feat: remove state slice when set as undefined

packages/core/src/reducers/core.ts

@@ -25,6 +25,7 @@
 
 import cloneDeep from 'lodash/cloneDeep';
 import setFp from 'lodash/fp/set';
+import unsetFp from 'lodash/fp/unset';
 import get from 'lodash/get';
 import filter from 'lodash/filter';
 import isEqual from 'lodash/isEqual';
@@ -285,11 +286,19 @@ export const coreReducer: Reducer<JsonFormsCore, CoreActions> = (
       } else {
         const oldData: any = get(state.data, action.path);
         const newData = action.updater(cloneDeep(oldData));
-        const newState: any = setFp(
-          action.path,
-          newData,
-          state.data === undefined ? {} : state.data
-        );
+        let newState: any;
+        if (newData !== undefined) {
+          newState = setFp(
+            action.path,
+            newData,
+            state.data === undefined ? {} : state.data
+          );
+        } else {
+          newState = unsetFp(
+            action.path,
+            state.data === undefined ? {} : state.data
+          );
+        }
         const errors = validate(state.validator, newState);
         return {
           ...state,

packages/core/test/reducers/core.test.ts

@@ -562,6 +562,44 @@ test('core reducer - update - should update errors', (t) => {
   });
 });
 
+test('core reducer - update - setting a state slice as undefined should remove the slice', (t) => {
+  const schema = {
+    type: 'object',
+    properties: {
+      foo: {
+        type: 'string',
+      },
+      fizz: {
+        type: 'string',
+      },
+    },
+  };
+
+  const before: JsonFormsCore = {
+    data: {
+      foo: 'bar',
+      fizz: 42,
+    },
+    schema: schema,
+    uischema: {
+      type: 'Label',
+    },
+    errors: [],
+    validator: new Ajv().compile(schema),
+  };
+
+  const after = coreReducer(
+    before,
+    update('foo', (_) => {
+      return undefined;
+    })
+  );
+
+  t.not(before, after);
+  t.not(before.data, after.data);
+  t.like(Object.keys(after.data), ['fizz']);
+});
+
 test('core reducer - updateErrors - should update errors with empty list', (t) => {
   const before: JsonFormsCore = {
     data: {},