValue[That] {
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def value: That = {
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x.value.map(f)
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}
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}
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}
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//for some reason using an implicit class does not work
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implicit def convertToTraversableMappable[T, Container[X] <: Traversable[X]](x: ObservableValue[Container[T]]) =
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new TraversableMappable(x)
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type HasMap[T, That[_]] = {
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def map[U](f: T => U): That[U]
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}
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class NestedMappable[T, Container[X] <: HasMap[X, Container]](x: ObservableValue[Container[T]]) {
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def map[U](f: T => U): ObservableValue[Container[U]] = new ObservableValue[Container[U]] {
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def value: Container[U] = x.value.map(f)
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}
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}
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//for some reason using an implicit class does not work
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implicit def convertToSimpleMappable[T, Container[X] <: ObservableValue.HasMap[X, Container]](x: ObservableValue[Container[T]]) =
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new NestedMappable(x)
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}
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object Main extends App {
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class TestCase extends ObservableValue[Int] {
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var value: Int = 0
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}
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val x = new TestCase
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val r = x.map(_ + 1)
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println(r.value) //1
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x.value = 42
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println(r.value) //43
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class TestCase1 extends ObservableValue[Option[Int]] {
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var value: Option[Int] = None
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}
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val x1 = new TestCase1
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val r1 = x1 map ((x: Int) => x + 1)
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println(r1.value) //None
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x1.value = Some(3)
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println(r1.value) //Some(4)
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class TestCase2 extends ObservableValue[List[Int]] {
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var value: List[Int] = List()
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}
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val y = new TestCase2
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val q = y map (_ + 1)
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println(q.value) //List()
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y.value = List(3, 4)
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println(q.value) //List(4, 5)
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}

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