Support sealed classes

This implements support for JEP 409: Sealed Classes, see
https://openjdk.java.net/jeps/409.

The implementation handles the sealed and non-sealed keywords and sorts them
according to their JLS order.  This requires us to look at the actual text of
the Tok, as there’s no TokenKind for sealed and non-sealed.

The optional permits clause is handled in the same manner as the implements
clause. A new private method, classDeclarationTypeList, has been added to
facilitate this.

This fixes google#603.

core/src/main/java/com/google/googlejavaformat/java/JavaInputAstVisitor.java

@@ -1963,6 +1963,7 @@ public void visitClassDeclaration(ClassTree node) {
             /* declarationAnnotationBreak= */ Optional.empty());
     boolean hasSuperclassType = node.getExtendsClause() != null;
     boolean hasSuperInterfaceTypes = !node.getImplementsClause().isEmpty();
+    boolean hasPermitsTypes = !node.getPermitsClause().isEmpty();
     builder.addAll(breaks);
     token(node.getKind() == Tree.Kind.INTERFACE ? "interface" : "class");
     builder.space();
@@ -1975,30 +1976,18 @@ public void visitClassDeclaration(ClassTree node) {
       if (!node.getTypeParameters().isEmpty()) {
         typeParametersRest(
             node.getTypeParameters(),
-            hasSuperclassType || hasSuperInterfaceTypes ? plusFour : ZERO);
+            hasSuperclassType || hasSuperInterfaceTypes || hasPermitsTypes ? plusFour : ZERO);
       }
       if (hasSuperclassType) {
         builder.breakToFill(" ");
         token("extends");
         builder.space();
         scan(node.getExtendsClause(), null);
       }
-      if (hasSuperInterfaceTypes) {
-        builder.breakToFill(" ");
-        builder.open(node.getImplementsClause().size() > 1 ? plusFour : ZERO);
-        token(node.getKind() == Tree.Kind.INTERFACE ? "extends" : "implements");
-        builder.space();
-        boolean first = true;
-        for (Tree superInterfaceType : node.getImplementsClause()) {
-          if (!first) {
-            token(",");
-            builder.breakOp(" ");
-          }
-          scan(superInterfaceType, null);
-          first = false;
-        }
-        builder.close();
-      }
+      classDeclarationTypeList(
+          node.getKind() == Tree.Kind.INTERFACE ? "extends" : "implements",
+          node.getImplementsClause());
+      classDeclarationTypeList("permits", node.getPermitsClause());
     }
     builder.close();
     if (node.getMembers() == null) {
@@ -2277,6 +2266,8 @@ boolean nextIsModifier() {
       case "native":
       case "strictfp":
       case "default":
+      case "sealed":
+      case "non-sealed":
         return true;
       default:
         return false;
@@ -3549,6 +3540,24 @@ protected void addBodyDeclarations(
     }
   }
 
+  private void classDeclarationTypeList(String token, List<? extends Tree> types) {
+    if (types.isEmpty()) return;
+    builder.breakToFill(" ");
+    builder.open(types.size() > 1 ? plusFour : ZERO);
+    token(token);
+    builder.space();
+    boolean first = true;
+    for (Tree type : types) {
+      if (!first) {
+        token(",");
+        builder.breakOp(" ");
+      }
+      scan(type, null);
+      first = false;
+    }
+    builder.close();
+  }
+
   /**
    * The parser expands multi-variable declarations into separate single-variable declarations. All
    * of the fragments in the original declaration have the same start position, so we use that as a

core/src/main/java/com/google/googlejavaformat/java/ModifierOrderer.java

@@ -152,7 +152,11 @@ private static void addTrivia(StringBuilder replacement, ImmutableList<? extends
    * is not a modifier.
    */
   private static Modifier asModifier(Token token) {
-    return getModifier(((JavaInput.Tok) token.getTok()).kind());
+    Modifier m = getModifier(((JavaInput.Tok) token.getTok()).kind());
+    if (m != null) return m;
+    else if (token.getTok().getText().equals("sealed")) return Modifier.SEALED;
+    else if (token.getTok().getText().equals("non-sealed")) return Modifier.NON_SEALED;
+    else return null;
   }
 
   /** Applies replacements to the given string. */

core/src/test/java/com/google/googlejavaformat/java/FormatterIntegrationTest.java

@@ -50,7 +50,7 @@ public class FormatterIntegrationTest {
   private static final ImmutableSet<String> JAVA14_TESTS =
       ImmutableSet.of("I477", "Records", "RSLs", "Var", "ExpressionSwitch", "I574", "I594");
 
-  private static final ImmutableSet<String> JAVA16_TESTS = ImmutableSet.of("I588");
+  private static final ImmutableSet<String> JAVA16_TESTS = ImmutableSet.of("I588", "I603");
 
   @Parameters(name = "{index}: {0}")
   public static Iterable<Object[]> data() throws IOException {

core/src/test/resources/com/google/googlejavaformat/java/testdata/I603.input

@@ -0,0 +1 @@
+sealed abstract class T permits D, E {}

core/src/test/resources/com/google/googlejavaformat/java/testdata/I603.output

@@ -0,0 +1 @@
+abstract sealed class T permits D, E {}