Handle named args in pattern matching

build.sbt

@@ -126,6 +126,10 @@ lazy val tastyQuery =
       mimaBinaryIssueFilters ++= {
         import com.typesafe.tools.mima.core.*
         Seq(
+          // New pattern tree node for named extractor patterns `case Foo(field = pat)`
+          ProblemFilters.exclude[MissingClassProblem]("tastyquery.Trees$NamedPattern"),
+          ProblemFilters.exclude[MissingClassProblem]("tastyquery.Trees$NamedPattern$"),
+          ProblemFilters.exclude[MissingFieldProblem]("tastyquery.Trees.NamedPattern"),
         )
       },
 

tasty-query/shared/src/main/scala/tastyquery/Printers.scala

@@ -607,6 +607,11 @@ private[tastyquery] object Printers:
       case ExprPattern(expr) =>
         print(expr)
 
+      case NamedPattern(name, body) =>
+        print(name)
+        print(" = ")
+        print(body)
+
       case QuotePattern(bindings, body, quotes, patternType) =>
         print("'<")
         print(quotes)

tasty-query/shared/src/main/scala/tastyquery/Traversers.scala

@@ -145,6 +145,8 @@ object Traversers:
         traverse(patterns)
       case ExprPattern(expr) =>
         traverse(expr)
+      case NamedPattern(name, body) =>
+        traverse(body)
       case WildcardPattern(tpe) =>
         ()
       case QuotePattern(bindings, body, quotes, patternType) =>

tasty-query/shared/src/main/scala/tastyquery/Trees.scala

@@ -638,6 +638,12 @@ object Trees {
     override final def withPos(pos: SourcePosition): ExprPattern = ExprPattern(expr)(pos)
   end ExprPattern
 
+  /** A named argument pattern `name = body` in an [[Unapply]], as in `case Foo(field = pat)`. */
+  final case class NamedPattern(name: UnsignedTermName, body: PatternTree)(pos: SourcePosition)
+      extends PatternTree(pos):
+    override final def withPos(pos: SourcePosition): NamedPattern = NamedPattern(name, body)(pos)
+  end NamedPattern
+
   /** A tree representing a quote pattern `'{ type binding1; ...; body }` or `'[ type binding1; ...; body ]`.
     *
     * The `bindings` contain the list of quote pattern type variable definitions (`TypeTreeBind`s)

tasty-query/shared/src/main/scala/tastyquery/reader/tasties/TreeUnpickler.scala

@@ -897,6 +897,13 @@ private[tasties] class TreeUnpickler private (
       reader.readByte()
       val shared = forkAt(reader.readAddr()).readPattern
       if spn.isUnknown then shared else shared.withPos(spn)
+    case NAMEDARG =>
+      // Named extractor patterns (e.g., `case Foo(field = value)`) wrap sub-patterns in NAMEDARG.
+      val spn = span
+      reader.readByte()
+      val name = readUnsignedName()
+      val body = readPattern
+      NamedPattern(name, body)(spn)
     case _ =>
       val expr = readTerm
       ExprPattern(expr)(expr.pos)

tasty-query/shared/src/test/scala/tastyquery/ReadTreeSuite.scala

@@ -596,6 +596,17 @@ class ReadTreeSuite extends RestrictedUnpicklingSuite {
     assert(containsSubtree(guardWithAlternatives)(clue(tree)))
   }
 
+  testUnpickle("named-extractor-pattern", "simple_trees.NamedExtractorPattern") { tree =>
+    // case Wrapper(value = Some(v)) => v
+    val namedPatternCheck: StructureCheck = {
+      case NamedPattern(
+            SimpleName("value"),
+            TypeTest(Unapply(_, _, List(Bind(SimpleName("v"), WildcardPattern(_), _))), _)
+          ) =>
+    }
+    assert(containsSubtree(namedPatternCheck)(clue(tree)))
+  }
+
   testUnpickle("assign", "simple_trees.Assign") { tree =>
     val assignBlockMatch: StructureCheck = {
       case Block(

test-sources/src/main/scala/simple_trees/NamedExtractorPattern.scala

@@ -0,0 +1,8 @@
+package simple_trees
+
+case class Wrapper(value: Option[String])
+
+class NamedExtractorPattern {
+  def extract(items: List[Wrapper]): List[String] =
+    items.collect { case Wrapper(value = Some(v)) => v }
+}