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Type computed to `any`, works in Scala 2
Compiler version
3.1.2
Rrror: https://github.com/akka/akka/runs/8294129202?check_suite_focus=true From: https://github.com/akka/akka/pull/31345
Minimized code
Sorry I have not minimized it :(
def combine[T, U, M](
sources: java.util.List[_ <: Graph[SourceShape[T], _<: M]],
fanInGraph: Graph[UniformFanInShape[T, U], NotUsed]): Source[U, java.util.List[M]] = {
val seq = if (sources != null) Util.immutableSeq(sources).collect {
case source: Source[T @unchecked, M @unchecked] => source.asScala
case other => other
} else immutable.Seq()
import akka.util.ccompat.JavaConverters._
new Source(scaladsl.Source.combine(seq)(fanInGraph).mapMaterializedValue(_.asJava))
}
if I change to ：
def combine[T, U, M](
sources: java.util.List[_ <: Graph[SourceShape[T], M]],
fanInGraph: Graph[UniformFanInShape[T, U], NotUsed]): Source[U, java.util.List[M]] = {
val seq = if (sources != null) Util.immutableSeq(sources).collect {
case source: Source[T @unchecked, M @unchecked] => source.asScala
case other => other
} else immutable.Seq()
import akka.util.ccompat.JavaConverters._
new Source(scaladsl.Source.combine(seq)(fanInGraph).mapMaterializedValue(_.asJava))
}
The only difference is _<:M and M.
Output
[error] -- [E007] Type Mismatch Error: /home/runner/work/akka/akka/akka-stream/src/main/scala/akka/stream/javadsl/Sink.scala:397:76
[error] 397 | new Sink(scaladsl.Sink.combine(seq)(fanoutGraph).mapMaterializedValue(_.asJava))
[error] | ^^^^^^^^
[error] | Found: java.util.List[Any]
[error] | Required: java.util.List[M]
[error] -- [E007] Type Mismatch Error: /home/runner/work/akka/akka/akka-stream/src/main/scala/akka/stream/javadsl/Source.scala:682:79
[error] 682 | new Source(scaladsl.Source.combine(seq)(fanInGraph).mapMaterializedValue(_.asJava))
[error] | ^^^^^^^^
[error] | Found: java.util.List[Any]
[error] | Required: java.util.List[M]
[error] two errors found
Expectation
Compile as Scala 2.
I think that should be computed to java.util.List[M] not java.util.List[Any]
Here is an attempt to minimize:
object Test {
class Box[T](val value: T)
def f[T](l: List[Box[_ <: T]]): List[T] = l.map(_.value)
}
I am not sure if this captures every aspect of your problem or if this is over-simplified.
The above snippet compiles with Scala 2.12, 3.1.2 and 3.2.0 but fails with Scala 2.13, 3.1.1 and 3.1.3.
Output
➜ ~/scala-snippets scala-cli compile --server=false --scala-version=2.12 type_param_any.scala
➜ ~/scala-snippets scala-cli compile --server=false --scala-version=2.13 type_param_any.scala
/Users/mbovel/scala-snippets/type_param_any.scala:3: error: type mismatch;
found : Test.Box[_ <: T] => x$1.value.type forSome { val x$1: Test.Box[_ <: T] }
required: Test.Box[_ <: T] => (some other)_$1(in value l)
def f[T](l: List[Box[_ <: T]]): List[T] = l.map(_.value)
^
1 error
Compilation failed
➜ ~/scala-snippets scala-cli compile --server=false --scala-version=3.1.1 type_param_any.scala
-- Error: /Users/mbovel/scala-snippets/type_param_any.scala:3:52 ---------------
3 | def f[T](l: List[Box[_ <: T]]): List[T] = l.map(_.value)
| ^^^^^^^
| return type B of lambda cannot be made hygienic;
| it is not a supertype of the hygienic type Any
-- Error: /Users/mbovel/scala-snippets/type_param_any.scala:3:51 ---------------
3 | def f[T](l: List[Box[_ <: T]]): List[T] = l.map(_.value)
| ^
| Inaccessible variables captured in instantation of type variable B.
| _$1.T was fixed to Any,
| but the latter type does not conform to the upper bound T
-- Error: /Users/mbovel/scala-snippets/type_param_any.scala:3:8 ----------------
3 | def f[T](l: List[Box[_ <: T]]): List[T] = l.map(_.value)
| ^
| Inaccessible variables captured in instantation of type variable B.
