squash: use Object.equals for comparing parsers and document the implications for parsers defined by lambdas

Author: dougxc

src/jdk.internal.vm.ci/share/classes/jdk/vm/ci/meta/annotation/AbstractAnnotated.java

@@ -22,7 +22,6 @@
  */
 package jdk.vm.ci.meta.annotation;
 
-import java.util.Objects;
 import java.util.function.Function;
 
 /**
@@ -56,7 +55,7 @@ public <T> T getDeclaredAnnotationInfo(Function<AnnotationsInfo, T> parser) {
             return (T) getRawDeclaredAnnotationInfo();
         }
         ParsedDeclaredAnnotationsCacheEntry<?> cache = parsedDeclaredAnnotationsCache;
-        if (cache == null || cache.parser != Objects.requireNonNull(parser)) {
+        if (cache == null || !parser.equals(cache.parser)) {
             AnnotationsInfo info = getRawDeclaredAnnotationInfo();
             cache = new ParsedDeclaredAnnotationsCacheEntry<>(parser, parser.apply(info));
             parsedDeclaredAnnotationsCache = cache;

src/jdk.internal.vm.ci/share/classes/jdk/vm/ci/meta/annotation/Annotated.java

@@ -38,17 +38,23 @@ public interface Annotated {
      * parser function to it and returns the result.
      * <p>
      * The result of the last call to this method is cached if {@code parser != null}.
-     * That is, if the same parser object is used again without any intervening calls with a different
-     * parser, the same result object will be returned.
+     * That is, if an {@linkplain Object#equals(Object) equivalent} parser object is
+     * used again without any intervening calls with a different parser, the same
+     * result object will be returned.
+     * <p>
+     * Note: Since lambda objects implement {@link Object#equals(Object)} with identity,
+     * if {@code parser} is a lambda object, it should be a singleton in a final
+     * static field. There is no guarantee about the identity of the result of a
+     * lambda expression (JLS {@jls 15.27.4}).
      *
      * @param <T>    the type of the result produced by the parser function
      * @param parser a function that takes the declared annotation information and
      *               produces a result of type T. If {@code null}, then the
      *               AnnotationsInfo value that would have been parsed is returned and
      *               the cache is not updated.
      * @return the result of applying the parser function to the declared annotation
-     * information, potentially retrieved from cache if the same parser
-     * object was previously used
+     * information, potentially retrieved from cache if the identical parser object
+     * was previously used
      */
     <T> T getDeclaredAnnotationInfo(Function<AnnotationsInfo, T> parser);