Menu Overlap When Embed Block is Initial Block

[mrjarbenne]

If you don't add any text, and instead insert an embed block as the first object, subsequently clicking on the + button renders the menu under the top bar, obscuring the first few options:

This is with the plugin version in the repo version 0.1.0

[aduth]

Related: #1193

This is an issue with the existing implementation detecting boundary collisions to flip the inserter. Currently it detects if it exceeds the top of the entire page (above admin bar), when it should be detecting against the bottom of the editor bar.

https://github.com/WordPress/gutenberg/blob/cab8713/components/popover/index.js#L51