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Regression with nested implicit lookups involving a type alias #6854

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scabug opened this issue Dec 20, 2012 · 4 comments
Closed

Regression with nested implicit lookups involving a type alias #6854

scabug opened this issue Dec 20, 2012 · 4 comments
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@retronym
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backend backport has PR implicit regression
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2.10.1

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@scabug
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scabug commented Dec 20, 2012

With argonaut we discovered the following regression(this works in 2.9.2):

scala> import org.scalacheck._
import org.scalacheck._
 
scala> type ListString = List[String]
defined type alias ListString
 
scala> implicitly[Arbitrary[List[String] => List[String]]]
res0: org.scalacheck.Arbitrary[List[String] => List[String]] = org.scalacheck.Arbitrary$$anon$2@7e4cd909
 
scala> implicitly[Arbitrary[ListString => ListString]]
<console>:24: error: could not find implicit value for parameter e: org.scalacheck.Arbitrary[ListString => ListString]
              implicitly[Arbitrary[ListString => ListString]]

As you can see replacing the type alias with the type it represents works, but with the type alias in place we get a failure.
@scabug
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scabug commented Dec 20, 2012

Imported From: https://issues.scala-lang.org/browse/SI-6854?orig=1
Reporter: Sean Parsons (seanparsons)
Affected Versions: 2.10.0-RC5, 2.10.0
See #6846

@scabug
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scabug commented Jan 7, 2013

@adriaanm said:
fixed in 2.11, likely by Paul's work on dealiasWiden -- should see if we can backport that to 2.10.x

@scabug
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scabug commented Jan 8, 2013

@retronym said (edited on Jan 8, 2013 6:25:58 PM UTC):
Backport for 2.10.x

I've manually checked that this works:

backport/1826 ~/code/scala squala -classpath build/quick/classes/scalacheck
Welcome to Scala version 2.10.1-20130108-190630-3b74691d35 (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_37).
Type in expressions to have them evaluated.
Type :help for more information.

scala> import org.scalacheck._
import org.scalacheck._

scala> type ListString = List[String]
defined type alias ListString

scala> implicitly[Arbitrary[List[String] => List[String]]]
res0: org.scalacheck.Arbitrary[List[String] => List[String]] = org.scalacheck.Arbitrary$$anon$1@7d365e01

scala> implicitly[Arbitrary[ListString => ListString]]
res1: org.scalacheck.Arbitrary[ListString => ListString] = org.scalacheck.Arbitrary$$anon$1@7fc4fe21

I haven't added this as a test case as this is a straight duplicate of #6846 which was already tested.

@scabug
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scabug commented Jan 12, 2013

@retronym said:
scala/scala#1869

@scabug scabug closed this as completed Jan 12, 2013
@scabug scabug added this to the 2.10.1 milestone Apr 7, 2017
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backend backport has PR implicit regression
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