Bug: schema combinators(allOf, anyOf, oneOf) cannot be modified when defaults were set

CHANGELOG.md

@@ -30,6 +30,10 @@ should change the heading of the (upcoming) version to include a major version b
 
 - Fixed issue in BaseInputTemplate where input props were passed to `slotProps.htmlInput`, which does not work in MUI v5.
 
+## @rjsf/utils
+
+- Fixed issue with schema combinators(allOf, anyOf, oneOf) could not be modified when defaults were set, fixing [#4555](https://github.com/rjsf-team/react-jsonschema-form/issues/4555)
+
 ## Dev / docs / playground
 
 - Updated docs for ArrayFieldItemTemplate to include prop `onCopyIndexClick`, fixing [#4507](https://github.com/rjsf-team/react-jsonschema-form/issues/4507)

packages/core/test/Form.test.jsx

@@ -1261,6 +1261,174 @@ describeRepeated('Form common', (createFormComponent) => {
       sinon.assert.callCount(onChange, 1);
       sinon.assert.callCount(secondOnChange, 1);
     });
+    it('should modify an allOf field when the defaults are set', () => {
+      const schema = {
+        properties: {
+          all_of_field: {
+            allOf: [
+              {
+                properties: {
+                  first: {
+                    type: 'string',
+                  },
+                },
+              },
+              {
+                properties: {
+                  second: {
+                    type: 'string',
+                  },
+                },
+              },
+            ],
+            default: {
+              second: 'second!',
+            },
+          },
+        },
+        type: 'object',
+      };
+
+      const { node, onChange } = createFormComponent({
+        schema,
+      });
+
+      const secondInputID = '#root_all_of_field_second';
+      expect(node.querySelector(secondInputID).value).to.equal('second!');
+
+      act(() => {
+        fireEvent.change(node.querySelector(secondInputID), {
+          target: { value: 'changed!' },
+        });
+      });
+
+      sinon.assert.calledWithMatch(
+        onChange.lastCall,
+        {
+          formData: {
+            all_of_field: {
+              second: 'changed!',
+            },
+          },
+          schema,
+        },
+        'root_all_of_field_second'
+      );
+
+      expect(node.querySelector(secondInputID).value).to.equal('changed!');
+    });
+    it('should modify an oneOf field when the defaults are set', () => {
+      const schema = {
+        properties: {
+          one_of_field: {
+            oneOf: [
+              {
+                properties: {
+                  first: {
+                    type: 'string',
+                  },
+                },
+              },
+              {
+                properties: {
+                  second: {
+                    type: 'string',
+                  },
+                },
+              },
+            ],
+            default: {
+              second: 'second!',
+            },
+          },
+        },
+        type: 'object',
+      };
+
+      const { node, onChange } = createFormComponent({
+        schema,
+      });
+
+      const secondInputID = '#root_one_of_field_second';
+      expect(node.querySelector(secondInputID).value).to.equal('second!');
+
+      act(() => {
+        fireEvent.change(node.querySelector(secondInputID), {
+          target: { value: 'changed!' },
+        });
+      });
+
+      sinon.assert.calledWithMatch(
+        onChange.lastCall,
+        {
+          formData: {
+            one_of_field: {
+              second: 'changed!',
+            },
+          },
+          schema,
+        },
+        'root_one_of_field_second'
+      );
+
+      expect(node.querySelector(secondInputID).value).to.equal('changed!');
+    });
+    it('should modify an anyOf field when the defaults are set', () => {
+      const schema = {
+        properties: {
+          any_of_field: {
+            anyOf: [
+              {
+                properties: {
+                  first: {
+                    type: 'string',
+                  },
+                },
+              },
+              {
+                properties: {
+                  second: {
+                    type: 'string',
+                  },
+                },
+              },
+            ],
+            default: {
+              second: 'second!',
+            },
+          },
+        },
+        type: 'object',
+      };
+
+      const { node, onChange } = createFormComponent({
+        schema,
+      });
+
+      const secondInputID = '#root_any_of_field_second';
+      expect(node.querySelector(secondInputID).value).to.equal('second!');
+
+      act(() => {
+        fireEvent.change(node.querySelector(secondInputID), {
+          target: { value: 'changed!' },
+        });
+      });
+
+      sinon.assert.calledWithMatch(
+        onChange.lastCall,
+        {
+          formData: {
+            any_of_field: {
+              second: 'changed!',
+            },
+          },
+          schema,
+        },
+        'root_any_of_field_second'
+      );
+
+      expect(node.querySelector(secondInputID).value).to.equal('changed!');
+    });
   });
 
   describe('Blur handler', () => {

packages/utils/src/schema/getDefaultFormState.ts

@@ -223,7 +223,9 @@ export function computeDefaults<T = any, S extends StrictRJSFSchema = RJSFSchema
     // For object defaults, only override parent defaults that are defined in
     // schema.default.
     defaults = mergeObjects(defaults!, schema.default as GenericObjectType) as T;
-  } else if (DEFAULT_KEY in schema) {
+  } else if (DEFAULT_KEY in schema && !schema[ANY_OF_KEY] && !schema[ONE_OF_KEY]) {
+    // If the schema has a default value, then we should use it as the default.
+    // And if the schema does not have anyOf or oneOf, this is done because we need to merge the defaults with the formData.
     defaults = schema.default as unknown as T;
   } else if (REF_KEY in schema) {
     const refName = schema[REF_KEY];
@@ -284,7 +286,7 @@ export function computeDefaults<T = any, S extends StrictRJSFSchema = RJSFSchema
       getClosestMatchingOption<T, S, F>(
         validator,
         rootSchema,
-        rawFormData,
+        rawFormData ?? (schema.default as T),
         oneOf as S[],
         0,
         discriminator,
@@ -302,7 +304,7 @@ export function computeDefaults<T = any, S extends StrictRJSFSchema = RJSFSchema
       getClosestMatchingOption<T, S, F>(
         validator,
         rootSchema,
-        rawFormData,
+        rawFormData ?? (schema.default as T),
         anyOf as S[],
         0,
         discriminator,
@@ -347,7 +349,9 @@ export function computeDefaults<T = any, S extends StrictRJSFSchema = RJSFSchema
       experimental_defaultFormStateBehavior,
       experimental_customMergeAllOf
     );
-    if (!isObject(rawFormData)) {
+    if (!isObject(rawFormData) || ALL_OF_KEY in schema) {
+      // If the formData is not an object which means it's a primitive field, then we need to merge the defaults into the formData.
+      // Or if the schema has allOf, we need to merge the defaults into the formData because we don't compute the defaults for allOf.
       defaultsWithFormData = mergeDefaultsWithFormData<T>(
         defaultsWithFormData as T,
         matchingFormData as T,