Only throw from Binder.bindInstanceFields if there are no bindings at all (#9487)

Fixes #8986

server/src/main/java/com/vaadin/data/Binder.java

@@ -2141,10 +2141,15 @@ public class Binder<BEAN> implements Serializable {
                         (property, type) -> bindProperty(objectWithMemberFields,
                                 memberField, property, type)))
                 .reduce(0, this::accumulate, Integer::sum);
-        if (numberOfBoundFields == 0) {
+        if (numberOfBoundFields == 0 && bindings.isEmpty()
+                && incompleteBindings.isEmpty()) {
+            // Throwing here for incomplete bindings would be wrong as they
+            // may be completed after this call. If they are not, setBean and
+            // other methods will throw for those cases
             throw new IllegalStateException("There are no instance fields "
                     + "found for automatic binding");
         }
+
     }
 
     private boolean isFieldBound(Field memberField,

server/src/test/java/com/vaadin/data/BeanBinderTest.java

@@ -4,6 +4,7 @@ import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertSame;
 
 import java.io.Serializable;
+import java.time.LocalDate;
 import java.util.List;
 import java.util.Set;
 
@@ -35,6 +36,9 @@ public class BeanBinderTest
         private TextField number = new TextField();
     }
 
+    private class TestClassWithoutFields {
+    }
+
     private static class TestBean implements Serializable {
         private Set<TestEnum> enums;
         private int number;
@@ -145,6 +149,22 @@ public class BeanBinderTest
         }
     }
 
+    public static class Person {
+        LocalDate mydate;
+
+        public LocalDate getMydate() {
+            return mydate;
+        }
+
+        public void setMydate(LocalDate mydate) {
+            this.mydate = mydate;
+        }
+    }
+
+    public static class PersonForm {
+        private TextField mydate = new TextField();
+    }
+
     @Before
     public void setUp() {
         binder = new BeanValidationBinder<>(BeanToValidate.class);
@@ -194,6 +214,35 @@ public class BeanBinderTest
         otherBinder.bindInstanceFields(testClass);
     }
 
+    @Test(expected = IllegalStateException.class)
+    public void bindInstanceFields_throw_if_no_fields_bound() {
+        Binder<TestBean> otherBinder = new Binder<>(TestBean.class);
+        TestClassWithoutFields testClass = new TestClassWithoutFields();
+
+        // Should throw an IllegalStateException no fields are bound
+        otherBinder.bindInstanceFields(testClass);
+    }
+
+    @Test
+    public void bindInstanceFields_does_not_throw_if_fields_are_bound_manually() {
+        PersonForm form = new PersonForm();
+        Binder<Person> binder = new Binder<>(Person.class);
+        binder.forMemberField(form.mydate)
+                .withConverter(str -> LocalDate.now(), date -> "Hello")
+                .bind("mydate");
+        binder.bindInstanceFields(form);
+
+    }
+
+    @Test
+    public void bindInstanceFields_does_not_throw_if_there_are_incomplete_bindings() {
+        PersonForm form = new PersonForm();
+        Binder<Person> binder = new Binder<>(Person.class);
+        binder.forMemberField(form.mydate).withConverter(str -> LocalDate.now(),
+                date -> "Hello");
+        binder.bindInstanceFields(form);
+    }
+
     @Test(expected = IllegalStateException.class)
     public void incomplete_forMemberField_bindings() {
         Binder<TestBean> otherBinder = new Binder<>(TestBean.class);

server/src/test/java/com/vaadin/data/BinderInstanceFieldTest.java

@@ -414,8 +414,8 @@ public class BinderInstanceFieldTest {
         Assert.assertEquals("90", form.age.getValue());
     }
 
-    @Test(expected = IllegalStateException.class)
-    public void bindInstanceFields_explicitelyBoundFieldAndNotBoundField_throwNoBoundFields() {
+    @Test
+    public void bindInstanceFields_explicitelyBoundFieldAndNotBoundField() {
         BindOnlyOneField form = new BindOnlyOneField();
         Binder<Person> binder = new Binder<>(Person.class);
 
@@ -424,8 +424,8 @@ public class BinderInstanceFieldTest {
         binder.bindInstanceFields(form);
     }
 
-    @Test(expected = IllegalStateException.class)
-    public void bindInstanceFields_tentativelyBoundFieldAndNotBoundField_throwNoBoundFields() {
+    @Test
+    public void bindInstanceFields_tentativelyBoundFieldAndNotBoundField() {
         BindOnlyOneField form = new BindOnlyOneField();
         Binder<Person> binder = new Binder<>(Person.class);
 
@@ -436,8 +436,9 @@ public class BinderInstanceFieldTest {
         // manually
         binder.forMemberField(field);
 
-        // bindInstance expects at least one auto configured field (there is no
-        // such, only incomplete one) and fails
+        // bindInstanceFields will not complain even though it can't bind
+        // anything as there is a binding in progress (an exception will be
+        // thrown later if the binding is not completed)
         binder.bindInstanceFields(form);
     }
 }