GROOVY-11196: tap/with/identity propagates null not NullObject

3_0_X backport

src/main/java/org/codehaus/groovy/runtime/DefaultGroovyMethods.java

@@ -255,14 +255,14 @@ public static boolean is(Object self, Object other) {
      * @see #with(Object, Closure)
      * @since 1.0
      */
-    public static <T,U> T identity(
+    public static <T, U> T identity(
             @DelegatesTo.Target("self") U self,
             @DelegatesTo(value=DelegatesTo.Target.class,
                     target="self",
                     strategy=Closure.DELEGATE_FIRST)
             @ClosureParams(FirstParam.class)
-                    Closure<T> closure) {
-        return DefaultGroovyMethods.with(self, closure);
+            Closure<T> closure) {
+        return with(self, closure);
     }
 
     /**
@@ -300,7 +300,7 @@ public static <T,U> T identity(
      * @since 1.5.0
      */
     @SuppressWarnings("unchecked")
-    public static <T,U> T with(
+    public static <T, U> T with(
             @DelegatesTo.Target("self") U self,
             @DelegatesTo(value=DelegatesTo.Target.class,
                     target="self",
@@ -348,20 +348,22 @@ public static <T,U> T with(
      * @see #tap(Object, Closure)
      * @since 2.5.0
      */
-    public static <T,U extends T, V extends T> T with(
+    public static <T, U extends T, V extends T> T with(
             @DelegatesTo.Target("self") U self,
             boolean returning,
             @DelegatesTo(value=DelegatesTo.Target.class,
                     target="self",
                     strategy=Closure.DELEGATE_FIRST)
             @ClosureParams(FirstParam.class)
-            Closure<T> closure) {
-        @SuppressWarnings("unchecked")
-        final Closure<V> clonedClosure = (Closure<V>) closure.clone();
-        clonedClosure.setResolveStrategy(Closure.DELEGATE_FIRST);
-        clonedClosure.setDelegate(self);
-        V result = clonedClosure.call(self);
-        return returning ? self : result;
+            Closure<T> closure) { // TODO: T -> V
+        if (self == NullObject.getNullObject()) {
+            self = null; // GROOVY-4526, et al.
+        }
+        @SuppressWarnings("unchecked") Closure<V> mutableClosure = (Closure<V>) closure.clone();
+        mutableClosure.setResolveStrategy(Closure.DELEGATE_FIRST);
+        mutableClosure.setDelegate(self);
+        V rv = mutableClosure.call(self);
+        return returning ? self : rv;
     }
 
     /**
@@ -394,7 +396,7 @@ public static <T,U extends T, V extends T> T with(
      * @since 2.5.0
      */
     @SuppressWarnings("unchecked")
-    public static <T,U> U tap(
+    public static <T, U> U tap(
             @DelegatesTo.Target("self") U self,
             @DelegatesTo(value=DelegatesTo.Target.class,
                     target="self",
@@ -18085,16 +18087,13 @@ public static MetaClass getMetaClass(GroovyObject obj) {
      * @since 1.6.0
      */
     public static void setMetaClass(Class self, MetaClass metaClass) {
-        final MetaClassRegistry metaClassRegistry = GroovySystem.getMetaClassRegistry();
-        if (metaClass == null)
-            metaClassRegistry.removeMetaClass(self);
-        else {
-            if (metaClass instanceof HandleMetaClass) {
-                metaClassRegistry.setMetaClass(self, ((HandleMetaClass)metaClass).getAdaptee());
-            } else {
-                metaClassRegistry.setMetaClass(self, metaClass);
-            }
-            if (self==NullObject.class) {
+        if (metaClass == null) {
+            GroovySystem.getMetaClassRegistry().removeMetaClass(self);
+        } else {
+            MetaClass mc = metaClass instanceof HandleMetaClass
+              ? ((HandleMetaClass)metaClass).getAdaptee() : metaClass;
+            GroovySystem.getMetaClassRegistry().setMetaClass(self,mc);
+            if (NullObject.class.equals(self)) { // GROOVY-3803
                 NullObject.getNullObject().setMetaClass(metaClass);
             }
         }

src/main/java/org/codehaus/groovy/runtime/NullObject.java

@@ -25,152 +25,158 @@
 import java.util.Iterator;
 
 public class NullObject extends GroovyObjectSupport {
-    private static final NullObject INSTANCE = new NullObject();
 
-    /**
-     * private constructor
-     */
-    private NullObject() {
-    }
+    private static final NullObject INSTANCE = new NullObject();
 
     /**
-     * get the NullObject reference
+     * Returns the NullObject reference.
      *
      * @return the null object
      */
     public static NullObject getNullObject() {
         return INSTANCE;
     }
 
+    private NullObject() {
+    }
+
+    //--------------------------------------------------------------------------
+
     /**
-     * Since this is implemented as a singleton, we should avoid the
-     * use of the clone method
+     * Since this is implemented as a singleton, avoid the use of the clone method.
+     *
+     * @return never
+     * @throws NullPointerException
      */
+    @Override
     public Object clone() {
         throw new NullPointerException("Cannot invoke method clone() on null object");
     }
 
