Merge child Messages that travel up to the parent ViewModel.

Co-authored-by: Cursor <cursoragent@cursor.com>

fx/src/main/java/de/neitzel/fx/view/ChildMessageMirror.java

@@ -0,0 +1,127 @@
+package de.neitzel.fx.view;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.IdentityHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+/**
+ * Carries one child ViewModel's current notices onto its parent.
+ * <p>
+ * Each copy is keyed by the identity of the child {@link Message}. A later text change on that
+ * child notice updates the same copy, and dropping the child notice drops the copy. The copy's
+ * source is the Attribute name, a dot, and the child source. A further parent carries that copy
+ * the same way, so the source grows into a Path. The copy is not logged again.
+ */
+final class ChildMessageMirror implements MessageListener {
+
+    private final ViewModel parent;
+    private final String attribute;
+    private final ViewModel child;
+    private final Map<Message, Message> copies = new IdentityHashMap<>();
+
+    private ChildMessageMirror(ViewModel parent, String attribute, ViewModel child) {
+        this.parent = parent;
+        this.attribute = attribute;
+        this.child = child;
+    }
+
+    /**
+     * Starts carrying {@code child} onto {@code parent} under {@code attribute}.
+     * <p>
+     * Notices already on the child are copied, and notices added later are copied as they arrive.
+     *
+     * @param parent    the parent ViewModel
+     * @param attribute the Attribute that leads to the child
+     * @param child     the child ViewModel
+     * @return the mirror, so it can be detached when the Attribute is cleared
+     */
+    static ChildMessageMirror attach(ViewModel parent, String attribute, ViewModel child) {
+        ChildMessageMirror mirror = new ChildMessageMirror(parent, attribute, child);
+        child.addMessageListener(mirror);
+        for (Message message : List.copyOf(child.getMessages())) {
+            mirror.carry(message);
+        }
+        return mirror;
+    }
+
+    /**
+     * Stops carrying and drops this Attribute's copies from the parent.
+     */
+    void detach() {
+        child.removeMessageListener(this);
+        List<Message> dropped = new ArrayList<>(copies.values());
+        copies.clear();
+        for (Message copy : dropped) {
+            parent.removeCarriedMessage(copy);
+        }
+    }
+
+    /**
+     * Copies {@code message} onto the parent unless this parent already holds it.
+     *
+     * @param message the child notice
+     */
+    @Override
+    public void added(Message message) {
+        carry(message);
+    }
+
+    /**
+     * Drops the parent's copy of {@code message}.
+     *
+     * @param message the child notice
+     */
+    @Override
+    public void removed(Message message) {
+        Message copy = copies.remove(message);
+        if (copy != null) {
+            parent.removeCarriedMessage(copy);
+        }
+    }
+
+    /**
+     * Writes the child's new text onto the same parent copy.
+     *
+     * @param message the child notice
+     */
+    @Override
+    public void textChanged(Message message) {
+        Message copy = copies.get(message);
+        if (copy == null) {
+            return;
+        }
+        copy.setText(message.getText());
+        parent.noteMessageText(copy);
+    }
+
+    private void carry(Message message) {
+        if (copies.containsKey(message) || repeats(message)) {
+            return;
+        }
+        Message copy = message.withExtendedSource(attribute + "." + message.getSource());
+        copies.put(message, copy);
+        parent.addCarriedMessage(copy);
+    }
+
+    /**
+     * A cycle would carry a notice back onto a ViewModel that already holds it, or that holds
+     * the notice it was copied from.
+     *
+     * @param message the child notice
+     * @return {@code true} when the parent already has this notice or its origin
+     */
+    private boolean repeats(Message message) {
+        Message current = message;
+        Set<Message> seen = Collections.newSetFromMap(new IdentityHashMap<>());
+        while (current != null && seen.add(current)) {
+            if (parent.getMessages().contains(current)) {
+                return true;
+            }
+            current = current.origin();
+        }
+        return false;
+    }
+}

fx/src/main/java/de/neitzel/fx/view/DirectBindingApplier.java

@@ -57,11 +57,11 @@ final class DirectBindingApplier {
         Converter converter = converter(context, converterName);
         switch (binding.getDirection()) {
             case "both" -> alignConverted(
-                    controlProperty, attribute, converter, viewModel, binding.getPath(), true, true);
+                    controlProperty, attribute, converter, resolved.owner, resolved.name, true, true);
             case "view" -> alignConverted(
-                    controlProperty, attribute, converter, viewModel, binding.getPath(), true, false);
+                    controlProperty, attribute, converter, resolved.owner, resolved.name, true, false);
             case "model" -> alignConverted(
-                    controlProperty, attribute, converter, viewModel, binding.getPath(), false, true);
+                    controlProperty, attribute, converter, resolved.owner, resolved.name, false, true);
             default -> throw new IllegalArgumentException("Not a direction: " + binding.getDirection());
         }
     }
@@ -76,15 +76,22 @@ final class DirectBindingApplier {
     }
 
