Sibling Inserter: Hide insertion point if it is not possible to inser…

…t the default block (#7226)

Fixes part of #6569.
Part of a general polishing to get #6993.

Insertion point was violating the allowedBlocks restriction of the parent block. The insertion point always inserts the default block and it may not be possible to insert the default block.

This PR makes sure insertion point only appears if it is possible to insert the default block.

editor/components/block-list/insertion-point.js

@@ -76,13 +76,16 @@ class BlockInsertionPoint extends Component {
 export default compose(
 	withSelect( ( select, { uid, rootUID, canShowInserter } ) => {
 		const {
+			canInsertBlockType,
 			getBlockIndex,
 			getBlockInsertionPoint,
 			getBlock,
 			isBlockInsertionPointVisible,
 			isTyping,
-			getTemplateLock,
 		} = select( 'core/editor' );
+		const {
+			getDefaultBlockName,
+		} = select( 'core/blocks' );
 		const blockIndex = uid ? getBlockIndex( uid, rootUID ) : -1;
 		const insertIndex = blockIndex;
 		const insertionPoint = getBlockInsertionPoint();
@@ -94,14 +97,15 @@ export default compose(
 			( ! block || ! isUnmodifiedDefaultBlock( block ) )
 		);
 
+		const defaultBlockName = getDefaultBlockName();
 		return {
-			isLocked: !! getTemplateLock( insertionPoint.rootUID ),
+			canInsertDefaultBlock: canInsertBlockType( defaultBlockName, rootUID ),
 			showInserter: ! isTyping() && canShowInserter,
 			index: insertIndex,
 			showInsertionPoint,
 		};
 	} ),
-	ifCondition( ( { isLocked } ) => ! isLocked ),
+	ifCondition( ( { canInsertDefaultBlock } ) => canInsertDefaultBlock ),
 	withDispatch( ( dispatch ) => {
 		const { insertDefaultBlock, startTyping } = dispatch( 'core/editor' );
 		return {