     /**
-     * Tries to get a property on null, which will always fail
+     * null is only equal to null.
      *
-     * @param property - the property to get
-     * @return a NPE
+     * @param o the reference object with which to compare
+     * @return true if this object is the same as the to argument
      */
-    public Object getProperty(String property) {
-        throw new NullPointerException("Cannot get property '" + property + "' on null object");
+    @Override
+    public boolean equals(final Object o) {
+        return o == null;
     }
 
     /**
-     * Allows the closure to be called for NullObject
-     *
-     * @param closure the closure to call on the object
-     * @return result of calling the closure
+     * @return never
+     * @throws NullPointerException
      */
-    public <T> T with( Closure<T> closure ) {
-        return DefaultGroovyMethods.with( null, closure ) ;
+    @Override
+    public int hashCode() {
+        throw new NullPointerException("Cannot invoke method hashCode() on null object");
+    }
+
+    @Override
+    public String toString() {
+        return "null";
     }
 
     /**
-     * Tries to set a property on null, which will always fail
+     * Tries to get a property on null, which fails.
      *
-     * @param property - the proprty to set
-     * @param newValue - the new value of the property
+     * @return never
+     * @throws NullPointerException
      */
-    public void setProperty(String property, Object newValue) {
-        throw new NullPointerException("Cannot set property '" + property + "' on null object");
+    @Override
+    public Object getProperty(final String name) {
+        throw new NullPointerException("Cannot get property '" + name + "' on null object");
     }
 
     /**
-     * Tries to invoke a method on null, which will always fail
+     * Tries to set a property on null, which fails.
      *
-     * @param name the name of the method to invoke
-     * @param args - arguments to the method
-     * @return a NPE
+     * @throws NullPointerException
      */
-    public Object invokeMethod(String name, Object args) {
-        throw new NullPointerException("Cannot invoke method " + name + "() on null object");
+    @Override
+    public  void  setProperty(final String name, final Object value) {
+        throw new NullPointerException("Cannot set property '" + name + "' on null object");
     }
 
     /**
-     * null is only equal to null
+     * Tries to invoke a method on null, which falis.
      *
-     * @param to - the reference object with which to compare
-     * @return - true if this object is the same as the to argument
+     * @return never
+     * @throws NullPointerException
      */
-    public boolean equals(Object to) {
-        return to == null;
+    @Override
+    public Object invokeMethod(final String name, final Object arguments) {
+        throw new NullPointerException("Cannot invoke method " + name + "() on null object");
     }
 
+    //--------------------------------------------------------------------------
+
     /**
-     * iterator() method to be able to iterate on null.
-     * Note: this part is from Invoker
+     * A null object coerces to false.
      *
-     * @return an iterator for an empty list
+     * @return false
      */
-    public Iterator iterator() {
-        return Collections.EMPTY_LIST.iterator();
+    public boolean asBoolean() {
+        return false;
     }
 
     /**
-     * Allows to add a String to null.
-     * The result is concatenated String of the result of calling
-     * toString() on this object and the String in the parameter.
+     * Type conversion method for null.
      *
-     * @param s - the String to concatenate
-     * @return the concatenated string
+     * @return null
      */
-    public Object plus(String s) {
-        return getMetaClass().invokeMethod(this, "toString", new Object[]{}) + s;
+    public Object asType(final Class c) {
+        return null;
     }
 
     /**
-     * Fallback for null+null.
-     * The result is always a NPE. The plus(String) version will catch 
-     * the case of adding a non null String to null.
+     * Tests for equal references.
      *
-     * @param o - the Object
-     * @return nothing
+     * @return true if object is null
      */
-    public Object plus(Object o) {
-        throw new NullPointerException("Cannot execute null+" + o);
+    public boolean is(final Object o) {
+        return equals(o);
     }
 
     /**
-     * The method "is" is used to test for equal references.
-     * This method will return true only if the given parameter
-     * is null
+     * Provides ability to iterate on null.
      *
-     * @param other - the object to test
-     * @return true if other is null
+     * @return an empty iterator
      */
-    public boolean is(Object other) {
-        return other == null;
+    public Iterator iterator() {
+        return Collections.emptyIterator();
     }
 
     /**
-     * Type conversion method for null.
+     * Fallback for {@code null+null}. The {@link plus(String)} variant catches
+     * the case of adding a non-null String to null.
      *
-     * @param c - the class to convert to
-     * @return always null
+     * @return never
+     * @throws NullPointerException
      */
-    public Object asType(Class c) {
-        return null;
+    public Object plus(final Object o) {
+        throw new NullPointerException("Cannot execute null+" + o);
     }
 
     /**
-     * A null object always coerces to false.
-     * 
-     * @return false
+     * Allows to add a String to null.
+     * The result is concatenated String of the result of calling
+     * toString() on this object and the String in the parameter.
+     *
+     * @return the concatenated string
      */
-    public boolean asBoolean() {
-        return false;
-    }
-
-    public String toString() {
-        return "null";
+    public Object plus(final String s) {
+        return getMetaClass().invokeMethod(this, "toString", new Object[0]) + s;
     }
 
-    public int hashCode() {
-        throw new NullPointerException("Cannot invoke method hashCode() on null object");
+    /**
+     * Allows the closure to be called for NullObject.
+     *
+     * @param closure the closure to call on the object
+     * @return result of calling the closure
+     */
+    public <T> T with(final Closure<T> closure) {
+        return DefaultGroovyMethods.with(null, closure); // GROOVY-4526, GROOVY-4985
     }
 }