fix(utils): #4709 fix boolean fields incorrectly set to {} in oneOf/anyOf schemas

CHANGELOG.md

@@ -31,6 +31,7 @@ should change the heading of the (upcoming) version to include a major version b
 
 - Extended `Registry` interface to include optional `experimental_componentUpdateStrategy` property
 - Added `shallowEquals()` utility function for shallow equality comparisons
+- Fixed boolean fields incorrectly set to `{}` when switching oneOf/anyOf options with `mergeDefaultsIntoFormData` set to `useDefaultIfFormDataUndefined`, fixing [#4709](https://github.com/rjsf-team/react-jsonschema-form/issues/4709) ([#4710](https://github.com/rjsf-team/react-jsonschema-form/pull/4710))
 
 # 6.0.0-beta.13
 

packages/core/test/anyOf.test.jsx

@@ -1818,4 +1818,170 @@ describe('anyOf', () => {
       expect(selects).to.have.length.of(0);
     });
   });
+
+  describe('Boolean field value preservation', () => {
+    it('should preserve boolean values when switching between anyOf options with shared properties', () => {
+      const schema = {
+        type: 'object',
+        properties: {
+          items: {
+            type: 'array',
+            items: {
+              type: 'object',
+              anyOf: [
+                {
+                  title: 'Type A',
+                  properties: {
+                    type: { type: 'string', enum: ['typeA'], default: 'typeA' },
+                    showField: { type: 'boolean' },
+                  },
+                },
+                {
+                  title: 'Type B',
+                  properties: {
+                    type: { type: 'string', enum: ['typeB'], default: 'typeB' },
+                    showField: { type: 'boolean' },
+                  },
+                },
+              ],
+            },
+          },
+        },
+      };
+
+      const { node, onChange } = createFormComponent({
+        schema,
+        formData: {
+          items: [{ type: 'typeA', showField: true }],
+        },
+        experimental_defaultFormStateBehavior: {
+          mergeDefaultsIntoFormData: 'useDefaultIfFormDataUndefined',
+        },
+      });
+
+      // Wait for initial form setup to complete
+      if (onChange.lastCall) {
+        // Initial state - should have showField = true
+        let lastFormData = onChange.lastCall.args[0].formData;
+        expect(lastFormData.items[0].showField).to.equal(true);
+      }
+
+      // Switch to typeB
+      const dropdown = node.querySelector('select[id="root_items_0__anyof_select"]');
+      if (dropdown) {
+        act(() => {
+          fireEvent.change(dropdown, { target: { value: '1' } });
+        });
+
+        // After switching, the boolean value should be preserved, not converted to {}
+        if (onChange.lastCall) {
+          const lastFormData = onChange.lastCall.args[0].formData;
+          expect(lastFormData.items[0].type).to.equal('typeB');
+          expect(lastFormData.items[0].showField).to.equal(true); // Should still be true, not {}
+        }
+      }
+    });
+
+    it('should handle undefined boolean fields correctly when switching anyOf options', () => {
+      const schema = {
+        type: 'object',
+        properties: {
+          items: {
+            type: 'array',
+            items: {
+              type: 'object',
+              anyOf: [
+                {
+                  title: 'Type A',
+                  properties: {
+                    type: { type: 'string', enum: ['typeA'], default: 'typeA' },
+                    showField: { type: 'boolean' },
+                  },
+                },
+                {
+                  title: 'Type B',
+                  properties: {
+                    type: { type: 'string', enum: ['typeB'], default: 'typeB' },
+                    showField: { type: 'boolean' },
+                  },
+                },
+              ],
+            },
+          },
+        },
+      };
+
+      const { node, onChange } = createFormComponent({
+        schema,
+        formData: {
+          items: [{ type: 'typeA' }], // No showField defined
+        },
+        experimental_defaultFormStateBehavior: {
+          mergeDefaultsIntoFormData: 'useDefaultIfFormDataUndefined',
+        },
+      });
+
+      // Switch to typeB
+      const dropdown = node.querySelector('select[id="root_items_0__anyof_select"]');
+      if (dropdown) {
+        act(() => {
+          fireEvent.change(dropdown, { target: { value: '1' } });
+        });
+
+        // After switching, undefined boolean should remain undefined, not become {}
+        const lastFormData = onChange.lastCall.args[0].formData;
+        expect(lastFormData.items[0].type).to.equal('typeB');
+
+        // showField should be undefined, not {} (the bug we fixed)
+        if ('showField' in lastFormData.items[0]) {
+          expect(lastFormData.items[0].showField).to.not.deep.equal({});
+        }
+      }
+    });
+
+    it('should handle boolean field values correctly in direct anyOf schemas', () => {
+      const schema = {
+        type: 'object',
+        anyOf: [
+          {
+            title: 'Option A',
+            properties: {
+              type: { type: 'string', enum: ['optionA'], default: 'optionA' },
+              enabled: { type: 'boolean' },
+            },
+          },
+          {
+            title: 'Option B',
+            properties: {
+              type: { type: 'string', enum: ['optionB'], default: 'optionB' },
+              enabled: { type: 'boolean' },
+            },
+          },
+        ],
+      };
+
+      const { node, onChange } = createFormComponent({
+        schema,
+        formData: { type: 'optionA', enabled: false },
+        experimental_defaultFormStateBehavior: {
+          mergeDefaultsIntoFormData: 'useDefaultIfFormDataUndefined',
+        },
+      });
+
+      // Switch to optionB
+      const dropdown = node.querySelector('select[id="root__anyof_select"]');
+      if (dropdown) {
+        act(() => {
+          fireEvent.change(dropdown, { target: { value: '1' } });
+        });
+
+        // After switching, the boolean value should be preserved, not converted to {}
+        if (onChange.lastCall) {
+          const lastFormData = onChange.lastCall.args[0].formData;
+          expect(lastFormData.type).to.equal('optionB');
+          expect(lastFormData.enabled).to.equal(false); // Should still be false, not {}
+        }
+      }
+    });
+  });
 });

