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Renaming specialized on import results in "unused import" warnings #20536

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satorg opened this issue Jun 8, 2024 · 3 comments · May be fixed by #20549
Open

Renaming specialized on import results in "unused import" warnings #20536

satorg opened this issue Jun 8, 2024 · 3 comments · May be fixed by #20549
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area:linting Linting warnings enabled with -W or -Xlint itype:bug

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@satorg
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satorg commented Jun 8, 2024 •
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Compiler version

v3.3.3, v3.4.2

Minimized code

import scala.{specialized => sp}

trait ImportUnusedSpecializedRename[@sp Int]

Script that I used for testing:

set -v

scala-cli clean ImportUnusedSpecializedRename.scala

scala-cli compile --server=false -j 17 -S 2.12.19 -Xlint:unused ImportUnusedSpecializedRename.scala
scala-cli compile --server=false -j 17 -S 2.13.14 -Wunused ImportUnusedSpecializedRename.scala
scala-cli compile --server=false -j 17 -S 3.3.3 -Wunused:imports ImportUnusedSpecializedRename.scala
scala-cli compile --server=false -j 17 -S 3.4.2 -Wunused:imports ImportUnusedSpecializedRename.scala

Output

scala-cli clean ImportUnusedSpecializedRename.scala

scala-cli compile --server=false -j 17 -S 2.12.19 -Xlint:unused ImportUnusedSpecializedRename.scala
scala-cli compile --server=false -j 17 -S 2.13.14 -Wunused ImportUnusedSpecializedRename.scala
scala-cli compile --server=false -j 17 -S 3.3.3 -Wunused:imports ImportUnusedSpecializedRename.scala
-- Warning: /Users/.../ImportUnusedSpecializedRename.scala:1:26 
1 |import scala.{specialized => sp}
  |              ^^^^^^^^^^^^^^^^^
  |              unused import
1 warning found
scala-cli compile --server=false -j 17 -S 3.4.2 -Wunused:imports ImportUnusedSpecializedRename.scala
-- Warning: /Users/.../ImportUnusedSpecializedRename.scala:1:26 
1 |import scala.{specialized => sp}
  |              ^^^^^^^^^^^^^^^^^
  |              unused import
1 warning found

Expectation

Scala3 should compile the above example without the "unused import" warnings.
As long as Scala2 compilers can do.

Additional Information

This issues causes a lot of extra warnings added up while compiling Cats for Scala3.
Historically, Cats uses import scala.{specialized => sp} in a bunch of files across the repository.
@satorg satorg added itype:bug stat:needs triage Every issue needs to have an "area" and "itype" label labels Jun 8, 2024
This was referenced Jun 8, 2024
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@som-snytt som-snytt linked a pull request Jun 11, 2024 that will close this issue
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@som-snytt
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The Scala 3 check was intentionally skipping the type parameter, but inadvertently skipping the annotation.

The rename was not germane.

Worth adding that Scala 2:

$ scalac -d /tmp/sandbox -Xlint i20536.scala
i20536.scala:3: warning: type parameter Int defined in trait ImportUnusedSpecializedRename shadows class Int defined in package scala. You may want to rename your type parameter, or possibly remove it.
trait ImportUnusedSpecializedRename[@sp Int]
                                        ^
1 warning

Scala 3

$ scalac -d /tmp/sandbox -Wshadow:all i20536.scala
-- Warning: i20536.scala:3:40 ------------------------------------------------------------------------------------------
3 |trait ImportUnusedSpecializedRename[@sp Int]
  |                                    ^^^^^^^
  | Type parameter Int for trait ImportUnusedSpecializedRename shadows the type defined by class Int in package scala
1 warning found

@som-snytt som-snytt added area:linting Linting warnings enabled with -W or -Xlint and removed stat:needs triage Every issue needs to have an "area" and "itype" label labels Jun 11, 2024
@satorg
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satorg commented Jun 11, 2024

Ah, sorry, I overworked it a little. In Cats it is a generic A, not Int:
https://github.com/typelevel/cats/blob/90db3cd0269cf2b621ad6460ded594aee2e6a135/kernel/src/main/scala/cats/kernel/Enumerable.scala#L25-L34

@som-snytt
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I didn't intend to rub it in. My point was going to be that scala 2 will lint that, but then I looked and scala 3 does it now too. I'll have to find some other clever thing to point out.

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CheckUnused checks type param annotations som-snytt/dotty
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