     /**
-     * The Attribute a Path names, and whether that Attribute is complex.
+     * The Attribute a Path names, the ViewModel that owns it, and whether that Attribute is complex.
+     * <p>
+     * {@code name} is the last segment. A conversion failure is recorded on {@code owner} with that
+     * name as the source, so a parent only carries the extended copy.
      */
     private static final class Resolved {
         private final Property<?> attribute;
         private final boolean complex;
+        private final ViewModel owner;
+        private final String name;
 
-        private Resolved(Property<?> attribute, boolean complex) {
+        private Resolved(Property<?> attribute, boolean complex, ViewModel owner, String name) {
             this.attribute = attribute;
             this.complex = complex;
+            this.owner = owner;
+            this.name = name;
         }
     }
 
@@ -123,7 +130,7 @@ final class DirectBindingApplier {
         if (attribute == null) {
             throw missing(path);
         }
-        return new Resolved(attribute, current.isComplex(last));
+        return new Resolved(attribute, current.isComplex(last), current, last);
     }
 
     private static IllegalArgumentException missing(String path) {
@@ -143,31 +150,35 @@ final class DirectBindingApplier {
         }
     }
 
+    /**
+     * Aligns a converted Attribute. Failures are recorded on {@code owner} with {@code sourceName},
+     * which is the last name of the Path.
+     */
     @SuppressWarnings("unchecked")
     private static void alignConverted(Property<?> controlProperty, Property<?> attribute, Converter converter,
-                                       ViewModel viewModel, String path, boolean towardView, boolean towardModel) {
+                                       ViewModel owner, String sourceName, boolean towardView, boolean towardModel) {
         Property<Object> control = (Property<Object>) controlProperty;
         Property<Object> source = (Property<Object>) attribute;
         Link link = new Link();
-        pushControl(control, source, converter, viewModel, path, link);
+        pushControl(control, source, converter, owner, sourceName, link);
         if (towardView) {
             source.addListener((observable, oldValue, newValue) -> {
                 if (!link.applying) {
-                    pushControl(control, source, converter, viewModel, path, link);
+                    pushControl(control, source, converter, owner, sourceName, link);
                 }
             });
         }
         if (towardModel) {
             control.addListener((observable, oldValue, newValue) -> {
                 if (!link.applying) {
-                    pushAttribute(control, source, converter, viewModel, path, link);
+                    pushAttribute(control, source, converter, owner, sourceName, link);
                 }
             });
         }
     }
 
     private static void pushControl(Property<Object> control, Property<Object> attribute, Converter converter,
-                                    ViewModel viewModel, String path, Link link) {
+                                    ViewModel owner, String source, Link link) {
         try {
             Object shown = converter.toControlValue(attribute.getValue());
             link.applying = true;
@@ -177,14 +188,14 @@ final class DirectBindingApplier {
             } finally {
                 link.applying = false;
             }
-            viewModel.clearBindingFailure(path);
+            owner.clearBindingFailure(source);
         } catch (RuntimeException failure) {
-            viewModel.reportBindingFailure(path, failureText(failure));
+            owner.reportBindingFailure(source, failureText(failure));
         }
     }
 
     private static void pushAttribute(Property<Object> control, Property<Object> attribute, Converter converter,
-                                      ViewModel viewModel, String path, Link link) {
+                                      ViewModel owner, String source, Link link) {
         try {
             Object converted = converter.toAttributeValue(control.getValue());
             link.applying = true;
@@ -194,7 +205,7 @@ final class DirectBindingApplier {
             } finally {
                 link.applying = false;
             }
-            viewModel.clearBindingFailure(path);
+            owner.clearBindingFailure(source);
         } catch (RuntimeException failure) {
             link.applying = true;
             try {
@@ -202,7 +213,7 @@ final class DirectBindingApplier {
             } finally {
                 link.applying = false;
             }
-            viewModel.reportBindingFailure(path, failureText(failure));
+            owner.reportBindingFailure(source, failureText(failure));
         }
     }
 

fx/src/main/java/de/neitzel/fx/view/Message.java

@@ -22,6 +22,7 @@ public final class Message {
     private final Severity severity;
     private String text;
     private final String source;
+    private Message origin;
 
