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Print the type parameter bounds of higher kinded types #13372

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Aug 25, 2021
Merged

Print the type parameter bounds of higher kinded types #13372

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a4c4767
[Fix #13306] Print paramInfo of HKTypeLambda
adpi2 Aug 24, 2021
7e27c2c
Update check file of i11637
adpi2 Aug 25, 2021
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10 changes: 6 additions & 4 deletions compiler/src/dotty/tools/dotc/printing/PlainPrinter.scala
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Expand Up @@ -348,15 +348,17 @@ class PlainPrinter(_ctx: Context) extends Printer {
case None => "?"
}

protected def decomposeLambdas(bounds: TypeBounds): (String, TypeBounds) =
def decompose(tp: Type) = tp.stripTypeVar match
protected def decomposeLambdas(bounds: TypeBounds): (Text, TypeBounds) =
def decompose(tp: Type): (Text, Type) = tp.stripTypeVar match
case lam: HKTypeLambda =>
val names =
if lam.isDeclaredVarianceLambda then
lam.paramNames.lazyZip(lam.declaredVariances).map((name, v) =>
varianceSign(v) + name)
else lam.paramNames
(names.mkString("[", ", ", "]"), lam.resType)
else lam.paramNames.map(_.toString)
val infos = lam.paramInfos.map(toText)
val tparams = names.zip(infos).map(_ ~ _)
("[" ~ Text(tparams, ",") ~ "]", lam.resType)
case _ =>
("", tp)
bounds match
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40 changes: 20 additions & 20 deletions tests/neg-custom-args/i11637.check
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@@ -1,21 +1,21 @@
-- [E057] Type Mismatch Error: tests/neg-custom-args/i11637.scala:11:33 ------------------------------------------------
11 | var h = new HKT3_1[FunctorImpl](); // error // error
| ^
| Type argument test2.FunctorImpl does not conform to upper bound [Generic2[T] <: Set[T]] =>> Any
| Type argument test2.FunctorImpl does not conform to upper bound [Generic2[T <: String] <: Set[T]] =>> Any

Explanation
===========

I tried to show that
test2.FunctorImpl
conforms to
[Generic2[T] <: Set[T]] =>> Any
[Generic2[T <: String] <: Set[T]] =>> Any
but the comparison trace ended with `false`:

==> test2.FunctorImpl <: [Generic2[T] <: Set[T]] =>> Any
==> test2.FunctorImpl <: [Generic2[T] <: Set[T]] =>> Any (recurring)
==> type bounds [[T] <: Set[T]] <: type bounds [[T] <: Iterable[T]]
==> type bounds [[T] <: Set[T]] <: type bounds [[T] <: Iterable[T]] (recurring)
==> test2.FunctorImpl <: [Generic2[T <: String] <: Set[T]] =>> Any
==> test2.FunctorImpl <: [Generic2[T <: String] <: Set[T]] =>> Any (recurring)
==> type bounds [[T <: String] <: Set[T]] <: type bounds [[T] <: Iterable[T]]
==> type bounds [[T <: String] <: Set[T]] <: type bounds [[T] <: Iterable[T]] (recurring)
==> [T <: String] =>> Set[T] <: Iterable
==> [T <: String] =>> Set[T] <: Iterable (recurring)
==> type bounds [] <: type bounds [ <: String]
Expand All @@ -30,31 +30,31 @@ but the comparison trace ended with `false`:
<== type bounds [] <: type bounds [ <: String] = false
<== [T <: String] =>> Set[T] <: Iterable (recurring) = false
<== [T <: String] =>> Set[T] <: Iterable = false
<== type bounds [[T] <: Set[T]] <: type bounds [[T] <: Iterable[T]] (recurring) = false
<== type bounds [[T] <: Set[T]] <: type bounds [[T] <: Iterable[T]] = false
<== test2.FunctorImpl <: [Generic2[T] <: Set[T]] =>> Any (recurring) = false
<== test2.FunctorImpl <: [Generic2[T] <: Set[T]] =>> Any = false
<== type bounds [[T <: String] <: Set[T]] <: type bounds [[T] <: Iterable[T]] (recurring) = false
<== type bounds [[T <: String] <: Set[T]] <: type bounds [[T] <: Iterable[T]] = false
<== test2.FunctorImpl <: [Generic2[T <: String] <: Set[T]] =>> Any (recurring) = false
<== test2.FunctorImpl <: [Generic2[T <: String] <: Set[T]] =>> Any = false

