Add support for JEP-409 (sealed classes) + Add javacOpt directive (#19080)

Closes #18533 

---

This PR also adds the following directive to the vulpix infrastructure:
```scala
//> using javacOpt *
```
inspired by :
https://scala-cli.virtuslab.org/docs/reference/directives#javac-options

Author: bishabosha

Diff for: compiler/src/dotty/tools/dotc/parsing/JavaParsers.scala

@@ -489,6 +489,18 @@ object JavaParsers {
             addAnnot(scalaDot(jtpnme.VOLATILEkw))
           case SYNCHRONIZED | STRICTFP =>
             in.nextToken()
+          case SEALED =>
+            flags |= Flags.Sealed
+            in.nextToken()
+          // JEP-409: Special trick for the 'non-sealed' java keyword
+          case IDENTIFIER if in.name.toString == "non" =>
+            val lookahead = in.LookaheadScanner()
+            ({lookahead.nextToken(); lookahead.token}, {lookahead.nextToken(); lookahead.name.toString}) match
+              case (MINUS, "sealed") =>
+                in.nextToken(); in.nextToken() // skip '-' and 'sealed'. Nothing more to do
+              case _ =>
+                syntaxError(em"Identifier '${in.name}' is not allowed here")
+            in.nextToken()
           case _ =>
             val privateWithin: TypeName =
               if (isPackageAccess && !inInterface) thisPackageName
@@ -812,6 +824,17 @@ 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 +848,7 @@ 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 +913,7 @@ object JavaParsers {
         }
         else
           List(ObjectTpt())
+      val permittedSubclasses = permittedSubclassesOpt(mods is Flags.Sealed)
       val (statics, body) = typeBody(INTERFACE, name)
       val iface = atSpan(start, nameOffset) {
         TypeDef(

Diff for: 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()

Diff for: 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")

Diff for: 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")

Diff for: 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)
        *
        * @param isJava  If true, the parent type is in Java mode, and we do not require a stable prefix
        */
@@ -1569,7 +1570,7 @@ 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,

Diff for: compiler/test/dotty/tools/utils.scala

@@ -81,7 +81,14 @@ def toolArgsFor(tool: ToolName, filename: Option[String])(lines: List[String]):
 // groups are (name, args)
 // note: ideally we would replace everything that requires this to use directive syntax, however scalajs: --skip has no directive equivalent yet.
 private val toolArg = raw"(?://|/\*| \*) ?(?i:(${ToolName.values.mkString("|")})):((?:[^*]|\*(?!/))*)".r.unanchored
+
+// ================================================================================================
+// =================================== VULPIX DIRECTIVES ==========================================
+// ================================================================================================
+
+/** Directive to specify to vulpix the options to pass to Dotty */
 private val directiveOptionsArg = raw"//> using options (.*)".r.unanchored
+private val directiveJavacOptions = raw"//> using javacOpt (.*)".r.unanchored
 
 // Inspect the lines for compiler options of the form
 // `//> using options args`, `// scalajs: args`, `/* scalajs: args`, ` * scalajs: args` etc.
@@ -90,10 +97,15 @@ private val directiveOptionsArg = raw"//> using options (.*)".r.unanchored
 def toolArgsParse(lines: List[String], filename: Option[String]): List[(String,String)] =
   lines.flatMap {
     case toolArg("scalac", _) => sys.error(s"`// scalac: args` not supported. Please use `//> using options args`${filename.fold("")(f => s" in file $f")}")
+    case toolArg("javac", _) => sys.error(s"`// javac: args` not supported. Please use `//> using javacOpt args`${filename.fold("")(f => s" in file $f")}")
     case toolArg(name, args) => List((name, args))
     case _ => Nil
   } ++
-  lines.flatMap { case directiveOptionsArg(args) => List(("scalac", args)) case _ => Nil }
+  lines.flatMap { 
+    case directiveOptionsArg(args) => List(("scalac", args))
+    case directiveJavacOptions(args) => List(("javac", args))
+    case _ => Nil 
+  }
 
