Replace block (TBD, perhaps replace or place?): use the marker workflow to place a new block at this location.

[rachel-fenichel]

Preconditions

• NavigationController.canCurrentlyEdit(workspace) is true
• Cursor is on a block node
  • Block can be either a stack block or a reporter. Can it be a shadow block?
• The block is editable, deletable, and movable

Callback

• Save the cursor location as originalBlockLocation
• Set a flag in the navigation state: shouldReplace = true
• Set the cursor location to the block's previous connection (for a stack block)
  • Where does the cursor location get set for a reporter block?
• Open the toolbox

Related work

The insertFromFlyout and insertFromToolbox actions will need to be updated to check for shouldReplace.
If shouldReplace is true, those actions should:

• Move the originalBlock to the workspace. This block can be found by inspecting the saved originalBlockLocation
• Connect the flyout/toolbox block at the cursor location
• Set shouldReplace to false
• Clear originalBlockLocation

If the user hits Escape from the flyout or toolbox:

• Set shouldReplace to false
• Clear originalBlockLocation

[rachel-fenichel]

Closing because all of the discussion about insert vs replace is on #132, and the details of correct replacement, splicing, and bumping are all handled by core Blockly's connect method.