Issue Overview

The allowedBlocks attribute of <InnerBlocks /> is intended to only allow certain blocks to be inserted into a block. However, by pressing Enter or by using the sibling inserter(fixed by #7226), you can still insert the default block: the Paragraph block.

Steps to Reproduce (for bugs)

1. Create a block type containing <div><InnerBlocks allowedBlocks={ [ 'core/list' ] } /></div> in its editor markup and <div><InnerBlocks.Content /></div> in its saved markup. This block should allow only allow List blocks to be inserted into it as children.
2. Insert the block into a post.
3. Insert multiple List blocks into the container block.
4. Try using the sibling inserter or Enter to insert a Paragraph block.
5. Notice that, although the Paragraph block is not shown in the inserter pop-up, it can still be inserted.

Expected Behavior

A block that sets allowedBlocks in its <InnerBlocks /> component should only allow the blocks listed in allowedBlocks to be inserted into it. Of course, the question of how to still use slash commands and/or the sibling inserter arise, as both involve inserting Paragraph blocks.

Current Behavior

Using Enter or the in-between inserter, you can insert any block into a block with an <InnerBlocks /> component.

Related Issues and/or PRs

• Implement nesting in cover image block #5452
• Introduce Child Blocks #5540
• Add shared blocks to the blocks autocompleter #6067
• Blocks should only be able to be transformed into other allowed blocks.  #6363
• List Block: Try nesting with InnerBlocks #6394
• Use nested blocks for quotes #6520
• Replace default block appender in nested blocks with in-between inserter #6834
• Only show transforms to blocks that can be inserted on the root block; Order transforms by frecency; #7184
• Hide insertion point if it is not possible to insert the default block #7226
• InnerBlocks have no inserter when core/paragraph is not in allowedBlocks #7763

Update: 2018-07-13

Updated this issue to no longer cover the slash command bug, which was already covered by #6070 and was fixed by #6067.