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Slack LUBs fail to capture constraints between type parameters and blow up in RefChecks if used in a TypeTree #7694

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scabug opened this issue Jul 25, 2013 · 2 comments
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Slack LUBs fail to capture constraints between type parameters and blow up in RefChecks if used in a TypeTree #7694

scabug opened this issue Jul 25, 2013 · 2 comments
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@retronym
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lub typer
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2.10.3-RC1

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@scabug
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scabug commented Jul 25, 2013 

trait A
trait B

trait L[A2, B2 <: A2]

object Lub {
  def lub = if (true) (null: L[A, A]) else (null: L[B, B])
  def foo(a: Any, b: Any) = (a, b)
  foo(b = lub, a = lub) // use named args transforms to include TypeTree(<lub.tpe>
}
<console>:13: error: type arguments [_1,_2] do not conform to trait L's type parameter bounds [A2,B2 <: A2]
         foo(b = lub, a = lub) // use named args transforms to include TypeTree(<lub.tpe>
                 ^

I suspect calculating the correct LUB will be to difficult, and we should instead disable the check for synthetic TypeTrees.
@scabug
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scabug commented Jul 25, 2013

Imported From: https://issues.scala-lang.org/browse/SI-7694?orig=1
Reporter: @retronym
Affected Versions: 2.10.0
Other Milestones: 2.11.0-M6

@scabug
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scabug commented Jul 25, 2013

@retronym said:
scala/scala#2771

@scabug scabug closed this as completed Aug 13, 2013
@scabug scabug added this to the 2.10.3-RC1 milestone Apr 7, 2017
This was referenced Apr 7, 2017
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@lrytz lrytz mentioned this issue Nov 15, 2017
Merged
milessabin added a commit to milessabin/scala that referenced this issue Jan 12, 2018
@milessabin
Addressed review comments.
0a1c62c 
+ Added uncheckedBounds to prevent issues similar to scala/bug#7694.
+ Inserted correct changeOwner
+ Assigned position correctly.
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lub typer
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