Add support for java records in pattern matching

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

@@ -315,4 +315,15 @@ object Annotations {
         case Some(Constant(msg: String)) => Some(msg)
         case _ => Some("")
   }
+
+  object JavaRecordFieldsAnnotation {
+    def unapply(a: Annotation)(using Context): Option[List[String]] =
+      if a.symbol ne defn.JavaRecordFieldsAnnot then None
+      else
+        a.tree match
+          case Apply(_, List(Typed(SeqLiteral(args, _), _))) =>
+            val fields = args.collect { case Literal(Constant(s: String)) => s }
+            Some(fields)
+          case _ => None
+  }
 }

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

@@ -1112,6 +1112,7 @@ class Definitions {
   @tu lazy val PublicInBinaryAnnot: ClassSymbol = requiredClass("scala.annotation.publicInBinary")
   @tu lazy val WitnessNamesAnnot: ClassSymbol = requiredClass("scala.annotation.internal.WitnessNames")
   @tu lazy val StableNullAnnot: ClassSymbol = requiredClass("scala.annotation.stableNull")
+  @tu lazy val JavaRecordFieldsAnnot: ClassSymbol = requiredClass("scala.annotation.internal.JavaRecordFields")
 
   @tu lazy val JavaRepeatableAnnot: ClassSymbol = requiredClass("java.lang.annotation.Repeatable")
 

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

@@ -271,6 +271,7 @@ object StdNames {
     final val MethodParametersATTR: N             = "MethodParameters"
     final val LineNumberTableATTR: N              = "LineNumberTable"
     final val LocalVariableTableATTR: N           = "LocalVariableTable"
+    final val RecordATTR: N                       = "Record"
     final val RuntimeVisibleAnnotationATTR: N     = "RuntimeVisibleAnnotations"   // RetentionPolicy.RUNTIME
     final val RuntimeInvisibleAnnotationATTR: N   = "RuntimeInvisibleAnnotations" // RetentionPolicy.CLASS
     final val RuntimeParamAnnotationATTR: N       = "RuntimeVisibleParameterAnnotations" // RetentionPolicy.RUNTIME (annotations on parameters)

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

@@ -403,6 +403,8 @@ class SymUtils:
       || isDefaultArgumentOfCheckedMethod
       || (!self.is(Package) && checkOwner(self.owner))
 
+    def isJavaRecord(using Context) = self.is(JavaDefined) && self.derivesFrom(defn.JavaRecordClass)
+
     /** The declared self type of this class, as seen from `site`, stripping
     *  all refinements for opaque types.
     */

compiler/src/dotty/tools/dotc/core/classfile/ClassfileParser.scala

@@ -535,6 +535,35 @@ class ClassfileParser(
     }
   }
 
+  class RecordUnapplyCompleter() extends LazyType {
+    override def complete(denot: SymDenotation)(using Context): Unit =
+      def methType(t: Type) = MethodType(List(nme.x_0), List(t), t)
+
+      val unapplyMethodType =
+        val recType = classRoot.typeRef
+        val tparams = classRoot.typeParams
+        if tparams.length > 0 then
+          PolyType(tparams.map(_.name))(
+            pt => tparams.map(_.info.subst(tparams, pt.paramRefs).bounds),
+            pt => methType(AppliedType(recType, pt.paramRefs))
+          )
+        else methType(recType)
+
+      // synthetic unapply generated here won't be invalidated by `invalidateIfClashingSynthetic`, so we handle that immediately
+      val clashes = denot.owner.unforcedDecls.lookupAll(nme.unapply)
+      if clashes.exists(c => c != denot.symbol && c.info.matches(unapplyMethodType)) then
+        denot.info = NoType
+      else
+        denot.info = unapplyMethodType
+        val sym = denot.symbol
+        val ddef = DefDef(sym.asTerm, _.last.last)
+          .withAddedFlags(Flags.JavaDefined | Flags.SyntheticMethod | Flags.Inline).withSpan(Span(0))
+        sym.defTree = ddef
+
+        // typed trees generated here are not a subject to typer's inline logic, so we do that manually
+        inlines.PrepareInlineable.registerInlineInfo(sym, ddef.rhs)
+  }
+
   def constantTagToType(tag: Int)(using Context): Type =
     (tag: @switch) match {
       case BYTE_TAG   => defn.ByteType
@@ -990,6 +1019,32 @@ class ClassfileParser(
             report.log(s"$sym in ${sym.owner} is a java 8+ default method.")
           }
 
