Implementing field sizing option in TextArea component

.changeset/textarea-auto-size.md

@@ -0,0 +1,5 @@
+---
+'@primer/react': minor
+---
+
+Textarea: Add an `autoSize` option that allows the field to grow with its content

packages/react/src/Textarea/TextArea.module.css

@@ -29,6 +29,11 @@
   resize: vertical;
 }
 
+.TextArea[data-auto-size='true'] {
+  min-height: 1lh;
+  field-sizing: content;
+}
+
 .TextArea:disabled {
   resize: none;
 }

packages/react/src/Textarea/Textarea.docs.json

@@ -67,6 +67,12 @@
       "defaultValue": "'both'",
       "description": "Changes the resize behavior"
     },
+    {
+      "name": "autoSize",
+      "type": "boolean",
+      "defaultValue": "false",
+      "description": "Allows the textarea to grow to fit its content"
+    },
     {
       "name": "characterLimit",
       "type": "number",
@@ -110,4 +116,4 @@
     }
   ],
   "subcomponents": []
-}
+}

packages/react/src/Textarea/Textarea.features.stories.tsx

@@ -108,6 +108,15 @@ export const CustomResizeBehavior = () => (
   </Stack>
 )
 
+export const AutoSize = () => (
+  <form>
+    <FormControl>
+      <FormControl.Label>Automatically growing textarea</FormControl.Label>
+      <Textarea autoSize />
+    </FormControl>
+  </form>
+)
+
 export const MinimumHeight = () => (
   <form>
     <FormControl>

packages/react/src/Textarea/Textarea.stories.tsx

@@ -30,6 +30,7 @@ Playground.args = {
   block: false,
   cols: DEFAULT_TEXTAREA_COLS,
   disabled: false,
+  autoSize: false,
   resize: DEFAULT_TEXTAREA_RESIZE,
   contrast: false,
   rows: DEFAULT_TEXTAREA_ROWS,
@@ -45,6 +46,9 @@ Playground.argTypes = {
   disabled: {
     control: {type: 'boolean'},
   },
+  autoSize: {
+    control: {type: 'boolean'},
+  },
   resize: {
     options: ['none', 'both', 'horizontal', 'vertical'],
     control: {type: 'radio'},

packages/react/src/Textarea/Textarea.test.tsx

@@ -104,6 +104,17 @@ describe('Textarea', () => {
     expect(hasResizeDeclaration).toBe(true)
   })
 
+  it('enables automatic sizing without changing resize behavior', () => {
+    render(<Textarea autoSize resize="vertical" />)
+    const textareaElement = screen.getByRole('textbox')
+
+    expect(textareaElement).toHaveAttribute('data-auto-size', 'true')
+    expect(textareaElement).toHaveAttribute('data-resize', 'vertical')
+
+    const rules = getCSSRules(`.${classes.TextArea}[data-auto-size="true"]`)
+    expect(rules.some(rule => rule.style.minHeight === '1lh' && rule.style.fieldSizing === 'content')).toBe(true)
+  })
+
   it('renders a value in the textarea', () => {
     const mockValue = 'mock value'
     const onChange = vi.fn()

packages/react/src/Textarea/Textarea.tsx

@@ -33,6 +33,10 @@ export type TextareaProps = {
    * Allows resizing of the textarea
    */
   resize?: 'none' | 'both' | 'horizontal' | 'vertical'
+  /**
+   * Allows the textarea to grow to fit its content
+   */
+  autoSize?: boolean
   /**
    * apply a high contrast color to background
    */
@@ -74,6 +78,7 @@ const Textarea = React.forwardRef<HTMLTextAreaElement, TextareaProps>(
       rows = DEFAULT_TEXTAREA_ROWS,
       cols = DEFAULT_TEXTAREA_COLS,
       resize = DEFAULT_TEXTAREA_RESIZE,
+      autoSize,
       block,
       contrast,
       className,
@@ -133,6 +138,7 @@ const Textarea = React.forwardRef<HTMLTextAreaElement, TextareaProps>(
             defaultValue={defaultValue}
             data-component="Textarea"
             data-resize={resize}
+            data-auto-size={autoSize || undefined}
             aria-required={required}
             aria-invalid={isValid === 'error' ? 'true' : 'false'}
             ref={ref}