feat: implement 'convert to named lambda parameters' code action

metals/src/main/scala/scala/meta/internal/metals/codeactions/CodeActionProvider.scala

@@ -49,6 +49,7 @@ final class CodeActionProvider(
     new ConvertCommentCodeAction(buffers),
     new RemoveInvalidImportQuickFix(trees, buildTargets),
     new SourceRemoveInvalidImports(trees, buildTargets, diagnostics),
+    new ConvertToNamedLambdaParameters(trees, compilers),
   )
 
   def actionsForParams(params: l.CodeActionParams): List[CodeAction] = {

metals/src/main/scala/scala/meta/internal/metals/codeactions/ConvertToNamedLambdaParameters.scala

@@ -0,0 +1,102 @@
+package scala.meta.internal.metals.codeactions
+
+import scala.concurrent.ExecutionContext
+import scala.concurrent.Future
+
+import scala.meta.Term
+import scala.meta.internal.metals.Compilers
+import scala.meta.internal.metals.JsonParser.XtensionSerializableToJson
+import scala.meta.internal.metals.MetalsEnrichments._
+import scala.meta.internal.metals.codeactions.CodeAction
+import scala.meta.internal.metals.codeactions.CodeActionBuilder
+import scala.meta.internal.metals.logging
+import scala.meta.internal.parsing.Trees
+import scala.meta.pc.CancelToken
+import scala.meta.pc.CodeActionId
+
+import org.eclipse.{lsp4j => l}
+
+/**
+ * Code action to convert a wildcard lambda to a lambda with named parameters
+ * e.g.
+ *
+ * List(1, 2).map(<<_>> + 1) => List(1, 2).map(i => i + 1)
+ */
+class ConvertToNamedLambdaParameters(
+    trees: Trees,
+    compilers: Compilers,
+) extends CodeAction {
+
+  override val kind: String = l.CodeActionKind.RefactorRewrite
+
+  private case class ConvertToNamedLambdaParametersData(
+      codeActionId: String,
+      position: l.TextDocumentPositionParams,
+  ) extends CodeActionResolveData
+
+  override def resolveCodeAction(
+      codeAction: l.CodeAction,
+      token: CancelToken,
+  )(implicit ec: ExecutionContext): Option[Future[l.CodeAction]] = {
+    parseData[ConvertToNamedLambdaParametersData](codeAction) match {
+      case Some(data) =>
+        Some {
+          val uri = data.position.getTextDocument().getUri()
+          for {
+            edits <- compilers.codeAction(
+              data.position,
+              token,
+              CodeActionId.ConvertToNamedLambdaParameters,
+              None,
+            )
+            _ = logging.logErrorWhen(
+              edits.isEmpty(),
+              s"Could not convert lambda at position ${data.position} to named lambda",
+            )
+            workspaceEdit = new l.WorkspaceEdit(Map(uri -> edits).asJava)
+            _ = codeAction.setEdit(workspaceEdit)
+          } yield codeAction
+        }
+      case _ => None
+    }
+  }
+
+  override def contribute(
+      params: l.CodeActionParams,
+      token: CancelToken,
+  )(implicit ec: ExecutionContext): Future[Seq[l.CodeAction]] = {
+    val path = params.getTextDocument().getUri().toAbsolutePath
+    val range = params.getRange()
+    val maybeLambda =
+      trees.findLastEnclosingAt[Term.AnonymousFunction](path, range.getStart())
+    maybeLambda
+      .map { lambda =>
+        val position = new l.TextDocumentPositionParams(
+          params.getTextDocument(),
+          new l.Position(lambda.pos.startLine, lambda.pos.startColumn),
+        )
+        val data =
+          ConvertToNamedLambdaParametersData(
+            codeActionId = CodeActionId.ConvertToNamedLambdaParameters,
+            position = position,
+          )
+        val codeAction = CodeActionBuilder.build(
+          title = ConvertToNamedLambdaParameters.title,
+          kind = kind,
+          data = Some(data.toJsonObject),
+        )
+        Future.successful(Seq(codeAction))
+      }
+      .filter(_ =>
+        compilers
+          .supportedCodeActions(path)
+          .contains(CodeActionId.ConvertToNamedLambdaParameters)
+      )
+      .getOrElse(Future.successful(Nil))
+  }
+
+}
+
+object ConvertToNamedLambdaParameters {
+  def title: String = "Convert to named lambda parameters"
+}

mtags-interfaces/src/main/java/scala/meta/pc/CodeActionId.java

@@ -12,4 +12,5 @@ public class CodeActionId {
   public static final String InlineValue = "InlineValue";
   public static final String InsertInferredType = "InsertInferredType";
   public static final String InsertInferredMethod = "InsertInferredMethod";
+  public static final String ConvertToNamedLambdaParameters = "ConvertToNamedLambdaParameters";
 }

mtags/src/main/scala-2/scala/meta/internal/pc/ExtractMethodProvider.scala

@@ -14,6 +14,7 @@ final class ExtractMethodProvider(
 )(implicit queryInfo: PcQueryContext)
     extends ExtractMethodUtils {
   import compiler._
+
   def extractMethod: List[l.TextEdit] = {
     val text = range.text()
     val unit = addCompilationUnit(

tests/cross/src/main/scala/tests/BaseExtractMethodSuite.scala

@@ -10,7 +10,6 @@ import scala.meta.internal.metals.TextEdits
 import munit.Location
 import munit.TestOptions
 import org.eclipse.{lsp4j => l}
-import tests.BaseCodeActionSuite
 
 class BaseExtractMethodSuite extends BaseCodeActionSuite {
   def checkEdit(

tests/slow/src/test/scala/tests/feature/Scala3CodeActionLspSuite.scala

@@ -2,6 +2,7 @@ package tests.feature
 
 import scala.meta.internal.metals.BuildInfo
 import scala.meta.internal.metals.codeactions.ConvertToNamedArguments
+import scala.meta.internal.metals.codeactions.ConvertToNamedLambdaParameters
 import scala.meta.internal.metals.codeactions.CreateCompanionObjectCodeAction
 import scala.meta.internal.metals.codeactions.ExtractMethodCodeAction
 import scala.meta.internal.metals.codeactions.ExtractRenameMember
@@ -771,6 +772,29 @@ class Scala3CodeActionLspSuite
        |""".stripMargin,
   )
 
+  check(
+    "wildcard lambda",
+    """|package a
+       |
+       |object A {
+       |  val l = List(1, 2, 3)
+       |  l.map(_ + <<1>>)
+       |}
+       |""".stripMargin,
+    s"""|${ConvertToNamedArguments.title("map(...)")}
+        |${ConvertToNamedLambdaParameters.title}
+        |""".stripMargin,
+    """|package a
+       |
+       |object A {
+       |  val l = List(1, 2, 3)
+       |  l.map(i => i + 1)
+       |}
+       |""".stripMargin,
+    selectedActionIndex = 1,
+    scalaVersion = "3.7.1-RC1-bin-20250501-83ffe00-NIGHTLY",
+  )
+
   private def getPath(name: String) = s"a/src/main/scala/a/$name"
 
   def checkExtractedMember(