8016285: Add java.lang.reflect.Parameter.isNamePresent()

Summary: Add isNamePresent method to parameter reflection library, which indicates whether or real parameter data is available
Reviewed-by: darcy

src/share/classes/java/lang/reflect/Executable.java

@@ -326,8 +326,12 @@ public abstract class Executable extends AccessibleObject
             tmp = getParameters0();
 
             // If we get back nothing, then synthesize parameters
-            if (tmp == null)
+            if (tmp == null) {
+                hasRealParameterData = false;
                 tmp = synthesizeAllParams();
+            } else {
+                hasRealParameterData = true;
+            }
 
             parameters = tmp;
         }
@@ -335,6 +339,16 @@ public abstract class Executable extends AccessibleObject
         return tmp;
     }
 
+    boolean hasRealParameterData() {
+        // If this somehow gets called before parameters gets
+        // initialized, force it into existence.
+        if (parameters == null) {
+            privateGetParameters();
+        }
+        return hasRealParameterData;
+    }
+
+    private transient volatile boolean hasRealParameterData;
     private transient volatile Parameter[] parameters;
 
     private native Parameter[] getParameters0();

src/share/classes/java/lang/reflect/Parameter.java

@@ -94,6 +94,19 @@ public final class Parameter implements AnnotatedElement {
         return executable.hashCode() ^ index;
     }
 
+    /**
+     * Returns true if the parameter has a name according to the class
+     * file; returns false otherwise. Whether a parameter has a name
+     * is determined by the {@literal MethodParameters} attribute of
+     * the method which declares the parameter.
+     *
+     * @return true if and only if the parameter has a name according
+     * to the class file.
+     */
+    public boolean isNamePresent() {
+        return executable.hasRealParameterData();
+    }
+
     /**
      * Returns a string describing this parameter.  The format is the
      * modifiers for the parameter, if any, in canonical order as
@@ -149,11 +162,15 @@ public final class Parameter implements AnnotatedElement {
 
     /**
      * Returns the name of the parameter.  If the parameter's name is
-     * defined in a class file, then that name will be returned by
-     * this method.  Otherwise, this method will synthesize a name of
-     * the form argN, where N is the index of the parameter.
+     * {@linkplain isNamePresent() present}, then this method returns
+     * the name provided by the class file. Otherwise, this method
+     * synthesizes a name of the form argN, where N is the index of
+     * the parameter in the descriptor of the method which declares
+     * the parameter.
      *
-     * @return the name of the parameter
+     * @return The name of the parameter, either provided by the class
+     *         file or synthesized if the class file does not provide
+     *         a name.
      */
     public String getName() {
         // Note: empty strings as paramete names are now outlawed.

test/java/lang/reflect/Parameter/WithParameters.java

@@ -73,6 +73,10 @@ public class WithParameters {
                 }
                 for(int i = 0; i < parameters.length; i++) {
                     Parameter p = parameters[i];
+                    if(!p.isNamePresent()) {
+                        System.err.println(p + ".isNamePresent == false");
+                        error++;
+                    }
                     if(!parameters[i].getName().equals(qux_names[i])) {
                         System.err.println("Wrong parameter name for " + parameters[i]);
                         error++;

test/java/lang/reflect/Parameter/WithoutParameters.java

@@ -69,6 +69,7 @@ public class WithoutParameters {
 
         for(int i = 0; i < parameters.length; i++) {
             Parameter p = parameters[i];
+            errorIfTrue(p.isNamePresent(), p + ".isNamePresent == true");
             errorIfTrue(!p.getDeclaringExecutable().equals(e), p + ".getDeclaringExecutable != " + e);
             Objects.requireNonNull(p.getType(), "getType() should not be null");
             Objects.requireNonNull(p.getParameterizedType(), "getParameterizedType() should not be null");