Add FieldArray component (#26993)

packages/grafana-ui/src/components/Forms/FieldArray.mdx

+import { Meta, Props } from '@storybook/addon-docs/blocks';
+import { FieldArray } from './FieldArray';
+
+<Meta title="MDX|FieldArray" component={FieldArray} />
+
+# FieldArray
+
+`FieldArray` provides a way to render a list of dynamic inputs. It exposes the functionality of `useFieldArray` in [react-hook-form](https://react-hook-form.com/advanced-usage/#FieldArrays). `FieldArray` must be wrapped at some level by a `<Form>` element.
+
+### Usage
+
+```jsx
+import { Form, FieldArray } from '@grafana/ui';
+
+<Form>
+  ({control, register}) => (
+  <FieldArray control={control} name="People">
+    {({ fields, append }) => (
+        <div>
+            {fields.map((field, index) => (
+                <div key={field.id}>
+                    <Input key={index} ref={register()} name=`people[${index}].firstName` value={field.firstName} />
+                    <Input ref={register()} name=`people[${index}].lastName` value={field.lastName} />
+                </div>
+            ))}
+            <Button onClick={() => append({firstName: 'Roger', lastName: 'Waters'})}>Append</Button>
+        </div>
+    )}
+  </FieldArray>
+  )
+</Form>;
+```
+
+### FieldArray API
+
+The `FieldArray` component exposes its API via render prop. Properties exposed are: `fields`, `append`, `prepend`, `remove`, `swap`, `move`, `insert`
+
+### Props
+
+<Props of={FieldArray} />

packages/grafana-ui/src/components/Forms/FieldArray.story.tsx

+import React from 'react';
+import { withCenteredStory } from '../../utils/storybook/withCenteredStory';
+import { withStoryContainer } from '../../utils/storybook/withStoryContainer';
+import { Form, Input, Button, HorizontalGroup } from '@grafana/ui';
+import { FieldArray } from './FieldArray';
+import mdx from './FieldArray.mdx';
+
+export default {
+  title: 'Forms/FieldArray',
+  component: FieldArray,
+  decorators: [withStoryContainer, withCenteredStory],
+  parameters: {
+    docs: {
+      page: mdx,
+    },
+  },
+};
+
+export const simple = () => {
+  const defaultValues = {
+    people: [{ firstName: 'Janis', lastName: 'Joplin' }],
+  };
+  return (
+    <Form onSubmit={values => console.log(values)} defaultValues={defaultValues}>
+      {({ control, register }) => (
+        <div>
+          <FieldArray control={control} name="people">
+            {({ fields, append }) => (
+              <>
+                <div style={{ marginBottom: '1rem' }}>
+                  {fields.map((field, index) => (
+                    <HorizontalGroup key={field.id}>
+                      <Input ref={register()} name={`people[${index}].firstName`} value={field.firstName} />
+                      <Input ref={register()} name={`people[${index}].lastName`} value={field.lastName} />
+                    </HorizontalGroup>
+                  ))}
+                </div>
+                <Button
+                  style={{ marginRight: '1rem' }}
+                  onClick={() => append({ firstName: 'Roger', lastName: 'Waters' })}
+                >
+                  Add another
+                </Button>
+              </>
+            )}
+          </FieldArray>
+          <Button type="submit">Submit</Button>
+        </div>
+      )}
+    </Form>
+  );
+};

packages/grafana-ui/src/components/Forms/FieldArray.tsx

+import { FC } from 'react';
+import { useFieldArray, UseFieldArrayProps } from 'react-hook-form';
+import { FieldArrayApi } from '../../types';
+
+export interface FieldArrayProps extends UseFieldArrayProps {
+  children: (api: FieldArrayApi) => JSX.Element;
+}
+
+export const FieldArray: FC<FieldArrayProps> = ({ name, control, children }) => {
+  const { fields, append, prepend, remove, swap, move, insert } = useFieldArray({
+    control,
+    name,
+  });
+  return children({ fields, append, prepend, remove, swap, move, insert });
+};

packages/grafana-ui/src/types/forms.ts

-import { FormContextValues } from 'react-hook-form';
+import { FormContextValues, FieldValues, ArrayField } from 'react-hook-form';
 export { OnSubmit as FormsOnSubmit, FieldErrors as FormFieldErrors } from 'react-hook-form';
 
 export type FormAPI<T> = Pick<
   FormContextValues<T>,
   'register' | 'errors' | 'control' | 'formState' | 'getValues' | 'watch'
 >;
+
+type FieldArrayValue = Partial<FieldValues> | Array<Partial<FieldValues>>;
+
+export interface FieldArrayApi {
+  fields: Array<Partial<ArrayField<FieldValues, 'id'>>>;
+  append: (value: FieldArrayValue) => void;
+  prepend: (value: FieldArrayValue) => void;
+  remove: (index?: number | number[]) => void;
+  swap: (indexA: number, indexB: number) => void;
+  move: (from: number, to: number) => void;
+  insert: (index: number, value: FieldArrayValue) => void;
+}