     /**
      * Creates a notice.
@@ -71,4 +72,28 @@ public final class Message {
     void setText(String text) {
         this.text = text;
     }
+
+    /**
+     * Returns a copy whose source is extended for a parent ViewModel.
+     * <p>
+     * The copy remembers this notice, so a cycle does not carry it back onto the ViewModel
+     * that already holds it.
+     *
+     * @param source the extended source
+     * @return the copy
+     */
+    Message withExtendedSource(String source) {
+        Message copy = new Message(severity, text, source);
+        copy.origin = this;
+        return copy;
+    }
+
+    /**
+     * Returns the notice this copy mirrors.
+     *
+     * @return that notice, or {@code null} when this notice was added on its own ViewModel
+     */
+    Message origin() {
+        return origin;
+    }
 }

fx/src/main/java/de/neitzel/fx/view/MessageListener.java

@@ -0,0 +1,28 @@
+package de.neitzel.fx.view;
+
+/**
+ * Hears a notice added, dropped, or edited on a ViewModel.
+ */
+interface MessageListener {
+
+    /**
+     * A notice was added.
+     *
+     * @param message the notice
+     */
+    void added(Message message);
+
+    /**
+     * A notice was dropped.
+     *
+     * @param message the notice
+     */
+    void removed(Message message);
+
+    /**
+     * A notice kept its place and changed its text.
+     *
+     * @param message the notice
+     */
+    void textChanged(Message message);
+}

fx/src/main/java/de/neitzel/fx/view/ViewLoader.java

@@ -33,7 +33,9 @@ public final class ViewLoader {
      * {@link javafx.collections.ObservableList}, so an add or remove is visible on both sides.
      * A path that is not a read-write Attribute fails the load. The context creates a Controller,
      * and a Converter when a Direct binding names one. A converter that cannot produce a value
-     * keeps the previous value and records one error Message. It does not fail the load.
+     * keeps the previous value and records one error Message on the ViewModel that owns the last
+     * Attribute, with that Attribute's name as the source. A parent carries a copy with the source
+     * extended. It does not fail the load.
      * A parent document names a Component class as an element. The context creates that Component
      * and injects its services. The Component document {@code ClassName.fxml}, in the same package,
      * is loaded with the Component as {@code fx:root} and as the Controller. That document's

fx/src/main/java/de/neitzel/fx/view/ViewModel.java

@@ -64,7 +64,9 @@ import java.util.Set;
  * <p>
  * Beside those attributes, the ViewModel keeps a list of {@link Message}s and the latest one.
  * The developer can add a message of any severity. Error and fatal messages are written to the log.
- * Info and warn are not.
+ * Info and warn are not. A parent carries each current child message, with the source extended by
+ * the Attribute that leads to that child. Each further parent prepends its own Attribute. The
+ * carried copy is not logged again. When the child drops the message, the parent drops that copy.
  */
 public class ViewModel {
 
@@ -75,6 +77,8 @@ public class ViewModel {
     private final Set<String> complexAttributes = new HashSet<>();
     private final List<Message> messages = new ArrayList<>();
     private final Map<String, Message> bindingFailures = new HashMap<>();
+    private final List<MessageListener> messageListeners = new ArrayList<>();
+    private final Map<String, ChildMessageMirror> childMirrors = new HashMap<>();
     private Message latestMessage;
 
     /**
@@ -268,12 +272,43 @@ public class ViewModel {
     }
 
     private void watchComplex(Property<?> property, Method setter, String name) {
+        if (property.getValue() instanceof ViewModel child) {
+            attachChild(name, child);
+        }
         property.addListener((observable, oldValue, newValue) -> {
+            if (oldValue != newValue) {
+                detachChild(name);
+            }
             Object written = newValue instanceof ViewModel viewModel ? viewModel.model() : newValue;
             write(setter, name, written);
+            if (oldValue != newValue && newValue instanceof ViewModel child) {
+                attachChild(name, child);
+            }
         });
     }
 
+    /**
+     * Carries the child ViewModel's current notices, extending each source with this Attribute.
+     *
+     * @param name  the Attribute that leads to the child
+     * @param child the child ViewModel
+     */
+    private void attachChild(String name, ViewModel child) {
+        childMirrors.put(name, ChildMessageMirror.attach(this, name, child));
+    }
+
+    /**
+     * Drops the copies carried for an Attribute and stops following that child.
+     *
+     * @param name the Attribute
+     */
+    private void detachChild(String name) {
+        ChildMessageMirror mirror = childMirrors.remove(name);
+        if (mirror != null) {
+            mirror.detach();
+        }
+    }
+
     private void write(Method setter, String name, Object value) {
         try {
             setter.invoke(model, value);
@@ -311,12 +346,103 @@ public class ViewModel {
         messages.add(message);
         latestMessage = message;
         logSevere(message);
+        notifyAdded(message);
     }
 
