Repository: mui/material-ui (TypeScript) — Bug Fix

Issue:
[RadioGroup] By default unnamed groups are not correctly grouped for accessibility purposes
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An unnamed RadioGroup will handle value changes as expected. However, the input elements of different groups will be on the same group in HTML.
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- [x] The issue is present in the latest release.
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## Current Behavior 😯

<!-- Describe what happens instead of the expected behavior. -->

Two unnamed groups handle the React state correctly, but the HTML will be unnamed. It makes the keyboard arrow navigation to move across groups.

## Expected Behavior 🤔

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Keyboard arrows should navigate only inside the group, while Tab should move between groups: https://www.w3.org/TR/wai-aria-practices-1.1/#keyboard-interaction-14

I see three possible options to handle this:
1. Auto-generate a name for unnamed groups (e.g. Reach UI, Material Angular does this). The biggest challenge of this option is how to correctly generate the id with support for SSR.
2. Emit a warning when the user doesn't provide a name
3. Make the `name` a required prop (breaking compatibility)

This is a subtle issue, since the user will not see any warning and React will handle the state as expected (MUI sets the checked state based on the RadioGroup context value). However, the end result will not handle keyboard focus correctly.

Personally, I prefer (1) since emitting a warning will left the user with the task of id generation (which is not easy, for reference see: https://github.com/reach/reach-ui/blob/master/packages/auto-id/src/index.ts)

## Steps to Reproduce 🕹

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https://codesandbox.io/s/eager-davinci-1hg9w?fontsize=14&hidenavigation=1&theme=dark

Steps:

1. Add an unnamed `RadioGroup`
2. Add another unnamed `RadioGroup`
3. Set the focus in any of the groups
4. Press arrow up or arrow down to select another option in the group.
5. When you move to the last item in the group, the keyboard will jump to the next group

## Context 🔦

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## Your Environment 🌎

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| Tech        | Version |
| ----------- | ------- |
| Material-UI | v4.9.4  |
| React       |  v16.12       |
| Browser     |  Chrome 79       |



Discussion:
@dfernandez-asapp Note that we are using (1) in

- https://github.com/mui-org/material-ui/blob/4fba0dafd30f608937efa32883d151ba01fc9681/packages/material-ui-lab/src/Rating/Rating.js#L168
- https://github.com/mui-org/material-ui/blob/4fba0dafd30f608937efa32883d151ba01fc9681/packages/material-ui-lab/src/useAutocomplete/useAutocomplete.js#L123
- https://github.com/mui-org/material-ui/blob/4fba0dafd30f608937efa32883d151ba01fc9681/packages/material-ui/src/Tooltip/Tooltip.js#L257

This issue is relevant in our context: #18172.
Many thanks for the info, I'll create a PR for this.

But I have two questions, out of curiosity:
1. I see that other frameworks like ReachUI are using a more complex logic for the ID generation, mainly because of SSR. In this approach the `setDefaultId` is called in a `useEffect`, meaning that these ids are ignored for SSR. Is there any undesired behavior for not having the ids in SSR?
2. Why store the id in a state, instead of using a ref?
1) What would you use the id for prior to hydration?
2) To rerender after hydration 
@dfernandez-asapp Do you want to work on a pull request with (1)? :) 
Yes

Resolving patch:
diff --git a/docs/pages/api/radio-group.md b/docs/pages/api/radio-group.md
--- a/docs/pages/api/radio-group.md
+++ b/docs/pages/api/radio-group.md
@@ -26,7 +26,7 @@ You can learn more about the difference by [reading this guide](/guides/minimizi
 |:-----|:-----|:--------|:------------|
 | <span class="prop-name">children</span> | <span class="prop-type">node</span> |  | The content of the component. |
 | <span class="prop-name">defaultValue</span> | <span class="prop-type">any</span> |  | The default `input` element value. Use when the component is not controlled. |
-| <span class="prop-name">name</span> | <span class="prop-type">string</span> |  | The name used to reference the value of the control. |
+| <span class="prop-name">name</span> | <span class="prop-type">string</span> |  | The name used to reference the value of the control. If you don't provide this prop, it falls back to a randomly generated name. |
 | <span class="prop-name">onChange</span> | <span class="prop-type">func</span> |  | Callback fired when a radio button is selected.<br><br>**Signature:**<br>`function(event: object) => void`<br>*event:* The event source of the callback. You can pull out the new value by accessing `event.target.value` (string). |
 | <span class="prop-name">value</span> | <span class="prop-type">any</span> |  | Value of the selected radio button. The DOM API casts this to a string. |
 