| _$1.T was fixed to Any,
| but the latter type does not conform to the upper bound T
-- Error: /Users/mbovel/scala-snippets/type_param_any.scala:1:7 ----------------
1 |object Test {
| ^
| Inaccessible variables captured in instantation of type variable B.
| _$1.T was fixed to Any,
| but the latter type does not conform to the upper bound T
-- Error: /Users/mbovel/scala-snippets/type_param_any.scala:1:0 ----------------
1 |object Test {
|^
|Inaccessible variables captured in instantation of type variable B.
|_$1.T was fixed to Any,
|but the latter type does not conform to the upper bound T
5 errors found
Compilation failed
➜ ~/scala-snippets scala-cli compile --server=false --scala-version=3.1.2 type_param_any.scala
➜ ~/scala-snippets scala-cli compile --server=false --scala-version=3.1.3 type_param_any.scala
-- Error: /Users/mbovel/scala-snippets/type_param_any.scala:3:52 ---------------
3 | def f[T](l: List[Box[_ <: T]]): List[T] = l.map(_.value)
| ^^^^^^^
| return type _$1.T of lambda cannot be made hygienic;
| it is not a supertype of the hygienic type Any
1 error found
Compilation failed
➜ ~/scala-snippets scala-cli compile --server=false --scala-version=3.2.0 type_param_any.scala
I believe this is linked to type avoidance and recent related work from @smarter and @odersky; can you please confirm?
@He-Pin have you tried to compile with Scala 3.2.0? And with 2.13?
I just updated it, it was 3.1.2 not 3.1.3 .~Akka not compiles with 3.1.3 now.~
Hard to tell whether it's avoidance or not. But it works in nightly, right?
But it works in nightly, right?
My simplified example compiles with 3.2.0, but I am not sure for the original one.
@He-Pin could please try with 3.2.0 and with the latest nightly?
@mbovel I am trying to get Akka built at: https://github.com/akka/akka/pull/31578 :) ,that will be the first to come, it currently only compiles with scala 3.1.2,
it's still the same.
[info] compiling 186 Scala sources and 3 Java sources to C:\Users\hepin\IdeaProjects\akka\akka-stream\target\scala-3.2.0\classes ...
[error] -- [E007] Type Mismatch Error: C:\Users\hepin\IdeaProjects\akka\akka-stream\src\main\scala\akka\stream\javadsl\Source.scala:682:79
[error] 682 | new Source(scaladsl.Source.combine(seq)(fanInGraph).mapMaterializedValue(_.asJava))
[error] | ^^^^^^^^
[error] | Found: java.util.List[Any]
[error] | Required: java.util.List[M]
[error] |
[error] | longer explanation available when compiling with `-explain`
[error] one error found
[error] (Compile / compileIncremental) Compilation failed
[error] Total time: 58 s, completed 2022-9-13 14:41:21
I rebased https://github.com/akka/akka/pull/31345 to https://github.com/akka/akka/pull/31579
and change the M to _<:M
and then run project akka-stream ++ 3.2.0 compile
It shows the same
@mbovel Sorry for not minimize it, you can have a try.
Mian.
import scala.collection.immutable
object Main {
class Source[+Out, +Mat] extends Graph[SourceShape[Out], Mat]
class Shape
class SourceShape[+T] extends Shape
class Graph[+S <: Shape, +M]
def combine[T, U, M](sources: java.util.List[_ <: Graph[SourceShape[T], _ <: M]]): Source[U, java.util.List[M]] = {
val seq: immutable.Seq[Graph[SourceShape[T], M]] = if (sources != null) immutableSeq(sources).collect {
case source: Source[T, M]@unchecked => source
case other => other
} else immutable.Seq()
???
}
def immutableSeq[T](iterable: java.lang.Iterable[T]): immutable.Seq[T] = ???
}
it gives me:
C:\Users\hepin\IdeaProjects\MtoAnyTest\src\main\scala\Main.scala:16:21
Found: (other : ?1.CAP)
Required: Main.Source[T, M] & ?1.CAP
where: ?1 is an unknown value of type scala.runtime.TypeBox[Nothing, Main.Graph[Main.SourceShape[T], ? <: M]]
case other => other
@mbovel @odersky this code compiles with 2.12.16 and 2.13.8