fix(Form): support conditional rendering of children

packages/main/src/components/Form/Form.cy.tsx

@@ -1,3 +1,4 @@
+import { useReducer } from 'react';
 import { createPortal } from 'react-dom';
 import { InputType } from '../../enums/index.js';
 import { Input, Label } from '../../webComponents/index.js';
@@ -30,6 +31,47 @@ const component = (
   </Form>
 );
 
+const ConditionRenderingExample = () => {
+  const [show, toggle] = useReducer((prev) => !prev, false);
+  const [show2, toggle2] = useReducer((prev) => !prev, false);
+  const [show3, toggle3] = useReducer((prev) => !prev, false);
+  return (
+    <>
+      <button onClick={toggle}>Toggle Input</button>
+      <button onClick={toggle2}>Toggle Group</button>
+      <button onClick={toggle3}>Toggle Group2</button>
+      <Form>
+        <FormItem label="Item 1">
+          <Input data-testid="1" />
+        </FormItem>
+        {show3 && <FormGroup titleText="Empty Group" />}
+        {show && (
+          <FormItem label="Item 2">
+            <Input data-testid="2" />
+          </FormItem>
+        )}
+        {show2 && (
+          <FormGroup titleText="Group 1">
+            <FormItem label="Item1 Grouped">
+              <Input data-testid="g1" />
+            </FormItem>
+            <FormItem label="Item2 Grouped">
+              <Input data-testid="g2" />
+            </FormItem>
+          </FormGroup>
+        )}
+
+        <FormItem label="Item 3">
+          <Input data-testid="3" />
+        </FormItem>
+        <FormItem label="Item 4">
+          <Input data-testid="4" />
+        </FormItem>
+      </Form>
+    </>
+  );
+};
+
 describe('Form', () => {
   it('size S - labels and fields should cover full width', () => {
     cy.viewport(393, 852); // iPhone 14 Pro
@@ -99,6 +141,53 @@ describe('Form', () => {
     cy.findByTestId('notSupported').should('not.exist');
   });
 
+  it('conditionally render FormItems & FormGroups', () => {
+    cy.mount(<ConditionRenderingExample />);
+    cy.findByText('Item 2').should('not.exist');
+
+    cy.findByText('Toggle Input').click();
+    cy.findByText('Item 2').should('exist');
+    cy.findByTestId('2').should('be.visible').as('item2');
+    cy.get('@item2').parent().should('have.css', 'grid-column-start', '17').and('have.css', 'grid-row-start', '1');
+
+    cy.findByText('Toggle Group').click();
+    cy.findByText('Group 1')
+      .should('be.visible')
+      .and('have.css', 'grid-column-start', '1')
+      .and('have.css', 'grid-row-start', '2');
+    cy.findByTestId('g2').should('be.visible').as('g2');
+    cy.get('@g2').parent().should('have.css', 'grid-column-start', '5').and('have.css', 'grid-row-start', '4');
+    cy.findByTestId('2').should('be.visible').as('item2');
+    cy.get('@item2').parent().should('have.css', 'grid-column-start', '17').and('have.css', 'grid-row-start', '1');
+
+    cy.findByText('Toggle Group2').click();
+    cy.findByText('Empty Group')
+      .should('be.visible')
+      .and('have.css', 'grid-column-start', '13')
+      .and('have.css', 'grid-row-start', '1');
+    cy.findByText('Group 1')
+      .should('be.visible')
+      .and('have.css', 'grid-column-start', '13')
+      .and('have.css', 'grid-row-start', '3');
+    cy.findByTestId('g2').should('be.visible').as('g2');
+    cy.get('@g2').parent().should('have.css', 'grid-column-start', '17').and('have.css', 'grid-row-start', '5');
+    cy.findByTestId('2').should('be.visible').as('item2');
+    cy.get('@item2').parent().should('have.css', 'grid-column-start', '5').and('have.css', 'grid-row-start', '4');
+
+    cy.findByText('Toggle Input').click();
+    cy.findByText('Empty Group')
+      .should('be.visible')
+      .and('have.css', 'grid-column-start', '13')
+      .and('have.css', 'grid-row-start', '1');
+    cy.findByText('Group 1')
+      .should('be.visible')
+      .and('have.css', 'grid-column-start', '1')
+      .and('have.css', 'grid-row-start', '3');
+    cy.findByTestId('g2').should('be.visible').as('g2');
+    cy.get('@g2').parent().should('have.css', 'grid-column-start', '5').and('have.css', 'grid-row-start', '5');
+    cy.findByTestId('2').should('not.exist');
+  });
+
   cypressPassThroughTestsFactory(Form, {
     children: (
       <FormItem label="Item">

