BaseControl: Add opt-in prop for margin-free styles

packages/components/CHANGELOG.md

@@ -10,6 +10,7 @@
 -   `InputControl`: Allow `onBlur` for empty values to commit the change when `isPressEnterToChange` is true, and move reset behavior to the ESCAPE key. ([#39109](https://github.com/WordPress/gutenberg/pull/39109)).
 -   `TreeGrid`: Add tests for Home/End keyboard navigation. Add `onFocusRow` callback for Home/End keyboard navigation, this was missed in the implementation PR. Modify test for expanding/collapsing a row as row 1 implements this now. Update README with latest changes. ([#39302](https://github.com/WordPress/gutenberg/pull/39302))
 -   `ToggleGroupControlOption`: Calculate width from button content and remove `LabelPlaceholderView` ([#39345](https://github.com/WordPress/gutenberg/pull/39345))
+-   `BaseControl`: Add `__nextHasNoMarginBottom` prop for opting into the new margin-free styles ([#39325](https://github.com/WordPress/gutenberg/pull/39325)).
 
 ### Bug Fix
 

packages/components/src/base-control/README.md

@@ -10,7 +10,7 @@ Render a BaseControl for a textarea input:
 import { BaseControl } from '@wordpress/components';
 
 const MyBaseControl = () => (
-	<BaseControl id="textarea-1" label="Text" help="Enter some text">
+	<BaseControl id="textarea-1" label="Text" help="Enter some text" __nextHasNoMarginBottom={ true }>
 		<textarea id="textarea-1" />
 	</BaseControl>
 );
@@ -63,6 +63,14 @@ The content to be displayed within the BaseControl.
 -   Type: `Element`
 -   Required: Yes
 
+### __nextHasNoMarginBottom
+
+Start opting into the new margin-free styles that will become the default in a future version.
+
+-   Type: `Boolean`
+-   Required: No
+-   Default: `false`
+
 ## BaseControl.VisualLabel
 
 `BaseControl.VisualLabel` component is used to render a purely visual label inside a `BaseControl` component.

packages/components/src/base-control/index.js

@@ -17,25 +17,27 @@ import {
 
 /**
  * @typedef Props
- * @property {string}                    [id]                  The id of the element to which labels and help text are being generated.
- *                                                             That element should be passed as a child.
- * @property {import('react').ReactNode} help                  If this property is added, a help text will be
- *                                                             generated using help property as the content.
- * @property {import('react').ReactNode} [label]               If this property is added, a label will be generated
- *                                                             using label property as the content.
- * @property {boolean}                   [hideLabelFromVision] If true, the label will only be visible to screen readers.
- * @property {string}                    [className]           The class that will be added with "components-base-control" to the
- *                                                             classes of the wrapper div. If no className is passed only
- *                                                             components-base-control is used.
- * @property {import('react').ReactNode} [children]            The content to be displayed within
- *                                                             the BaseControl.
+ * @property {boolean}                   [__nextHasNoMarginBottom] Start opting into the new margin-free styles that will become the default in a future version.
+ * @property {string}                    [id]                      The id of the element to which labels and help text are being generated.
+ *                                                                 That element should be passed as a child.
+ * @property {import('react').ReactNode} help                      If this property is added, a help text will be
+ *                                                                 generated using help property as the content.
+ * @property {import('react').ReactNode} [label]                   If this property is added, a label will be generated
+ *                                                                 using label property as the content.
+ * @property {boolean}                   [hideLabelFromVision]     If true, the label will only be visible to screen readers.
+ * @property {string}                    [className]               The class that will be added with "components-base-control" to the
+ *                                                                 classes of the wrapper div. If no className is passed only
+ *                                                                 components-base-control is used.
+ * @property {import('react').ReactNode} [children]                The content to be displayed within
+ *                                                                 the BaseControl.
  */
 
 /**
  * @param {Props} props
  * @return {JSX.Element} Element
  */
 function BaseControl( {
+	__nextHasNoMarginBottom = false,
 	id,
 	label,
 	hideLabelFromVision,
@@ -47,7 +49,11 @@ function BaseControl( {
 		<Wrapper
 			className={ classnames( 'components-base-control', className ) }
 		>
-			<StyledField className="components-base-control__field">
+			<StyledField
+				className="components-base-control__field"
+				// TODO: Official deprecation for this should start after all internal usages have been migrated
+				__nextHasNoMarginBottom={ __nextHasNoMarginBottom }
+			>
 				{ label &&
 					id &&
 					( hideLabelFromVision ? (
@@ -77,6 +83,7 @@ function BaseControl( {
 				<StyledHelp
 					id={ id ? id + '__help' : undefined }
 					className="components-base-control__help"
+					__nextHasNoMarginBottom={ __nextHasNoMarginBottom }
 				>
 					{ help }
 				</StyledHelp>

packages/components/src/base-control/stories/index.js

@@ -4,7 +4,6 @@
 import BaseControl from '../';
 import Button from '../../button';
 import { Spacer } from '../../spacer';
-import TextareaControl from '../../textarea-control';
 
 export default {
 	title: 'Components/BaseControl',
@@ -15,13 +14,14 @@ export default {
 const BaseControlWithTextarea = ( { id, ...props } ) => {
 	return (
 		<BaseControl id={ id } { ...props }>
-			<TextareaControl id={ id } />
+			<textarea style={ { display: 'block' } } id={ id } />
 		</BaseControl>
 	);
 };
 
 export const Default = BaseControlWithTextarea.bind( {} );
 Default.args = {
+	__nextHasNoMarginBottom: true,
 	id: 'textarea-1',
 	label: '',
 	hideLabelFromVision: false,

packages/components/src/base-control/styles/base-control-styles.js

@@ -15,8 +15,17 @@ export const Wrapper = styled.div`
 	font-size: ${ font( 'default.fontSize' ) };
 `;
 
+const deprecatedMarginField = ( { __nextHasNoMarginBottom = false } ) => {
+	return (
+		! __nextHasNoMarginBottom &&
+		css`
+			margin-bottom: ${ space( 2 ) };
+		`
+	);
+};
+
 export const StyledField = styled.div`
-	margin-bottom: ${ space( 2 ) };
+	${ deprecatedMarginField }
 
 	.components-panel__row & {
 		margin-bottom: inherit;
@@ -32,10 +41,23 @@ export const StyledLabel = styled.label`
 	${ labelStyles }
 `;
 
+const deprecatedMarginHelp = ( { __nextHasNoMarginBottom = false } ) => {
+	return (
+		! __nextHasNoMarginBottom &&
+		css`
+			margin-bottom: revert;
+		`
+	);
+};
+
 export const StyledHelp = styled.p`
+	margin-top: ${ space( 2 ) };
+	margin-bottom: 0;
 	font-size: ${ font( 'helpText.fontSize' ) };
 	font-style: normal;
 	color: ${ COLORS.mediumGray.text };
+
+	${ deprecatedMarginHelp }
 `;
 
 export const StyledVisualLabel = styled.span`