[fields] Handle focusing container with inputRef.current.focus on accessibleFieldDOMStructure (mui#15985)

Author: LukasTy

packages/x-date-pickers/src/DateField/tests/selection.DateField.test.tsx

@@ -1,6 +1,7 @@
+import * as React from 'react';
 import { expect } from 'chai';
 import { DateField } from '@mui/x-date-pickers/DateField';
-import { act, fireEvent } from '@mui/internal-test-utils';
+import { act, fireEvent, screen } from '@mui/internal-test-utils';
 import {
   createPickerRenderer,
   expectFieldValueV7,
@@ -351,5 +352,22 @@ describe('<DateField /> - Selection', () => {
       fireEvent.keyDown(input, { key: 'ArrowLeft' });
       expect(getCleanedSelectedContent()).to.equal('MM');
     });
+
+    it('should select the first section when `inputRef.current` is focused', () => {
+      function TestCase() {
+        const inputRef = React.useRef<HTMLInputElement>(null);
+        return (
+          <React.Fragment>
+            <DateField inputRef={inputRef} />
+            <button onClick={() => inputRef.current?.focus()}>Focus input</button>
+          </React.Fragment>
+        );
+      }
+      render(<TestCase />);
+
+      fireEvent.click(screen.getByRole('button', { name: 'Focus input' }));
+
+      expect(getCleanedSelectedContent()).to.equal('MM');
+    });
   });
 });

packages/x-date-pickers/src/PickersTextField/PickersInputBase/PickersInputBase.tsx

@@ -247,6 +247,10 @@ const PickersInputBase = React.forwardRef(function PickersInputBase(
     onFocus?.(event);
   };
 
+  const handleHiddenInputFocus = (event: React.FocusEvent<HTMLInputElement>) => {
+    handleInputFocus(event);
+  };
+
   const handleInputBlur = (event: React.FocusEvent<HTMLDivElement>) => {
     muiFormControl.onBlur?.(event);
     onBlur?.(event);
@@ -338,6 +342,9 @@ const PickersInputBase = React.forwardRef(function PickersInputBase(
         readOnly={readOnly}
         required={muiFormControl.required}
         disabled={muiFormControl.disabled}
+        // Hidden input element cannot be focused, trigger the root focus instead
+        // This allows to maintain the ability to do `inputRef.current.focus()` to focus the field
+        onFocus={handleHiddenInputFocus}
         {...inputProps}
         ref={handleInputRef}
       />