Ignore language version imports

Author: som-snytt

compiler/src/dotty/tools/dotc/core/Contexts.scala

@@ -20,6 +20,7 @@ import Nullables._
 import Implicits.ContextualImplicits
 import config.Settings._
 import config.Config
+import config.SourceVersion.allSourceVersionNames
 import reporting._
 import io.{AbstractFile, NoAbstractFile, PlainFile, Path}
 import scala.io.Codec
@@ -1031,7 +1032,8 @@ object Contexts:
 
     // register an import
     def +=(info: ImportInfo)(using Context): Unit =
-      if ctx.settings.WunusedHas.imports && !ctx.owner.is(Enum) && !ctx.compilationUnit.isJava then
+      def isLanguageImport = info.isLanguageImport && allSourceVersionNames.exists(info.forwardMapping.contains)
+      if ctx.settings.WunusedHas.imports && !isLanguageImport && !ctx.owner.is(Enum) && !ctx.compilationUnit.isJava then
         importInfos(ctx.compilationUnit) ::= ((info, ctx.owner))
 
     // mark a selector as used

compiler/src/dotty/tools/dotc/typer/ImportInfo.scala

@@ -187,8 +187,7 @@ class ImportInfo(symf: Context ?=> Symbol,
       assert(myUnimported != null)
     myUnimported.uncheckedNN
 
-  @unused
-  private val isLanguageImport: Boolean = untpd.languageImport(qualifier).isDefined
+  val isLanguageImport: Boolean = untpd.languageImport(qualifier).isDefined
 
   private var myUnimported: Symbol | Null = _
 
@@ -211,6 +210,7 @@ class ImportInfo(symf: Context ?=> Symbol,
           else None
         case _ => None
     feature match
+      case _ if !isLanguageImport => None
       case QualifiedName(prefix, name) => test(prefix, name)
       case _ => test(EmptyTermName, feature)
 

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -947,7 +947,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
       val tag = withTag(defn.TypeTestClass.typeRef.appliedTo(pt, tpe))
           .orElse(withTag(defn.ClassTagClass.typeRef.appliedTo(tpe)))
           .getOrElse(tree)
-      if tag.symbol.maybeOwner == defn.ClassTagClass && config.Feature.sourceVersion.isAtLeast(config.SourceVersion.future) then
+      if tag.symbol.maybeOwner == defn.ClassTagClass && sourceVersion.isAtLeast(future) then
         report.warning("Use of `scala.reflect.ClassTag` for type testing may be unsound. Consider using `scala.reflect.TypeTest` instead.", tree.srcPos)
       tag
     }

tests/neg-with-compiler/unused-imports.scala

@@ -1,6 +1,6 @@
 // scalac: -Wunused:imports -Werror -feature
 
-//import language.future
+import language.future
 import language.implicitConversions
 import language.postfixOps // error
 import scala.concurrent.* // error