+        case tpnme.RecordATTR =>
+          val components = List.fill(in.nextChar):
+            val name = pool.getName(in.nextChar).value
+            val _ = in.nextChar
+            skipAttributes()
+            name
+
+          classRoot.addAnnotation(
+            Annotation(
+              defn.JavaRecordFieldsAnnot,
+              Typed(
+                SeqLiteral(components.map(field => Literal(Constant(field))), TypeTree(defn.StringType)),
+                TypeTree(defn.RepeatedParamType.appliedTo(defn.StringType))
+              ),
+              NoSpan
+            )
+          )
+          val completer = RecordUnapplyCompleter()
+          val member = newSymbol(
+            moduleRoot.symbol,
+            nme.unapply,
+            Flags.JavaDefined | Flags.SyntheticMethod | Flags.Inline,
+            completer,
+          )
+          staticScope.enter(member)
+
         case _ =>
       }
       in.bp = end

compiler/src/dotty/tools/dotc/parsing/JavaParsers.scala

@@ -900,8 +900,31 @@ object JavaParsers {
             needsDummyConstr = true
           )
         ).withMods(mods.withFlags(Flags.JavaDefined | Flags.Final))
+          .withAddedAnnotation(
+            New(
+              ref(defn.JavaRecordFieldsAnnot),
+              header.map(field => Literal(Constant(field.name.toString))) :: Nil,
+            ).withSpan(Span(start))
+          )
       }
-      addCompanionObject(statics, recordTypeDef)
+
+      val unapplyDef = {
+        val tparams2 = tparams.map(td => TypeDef(td.name, td.rhs).withMods(Modifiers(Flags.Param)))
+
+        val selfTpt = if tparams2.isEmpty then Ident(name) else
+          AppliedTypeTree(Ident(name), tparams2.map(tp => Ident(tp.name)))
+        val param = ValDef(nme.x_0, selfTpt, EmptyTree)
+          .withMods(Modifiers(Flags.JavaDefined | Flags.SyntheticParam))
+
+        DefDef(
+          nme.unapply,
+          joinParams(tparams2, List(List(param))),
+          selfTpt,
+          Ident(nme.x_0)
+        ).withMods(Modifiers(Flags.JavaDefined | Flags.SyntheticMethod | Flags.Inline))
+      }
+
+      addCompanionObject(unapplyDef :: statics, recordTypeDef)
     end recordDecl
 
     def interfaceDecl(start: Offset, mods: Modifiers): List[Tree] = {

compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala

@@ -422,8 +422,7 @@ object PatternMatcher {
                 (0 until unappResult.denot.info.tupleElementTypes.getOrElse(Nil).length)
                   .toList.map(tupleApp(_, ref(unappResult)))
               matchArgsPlan(components, args, onSuccess)
-            else {
-              assert(isGetMatch(unappType))
+            else if (isGetMatch(unappType)) {
               val argsPlan = {
                 val get = getOfGetMatch(ref(unappResult))
                 val arity = productArity(get.tpe.stripNamedTuple, unapp.srcPos)
@@ -450,6 +449,11 @@ object PatternMatcher {
                   }
               }
               TestPlan(NonEmptyTest, unappResult, unapp.span, argsPlan)
+            } else {
+              assert(unappType.classSymbol.isJavaRecord)
+              val selectors = javaRecordFields(unappType).map: field =>
+                ref(unappResult).select(field, _.paramSymss == List(Nil)).appliedToArgs(Nil)
+              matchArgsPlan(selectors, args, onSuccess)
             }
           }
       }

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

@@ -30,7 +30,7 @@ import util.chaining.tap
 import collection.mutable
 import config.Printers.{overload, typr, unapp}
 import TypeApplications.*
-import Annotations.Annotation
+import Annotations.{Annotation, JavaRecordFieldsAnnotation}
 
 import Constants.{Constant, IntTag}
 import Denotations.SingleDenotation
@@ -185,6 +185,11 @@ object Applications {
     (0 until argsNum).map(i => if (i < arity - 1) selectorTypes(i) else elemTp).toList
   end seqSelectors
 
+  def javaRecordFields(tp: Type)(using Context): List[Name] =
+    tp.typeSymbol.getAnnotation(defn.JavaRecordFieldsAnnot) match
+      case Some(JavaRecordFieldsAnnotation(fields)) => fields.map(termName)
+      case _ => assert(false)
+
   /** A utility class that matches results of unapplys with patterns. Two queriable members:
    *     val argTypes: List[Type]
    *     def typedPatterns(qual: untpd.Tree, typer: Typer): List[Tree]
@@ -263,6 +268,10 @@ object Applications {
             case _ => None
         case _ => None
 
