add javac and javap support for the ACC_NULL_CHECKED flag

Reviewed-by: liach

Author: Vicente Romero

src/java.base/share/classes/java/lang/classfile/ClassFile.java

@@ -847,6 +847,14 @@ default List<VerifyError> verify(Path path) throws IOException {
     /** The bit mask of {@link AccessFlag#STRICT} access and property modifier. */
     int ACC_STRICT = 0x0800;
 
+    /**
+     * The bit mask of {@link AccessFlag#NULL_CHECKED} access and property modifier.
+     *
+     * @since Valhalla
+     */
+    @PreviewFeature(feature = PreviewFeature.Feature.NULL_RESTRICTION, reflective = true)
+    int ACC_NULL_CHECKED = 0x0200;
+
     /**
      * The bit mask of {@link AccessFlag#STRICT_INIT} access and property modifier.
      *

src/java.base/share/classes/java/lang/reflect/AccessFlag.java

@@ -283,6 +283,18 @@ public enum AccessFlag {
            List.of(Map.entry(RELEASE_16, Location.SET_METHOD),
                    Map.entry(RELEASE_1, Location.EMPTY_SET))),
 
+    /**
+     * The access flag {@code ACC_NULL_CHECKED}, with a mask value of
+     * <code>{@value "0x%01x" ClassFile#ACC_NULL_CHECKED}</code>.
+     *
+     * @jvms TBD
+     * @since Valhalla
+     */
+    @PreviewFeature(feature = PreviewFeature.Feature.NULL_RESTRICTION, reflective=true)
+    NULL_CHECKED(ACC_NULL_CHECKED, false,
+            Location.SET_FIELD,
+            List.of(Map.entry(latest(), Location.EMPTY_SET))),
+
     /**
      * The access flag {@code ACC_STRICT_INIT}, with a mask value of
      * <code>{@value "0x%04x" ClassFile#ACC_STRICT_INIT}</code>.
@@ -479,7 +491,7 @@ public enum Location {
          */
         FIELD(ACC_PUBLIC | ACC_PRIVATE | ACC_PROTECTED |
               ACC_STATIC | ACC_FINAL | ACC_VOLATILE |
-              ACC_TRANSIENT | ACC_SYNTHETIC | ACC_ENUM | ACC_STRICT_INIT,
+              ACC_TRANSIENT | ACC_SYNTHETIC | ACC_ENUM | ACC_STRICT_INIT | ACC_NULL_CHECKED,
               List.of(Map.entry(latest(), // no strict_init
                                 ACC_PUBLIC | ACC_PRIVATE | ACC_PROTECTED |
                                 ACC_STATIC | ACC_FINAL | ACC_VOLATILE |
@@ -763,7 +775,7 @@ private static AccessFlag[] findDefinition(Location location, ClassFileFormatVer
             CLASS_FLAGS         = createDefinition(PUBLIC, FINAL, SUPER, INTERFACE, ABSTRACT, SYNTHETIC, ANNOTATION, ENUM, MODULE),
             CLASS_PREVIEW_FLAGS = createDefinition(PUBLIC, FINAL, IDENTITY, INTERFACE, ABSTRACT, SYNTHETIC, ANNOTATION, ENUM, MODULE), // identity
             FIELD_FLAGS         = createDefinition(PUBLIC, PRIVATE, PROTECTED, STATIC, FINAL, VOLATILE, TRANSIENT, SYNTHETIC, ENUM),
-            FIELD_PREVIEW_FLAGS = createDefinition(PUBLIC, PRIVATE, PROTECTED, STATIC, FINAL, VOLATILE, TRANSIENT, SYNTHETIC, ENUM, STRICT_INIT), // strict
+            FIELD_PREVIEW_FLAGS = createDefinition(PUBLIC, PRIVATE, PROTECTED, STATIC, FINAL, VOLATILE, TRANSIENT, SYNTHETIC, ENUM, STRICT_INIT, NULL_CHECKED), // strict
             METHOD_FLAGS = createDefinition(PUBLIC, PRIVATE, PROTECTED, STATIC, FINAL, SYNCHRONIZED, BRIDGE, VARARGS, NATIVE, ABSTRACT, STRICT, SYNTHETIC),
             INNER_CLASS_FLAGS         = createDefinition(PUBLIC, PRIVATE, PROTECTED, STATIC, FINAL, INTERFACE, ABSTRACT, SYNTHETIC, ANNOTATION, ENUM),
             INNER_CLASS_PREVIEW_FLAGS = createDefinition(PUBLIC, PRIVATE, PROTECTED, IDENTITY, STATIC, FINAL, INTERFACE, ABSTRACT, SYNTHETIC, ANNOTATION, ENUM),  // identity