     /**
-     * Records one error for a binding Path. A further failure of that Path replaces the text.
+     * Adds a copy of a child notice. The copy is not written to the log.
      *
-     * @param path the binding Path
+     * @param copy the carried notice
+     */
+    void addCarriedMessage(Message copy) {
+        messages.add(copy);
+        latestMessage = copy;
+        notifyAdded(copy);
+    }
+
+    /**
+     * Drops a carried copy. When it was the latest notice, the previous one becomes latest.
+     *
+     * @param copy the carried notice
+     */
+    void removeCarriedMessage(Message copy) {
+        if (!messages.remove(copy)) {
+            return;
+        }
+        if (latestMessage == copy) {
+            latestMessage = messages.isEmpty() ? null : messages.get(messages.size() - 1);
+        }
+        notifyRemoved(copy);
+    }
+
+    /**
+     * Hears notices added on this ViewModel, including carried copies, and hears when they are
+     * dropped or their text changes.
+     *
+     * @param listener the listener
+     */
+    void addMessageListener(MessageListener listener) {
+        messageListeners.add(listener);
+    }
+
+    /**
+     * Stops hearing notices added on this ViewModel.
+     *
+     * @param listener the listener
+     */
+    void removeMessageListener(MessageListener listener) {
+        messageListeners.remove(listener);
+    }
+
+    /**
+     * Tells listeners that a notice was added.
+     *
+     * @param message the notice
+     */
+    private void notifyAdded(Message message) {
+        for (MessageListener listener : List.copyOf(messageListeners)) {
+            listener.added(message);
+        }
+    }
+
+    /**
+     * Tells listeners that a notice kept its place and changed its text.
+     * <p>
+     * An in-place change does not log again and does not become a new latest notice.
+     *
+     * @param message the notice
+     */
+    void noteMessageText(Message message) {
+        notifyTextChanged(message);
+    }
+
+    /**
+     * Tells listeners that a notice was dropped.
+     *
+     * @param message the notice
+     */
+    private void notifyRemoved(Message message) {
+        for (MessageListener listener : List.copyOf(messageListeners)) {
+            listener.removed(message);
+        }
+    }
+
+    /**
+     * Tells listeners that a notice kept its place and changed its text.
+     *
+     * @param message the notice
+     */
+    private void notifyTextChanged(Message message) {
+        for (MessageListener listener : List.copyOf(messageListeners)) {
+            listener.textChanged(message);
+        }
+    }
+
+    /**
+     * Records one error whose source is an Attribute name. A further failure of that Attribute
+     * replaces the text of the same notice. Parents that carry the notice hear the new text.
+     *
+     * @param path the Attribute name that owns the failure
      * @param text the error text
      */
     void reportBindingFailure(String path, String text) {
@@ -324,6 +450,7 @@ public class ViewModel {
         if (existing != null) {
             existing.setText(text);
             logSevere(existing);
+            notifyTextChanged(existing);
             return;
         }
         Message message = new Message(Message.Severity.ERROR, text, path);
@@ -332,9 +459,9 @@ public class ViewModel {
     }
 
     /**
-     * Drops the error recorded for a binding Path after a later conversion succeeds.
+     * Drops the error recorded for an Attribute after a later conversion succeeds.
      *
-     * @param path the binding Path
+     * @param path the Attribute name that owned the failure
      */
     void clearBindingFailure(String path) {
         Message existing = bindingFailures.remove(path);
@@ -345,6 +472,7 @@ public class ViewModel {
         if (latestMessage == existing) {
             latestMessage = messages.isEmpty() ? null : messages.get(messages.size() - 1);
         }
+        notifyRemoved(existing);
     }
 
