Block editor: Self nesting and circular nesting block fix

packages/block-editor/src/store/selectors.js

@@ -1552,19 +1552,26 @@ export function getTemplateLock( state, rootClientId ) {
  * @param {string|Object} blockNameOrType The block type object, e.g., the response
  *                                        from the block directory; or a string name of
  *                                        an installed block type, e.g.' core/paragraph'.
+ * @param {Set}           checkedBlocks   Set of block names that have already been checked.
  *
  * @return {boolean} Whether the given block type is allowed to be inserted.
  */
-const isBlockVisibleInTheInserter = ( state, blockNameOrType ) => {
+const isBlockVisibleInTheInserter = (
+	state,
+	blockNameOrType,
+	checkedBlocks = new Set()
+) => {
 	let blockType;
 	let blockName;
+
 	if ( blockNameOrType && 'object' === typeof blockNameOrType ) {
 		blockType = blockNameOrType;
 		blockName = blockNameOrType.name;
 	} else {
 		blockType = getBlockType( blockNameOrType );
 		blockName = blockNameOrType;
 	}
+
 	if ( ! blockType ) {
 		return false;
 	}
@@ -1580,11 +1587,22 @@ const isBlockVisibleInTheInserter = ( state, blockNameOrType ) => {
 		return false;
 	}
 
+	if ( checkedBlocks.has( blockName ) ) {
+		return false;
+	}
+
+	checkedBlocks.add( blockName );
+
 	// If parent blocks are not visible, child blocks should be hidden too.
 	if ( !! blockType.parent?.length ) {
 		return blockType.parent.some(
 			( name ) =>
-				isBlockVisibleInTheInserter( state, name ) ||
+				( blockName !== name &&
+					isBlockVisibleInTheInserter(
+						state,
+						name,
+						checkedBlocks
+					) ) ||
 				// Exception for blocks with post-content parent,
 				// the root level is often consider as "core/post-content".
 				// This exception should only apply to the post editor ideally though.

packages/blocks/src/api/registration.js

@@ -232,6 +232,15 @@ export function registerBlockType( blockNameOrMetadata, settings ) {
 		return;
 	}
 
+	if ( 1 === settings?.parent?.length && name === settings.parent[ 0 ] ) {
+		warning(
+			'Block "' +
+				name +
+				'" cannot be a parent of itself. Please remove the block name from the parent list.'
+		);
+		return;
+	}
+
 	if ( ! /^[a-z][a-z0-9-]*\/[a-z][a-z0-9-]*$/.test( name ) ) {
 		warning(
 			'Block names must contain a namespace prefix, include only lowercase alphanumeric characters or dashes, and start with a letter. Example: my-plugin/my-custom-block'

packages/blocks/src/api/test/registration.js

@@ -104,6 +104,17 @@ describe( 'blocks', () => {
 			expect( block ).toBeUndefined();
 		} );
 
+		it( 'Should reject blocks with the block name itself as the only parent attribute value', () => {
+			const block = registerBlockType( 'core/test-block', {
+				...defaultBlockSettings,
+				parent: [ 'core/test-block' ],
+			} );
+			expect( console ).toHaveWarnedWith(
+				'Block "core/test-block" cannot be a parent of itself. Please remove the block name from the parent list.'
+			);
+			expect( block ).toBeUndefined();
+		} );
+
 		it( 'should reject blocks with uppercase characters', () => {
 			const block = registerBlockType( 'Core/Paragraph' );
 			expect( console ).toHaveWarnedWith(