+    private def javaRecordTypes(tp: Type): List[Type] =
+      javaRecordFields(tp).map: name =>
+        tp.member(name).suchThat(_.paramSymss == List(Nil)).info.resultType
+
     /** The computed argument types which will be the scutinees of the sub-patterns. */
     val argTypes: List[Type] =
       if unapplyName == nme.unapplySeq then
@@ -282,6 +291,8 @@ object Applications {
             productSelectorTypes(unapplyResult, pos)
               // this will cause a "wrong number of arguments in pattern" error later on,
               // which is better than the message in `fail`.
+          else if unapplyResult.classSymbol.isJavaRecord then
+            javaRecordTypes(unapplyResult)
           else fail
 
     /** The typed pattens of this unapply */

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

@@ -928,9 +928,6 @@ class Namer { typer: Typer =>
      */
     private def invalidateIfClashingSynthetic(denot: SymDenotation): Unit =
 
-      def isJavaRecord(owner: Symbol) =
-        owner.is(JavaDefined) && owner.derivesFrom(defn.JavaRecordClass)
-
       def isCaseClassOrCompanion(owner: Symbol) =
         owner.isClass && {
           if (owner.is(Module)) owner.linkedClass.is(CaseClass)
@@ -954,8 +951,8 @@ class Namer { typer: Typer =>
             && (definesMember || inheritsConcreteMember)
           )
           ||
-          // remove synthetic constructor or method of a java Record if it clashes with a non-synthetic constructor
-          (isJavaRecord(denot.owner)
+          // remove synthetic constructor, method or companion's unapply of a java Record if it clashes with a non-synthetic one
+          ((denot.owner.isJavaRecord || (denot.owner.companionClass.isJavaRecord && denot.name == nme.unapply))
             && denot.is(Method)
             && denot.owner.unforcedDecls.lookupAll(denot.name).exists(c => c != denot.symbol && c.info.matches(denot.info))
           )

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

@@ -2996,7 +2996,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
     val canBeInvalidated: Boolean =
       sym.is(Synthetic)
       && (desugar.isRetractableCaseClassMethodName(sym.name) ||
-         (sym.owner.is(JavaDefined) && sym.owner.derivesFrom(defn.JavaRecordClass) && sym.is(Method)))
+         (sym.owner.isJavaRecord && sym.is(Method)))
     assert(canBeInvalidated)
     sym.owner.info.decls.openForMutations.unlink(sym)
     EmptyTree

compiler/test/dotty/tools/dotc/CompilationTests.scala

@@ -169,13 +169,23 @@ class CompilationTests {
 
   @Test def runAll: Unit = {
     implicit val testGroup: TestGroup = TestGroup("runAll")
-    aggregateTests(
+    var tests = List(
       compileFilesInDir("tests/run", defaultOptions.and("-Wsafe-init")),
       compileFilesInDir("tests/run-deep-subtype", allowDeepSubtypes),
       compileFilesInDir("tests/run-custom-args/captures", allowDeepSubtypes.and("-language:experimental.captureChecking", "-language:experimental.separationChecking", "-source", "3.8")),
       // Run tests for legacy lazy vals.
       compileFilesInDir("tests/run", defaultOptions.and("-Wsafe-init", "-Ylegacy-lazy-vals", "-Ycheck-constraint-deps"), FileFilter.include(TestSources.runLazyValsAllowlist)),
-    ).checkRuns()
+    )
+
+    if scala.util.Properties.isJavaAtLeast("16") then
+      tests ++= List(
+        // for separate compilation
+        compileFilesInDir("tests/run-java16+", defaultOptions),
+        // for joint compilation
+        compileDir("tests/run-java16+/java-records-match", defaultOptions),
+      )
+
+    aggregateTests(tests*).checkRuns()
   }
 
