Erroneous unused import warning on Scala 3.7.4-RC2

[Gedochao]

Compiler version

3.7.4-RC2, 3.8.0-RC1-bin-20251024-41d321d-NIGHTLY
does not occur on 3.7.4-RC1 or earlier

Code

//> using options -Wunused:imports
//> using dep org.virtuslab.scala-cli-signing::cli:0.2.11
//> using dep com.github.alexarchambault::case-app:2.1.0
import caseapp.Parser
import caseapp.Help
import scala.cli.signing.shared.{PasswordOption, Secret}

case class SharedSecretOptions(token: PasswordOption = PasswordOption.Value(Secret("")))
object SharedSecretOptions {
  import scala.cli.signing.util.ArgParsers.argParser
  implicit lazy val parser: Parser[SharedSecretOptions] = Parser.derive
  implicit lazy val help: Help[SharedSecretOptions]     = Help.derive
}

I will try to bisect & minimize this later.

Output

[warn] ./repro.scala:10:44
[warn] unused import
[warn]   import scala.cli.signing.util.ArgParsers.argParser
[warn]                                            ^^^^^^^^^

Expectation

No warning.

Extra context

• discovered in: Bump Scala 3 Next RC to 3.7.4-RC2 VirtusLab/scala-cli#3921

[Gedochao]

Last good release: 3.8.0-RC1-bin-20251008-6194563-NIGHTLY
First bad release: 3.8.0-RC1-bin-20251009-eb67a9c-NIGHTLY
912e89b is the first bad commit (#24043)
cc @som-snytt

[som-snytt]

Thanks for the reproduction with few moving parts.

The lint learned to use enclosingInlineds to decide whether to look up a reference in enclosing imports. It will look up for a tree that is "zero-extent synthetic" (summonInline) or that is enclosed in the "outermost" position, which is the user's span.

The goal is not to look up idents at the user site that were resolved in library code.

Here, the library does an Implicits.search, which produces a tree that is zero-extent, but the quoting changes the position to the position in the quote.

                val argParserExpr = Implicits.search(TypeRepr.of[ArgParser[t]]) match {
                  case iss: ImplicitSearchSuccess =>
                    iss.tree.asExpr.asExprOf[ArgParser[t]]
                  case isf: ImplicitSearchFailure =>
                    throw new Exception(s"No given ${Type.show[ArgParser[t]]} instance found")
                }
                '{
                  val argParser = $argParserExpr

Debug for search says that result is zero-extent

search AppliedType(TypeRef(TermRef(ThisType(TypeRef(NoPrefix,module class core)),object argparser),ArgParser),List(TypeRef(TermRef(TermRef(TermRef(TermRef(ThisType(TypeRef(NoPrefix,module class <root>)),object scala),object cli),object signing),object shared),class PasswordOption))) at /home/amarki/snips/i24248.scala:<604..617>
implicit tree at /home/amarki/snips/i24248.scala:<604..604>

but debug for the result seen by the linter

    ValDef(argParser, TypeTree(),
      Inlined(Thicket(List()), List(), Ident(argParser))),

says the pos for the valdef, the ident, and the enclosingInlineds

/home/runner/work/case-app/case-app/core/shared/src/main/scala-3/caseapp/core/parser/LowPriorityParserImplicits.scala:[6494..6498..6524],
/home/runner/work/case-app/case-app/core/shared/src/main/scala-3/caseapp/core/parser/LowPriorityParserImplicits.scala:<6511..6524>,
List(/home/runner/work/case-app/case-app/core/shared/src/main/scala-3/caseapp/core/parser/LowPriorityParserImplicits.scala:<6494..7438>, /home/runner/work/case-app/case-app/core/shared/src/main/scala-3/caseapp/core/parser/LowPriorityParserImplicits.scala:[9364..9402..9405], /home/amarki/snips/i24248.scala:<604..617>)

another thought, the Inlined pos is

inlinee /home/runner/work/case-app/case-app/core/shared/src/main/scala-3/caseapp/core/help/HelpCompanion.scala:<2060..2070>

It seems to be a problem with fidelity of inlined positions, but I have to recover a bit before thinking about how to address it.

Maybe detecting the empty thicket call in Inlined(Thicket(List()), List(), ...), maybe only if the expansion is a simple ident. (To do something in the linter and not touch quoting.)

If there is institutional knowledge and they are reading this, I'm open to suggestions.

I'll probably skip the baseball World Series.