src/jdk.compiler/share/classes/com/sun/tools/javac/code/Flags.java

@@ -134,6 +134,9 @@ public static EnumSet<FlagsEnum> asFlagSet(long flags) {
     public static final int ACC_VARARGS  = 1<<7;
     @Use({FlagTarget.VARIABLE})
     @NoToStringValue
+    public static final int ACC_NULL_CHECKED = 1<<9;
+    @Use({FlagTarget.VARIABLE})
+    @NoToStringValue
     public static final int ACC_STRICT   = 1<<11;
     @Use({FlagTarget.CLASS})
     @NoToStringValue

src/jdk.compiler/share/classes/com/sun/tools/javac/jvm/ClassReader.java

@@ -3343,9 +3343,14 @@ public void readClassFile(ClassSymbol c) {
 
     long adjustFieldFlags(long flags) {
         boolean previewClassFile = minorVersion == ClassFile.PREVIEW_MINOR_VERSION;
-        if (allowValueClasses && previewClassFile && (flags & ACC_STRICT) != 0) {
-            flags &= ~ACC_STRICT;
-            flags |= STRICT;
+        if (allowValueClasses && previewClassFile) {
+            if ((flags & ACC_STRICT) != 0) {
+                flags &= ~ACC_STRICT;
+                flags |= STRICT;
+            }
+            if ((flags & ACC_NULL_CHECKED) != 0) {
+                flags &= ~ACC_NULL_CHECKED;
+            }
         }
         return flags;
     }

src/jdk.compiler/share/classes/com/sun/tools/javac/jvm/ClassWriter.java

@@ -1932,9 +1932,12 @@ int adjustFlags(Symbol sym, final long flags) {
             }
         }
         if (sym.kind == VAR) {
-            if ((flags & STRICT) != 0 || (flags & MARK_STRICT_INIT) != 0 || types.isNonNullable(sym.type)) {
+            if ((flags & STRICT) != 0 || (flags & MARK_STRICT_INIT) != 0) {
                 result |= ACC_STRICT;
             }
+            if (types.isNonNullable(sym.type)) {
+                result |= ACC_NULL_CHECKED;
+            }
         }
         return result;
     }

test/langtools/tools/javac/nullability/NullabilityCompilationTests.java

@@ -620,10 +620,15 @@ class Test {
                 for (var field : classFile.fields()) {
                     if (!field.flags().has(AccessFlag.STATIC)) {
                         Set<AccessFlag> fieldFlags = field.flags().flags();
-                        Assert.check(fieldFlags.size() == 1 && fieldFlags.contains(AccessFlag.STRICT_INIT));
+                        Assert.check(fieldFlags.size() == 2 &&
+                                fieldFlags.contains(AccessFlag.STRICT_INIT) &&
+                                fieldFlags.contains(AccessFlag.NULL_CHECKED));
                     } else {
                         Set<AccessFlag> fieldFlags = field.flags().flags();
-                        Assert.check(fieldFlags.size() == 2 && fieldFlags.contains(AccessFlag.STRICT_INIT) && fieldFlags.contains(AccessFlag.STATIC));
+                        Assert.check(fieldFlags.size() == 3 &&
+                                fieldFlags.contains(AccessFlag.STRICT_INIT) &&
+                                fieldFlags.contains(AccessFlag.STATIC) &&
+                                fieldFlags.contains(AccessFlag.NULL_CHECKED));
                     }
                 }
             }