Add Columns template options, support InnerBlock templateOptions

packages/block-editor/src/components/inner-blocks/README.md

@@ -90,6 +90,69 @@ const TEMPLATE = [ [ 'core/columns', {}, [
 
 The previous example creates an InnerBlocks area containing two columns one with an image and the other with a paragraph.
 
+### `__experimentaltemplateOptions`
+
+* **Type:** `Array<Object>`
+
+To present the user with a set of template choices for the inner blocks, you may provide an array of template options.
+
+A template option is an object consisting of the following properties:
+
+- `title` (`string`): A human-readable label which describes the template. 
+- `icon` (`WPElement|string`): An element or [Dashicon](https://developer.wordpress.org/resource/dashicons/) slug to show as a visual approximation of the template.
+- `template` (`Array<Array>`): The template to apply when the option has been selected. See [`template` documentation](#template) for more information.
+
+For the template placeholder selection to be displayed, you must render `InnerBlocks` with a `template` prop value of `null`. You may track this as state of your component, updating its value when receiving the selected template via `onSelectTemplateOption`.
+
+```jsx
+import { useState } from '@wordpress/element';
+
+const TEMPLATE_OPTIONS = [
+	{
+		title: 'Two Columns',
+		icon: <svg />,
+		template: [
+			[ 'core/column', { width: 50 } ],
+			[ 'core/column', { width: 50 } ],
+		],
+	},
+	{
+		title: 'Three Columns',
+		icon: <svg />,
+		template: [
+			[ 'core/column', { width: 33.33 } ],
+			[ 'core/column', { width: 33.33 } ],
+			[ 'core/column', { width: 33.33 } ],
+		],
+	},
+];
+
+function edit() {
+	const [ template, setTemplate ] = useState( null );
+
+	return (
+		<InnerBlocks
+			template={ template }
+		    templateOptions={ TEMPLATE_OPTIONS }
+		    onSelectTemplateOption={ setTemplate }
+		/>
+	);
+}
+```
+
+### `__experimentalOnSelectTemplateOption`
+
+* **Type:** `Function`
+
+Callback function invoked when the user makes a template selection, used in combination with the `templateOptions` props. The selected template is passed as the first and only argument. The value of the template may be `undefined` if the `allowTemplateOptionSkip` prop is passed to `InnerBlocks` and the user opts to skip template selection.
+
+### `__experimentalAllowTemplateOptionSkip`
+
+* **Type:** `Boolean`
+* **Default:** `false`
+
+Whether to include a button in the template selection placeholder to allow the user to skip selection, used in combination with the `templateOptions` prop. When clicked, the `onSelectTemplateOption` callback will be passed an `undefined` value as the template.
+
 ### `templateInsertUpdatesSelection`
 * **Type:** `Boolean`
 * **Default:** `true`

packages/block-editor/src/components/inner-blocks/index.js

@@ -24,6 +24,7 @@ import DefaultBlockAppender from './default-block-appender';
  */
 import BlockList from '../block-list';
 import { withBlockEditContext } from '../block-edit/context';
+import TemplatePicker from './template-picker';
 
 class InnerBlocks extends Component {
 	constructor() {
@@ -48,6 +49,7 @@ class InnerBlocks extends Component {
 		if ( innerBlocks.length === 0 || this.getTemplateLock() === 'all' ) {
 			this.synchronizeBlocksWithTemplate();
 		}
+
 		if ( this.state.templateInProcess ) {
 			this.setState( {
 				templateInProcess: false,
@@ -107,20 +109,32 @@ class InnerBlocks extends Component {
 			clientId,
 			hasOverlay,
 			renderAppender,
+			template,
+			__experimentalTemplateOptions: templateOptions,
+			__experimentalOnSelectTemplateOption: onSelectTemplateOption,
+			__experimentalAllowTemplateOptionSkip: allowTemplateOptionSkip,
 		} = this.props;
 		const { templateInProcess } = this.state;
 
+		const isPlaceholder = template === null && !! templateOptions;
+
 		const classes = classnames( 'editor-inner-blocks block-editor-inner-blocks', {
-			'has-overlay': hasOverlay,
+			'has-overlay': hasOverlay && ! isPlaceholder,
 		} );
 
 		return (
 			<div className={ classes }>
 				{ ! templateInProcess && (
-					<BlockList
-						rootClientId={ clientId }
-						renderAppender={ renderAppender }
-					/>
+					isPlaceholder ?
+						<TemplatePicker
+							options={ templateOptions }
+							onSelect={ onSelectTemplateOption }
+							allowSkip={ allowTemplateOptionSkip }
+						/> :
+						<BlockList
+							rootClientId={ clientId }
+							renderAppender={ renderAppender }
+						/>
 				) }
 			</div>
 		);