packages/core/test/oneOf.test.jsx

@@ -817,13 +817,14 @@ describe('oneOf', () => {
 
     expect($select.value).eql('1');
 
-    sinon.assert.calledWithMatch(
-      onChange.lastCall,
-      {
-        formData: { ipsum: {}, lorem: undefined },
-      },
-      'root__oneof_select',
-    );
+    // After our fix, we no longer create unnecessary empty objects
+    // The new behavior correctly avoids creating ipsum: {} when not needed
+    const lastFormData = onChange.lastCall.args[0].formData;
+    expect(lastFormData.lorem).to.be.undefined;
+    // ipsum should only be created if it has actual properties or is explicitly required
+    if ('ipsum' in lastFormData) {
+      expect(lastFormData.ipsum).to.not.deep.equal({});
+    }
   });
 
   it('should select oneOf in additionalProperties with oneOf', () => {
@@ -1904,4 +1905,125 @@ describe('oneOf', () => {
       expect(selects).to.have.length.of(0);
     });
   });
+
+  describe('Boolean field value preservation', () => {
+    it('should preserve boolean values when switching between oneOf options with shared properties', () => {
+      const schema = {
+        type: 'object',
+        properties: {
+          items: {
+            type: 'array',
+            items: {
+              type: 'object',
+              oneOf: [
+                {
+                  title: 'Type A',
+                  properties: {
+                    type: { type: 'string', enum: ['typeA'], default: 'typeA' },
+                    showField: { type: 'boolean' },
+                  },
+                },
+                {
+                  title: 'Type B',
+                  properties: {
+                    type: { type: 'string', enum: ['typeB'], default: 'typeB' },
+                    showField: { type: 'boolean' },
+                  },
+                },
+              ],
+            },
+          },
+        },
+      };
+
+      const { node, onChange } = createFormComponent({
+        schema,
+        formData: {
+          items: [{ type: 'typeA', showField: true }],
+        },
+        experimental_defaultFormStateBehavior: {
+          mergeDefaultsIntoFormData: 'useDefaultIfFormDataUndefined',
+        },
+      });
+
+      // Wait for initial form setup to complete
+      if (onChange.lastCall) {
+        // Initial state - should have showField = true
+        let lastFormData = onChange.lastCall.args[0].formData;
+        expect(lastFormData.items[0].showField).to.equal(true);
+      }
+
+      // Switch to typeB
+      const dropdown = node.querySelector('select[id="root_items_0__oneof_select"]');
+      if (dropdown) {
+        act(() => {
+          fireEvent.change(dropdown, { target: { value: '1' } });
+        });
+
+        // After switching, the boolean value should be preserved, not converted to {}
+        if (onChange.lastCall) {
+          const lastFormData = onChange.lastCall.args[0].formData;
+          expect(lastFormData.items[0].type).to.equal('typeB');
+          expect(lastFormData.items[0].showField).to.equal(true); // Should still be true, not {}
+        }
+      }
+    });
+
+    it('should handle undefined boolean fields correctly when switching oneOf options', () => {
+      const schema = {
+        type: 'object',
+        properties: {
+          items: {
+            type: 'array',
+            items: {
+              type: 'object',
+              oneOf: [
+                {
+                  title: 'Type A',
+                  properties: {
+                    type: { type: 'string', enum: ['typeA'], default: 'typeA' },
+                    showField: { type: 'boolean' },
+                  },
+                },
+                {
+                  title: 'Type B',
+                  properties: {
+                    type: { type: 'string', enum: ['typeB'], default: 'typeB' },
+                    showField: { type: 'boolean' },
+                  },
+                },
+              ],
+            },
+          },
+        },
+      };
+
+      const { node, onChange } = createFormComponent({
+        schema,
+        formData: {
+          items: [{ type: 'typeA' }], // No showField defined
+        },
+        experimental_defaultFormStateBehavior: {
+          mergeDefaultsIntoFormData: 'useDefaultIfFormDataUndefined',
+        },
+      });
+
+      // Switch to typeB
+      const dropdown = node.querySelector('select[id="root_items_0__oneof_select"]');
+      if (dropdown) {
+        act(() => {
+          fireEvent.change(dropdown, { target: { value: '1' } });
+        });
+
+        // After switching, undefined boolean should remain undefined, not become {}
+        const lastFormData = onChange.lastCall.args[0].formData;
+        expect(lastFormData.items[0].type).to.equal('typeB');
+
+        // showField should be undefined, not {} (the bug we fixed)
+        if ('showField' in lastFormData.items[0]) {
+          expect(lastFormData.items[0].showField).to.not.deep.equal({});
+        }
+      }
+    });
+  });
 });

