[Popper] Fix deep merge of PopperProps

docs/pages/api/tooltip.md

@@ -41,7 +41,7 @@ You can learn more about the difference by [reading this guide](/guides/minimizi
 | <span class="prop-name">onOpen</span> | <span class="prop-type">func</span> |  | Callback fired when the component requests to be open.<br><br>**Signature:**<br>`function(event: object) => void`<br>*event:* The event source of the callback. |
 | <span class="prop-name">open</span> | <span class="prop-type">bool</span> |  | If `true`, the tooltip is shown. |
 | <span class="prop-name">placement</span> | <span class="prop-type">'bottom-end'<br>&#124;&nbsp;'bottom-start'<br>&#124;&nbsp;'bottom'<br>&#124;&nbsp;'left-end'<br>&#124;&nbsp;'left-start'<br>&#124;&nbsp;'left'<br>&#124;&nbsp;'right-end'<br>&#124;&nbsp;'right-start'<br>&#124;&nbsp;'right'<br>&#124;&nbsp;'top-end'<br>&#124;&nbsp;'top-start'<br>&#124;&nbsp;'top'</span> | <span class="prop-default">'bottom'</span> | Tooltip placement. |
-| <span class="prop-name">PopperProps</span> | <span class="prop-type">object</span> |  | Props applied to the [`Popper`](/api/popper/) element. |
+| <span class="prop-name">PopperProps</span> | <span class="prop-type">object</span> | <span class="prop-default">{}</span> | Props applied to the [`Popper`](/api/popper/) element. |
 | <span class="prop-name required">title&nbsp;*</span> | <span class="prop-type">node</span> |  | Tooltip title. Zero-length titles string are never displayed. |
 | <span class="prop-name">TransitionComponent</span> | <span class="prop-type">elementType</span> | <span class="prop-default">Grow</span> | The component used for the transition. [Follow this guide](/components/transitions/#transitioncomponent-prop) to learn more about the requirements for this component. |
 | <span class="prop-name">TransitionProps</span> | <span class="prop-type">object</span> |  | Props applied to the [`Transition`](http://reactcommunity.org/react-transition-group/transition#Transition-props) element. |

packages/material-ui/src/Tooltip/Tooltip.js

@@ -2,7 +2,7 @@ import * as React from 'react';
 import * as ReactDOM from 'react-dom';
 import PropTypes from 'prop-types';
 import clsx from 'clsx';
-import { elementAcceptingRef } from '@material-ui/utils';
+import { deepmerge, elementAcceptingRef } from '@material-ui/utils';
 import { fade } from '../styles/colorManipulator';
 import withStyles from '../styles/withStyles';
 import capitalize from '../utils/capitalize';
@@ -194,7 +194,7 @@ const Tooltip = React.forwardRef(function Tooltip(props, ref) {
     onOpen,
     open: openProp,
     placement = 'bottom',
-    PopperProps,
+    PopperProps = {},
     title,
     TransitionComponent = Grow,
     TransitionProps,
@@ -484,18 +484,21 @@ const Tooltip = React.forwardRef(function Tooltip(props, ref) {
     }
   }
 
-  // Avoid the creation of a new Popper.js instance at each render.
-  const popperOptions = React.useMemo(
-    () => ({
-      modifiers: {
-        arrow: {
-          enabled: Boolean(arrowRef),
-          element: arrowRef,
+  const mergedPopperProps = React.useMemo(() => {
+    return deepmerge(
+      {
+        popperOptions: {
+          modifiers: {
+            arrow: {
+              enabled: Boolean(arrowRef),
+              element: arrowRef,
+            },
+          },
         },
       },
-    }),
-    [arrowRef],
-  );
+      PopperProps,
+    );
+  }, [arrowRef, PopperProps]);
 
   return (
     <React.Fragment>
@@ -510,9 +513,8 @@ const Tooltip = React.forwardRef(function Tooltip(props, ref) {
         open={childNode ? open : false}
         id={childrenProps['aria-describedby']}
         transition
-        popperOptions={popperOptions}
         {...interactiveWrapperListeners}
-        {...PopperProps}
+        {...mergedPopperProps}
       >
         {({ placement: placementInner, TransitionProps: TransitionPropsInner }) => (
           <TransitionComponent

packages/material-ui/src/Tooltip/Tooltip.test.js

@@ -397,6 +397,38 @@ describe('<Tooltip />', () => {
     });
   });
 
+  describe('prop: PopperProps', () => {
+    it('should pass PopperProps to Popper Component', () => {
+      const { getByTestId } = render(
+        <Tooltip {...defaultProps} open PopperProps={{ 'data-testid': 'popper' }} />,
+      );
+
+      expect(getByTestId('popper')).to.be.ok;
+    });
+
+    it('should merge popperOptions with arrow modifier', () => {
+      const popperRef = React.createRef();
+      render(
+        <Tooltip
+          {...defaultProps}
+          open
+          arrow
+          PopperProps={{
+            popperRef,
+            popperOptions: {
+              modifiers: {
+                arrow: {
+                  foo: 'bar',
+                },
+              },
+            },
+          }}
+        />,
+      );
+      expect(popperRef.current.modifiers.find(x => x.name === 'arrow').foo).to.equal('bar');
+    });
+  });
+
   describe('forward', () => {
     it('should forward props to the child element', () => {
       const wrapper = mount(