     /**

fx/src/test/java/de/neitzel/fx/view/CarryChildMessageTest.java

@@ -0,0 +1,356 @@
+package de.neitzel.fx.view;
+
+import de.neitzel.fx.view.fixture.Address;
+import de.neitzel.fx.view.fixture.Household;
+import de.neitzel.fx.view.fixture.Person;
+import de.neitzel.injection.ApplicationContext;
+import javafx.application.Platform;
+import javafx.beans.property.Property;
+import javafx.scene.control.TextField;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import java.net.URL;
+import java.util.HashSet;
+import java.util.Set;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicReference;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNotSame;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertSame;
+import static org.junit.jupiter.api.Assertions.fail;
+
+class CarryChildMessageTest {
+
+    @BeforeAll
+    static void startJavaFx() throws InterruptedException {
+        CountDownLatch started = new CountDownLatch(1);
+        try {
+            Platform.startup(started::countDown);
+        } catch (IllegalStateException alreadyStarted) {
+            started.countDown();
+        }
+        if (!started.await(10, TimeUnit.SECONDS)) {
+            fail("JavaFX toolkit did not start");
+        }
+    }
+
+    @Test
+    void aStreetNoticeOnTheAddressAppearsOnThePersonAsAddressStreet() throws Exception {
+        onFx(() -> {
+            Person person = new Person("Ada");
+            person.setAddress(new Address("Main"));
+            URL fxml = CarryChildMessageTest.class.getResource("name-both-ways.fxml");
+            assertNotNull(fxml);
+            ApplicationContext context = new ApplicationContext("de.neitzel.fx.view.fixture");
+            LoadedView loaded = ViewLoader.load(fxml, person, context);
+            ViewModel personModel = loaded.getViewModel();
+            ViewModel addressModel = (ViewModel) personModel.property("address").getValue();
+            addressModel.addMessage(new Message(Message.Severity.INFO, "lane is closed", "street"));
+
+            assertEquals(1, addressModel.getMessages().size());
+            assertEquals("street", addressModel.getMessages().get(0).getSource());
+            assertEquals(1, personModel.getMessages().size());
+            Message carried = personModel.getMessages().get(0);
+            assertEquals("address.street", carried.getSource());
+            assertEquals("lane is closed", carried.getText());
+            assertEquals(Message.Severity.INFO, carried.getSeverity());
+            assertNotSame(addressModel.getMessages().get(0), carried);
+            assertEquals(carried, personModel.getLatestMessage());
+        });
+    }
+
+    @Test
+    void aNestedStreetNoticeReadsAsPersonAddressStreet() throws Exception {
+        onFx(() -> {
+            Person person = new Person("Ada");
+            person.setAddress(new Address("Main"));
+            Household household = new Household();
+            household.setPerson(person);
+            URL fxml = CarryChildMessageTest.class.getResource("plain-view.fxml");
+            assertNotNull(fxml);
+            ApplicationContext context = new ApplicationContext("de.neitzel.fx.view.fixture");
+            LoadedView loaded = ViewLoader.load(fxml, household, context);
+            ViewModel householdModel = loaded.getViewModel();
+            ViewModel personModel = (ViewModel) householdModel.property("person").getValue();
+            ViewModel addressModel = (ViewModel) personModel.property("address").getValue();
+            addressModel.addMessage(new Message(Message.Severity.INFO, "lane is closed", "street"));
+
+            assertEquals("street", addressModel.getMessages().get(0).getSource());
+            assertEquals("address.street", personModel.getMessages().get(0).getSource());
+            assertEquals(1, householdModel.getMessages().size());
+            Message carried = householdModel.getMessages().get(0);
+            assertEquals("person.address.street", carried.getSource());
+            assertEquals("lane is closed", carried.getText());
+            assertEquals(Message.Severity.INFO, carried.getSeverity());
+        });
+    }
+
+    @Test
+    void aBadStreetIsOwnedByTheAddressAndCarriedAsAddressStreet() throws Exception {
+        onFx(() -> {
+            Person person = new Person("Ada");
+            person.setAddress(new Address("Main"));
+            URL fxml = CarryChildMessageTest.class.getResource("address-street-converted.fxml");
+            assertNotNull(fxml);
+            ApplicationContext context = new ApplicationContext("de.neitzel.fx.view.fixture");
+            LoadedView loaded = ViewLoader.load(fxml, person, context);
+            TextField streetField = (TextField) loaded.getRoot().lookup("#streetField");
+            streetField.setText("nope");
+
+            assertEquals("Main", person.getAddress().getStreet());
+            assertEquals("Main", streetField.getText());
+            ViewModel personModel = loaded.getViewModel();
+            ViewModel addressModel = (ViewModel) personModel.property("address").getValue();
+            assertEquals(1, addressModel.getMessages().size());
+            Message owned = addressModel.getMessages().get(0);
+            assertEquals(Message.Severity.ERROR, owned.getSeverity());
+            assertEquals("street", owned.getSource());
+            assertEquals("not a street: nope", owned.getText());
+            assertEquals(1, personModel.getMessages().size());
+            Message carried = personModel.getMessages().get(0);
+            assertEquals("address.street", carried.getSource());
+            assertEquals("not a street: nope", carried.getText());
+            assertEquals(Message.Severity.ERROR, carried.getSeverity());
+            assertNotSame(owned, carried);
+        });
+    }
+
+    @Test