 import org.junit.Test
 import org.junit.Assert._
@@ -104,6 +116,6 @@ class ToolArgsTest:
   @Test def `tool is present`: Unit = assertEquals("-hey" :: Nil, toolArgsFor(ToolName.Test, None)("// test: -hey" :: Nil))
   @Test def `missing tool is absent`: Unit = assertEquals(Nil, toolArgsFor(ToolName.Javac, None)("// test: -hey" :: Nil))
   @Test def `multitool is present`: Unit =
-    assertEquals("-hey" :: Nil, toolArgsFor(ToolName.Test, None)("// test: -hey" :: "// javac: -d /tmp" :: Nil))
-    assertEquals("-d" :: "/tmp" :: Nil, toolArgsFor(ToolName.Javac, None)("// test: -hey" :: "// javac: -d /tmp" :: Nil))
+    assertEquals("-hey" :: Nil, toolArgsFor(ToolName.Test, None)("// test: -hey" :: "// java: -d /tmp" :: Nil))
+    assertEquals("-d" :: "/tmp" :: Nil, toolArgsFor(ToolName.Java, None)("// test: -hey" :: "// java: -d /tmp" :: Nil))
 end ToolArgsTest

Diff for: compiler/test/dotty/tools/vulpix/ParallelTesting.scala

@@ -498,6 +498,7 @@ trait ParallelTesting extends RunnerOrchestration { self =>
         case None => true
 
       def scalacOptions = toolArgs.getOrElse(ToolName.Scalac, Nil)
+      def javacOptions  = toolArgs.getOrElse(ToolName.Javac, Nil)
 
       val flags = flags0
         .and(scalacOptions*)
@@ -512,11 +513,10 @@ trait ParallelTesting extends RunnerOrchestration { self =>
 
       def compileWithJavac(fs: Array[String]) = if (fs.nonEmpty) {
         val fullArgs = Array(
-          "javac",
           "-encoding", StandardCharsets.UTF_8.name,
-        ) ++ flags.javacFlags ++ fs
+        ) ++ flags.javacFlags ++ javacOptions++ fs
 
-        val process = Runtime.getRuntime.exec(fullArgs)
+        val process = Runtime.getRuntime.exec("javac" +: fullArgs)
         val output = Source.fromInputStream(process.getErrorStream).mkString
 
         if waitForJudiciously(process) != 0 then Some(output)

Diff for: tests/neg/i18533.check

@@ -0,0 +1,8 @@
+-- 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
+-- Error: tests/neg/i18533/non-SCALA_ONLY.java:4:7 ---------------------------------------------------------------------
+4 |public non class Test { // error
+  |       ^^^
+  |       Identifier 'non' is not allowed here

Diff for: tests/neg/i18533/Cat_SCALA_ONLY.java

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

Diff for: tests/neg/i18533/Pet_SCALA_ONLY.java

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

Diff for: tests/neg/i18533/non-SCALA_ONLY.java

@@ -0,0 +1,6 @@
+package i18533;
+
+// Special test for the non-sealed trick (See JavaParsers.scala::modifiers)
+public non class Test { // error
+
+}

Diff for: tests/pos/i18533/Cat.java

@@ -0,0 +1,8 @@
+//> using javacOpt --enable-preview --source 17
+//> test: -jvm 17+
+
+package i18533;
+
+public final class Cat extends Pet {
+
+}

Diff for: tests/pos/i18533/Dog.java

@@ -0,0 +1,8 @@
+//> using javacOpt --enable-preview --source 17
+//> test: -jvm 17+
+
+package i18533;
+
+public non-sealed class Dog extends Pet {
+
+}

Diff for: tests/pos/i18533/Pet.java

@@ -0,0 +1,8 @@
+//> using javacOpt --enable-preview --source 17
+//> test: -jvm 17+
+
+package i18533;
+
+public sealed class Pet permits Cat, Dog {
+
+}

Diff for: tests/run/t9915/C_1.java

@@ -1,6 +1,3 @@
-/*
- * javac: -encoding UTF-8
- */
 public class C_1 {
     public static final String NULLED = "X\000ABC";
     public static final String SUPPED = "𐒈𐒝𐒑𐒛𐒐𐒘𐒕𐒖";