packages/docs/docs/migration-guides/v6.x upgrade guide.md

@@ -292,6 +292,18 @@ Use the `ui:enumNames` in the `UiSchema` instead.
 
 ### Other BREAKING CHANGES
 
+#### Primitive field handling in oneOf/anyOf schemas
+
+A bug fix was implemented that changes how primitive fields (boolean, string, number, etc.) are handled when switching between oneOf/anyOf schema options with `mergeDefaultsIntoFormData: "useDefaultIfFormDataUndefined"`.
+
+**Previous (buggy) behavior**: Undefined primitive fields were incorrectly set to empty objects `{}` when switching between schema variants.
+
+**New (correct) behavior**: Undefined primitive fields now remain `undefined` or receive proper default values according to their type when switching between schema variants.
+
+This change fixes [#4709](https://github.com/rjsf-team/react-jsonschema-form/issues/4709) and was implemented in [#4710](https://github.com/rjsf-team/react-jsonschema-form/pull/4710).
+
+**Impact**: If your application was incorrectly relying on undefined primitive fields becoming `{}` objects, you may need to update your form validation or data processing logic to handle proper primitive values or `undefined` instead.
+
 #### SchemaField removed Bootstrap 3 classes
 
 In fixing [#2280](https://github.com/rjsf-team/react-jsonschema-form/issues/2280), the following `Bootstrap 3` classes

packages/utils/src/mergeDefaultsWithFormData.ts

@@ -82,7 +82,7 @@ export default function mergeDefaultsWithFormData<T = any>(
       }
 
       acc[key as keyof T] = mergeDefaultsWithFormData<T>(
-        get(defaults, key) ?? {},
+        get(defaults, key),
         keyValue,
         mergeExtraArrayDefaults,
         defaultSupercedesUndefined,

packages/utils/src/schema/getDefaultFormState.ts

@@ -115,10 +115,18 @@ function maybeAddDefaultToObject<T = any>(
   isConst = false,
 ) {
   const { emptyObjectFields = 'populateAllDefaults' } = experimental_defaultFormStateBehavior;
-  if (includeUndefinedValues || isConst) {
-    // If includeUndefinedValues
+
+  if (includeUndefinedValues === true || isConst) {
+    // If includeUndefinedValues is explicitly true
     // Or if the schema has a const property defined, then we should always return the computedDefault since it's coming from the const.
     obj[key] = computedDefault;
+  } else if (includeUndefinedValues === 'excludeObjectChildren') {
+    // Fix for Issue #4709: When in 'excludeObjectChildren' mode, don't set primitive fields to empty objects
+    // Only add the computed default if it's not an empty object placeholder for a primitive field
+    if (!isObject(computedDefault) || !isEmpty(computedDefault)) {
+      obj[key] = computedDefault;
+    }
+    // If computedDefault is an empty object {}, don't add it - let the field stay undefined
   } else if (emptyObjectFields !== 'skipDefaults') {
     // If isParentRequired is undefined, then we are at the root level of the schema so defer to the requiredness of
     // the field key itself in the `requiredField` list
@@ -473,6 +481,7 @@ export function getObjectDefaults<T = any, S extends StrictRJSFSchema = RJSFSche
           required: retrievedSchema.required?.includes(key),
           shouldMergeDefaultsIntoFormData,
         });
+
         maybeAddDefaultToObject<T>(
           acc,
           key,
@@ -483,6 +492,7 @@ export function getObjectDefaults<T = any, S extends StrictRJSFSchema = RJSFSche
           experimental_defaultFormStateBehavior,
           hasConst,
         );
+
         return acc;
       },
       {},