+    void aFixedStreetDropsTheNoticeFromTheAddressAndThePerson() throws Exception {
+        onFx(() -> {
+            Person person = new Person("Ada");
+            person.setAddress(new Address("Main"));
+            URL fxml = CarryChildMessageTest.class.getResource("address-street-converted.fxml");
+            assertNotNull(fxml);
+            ApplicationContext context = new ApplicationContext("de.neitzel.fx.view.fixture");
+            LoadedView loaded = ViewLoader.load(fxml, person, context);
+            TextField streetField = (TextField) loaded.getRoot().lookup("#streetField");
+            streetField.setText("nope");
+            streetField.setText("ok Oak");
+
+            assertEquals("Oak", person.getAddress().getStreet());
+            ViewModel personModel = loaded.getViewModel();
+            ViewModel addressModel = (ViewModel) personModel.property("address").getValue();
+            assertEquals(0, addressModel.getMessages().size());
+            assertNull(addressModel.getLatestMessage());
+            assertEquals(0, personModel.getMessages().size());
+            assertNull(personModel.getLatestMessage());
+        });
+    }
+
+    @Test
+    void anotherBadStreetUpdatesTheCarriedNoticeInPlace() throws Exception {
+        onFx(() -> {
+            Person person = new Person("Ada");
+            person.setAddress(new Address("Main"));
+            Household household = new Household();
+            household.setPerson(person);
+            URL fxml = CarryChildMessageTest.class.getResource("household-street-converted.fxml");
+            assertNotNull(fxml);
+            ApplicationContext context = new ApplicationContext("de.neitzel.fx.view.fixture");
+            LoadedView loaded = ViewLoader.load(fxml, household, context);
+            TextField streetField = (TextField) loaded.getRoot().lookup("#streetField");
+            streetField.setText("nope");
+
+            ViewModel householdModel = loaded.getViewModel();
+            ViewModel personModel = (ViewModel) householdModel.property("person").getValue();
+            ViewModel addressModel = (ViewModel) personModel.property("address").getValue();
+            assertEquals(1, addressModel.getMessages().size());
+            assertEquals(1, personModel.getMessages().size());
+            assertEquals(1, householdModel.getMessages().size());
+            Message owned = addressModel.getMessages().get(0);
+            Message personCopy = personModel.getMessages().get(0);
+            Message householdCopy = householdModel.getMessages().get(0);
+            assertEquals("street", owned.getSource());
+            assertEquals("address.street", personCopy.getSource());
+            assertEquals("person.address.street", householdCopy.getSource());
+
+            streetField.setText("still-bad");
+
+            assertEquals("Main", person.getAddress().getStreet());
+            assertEquals(1, addressModel.getMessages().size());
+            assertEquals(1, personModel.getMessages().size());
+            assertEquals(1, householdModel.getMessages().size());
+            assertSame(owned, addressModel.getMessages().get(0));
+            assertSame(personCopy, personModel.getMessages().get(0));
+            assertSame(householdCopy, householdModel.getMessages().get(0));
+            assertEquals("not a street: still-bad", owned.getText());
+            assertEquals("not a street: still-bad", personCopy.getText());
+            assertEquals("not a street: still-bad", householdCopy.getText());
+            assertSame(householdCopy, householdModel.getLatestMessage());
+        });
+    }
+
+    @Test
+    void clearingTheAddressDropsTheCarriedNoticeAndANewAddressBringsItsOwn() throws Exception {
+        onFx(() -> {
+            Person person = new Person("Ada");
+            person.setAddress(new Address("Main"));
+            URL fxml = CarryChildMessageTest.class.getResource("plain-view.fxml");
+            assertNotNull(fxml);
+            ApplicationContext context = new ApplicationContext("de.neitzel.fx.view.fixture");
+            LoadedView loaded = ViewLoader.load(fxml, person, context);
+            ViewModel personModel = loaded.getViewModel();
+            ViewModel addressModel = (ViewModel) personModel.property("address").getValue();
+            addressModel.addMessage(new Message(Message.Severity.INFO, "lane is closed", "street"));
+            assertEquals("address.street", personModel.getMessages().get(0).getSource());
+
+            @SuppressWarnings("unchecked")
+            Property<Object> address = (Property<Object>) personModel.property("address");
+            address.setValue(null);
+
+            assertNull(person.getAddress());
+            assertEquals(0, personModel.getMessages().size());
+            assertNull(personModel.getLatestMessage());
+            assertEquals(1, addressModel.getMessages().size());
+            assertEquals("lane is closed", addressModel.getMessages().get(0).getText());
+
+            Address moved = new Address("Oak");
+            LoadedView movedView = ViewLoader.load(fxml, moved, context);
+            movedView.getViewModel().addMessage(new Message(Message.Severity.WARN, "under repair", "street"));
+            address.setValue(movedView.getViewModel());
+
+            assertSame(moved, person.getAddress());
+            assertEquals(1, personModel.getMessages().size());
+            Message carried = personModel.getMessages().get(0);
+            assertEquals("address.street", carried.getSource());
+            assertEquals("under repair", carried.getText());
+            assertEquals(Message.Severity.WARN, carried.getSeverity());
+            assertSame(carried, personModel.getLatestMessage());
+        });
+    }
+
+    @Test
+    void fixingTheStreetLeavesThePersonsOwnNotice() throws Exception {
+        onFx(() -> {