packages/block-editor/src/components/inner-blocks/style.scss

@@ -17,3 +17,69 @@
 	right: 0;
 	left: 0;
 }
+
+.block-editor-inner-blocks__template-picker {
+	.components-placeholder__instructions {
+		// Defer to vertical margins applied by template picker options.
+		margin-bottom: 0;
+	}
+
+	.components-placeholder__fieldset {
+		// Options will render horizontally, but the immediate children of the
+		// fieldset are the options and the skip button, oriented vertically.
+		flex-direction: column;
+	}
+
+	&.has-many-options .components-placeholder__fieldset {
+		// Allow options to occupy a greater amount of the available space if
+		// many options exist.
+		max-width: 90%;
+	}
+}
+
+.block-editor-inner-blocks__template-picker-options.block-editor-inner-blocks__template-picker-options {
+	display: flex;
+	flex-direction: row;
+	flex-wrap: nowrap;
+	width: 100%;
+	margin: $grid-size-large 0;
+	list-style: none;
+
+	> li {
+		flex-basis: 100%;
+		flex-shrink: 1;
+		margin: 0 $grid-size;
+		max-width: 100px;
+	}
+}
+
+.block-editor-inner-blocks__template-picker-option {
+	width: 100%;
+
+	&.components-icon-button {
+		// Override default styles inherited from <IconButton /> to center
+		// icon horizontally.
+		justify-content: center;
+	}
+
+	&.components-button {
+		// Override default styles inherited from <Button /> to allow button
+		// to grow vertically.
+		height: auto;
+		padding: 0;
+	}
+
+	&::before {
+		// Use `padding-bottom` trick to style element as perfect square.
+		content: "";
+		padding-bottom: 100%;
+	}
+
+	&:first-child {
+		margin-left: 0;
+	}
+
+	&:last-child {
+		margin-right: 0;
+	}
+}

packages/block-editor/src/components/inner-blocks/template-picker.js

@@ -0,0 +1,67 @@
+/**
+ * External dependencies
+ */
+import classnames from 'classnames';
+
+/**
+ * WordPress dependencies
+ */
+import { __ } from '@wordpress/i18n';
+import { Button, IconButton, Placeholder } from '@wordpress/components';
+
+function InnerBlocksTemplatePicker( {
+	options,
+	onSelect,
+	allowSkip,
+} ) {
+	const classes = classnames( 'block-editor-inner-blocks__template-picker', {
+		'has-many-options': options.length > 4,
+	} );
+
+	const instructions = allowSkip ?
+		__( 'Select a layout to start with, or make one yourself.' ) :
+		__( 'Select a layout to start with.' );
+
+	return (
+		<Placeholder
+			icon="layout"
+			label={ __( 'Choose Layout' ) }
+			instructions={ instructions }
+			className={ classes }
+		>
+			{
+				/*
+				* Disable reason: The `list` ARIA role is redundant but
+				* Safari+VoiceOver won't announce the list otherwise.
+				*/
+				/* eslint-disable jsx-a11y/no-redundant-roles */
+			}
+			<ul className="block-editor-inner-blocks__template-picker-options" role="list">
+				{ options.map( ( templateOption, index ) => (
+					<li key={ index }>
+						<IconButton
+							isLarge
+							icon={ templateOption.icon }
+							onClick={ () => onSelect( templateOption.template ) }
+							className="block-editor-inner-blocks__template-picker-option"
+							label={ templateOption.title }
+						/>
+					</li>
+				) ) }
+			</ul>
+			{ /* eslint-enable jsx-a11y/no-redundant-roles */ }
+			{ allowSkip && (
+				<div className="block-editor-inner-blocks__template-picker-skip">
+					<Button
+						isLink
+						onClick={ () => onSelect( undefined ) }
+					>
+						{ __( 'Skip' ) }
+					</Button>
+				</div>
+			) }
+		</Placeholder>
+	);
+}
+
+export default InnerBlocksTemplatePicker;

packages/block-library/src/columns/block.json

@@ -2,10 +2,6 @@
 	"name": "core/columns",
 	"category": "layout",
 	"attributes": {
-		"columns": {
-			"type": "number",
-			"default": 2
-		},
 		"verticalAlignment": {
 			"type": "string"
 		}

packages/block-library/src/columns/deprecated.js

@@ -1,3 +1,8 @@
+/**
+ * External dependencies
+ */
+import classnames from 'classnames';
+
 /**
  * WordPress dependencies
  */
@@ -96,4 +101,33 @@ export default [
 			);
 		},
 	},
+	{
+		attributes: {
+			columns: {
+				type: 'number',
+				default: 2,
+			},
+		},
+		migrate( attributes, innerBlocks ) {
+			attributes = {
+				...attributes,
+				columns: innerBlocks.length,
+			};
+
+			return [ attributes, innerBlocks ];
+		},
+		save( { attributes } ) {
+			const { verticalAlignment, columns } = attributes;
+
+			const wrapperClasses = classnames( `has-${ columns }-columns`, {
+				[ `are-vertically-aligned-${ verticalAlignment }` ]: verticalAlignment,
+			} );
+
+			return (
+				<div className={ wrapperClasses }>
+					<InnerBlocks.Content />
+				</div>
+			);
+		},
+	},
 ];