Extend javax.lang.model to cover binding variables

Summary

The javax.lang.model.element.ElementKind models various local variables, but, with the recent addition of binding variables (for pattern matching), a new ElementKind was not added. The proposal here is to add a new ElementKind for binding variables.

Problem

Various types of variables local to methods have their own enum constant in ElementKind, but binding variables don't.

Solution

A new enum constant, BINDING_VARIABLE, is added into the ElementKind.

Specification

diff --git a/src/java.compiler/share/classes/javax/lang/model/element/ElementKind.java b/src/java.compiler/share/classes/javax/lang/model/element/ElementKind.java
--- a/src/java.compiler/share/classes/javax/lang/model/element/ElementKind.java
+++ b/src/java.compiler/share/classes/javax/lang/model/element/ElementKind.java
@@ -137,7 +137,24 @@
      */
     @jdk.internal.PreviewFeature(feature=jdk.internal.PreviewFeature.Feature.RECORDS,
                                  essentialAPI=false)
-    RECORD_COMPONENT;
+    RECORD_COMPONENT,
+
+    /**
+     * {@preview Associated with pattern matching for {@code
+     * instanceof}, a preview feature of the Java language.
+     *
+     *           This enum constant is associated with <i>pattern
+     *           matching for {@code instanceof}</i>, a preview
+     *           feature of the Java language. Preview features
+     *           may be removed in a future release, or upgraded to permanent
+     *           features of the Java language.}
+     *
+     * A binding variable in a pattern .
+     * @since 14
+     */
+    @jdk.internal.PreviewFeature(feature=jdk.internal.PreviewFeature.Feature.PATTERN_MATCHING_IN_INSTANCEOF,
+                                 essentialAPI=false)
+    BINDING_VARIABLE;

     /**
      * Returns {@code true} if this is a kind of class:
diff --git a/src/java.compiler/share/classes/javax/lang/model/util/ElementKindVisitor14.java b/src/java.compiler/share/classes/javax/lang/model/util/ElementKindVisitor14.java
--- a/src/java.compiler/share/classes/javax/lang/model/util/ElementKindVisitor14.java
+++ b/src/java.compiler/share/classes/javax/lang/model/util/ElementKindVisitor14.java
@@ -136,4 +136,20 @@
     public R visitTypeAsRecord(TypeElement e, P p) {
         return defaultAction(e, p);
     }
+
+    /**
+     * Visits a {@code BINDING_VARIABLE} variable element.
+     *
+     * @implSpec This implementation calls {@code defaultAction}.
+     *
+     * @param e {@inheritDoc}
+     * @param p {@inheritDoc}
+     * @return  the result of {@code defaultAction}
+     *
+     * @since 14
+     */
+    @Override
+    public R visitVariableAsBindingVariable(VariableElement e, P p) {
+        return defaultAction(e, p);
+    }
 }
diff --git a/src/java.compiler/share/classes/javax/lang/model/util/ElementKindVisitor6.java b/src/java.compiler/share/classes/javax/lang/model/util/ElementKindVisitor6.java
--- a/src/java.compiler/share/classes/javax/lang/model/util/ElementKindVisitor6.java
+++ b/src/java.compiler/share/classes/javax/lang/model/util/ElementKindVisitor6.java
@@ -360,6 +363,21 @@
     }

     /**
+     * Visits a {@code BINDING_VARIABLE} variable element.
+     *
+     * @implSpec This implementation calls {@code visitUnknown}.
+     *
+     * @param e the element to visit
+     * @param p a visitor-specified parameter
+     * @return  the result of {@code visitUnknown}
+     *
+     * @since 14
+     */
+    public R visitVariableAsBindingVariable(VariableElement e, P p) {
+        return visitUnknown(e, p);
+    }
+
+    /**
      * {@inheritDoc}
      *
      * @implSpec This implementation dispatches to the visit method

A specdiff is also attached, and also available at the following location for convenience: http://cr.openjdk.java.net/~jlahoda/8235541/specdiff.00/overview-summary.html