+            Person person = new Person("Ada");
+            person.setAddress(new Address("Main"));
+            URL fxml = CarryChildMessageTest.class.getResource("address-street-converted.fxml");
+            assertNotNull(fxml);
+            ApplicationContext context = new ApplicationContext("de.neitzel.fx.view.fixture");
+            LoadedView loaded = ViewLoader.load(fxml, person, context);
+            ViewModel personModel = loaded.getViewModel();
+            personModel.addMessage(new Message(Message.Severity.INFO, "keep me", "form"));
+            TextField streetField = (TextField) loaded.getRoot().lookup("#streetField");
+            streetField.setText("nope");
+
+            ViewModel addressModel = (ViewModel) personModel.property("address").getValue();
+            assertEquals(1, addressModel.getMessages().size());
+            assertEquals(2, personModel.getMessages().size());
+            Message carried = personModel.getMessages().get(1);
+            assertEquals("address.street", carried.getSource());
+            assertEquals("not a street: nope", carried.getText());
+            assertSame(carried, personModel.getLatestMessage());
+
+            streetField.setText("still-bad");
+
+            assertEquals(2, personModel.getMessages().size());
+            assertSame(carried, personModel.getMessages().get(1));
+            assertEquals("not a street: still-bad", carried.getText());
+            assertSame(carried, personModel.getLatestMessage());
+            assertEquals("keep me", personModel.getMessages().get(0).getText());
+
+            streetField.setText("ok Oak");
+
+            assertEquals("Oak", person.getAddress().getStreet());
+            assertEquals(0, addressModel.getMessages().size());
+            assertEquals(1, personModel.getMessages().size());
+            assertEquals("keep me", personModel.getLatestMessage().getText());
+            assertEquals("form", personModel.getLatestMessage().getSource());
+        });
+    }
+
+    @Test
+    void aFixedNestedStreetDropsTheNoticeUpThePath() throws Exception {
+        onFx(() -> {
+            Person person = new Person("Ada");
+            person.setAddress(new Address("Main"));
+            Household household = new Household();
+            household.setPerson(person);
+            URL fxml = CarryChildMessageTest.class.getResource("household-street-converted.fxml");
+            assertNotNull(fxml);
+            ApplicationContext context = new ApplicationContext("de.neitzel.fx.view.fixture");
+            LoadedView loaded = ViewLoader.load(fxml, household, context);
+            TextField streetField = (TextField) loaded.getRoot().lookup("#streetField");
+            streetField.setText("nope");
+            streetField.setText("ok Oak");
+
+            assertEquals("Oak", person.getAddress().getStreet());
+            ViewModel householdModel = loaded.getViewModel();
+            ViewModel personModel = (ViewModel) householdModel.property("person").getValue();
+            ViewModel addressModel = (ViewModel) personModel.property("address").getValue();
+            assertEquals(0, addressModel.getMessages().size());
+            assertEquals(0, personModel.getMessages().size());
+            assertEquals(0, householdModel.getMessages().size());
+            assertNull(addressModel.getLatestMessage());
+            assertNull(personModel.getLatestMessage());
+            assertNull(householdModel.getLatestMessage());
+        });
+    }
+
+    @Test
+    void aSharedAddressCarriesTheStreetNoticeOnHomeAndOnWork() throws Exception {
+        onFx(() -> {
+            Address shared = new Address("Main");
+            Person person = new Person("Ada");
+            person.setHome(shared);
+            person.setWork(shared);
+            URL fxml = CarryChildMessageTest.class.getResource("plain-view.fxml");
+            assertNotNull(fxml);
+            ApplicationContext context = new ApplicationContext("de.neitzel.fx.view.fixture");
+            LoadedView loaded = ViewLoader.load(fxml, person, context);
+            ViewModel personModel = loaded.getViewModel();
+            ViewModel homeModel = (ViewModel) personModel.property("home").getValue();
+            homeModel.addMessage(new Message(Message.Severity.INFO, "lane is closed", "street"));
+
+            assertEquals(2, personModel.getMessages().size());
+            Set<String> sources = new HashSet<>();
+            for (Message message : personModel.getMessages()) {
+                sources.add(message.getSource());
+                assertEquals("lane is closed", message.getText());
+            }
+            assertEquals(Set.of("home.street", "work.street"), sources);
+        });
+    }
+
+    private static void onFx(FxAction action) throws Exception {
+        if (Platform.isFxApplicationThread()) {
+            action.run();
+            return;
+        }
+        AtomicReference<Throwable> thrown = new AtomicReference<>();
+        CountDownLatch done = new CountDownLatch(1);
+        Platform.runLater(() -> {
+            try {
+                action.run();
+            } catch (Throwable failure) {
+                thrown.set(failure);
+            } finally {
+                done.countDown();
+            }
+        });
+        if (!done.await(10, TimeUnit.SECONDS)) {
+            fail("JavaFX thread did not finish");
+        }
+        Throwable failure = thrown.get();
+        if (failure instanceof Exception exception) {
+            throw exception;
+        }
+        if (failure instanceof Error error) {
+            throw error;
+        }
+        if (failure != null) {
+            throw new AssertionError(failure);
+        }
+    }
+
+    @FunctionalInterface
+    private interface FxAction {
+        void run() throws Exception;
+    }
+}

