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Dealias for unused param check #23256

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Merged
merged 3 commits into from
Jun 3, 2025
+41 −6
Merged

Dealias for unused param check #23256

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a97b162
Dealias for unused param check
som-snytt May 23, 2025
f699811
No warn implicit param of abstract type as empty interface
som-snytt May 23, 2025
c052463
Take the high bound
som-snytt May 31, 2025
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2 changes: 1 addition & 1 deletion compiler/src/dotty/tools/dotc/core/SymDenotations.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -685,7 +685,7 @@ object SymDenotations {
isAbstractOrAliasType && !isAbstractOrParamType

/** Is this symbol an abstract or alias type? */
final def isAbstractOrAliasType: Boolean = isType & !isClass
final def isAbstractOrAliasType: Boolean = isType && !isClass

/** Is this symbol an abstract type or type parameter? */
final def isAbstractOrParamType(using Context): Boolean = this.isOneOf(DeferredOrTypeParam)
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6 changes: 3 additions & 3 deletions compiler/src/dotty/tools/dotc/transform/CheckUnused.scala
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Expand Up @@ -575,14 +575,14 @@ object CheckUnused:
|| m.hasAnnotation(dd.UnusedAnnot) // param of unused method
|| sym.name.is(ContextFunctionParamName) // a ubiquitous parameter
|| sym.isCanEqual
|| sym.info.typeSymbol.match // more ubiquity
|| sym.info.dealias.typeSymbol.match // more ubiquity
case dd.DummyImplicitClass | dd.SubTypeClass | dd.SameTypeClass => true
case tps =>
tps.isMarkerTrait // no members to use; was only if sym.name.is(ContextBoundParamName)
|| // but consider NotGiven
tps.hasAnnotation(dd.LanguageFeatureMetaAnnot)
|| sym.info.isSingleton // DSL friendly
|| sym.info.isInstanceOf[RefinedType] // can't be expressed as a context bound
|| sym.info.dealias.isInstanceOf[RefinedType] // can't be expressed as a context bound
if ctx.settings.WunusedHas.implicits
&& !infos.skip(m)
&& !m.isEffectivelyOverride
Expand Down Expand Up @@ -905,7 +905,7 @@ object CheckUnused:
def isCanEqual: Boolean =
sym.isOneOf(GivenOrImplicit) && sym.info.finalResultType.baseClasses.exists(_.derivesFrom(defn.CanEqualClass))
def isMarkerTrait: Boolean =
sym.isClass && sym.info.allMembers.forall: d =>
sym.info.hiBound.allMembers.forall: d =>
val m = d.symbol
!m.isTerm || m.isSelfSym || m.is(Method) && (m.owner == defn.AnyClass || m.owner == defn.ObjectClass)
def isEffectivelyPrivate: Boolean =
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4 changes: 2 additions & 2 deletions tests/warn/i17314.scala
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@@ -1,4 +1,4 @@
//> using options -Wunused:all -deprecation -feature
//> using options -Wunused:all -deprecation -feature -Werror

import java.net.URI

Expand All @@ -10,7 +10,7 @@ object circelike {
type Configuration
trait ConfiguredCodec[T]
object ConfiguredCodec:
inline final def derived[A](using conf: Configuration)(using inline mirror: Mirror.Of[A]): ConfiguredCodec[A] = // warn // warn
inline final def derived[A](using conf: Configuration)(using inline mirror: Mirror.Of[A]): ConfiguredCodec[A] =
class InlinedConfiguredCodec extends ConfiguredCodec[A]:
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These warning seemed valid, neither mirror nor conf is actually used.

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Is that a consequence of In addition, take an abstract type as not warnable, unless it has an upper bound that is warnable (has non-universal members). ?

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Yes, Mirror doesn't have terms to use. Also Of is an alias so warned previously.

val codec = summonInline[Codec[URI]] // simplification
new InlinedConfiguredCodec
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17 changes: 17 additions & 0 deletions tests/warn/i23250.scala
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@@ -0,0 +1,17 @@
//> using options -Wunused:all -Werror

trait MonadError[F[_], E]
type MonadThrow[F[_]] = MonadError[F, Throwable]

trait MetaStreams[F[_]]:
def use[A]: F[A] = ???
trait WriteResult

trait MetaStreamsSyntax:
extension [F[_]](ms: MetaStreams[F])(using MonadThrow[F])
def setMaxAge(): F[WriteResult] =
summon[MonadThrow[F]]
ms.use[WriteResult]

def setTruncateBefore(): F[WriteResult] =
ms.use[WriteResult]
18 changes: 18 additions & 0 deletions tests/warn/i23250b.scala
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@@ -0,0 +1,18 @@
//> using options -Wunused:all

trait Memberly:
def member: Int

object Members:
type MemberType <: Memberly
type Empty

object Test:
import Members.*

type MT = MemberType
def membered(using MT) = println() // warn abstract type offers member in upper bound
def remembered(using mt: MT) = mt.member

type Ignore = Empty
def emptily(using Ignore) = println()
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