[JEP-409] Add support for sealed classes and interfaces in Java

Author: hamzaremmal

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

@@ -489,6 +489,9 @@ object JavaParsers {
             addAnnot(scalaDot(jtpnme.VOLATILEkw))
           case SYNCHRONIZED | STRICTFP =>
             in.nextToken()
+          case SEALED =>
+            flags |= Flags.Sealed
+            in.nextToken()
           case _ =>
             val privateWithin: TypeName =
               if (isPackageAccess && !inInterface) thisPackageName
@@ -812,6 +815,17 @@ object JavaParsers {
       else
         List()
 
+
+    def permittedSubclassesOpt(isSealed: Boolean) : List[Tree] =
+      if in.token == PERMITS && !isSealed then
+        syntaxError(em"A type declaration that has a permits clause should have a sealed modifier")
+      if in.token == PERMITS then
+        in.nextToken()
+        repsep(() => typ(), COMMA)
+      else
+        // JEP-409: Class/Interface may omit the permits clause
+        Nil
+
     def classDecl(start: Offset, mods: Modifiers): List[Tree] = {
       accept(CLASS)
       val nameOffset = in.offset
@@ -825,6 +839,7 @@ object JavaParsers {
         else
           ObjectTpt()
       val interfaces = interfacesOpt()
+      val permittedSubclasses = permittedSubclassesOpt(mods.is(Flags.Sealed))
       val (statics, body) = typeBody(CLASS, name)
       val cls = atSpan(start, nameOffset) {
         TypeDef(name, makeTemplate(superclass :: interfaces, body, tparams, needsDummyConstr = true)).withMods(mods)
@@ -889,6 +904,7 @@ object JavaParsers {
         }
         else
           List(ObjectTpt())
+      val permittedSubclasses = permittedSubclassesOpt(mods is Flags.Sealed)
       val (statics, body) = typeBody(INTERFACE, name)
       val iface = atSpan(start, nameOffset) {
         TypeDef(

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

@@ -393,7 +393,6 @@ object JavaScanners {
                '5' | '6' | '7' | '8' | '9' =>
             putChar(ch)
             nextChar()
-
           case '_' =>
             putChar(ch)
             nextChar()

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

@@ -10,7 +10,7 @@ object JavaTokens extends TokensCommon {
 
   final val javaOnlyKeywords: TokenSet = tokenRange(INSTANCEOF, ASSERT)
   final val sharedKeywords: BitSet = BitSet( IF, FOR, ELSE, THIS, NULL, NEW, SUPER, ABSTRACT, FINAL, PRIVATE, PROTECTED,
-    EXTENDS, TRUE, FALSE, CLASS, IMPORT, PACKAGE, DO, THROW, TRY, CATCH, FINALLY, WHILE, RETURN )
+    EXTENDS, TRUE, FALSE, CLASS, IMPORT, PACKAGE, DO, THROW, TRY, CATCH, FINALLY, WHILE, RETURN, SEALED)
   final val primTypes: TokenSet = tokenRange(VOID, DOUBLE)
   final val keywords: BitSet = sharedKeywords | javaOnlyKeywords | primTypes
 
@@ -22,6 +22,7 @@ object JavaTokens extends TokensCommon {
   inline val INTERFACE = 105;        enter(INTERFACE, "interface")
   inline val ENUM = 106;             enter(ENUM, "enum")
   inline val IMPLEMENTS = 107;       enter(IMPLEMENTS, "implements")
+  inline val PERMITS = 108;          enter(PERMITS, "permits")
 
   /** modifiers */
   inline val PUBLIC = 110;           enter(PUBLIC, "public")

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

@@ -78,7 +78,7 @@ abstract class TokensCommon {
   //inline val YIELD = 48;            enter(YIELD, "yield")
   inline val DO = 49;               enter(DO, "do")
   //inline val TRAIT = 50;            enter(TRAIT, "trait")
-  //inline val SEALED = 51;           enter(SEALED, "sealed")
+  inline val SEALED = 51;           enter(SEALED, "sealed")
   inline val THROW = 52;            enter(THROW, "throw")
   inline val TRY = 53;              enter(TRY, "try")
   inline val CATCH = 54;            enter(CATCH, "catch")
@@ -169,7 +169,7 @@ object Tokens extends TokensCommon {
   inline val OBJECT = 44;           enter(OBJECT, "object")
   inline val YIELD = 48;            enter(YIELD, "yield")
   inline val TRAIT = 50;            enter(TRAIT, "trait")
-  inline val SEALED = 51;           enter(SEALED, "sealed")
+  //inline val SEALED = 51;           enter(SEALED, "sealed")
   inline val MATCH = 58;            enter(MATCH, "match")
   inline val LAZY = 59;             enter(LAZY, "lazy")
   inline val THEN = 60;             enter(THEN, "then")

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

@@ -1546,6 +1546,7 @@ class Namer { typer: Typer =>
        *  (2) If may not derive from itself
        *  (3) The class is not final
        *  (4) If the class is sealed, it is defined in the same compilation unit as the current class
+       *      (unless defined in Java. See JEP-409)
        */
       def checkedParentType(parent: untpd.Tree): Type = {
         val ptype = parentType(parent)(using completerCtx.superCallContext).dealiasKeepAnnots
@@ -1567,7 +1568,7 @@ class Namer { typer: Typer =>
             if pclazz.is(Final) then
               report.error(ExtendFinalClass(cls, pclazz), cls.srcPos)
             else if pclazz.isEffectivelySealed && pclazz.associatedFile != cls.associatedFile then
-              if pclazz.is(Sealed) then
+              if pclazz.is(Sealed) && !pclazz.is(JavaDefined) then
                 report.error(UnableToExtendSealedClass(pclazz), cls.srcPos)
               else if sourceVersion.isAtLeast(future) then
                 checkFeature(nme.adhocExtensions,

tests/neg/i18533.check

@@ -0,0 +1,4 @@
+-- Error: tests/neg/i18533/Pet_SCALA_ONLY.java:3:10 --------------------------------------------------------------------
+3 |class Pet permits Cat { // error
+  |          ^^^^^^^
+  |          A type declaration that has a permits clause should have a sealed modifier

tests/neg/i18533/Cat_SCALA_ONLY.java

@@ -0,0 +1,5 @@
+package i18533;
+
+public class Cat extends Pet {
+
+}

tests/neg/i18533/Pet_SCALA_ONLY.java

@@ -0,0 +1,5 @@
+package i18533;
+
+class Pet permits Cat { // error
+
+}

tests/pos/i18533/Cat.java

@@ -0,0 +1,5 @@
+package i18533;
+
+public final class Cat extends Pet {
+
+}

tests/pos/i18533/Pet.java

@@ -0,0 +1,5 @@
+package i18533;
+
+public sealed class Pet permits Cat {
+
+}