packages/main/src/components/Form/FormContext.ts

@@ -1,7 +1,7 @@
 import { createContext, useContext } from 'react';
 import type { FormContextType, GroupContextType } from './types.js';
 
-export const FormContext = createContext<FormContextType>({ labelSpan: null });
+export const FormContext = createContext<FormContextType>({ labelSpan: null, recalcTrigger: 0 });
 
 export function useFormContext() {
   return useContext(FormContext);

packages/main/src/components/Form/index.tsx

@@ -3,7 +3,7 @@
 import { Device, useSyncRef } from '@ui5/webcomponents-react-base';
 import { clsx } from 'clsx';
 import type { ElementType, ReactNode } from 'react';
-import React, { forwardRef, useCallback, useEffect, useMemo, useRef, useState } from 'react';
+import React, { forwardRef, useCallback, useEffect, useMemo, useReducer, useRef, useState } from 'react';
 import { createUseStyles } from 'react-jss';
 import { FormBackgroundDesign, TitleLevel } from '../../enums/index.js';
 import type { CommonProps } from '../../interfaces/index.js';
@@ -12,6 +12,10 @@ import { styles } from './Form.jss.js';
 import { FormContext } from './FormContext.js';
 import type { FormContextType, FormElementTypes, FormGroupLayoutInfo, FormItemLayoutInfo, ItemInfo } from './types.js';
 
+const recalcReducerFn = (prev: number) => {
+  return prev + 1;
+};
+
 const useStyles = createUseStyles(styles, { name: 'Form' });
 
 export interface FormPropTypes extends CommonProps {
@@ -165,8 +169,8 @@ const Form = forwardRef<HTMLFormElement, FormPropTypes>((props, ref) => {
   const currentNumberOfColumns = columnsMap.get(currentRange);
 
   const registerItem = useCallback((id: string, type: FormElementTypes, groupId?: string) => {
-    setItems((state) => {
-      const clonedMap = new Map(state);
+    setItems((prev) => {
+      const clonedMap = new Map(prev);
       if (groupId) {
         const groupItem = clonedMap.get(groupId);
         if (groupItem) {
@@ -201,7 +205,7 @@ const Form = forwardRef<HTMLFormElement, FormPropTypes>((props, ref) => {
     });
   }, []);
 
-  const formLayoutContextValue = useMemo((): Omit<FormContextType, 'labelSpan'> => {
+  const formLayoutContextValue = useMemo((): Omit<FormContextType, 'labelSpan' | 'recalcTrigger'> => {
     const formItems: FormItemLayoutInfo[] = [];
     const formGroups: FormGroupLayoutInfo[] = [];
 
@@ -261,8 +265,35 @@ const Form = forwardRef<HTMLFormElement, FormPropTypes>((props, ref) => {
   const formClassNames = clsx(classes.form, classes[backgroundDesign.toLowerCase()]);
   const CustomTag = as as ElementType;
 