   // Generic java signatures tests ---------------------------------------------

library/src/scala/annotation/internal/JavaRecordFields.scala

@@ -0,0 +1,8 @@
+package scala.annotation.internal
+
+import scala.annotation.StaticAnnotation
+
+/** An annotation attached by JavaParsers/ClassfileParser to Java record class
+ *  with a list of that record's fields. Used in pattern matching on records.
+ */
+final class JavaRecordFields(args: String*) extends StaticAnnotation

project/Build.scala

@@ -1315,6 +1315,7 @@ object Build {
         file(s"${baseDirectory.value}/src/scala/quoted/runtime/StopMacroExpansion.scala"),
         file(s"${baseDirectory.value}/src/scala/compiletime/Erased.scala"),
         file(s"${baseDirectory.value}/src/scala/annotation/internal/onlyCapability.scala"),
+        file(s"${baseDirectory.value}/src/scala/annotation/internal/JavaRecordFields.scala"),
         file(s"${baseDirectory.value}/src/scala/runtime/VarArgsBuilder.scala"),
       )
     )

project/MiMaFilters.scala

@@ -19,6 +19,7 @@ object MiMaFilters {
         ProblemFilters.exclude[MissingClassProblem]("scala.Conversion$"),
         ProblemFilters.exclude[MissingClassProblem]("scala.annotation.internal.RuntimeChecked"),
         ProblemFilters.exclude[MissingClassProblem]("scala.annotation.stableNull"),
+        ProblemFilters.exclude[MissingClassProblem]("scala.annotation.internal.JavaRecordFields"),
 
         ProblemFilters.exclude[DirectMissingMethodProblem]("scala.NamedTuple.namedTupleOrdering"),
         ProblemFilters.exclude[MissingClassProblem]("scala.NamedTuple$namedTupleOrdering"),

tests/run-java16+/java-records-match.check

@@ -0,0 +1,9 @@
+empty
+hello
+hahaha
+hehehe
+21
+hihihi
+hohoho
+unapply
+hejhejhejhej

tests/run-java16+/java-records-match/Rec0_1.java

@@ -0,0 +1 @@
+public record Rec0_1() {}

tests/run-java16+/java-records-match/Rec1_1.java

@@ -0,0 +1 @@
+public record Rec1_1(String s) {}

tests/run-java16+/java-records-match/Rec2_1.java

@@ -0,0 +1 @@
+public record Rec2_1(int x, String y) {}

tests/run-java16+/java-records-match/Rec3_1.java

@@ -0,0 +1 @@
+public record Rec3_1<T>(int x, T y) {}

tests/run-java16+/java-records-match/Rec4_1.java

@@ -0,0 +1 @@
+public record Rec4_1<T extends Comparable<Integer>>(int x, T y) {}

tests/run-java16+/java-records-match/Rec5_1.java

@@ -0,0 +1 @@
+public record Rec5_1<T, U extends Comparable<T>, W extends Comparable<W>>(T t, U u, W w) {}

tests/run-java16+/java-records-match/RecUnapply_1.java

@@ -0,0 +1,3 @@
+public record RecUnapply_1(int i, String s) {
+  public static boolean unapply(RecUnapply_1 r) { return true; }
+}

tests/run-java16+/java-records-match/Test_2.scala

@@ -0,0 +1,42 @@
+case class Foo(val value: String) extends Comparable[Integer]:
+  override def compareTo(other: Integer) = 0
+
+case class Bar(val value: String) extends Comparable[Bar]:
+  override def compareTo(other: Bar) = 0
+
+case class Baz(val s: String, val i: Int)
+
+object Baz:
+  def unapply(b: Baz): Rec2_1 = Rec2_1(b.i + 1, b.s + "j")
+
+@main def Test =
+  val r0 = Rec0_1()
+  r0 match { case Rec0_1() => println("empty") }
+
+  val r1 = Rec1_1("hello")
+  r1 match { case Rec1_1(s) => println(s) }
+
+  val r2 = Rec2_1(3, "ha")
+  r2 match { case Rec2_1(i, s) => println(s * i) }
+
+  // type param (no bounds)
+  val r3a = Rec3_1(3, "he")
+  r3a match { case Rec3_1(i, s) => println(s * i) }
+  val r3b = Rec3_1(3, 7)
+  r3b match { case Rec3_1(i, j) => println(i * j) }
+
+  // type param with simple bounds
+  val r4 = Rec4_1(3, Foo("hi"))
+  r4 match { case Rec4_1(i, f) => println(f.value * i) }
+
+  // type params with recursion / mutual reference
+  val r5 = Rec5_1(3 : Integer, Foo("h"), Bar("o"))
+  r5 match { case Rec5_1(i, f, b) => println((f.value + b.value) * i) }
+
+  // custom unapply
+  val r6 = RecUnapply_1(3, "x")
+  r6 match { case RecUnapply_1() => println("unapply") }
+
+  // scala class returning record from unapply
+  val r7 = Baz("he", 3)
+  r7 match { case Baz(i, s) => println(s * i) }