fx/src/test/java/de/neitzel/fx/view/fixture/CheckedStreetConverter.java

@@ -0,0 +1,37 @@
+package de.neitzel.fx.view.fixture;
+
+import de.neitzel.fx.view.Converter;
+import jakarta.inject.Singleton;
+
+/**
+ * Accepts a street written as {@code ok } plus the street, and rejects anything else.
+ */
+@Singleton
+public class CheckedStreetConverter implements Converter {
+
+    /**
+     * Shows the street as it is stored.
+     *
+     * @param attributeValue the street
+     * @return the control text
+     */
+    @Override
+    public Object toControlValue(Object attributeValue) {
+        return attributeValue == null ? "" : attributeValue.toString();
+    }
+
+    /**
+     * Reads a street that starts with {@code ok }.
+     *
+     * @param controlValue the control text
+     * @return the street
+     */
+    @Override
+    public Object toAttributeValue(Object controlValue) {
+        String text = controlValue == null ? "" : controlValue.toString();
+        if (!text.startsWith("ok ")) {
+            throw new IllegalArgumentException("not a street: " + text);
+        }
+        return text.substring("ok ".length());
+    }
+}

fx/src/test/java/de/neitzel/fx/view/fixture/Household.java

@@ -0,0 +1,27 @@
+package de.neitzel.fx.view.fixture;
+
+/**
+ * Ordinary model that holds a person, so a test can read a message two levels up.
+ */
+public class Household {
+
+    private Person person;
+
+    /**
+     * Returns the person.
+     *
+     * @return the person, or {@code null} when the household has none
+     */
+    public Person getPerson() {
+        return person;
+    }
+
+    /**
+     * Sets the person.
+     *
+     * @param person the person
+     */
+    public void setPerson(Person person) {
+        this.person = person;
+    }
+}

fx/src/test/resources/de/neitzel/fx/view/address-street-converted.fxml

@@ -0,0 +1,16 @@
+<?xml version="1.0" encoding="UTF-8"?>
+
+<?import javafx.scene.control.TextField?>
+<?import javafx.scene.layout.VBox?>
+<?import de.neitzel.fx.view.BindingList?>
+<?import de.neitzel.fx.view.DirectBinding?>
+
+<VBox xmlns="http://javafx.com/javafx" xmlns:fx="http://javafx.com/fxml">
+    <fx:define>
+        <BindingList>
+            <DirectBinding control="streetField" property="text" path="address.street" direction="both"
+                           converter="de.neitzel.fx.view.fixture.CheckedStreetConverter"/>
+        </BindingList>
+    </fx:define>
+    <TextField fx:id="streetField" id="streetField"/>
+</VBox>

fx/src/test/resources/de/neitzel/fx/view/household-street-converted.fxml

@@ -0,0 +1,16 @@
+<?xml version="1.0" encoding="UTF-8"?>
+
+<?import javafx.scene.control.TextField?>
+<?import javafx.scene.layout.VBox?>
+<?import de.neitzel.fx.view.BindingList?>
+<?import de.neitzel.fx.view.DirectBinding?>
+
+<VBox xmlns="http://javafx.com/javafx" xmlns:fx="http://javafx.com/fxml">
+    <fx:define>
+        <BindingList>
+            <DirectBinding control="streetField" property="text" path="person.address.street" direction="both"
+                           converter="de.neitzel.fx.view.fixture.CheckedStreetConverter"/>
+        </BindingList>
+    </fx:define>
+    <TextField fx:id="streetField" id="streetField"/>
+</VBox>

fx/src/test/resources/de/neitzel/fx/view/plain-view.fxml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="UTF-8"?>
+
+<?import javafx.scene.layout.VBox?>
+
+<VBox xmlns="http://javafx.com/javafx" xmlns:fx="http://javafx.com/fxml"/>