+  const prevFormItems = useRef<undefined | FormItemLayoutInfo[]>(undefined);
+  const prevFormGroups = useRef<undefined | FormGroupLayoutInfo[]>(undefined);
+
+  const [recalcTrigger, fireRecalc] = useReducer(recalcReducerFn, 0, undefined);
+  useEffect(() => {
+    if (prevFormItems.current || prevFormGroups.current) {
+      let hasChanged =
+        formLayoutContextValue.formItems.length !== prevFormItems.current.length ||
+        formLayoutContextValue.formGroups.length !== prevFormGroups.current.length;
+      if (!hasChanged) {
+        hasChanged = !formLayoutContextValue.formGroups.every(
+          (item, index) => prevFormGroups.current.findIndex((element) => element.id === item.id) === index
+        );
+      }
+      if (!hasChanged) {
+        hasChanged = !formLayoutContextValue.formItems.every(
+          (item, index) => prevFormItems.current.findIndex((element) => element.id === item.id) === index
+        );
+      }
+      if (hasChanged) {
+        fireRecalc();
+      }
+    }
+    prevFormItems.current = formLayoutContextValue.formItems;
+    prevFormGroups.current = formLayoutContextValue.formGroups;
+  }, [formLayoutContextValue.formItems, formLayoutContextValue.formGroups]);
+
   return (
-    <FormContext.Provider value={{ ...formLayoutContextValue, labelSpan: currentLabelSpan }}>
+    <FormContext.Provider value={{ ...formLayoutContextValue, labelSpan: currentLabelSpan, recalcTrigger }}>
       <CustomTag
         className={clsx(classes.formContainer, className)}
         suppressHydrationWarning={true}

packages/main/src/components/Form/types.ts

@@ -16,6 +16,7 @@ export type FormContextType = {
   unregisterItem?: (id: string, groupId?: string) => void;
   labelSpan: null | number;
   rowsWithGroup?: Record<number, boolean>;
+  recalcTrigger: number;
 };
 
 export type GroupContextType = {

packages/main/src/components/FormGroup/index.tsx

@@ -26,15 +26,18 @@ export interface FormGroupPropTypes {
  */
 const FormGroup = (props: FormGroupPropTypes) => {
   const { titleText, children } = props;
-  const { formGroups: layoutInfos, registerItem, unregisterItem, labelSpan } = useFormContext();
+  const { formGroups: layoutInfos, registerItem, unregisterItem, labelSpan, recalcTrigger } = useFormContext();
   const uniqueId = useIsomorphicId();
 
   useEffect(() => {
     registerItem?.(uniqueId, 'formGroup');
     return () => unregisterItem?.(uniqueId);
-  }, [uniqueId, registerItem, unregisterItem]);
+  }, [uniqueId, registerItem, unregisterItem, recalcTrigger]);
 
-  const layoutInfo = useMemo(() => layoutInfos?.find(({ id: groupId }) => uniqueId === groupId), [layoutInfos]);
+  const layoutInfo = useMemo(
+    () => layoutInfos?.find(({ id: groupId }) => uniqueId === groupId),
+    [layoutInfos, uniqueId]
+  );
 
   if (!layoutInfo) return null;
   const { columnIndex, rowIndex } = layoutInfo;

packages/main/src/components/FormItem/index.tsx

@@ -124,9 +124,16 @@ const getContentForHtmlLabel = (label: ReactNode) => {
  * __Note__: The `FormItem` is only used for calculating the final layout of the `Form`, thus it doesn't accept any other props than `label` and `children`, especially no `className`, `style` or `ref`.
  */
 const FormItem = (props: FormItemPropTypes) => {
-  const { label, children } = props as InternalProps;
   const uniqueId = useIsomorphicId();
-  const { formItems: layoutInfos, registerItem, unregisterItem, labelSpan, rowsWithGroup } = useFormContext();
+  const { label, children } = props as InternalProps;
+  const {
+    formItems: layoutInfos,
+    registerItem,
+    unregisterItem,
+    labelSpan,
+    rowsWithGroup,
+    recalcTrigger
+  } = useFormContext();
   const groupContext = useFormGroupContext();
   const classes = useStyles();
 
@@ -135,7 +142,7 @@ const FormItem = (props: FormItemPropTypes) => {
     return () => {
       unregisterItem?.(uniqueId, groupContext.id);
     };
-  }, [uniqueId, registerItem, unregisterItem, groupContext.id]);
+  }, [uniqueId, registerItem, unregisterItem, groupContext.id, recalcTrigger]);
 
   const layoutInfo = useMemo(() => layoutInfos?.find(({ id: itemId }) => uniqueId === itemId), [layoutInfos, uniqueId]);