diff --git a/packages/material-ui/src/RadioGroup/RadioGroup.js b/packages/material-ui/src/RadioGroup/RadioGroup.js
--- a/packages/material-ui/src/RadioGroup/RadioGroup.js
+++ b/packages/material-ui/src/RadioGroup/RadioGroup.js
@@ -6,7 +6,7 @@ import useControlled from '../utils/useControlled';
 import RadioGroupContext from './RadioGroupContext';
 
 const RadioGroup = React.forwardRef(function RadioGroup(props, ref) {
-  const { actions, children, name, value: valueProp, onChange, ...other } = props;
+  const { actions, children, name: nameProp, value: valueProp, onChange, ...other } = props;
   const rootRef = React.useRef(null);
 
   const [value, setValue] = useControlled({
@@ -43,6 +43,15 @@ const RadioGroup = React.forwardRef(function RadioGroup(props, ref) {
     }
   };
 
+  const [defaultName, setDefaultName] = React.useState();
+  const name = nameProp || defaultName;
+  React.useEffect(() => {
+    // Fallback to this default name when possible.
+    // Use the random value for client-side rendering only.
+    // We can't use it server-side.
+    setDefaultName(`mui-radiogroup-${Math.round(Math.random() * 1e5)}`);
+  }, []);
+
   return (
     <RadioGroupContext.Provider value={{ name, onChange: handleChange, value }}>
       <FormGroup role="radiogroup" ref={handleRef} {...other}>
@@ -67,6 +76,7 @@ RadioGroup.propTypes = {
   defaultValue: PropTypes.any,
   /**
    * The name used to reference the value of the control.
+   * If you don't provide this prop, it falls back to a randomly generated name.
    */
   name: PropTypes.string,
   /**


Test patch:
diff --git a/packages/material-ui/src/RadioGroup/RadioGroup.test.js b/packages/material-ui/src/RadioGroup/RadioGroup.test.js
--- a/packages/material-ui/src/RadioGroup/RadioGroup.test.js
+++ b/packages/material-ui/src/RadioGroup/RadioGroup.test.js
@@ -85,6 +85,18 @@ describe('<RadioGroup />', () => {
     assert.strictEqual(findRadio(wrapper, 'one').props().checked, true);
   });
 
+  it('should have a default name', () => {
+    const wrapper = mount(
+      <RadioGroup>
+        <Radio value="zero" />
+        <Radio value="one" />
+      </RadioGroup>,
+    );
+
+    assert.match(findRadio(wrapper, 'zero').props().name, /^mui-radiogroup-[0-9]+/);
+    assert.match(findRadio(wrapper, 'one').props().name, /^mui-radiogroup-[0-9]+/);
+  });
+
   describe('imperative focus()', () => {
     it('should focus the first non-disabled radio', () => {
       const actionsRef = React.createRef();
@@ -295,6 +307,16 @@ describe('<RadioGroup />', () => {
         setProps({ value: 'one' });
         expect(radioGroupRef.current).to.have.property('value', 'one');
       });
+
+      it('should have a default name from the instance', () => {
+        const radioGroupRef = React.createRef();
+        const { setProps } = render(<RadioGroupControlled ref={radioGroupRef} />);
+
+        expect(radioGroupRef.current.name).to.match(/^mui-radiogroup-[0-9]+/);
+
+        setProps({ name: 'anotherGroup' });
+        expect(radioGroupRef.current).to.have.property('name', 'anotherGroup');
+      });
     });
 
     describe('callbacks', () => {