The tests were made under the empty constraint

-- [E057] Type Mismatch Error: tests/neg-custom-args/i11637.scala:11:21 ------------------------------------------------
11 | var h = new HKT3_1[FunctorImpl](); // error // error
| ^
| Type argument test2.FunctorImpl does not conform to upper bound [Generic2[T] <: Set[T]] =>> Any
| Type argument test2.FunctorImpl does not conform to upper bound [Generic2[T <: String] <: Set[T]] =>> Any

Explanation
===========

I tried to show that
test2.FunctorImpl
conforms to
[Generic2[T] <: Set[T]] =>> Any
[Generic2[T <: String] <: Set[T]] =>> Any
but the comparison trace ended with `false`:

==> test2.FunctorImpl <: [Generic2[T] <: Set[T]] =>> Any
==> test2.FunctorImpl <: [Generic2[T] <: Set[T]] =>> Any (recurring)
==> type bounds [[T] <: Set[T]] <: type bounds [[T] <: Iterable[T]]
==> type bounds [[T] <: Set[T]] <: type bounds [[T] <: Iterable[T]] (recurring)
==> test2.FunctorImpl <: [Generic2[T <: String] <: Set[T]] =>> Any
==> test2.FunctorImpl <: [Generic2[T <: String] <: Set[T]] =>> Any (recurring)
==> type bounds [[T <: String] <: Set[T]] <: type bounds [[T] <: Iterable[T]]
==> type bounds [[T <: String] <: Set[T]] <: type bounds [[T] <: Iterable[T]] (recurring)
==> [T <: String] =>> Set[T] <: Iterable
==> [T <: String] =>> Set[T] <: Iterable (recurring)
==> type bounds [] <: type bounds [ <: String]
Expand All @@ -69,9 +69,9 @@ but the comparison trace ended with `false`:
<== type bounds [] <: type bounds [ <: String] = false
<== [T <: String] =>> Set[T] <: Iterable (recurring) = false
<== [T <: String] =>> Set[T] <: Iterable = false
<== type bounds [[T] <: Set[T]] <: type bounds [[T] <: Iterable[T]] (recurring) = false
<== type bounds [[T] <: Set[T]] <: type bounds [[T] <: Iterable[T]] = false
<== test2.FunctorImpl <: [Generic2[T] <: Set[T]] =>> Any (recurring) = false
<== test2.FunctorImpl <: [Generic2[T] <: Set[T]] =>> Any = false
<== type bounds [[T <: String] <: Set[T]] <: type bounds [[T] <: Iterable[T]] (recurring) = false
<== type bounds [[T <: String] <: Set[T]] <: type bounds [[T] <: Iterable[T]] = false
<== test2.FunctorImpl <: [Generic2[T <: String] <: Set[T]] =>> Any (recurring) = false
<== test2.FunctorImpl <: [Generic2[T <: String] <: Set[T]] =>> Any = false

The tests were made under the empty constraint
14 changes: 14 additions & 0 deletions tests/printing/i13306.check
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@@ -0,0 +1,14 @@
[[syntax trees at end of typer]] // tests/printing/i13306.scala
package example {
class MyClass() extends Object() {}
class MembersContainer() extends Object() {
type MyType[T >: Nothing <: example.MyClass] = Comparable[T]
}
final lazy module val Exports: example.Exports = new example.Exports()
final module class Exports() extends Object() { this: example.Exports.type =>
val instance: example.MembersContainer = new example.MembersContainer()
export example.Exports.instance.*
final type MyType[T <: example.MyClass] = Comparable[T]
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@bishabosha bishabosha Aug 25, 2021 •
edited
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i noticed the lower bound does not print either, implying it's Nothing, however it is still inconsistent with how a TypeBoundsTree is printed - if you look at the original MyType - but that would lead to very verbose error messages I think.

One solution could be some print mode parameter which knows if we are printing "full trees" or just the type, which could allow you to decide when to always print the lower bound

}
}

12 changes: 12 additions & 0 deletions tests/printing/i13306.scala
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@@ -0,0 +1,12 @@
package example

class MyClass

class MembersContainer {
type MyType[T <: MyClass] = Comparable[T]
}

object Exports {
val instance = new MembersContainer
export instance.*
}