Summary

JEP 445 involves language changes and javax.lang.model needs supporting updates.

Problem

Add and update API elements in javax.lang.model to support JEP 445's unnamed classes.

Solution

Add a predicate to TypeElement to query for an unnamed class and update Filer to support creating unnamed classes.

Specification

diff --git a/src/java.compiler/share/classes/javax/annotation/processing/Filer.java b/src/java.compiler/share/classes/javax/annotation/processing/Filer.java
index a2e73ee8786..9ebcf2c5908 100644
--- a/src/java.compiler/share/classes/javax/annotation/processing/Filer.java
+++ b/src/java.compiler/share/classes/javax/annotation/processing/Filer.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2005, 2022, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2005, 2023, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -28,6 +28,7 @@ package javax.annotation.processing;
 import javax.tools.JavaFileManager;
 import javax.tools.*;
 import javax.lang.model.element.Element;
+import javax.lang.model.element.TypeElement;
 import javax.lang.model.util.Elements;
 import java.io.IOException;

@@ -176,6 +177,13 @@ public interface Filer {
      * <p>Creating a source file in or for an <em>unnamed</em> package in a <em>named</em>
      * module is <em>not</em> supported.
      *
+     * <p>If the environment is configured to support {@linkplain
+     * TypeElement#isUnnamed unnamed classes}, the name argument is
+     * used to provide the leading component of the name used for the
+     * output file. For example {@code filer.createSourceFile("Foo")}
+     * to create an unnamed class hosted in {@code Foo.java}. All
+     * unnamed classes must be in an unnamed package.
+     *
      * @apiNote To use a particular {@linkplain
      * java.nio.charset.Charset charset} to encode the contents of the
      * file, an {@code OutputStreamWriter} with the chosen charset can
@@ -255,6 +263,13 @@ public interface Filer {
      * <p>Creating a class file in or for an <em>unnamed</em> package in a <em>named</em>
      * module is <em>not</em> supported.
      *
+     * <p>If the environment is configured to support {@linkplain
+     * TypeElement#isUnnamed unnamed classes}, the name argument is
+     * used to provide the leading component of the name used for the
+     * output file. For example {@code filer.createClassFile("Foo")} to
+     * create an unnamed class hosted in {@code Foo.class}. All unnamed
+     * classes must be in an unnamed package.
+     *
      * @apiNote To avoid subsequent errors, the contents of the class
      * file should be compatible with the {@linkplain
      * ProcessingEnvironment#getSourceVersion source version} being
diff --git a/src/java.compiler/share/classes/javax/lang/model/element/TypeElement.java b/src/java.compiler/share/classes/javax/lang/model/element/TypeElement.java
index 68df8920342..ab83acb344c 100644
diff --git a/src/java.compiler/share/classes/javax/lang/model/element/TypeElement.java b/src/java.compiler/share/classes/javax/lang/model/element/TypeElement.java
index 68df8920342..48bc4132eea 100644
--- a/src/java.compiler/share/classes/javax/lang/model/element/TypeElement.java
+++ b/src/java.compiler/share/classes/javax/lang/model/element/TypeElement.java
@@ -25,6 +25,8 @@

 package javax.lang.model.element;

+import jdk.internal.javac.PreviewFeature;
+
 import java.util.List;
 import javax.lang.model.type.*;
 import javax.lang.model.util.*;
@@ -147,7 +149,7 @@ public interface TypeElement extends Element, Parameterizable, QualifiedNameable
     /**
      * Returns the fully qualified name of this class or interface
      * element.  More precisely, it returns the <i>canonical</i> name.
-     * For local and anonymous classes, which do not have canonical
+     * For local, anonymous, and {@linkplain #isUnnamed() unnamed} classes, which do not have canonical
      * names, an {@linkplain Name##empty_name empty name} is
      * returned.
      *
@@ -163,6 +165,7 @@ public interface TypeElement extends Element, Parameterizable, QualifiedNameable
      *
      * @see Elements#getBinaryName
      * @jls 6.7 Fully Qualified Names and Canonical Names
+     * @jls 7.3 Compilation Units
      */
     Name getQualifiedName();

@@ -172,6 +175,10 @@ public interface TypeElement extends Element, Parameterizable, QualifiedNameable
      * For an anonymous class, an {@linkplain Name##empty_name empty
      * name} is returned.
      *
+     * For an {@linkplain #isUnnamed() unnamed} class, a name matching
+     * the base name of the hosting file, minus any extension, is
+     * returned.
+     *
      * @return the simple name of this class or interface,
      * an empty name for an anonymous class
      *
@@ -179,6 +186,22 @@ public interface TypeElement extends Element, Parameterizable, QualifiedNameable
     @Override
     Name getSimpleName();

+    /**
+     * {@return {@code true} if this is an unnamed class and {@code
+     * false} otherwise}
+     *
+     * @implSpec
+     * The default implementation of this method returns {@code false}.
+     *
+     * @jls 7.3 Compilation Units
+     * @since 21
+     */
+    @PreviewFeature(feature=PreviewFeature.Feature.UNNAMED_CLASSES,
+                    reflective=true)
+    default boolean isUnnamed() {
+        return false;
+    }
+
     /**
      * Returns the direct superclass of this class or interface element.
      * If this class or interface element represents an interface or the class