Fix initial focus selection

packages/mui-base/src/NumberField/NumberFieldInput.test.tsx

@@ -3,6 +3,7 @@ import { expect } from 'chai';
 import { act, createRenderer, screen } from '@mui/internal-test-utils';
 import { NumberField } from '@base_ui/react/NumberField';
 import { fireEvent } from '@testing-library/react';
+import { userEvent } from '@testing-library/user-event';
 import { describeConformance } from '../../test/describeConformance';
 import { NumberFieldContext, NumberFieldContextValue } from './NumberFieldContext';
 
@@ -193,4 +194,33 @@ describe('<NumberField.Group />', () => {
     fireEvent.blur(input);
     expect(input).to.have.value('4');
   });
+
+  it('should set selection to the logical end of the input on first focus', async () => {
+    if (/jsdom/.test(window.navigator.userAgent)) {
+      // JSDOM does not support selectionStart/selectionEnd
+      return;
+    }
+
+    render(
+      <NumberField id="test" defaultValue={100}>
+        <label htmlFor="test">label</label>
+        <NumberField.Input />
+      </NumberField>,
+    );
+    const input = screen.getByRole<HTMLInputElement>('textbox');
+    const label = screen.getByLabelText('label');
+
+    await userEvent.click(label);
+
+    expect(input.selectionStart).to.equal(3);
+    expect(input.selectionEnd).to.equal(3);
+
+    input.setSelectionRange(0, 3);
+
+    await userEvent.click(document.body);
+    await userEvent.click(label);
+
+    expect(input.selectionStart).to.equal(0);
+    expect(input.selectionEnd).to.equal(3);
+  });
 });

packages/mui-base/src/useNumberField/useNumberField.ts

@@ -84,7 +84,8 @@ export function useNumberField(params: NumberFieldProps): UseNumberFieldReturnVa
   const movesAfterTouchRef = React.useRef(0);
   const allowInputSyncRef = React.useRef(true);
   const unsubscribeFromGlobalContextMenuRef = React.useRef<() => void>(() => {});
-  const isTouchingRef = React.useRef(false);
+  const isTouchingButtonRef = React.useRef(false);
+  const hasTouchedInputRef = React.useRef(false);
 
   const [valueUnwrapped, setValueUnwrapped] = useControlled<number | null>({
     controlled: externalValue,
@@ -361,10 +362,10 @@ export function useNumberField(params: NumberFieldProps): UseNumberFieldReturnVa
           userSelect: 'none',
         },
         onTouchStart() {
-          isTouchingRef.current = true;
+          isTouchingButtonRef.current = true;
         },
         onTouchEnd() {
-          isTouchingRef.current = false;
+          isTouchingButtonRef.current = false;
         },
         onClick(event) {
           const isDisabled = disabled || readOnly || (isIncrement ? isMax : isMin);
@@ -434,22 +435,22 @@ export function useNumberField(params: NumberFieldProps): UseNumberFieldReturnVa
             event.defaultPrevented ||
             isDisabled ||
             !isPressedRef.current ||
-            isTouchingRef.current
+            isTouchingButtonRef.current
           ) {
             return;
           }
 
           startAutoChange(isIncrement);
         },
         onMouseLeave() {
-          if (isTouchingRef.current) {
+          if (isTouchingButtonRef.current) {
             return;
           }
 
           stopAutoChange();
         },
         onMouseUp() {
-          if (isTouchingRef.current) {
+          if (isTouchingButtonRef.current) {
             return;
           }
 
@@ -498,6 +499,19 @@ export function useNumberField(params: NumberFieldProps): UseNumberFieldReturnVa
         spellCheck: 'false',
         'aria-roledescription': 'Number field',
         'aria-invalid': invalid || undefined,
+        onFocus(event) {
+          if (event.defaultPrevented || readOnly || disabled || hasTouchedInputRef.current) {
+            return;
+          }
+
+          hasTouchedInputRef.current = true;
+
+          // Browsers set selection at the start of the input field by default. We want to set it at
+          // the end for the first focus.
+          const target = event.currentTarget;
+          const length = target.value.length;
+          target.setSelectionRange(length, length);
+        },
         onBlur(event) {
           if (event.defaultPrevented || readOnly || disabled) {
             return;