Control blocks can be wrapped around procedure prototype blocks

[howettl]

Expected Behavior

Procedure prototype blocks should be non-interactive.

Actual Behavior

If I create a custom procedure, then drag a control block (C-shape) onto the workspace and near to the procedure prototype block inside of the procedure definition block, the grey area appears around the prototype block indicating that I can wrap the control block around it. Releasing the block at this point causes the prototype block to be duplicated within the control block and draggable around the workspace.
A third, non-draggable copy of the prototype block is also added to the workspace.

Steps to Reproduce

1. Create a custom procedure

2. Drag a C-shaped control block close to the prototype block within the procedure definition
   

3. Release the control block when the highlight appears
   

Operating System and Browser

Mac OS 10.13.4 Chrome 66

[thisandagain]

Thanks for finding this @howettl!

[thisandagain]

/cc @paulkaplan @rachel-fenichel

[rachel-fenichel]

Relevant bits of code:

Blockly.InsertionMarkerManager.prototype.getCandidate_ calls myConnection.closest(radius, dxy).

Blockly.Connection.prototype.isConnectionAllowed gets called. It calls canConnectWithReason_.

Blockly.Connection.prototype.canConnectWithReason_ has some hacks for handling procedure blocks (gross but got the job done): https://github.com/LLK/scratch-blocks/blob/develop/core/connection.js#L315

If canConnectWithReason_ passes, there are other checks:
Blockly.Connection.prototype.canConnectToPrevious_ is probably the relevant check here. That has a bunch of special cases for various insertion marker and shadow cases. I've tried to keep the number of extra checks to a minimum, but if you need to hack something in that's probably where it will go.

[ZenithRogue]

This will also leave behind a "ghost" that is immobile, and the block picked up into the c will be permanently fused

[picklesrus]

whoops. wrong github tab. PR to fix this looks good... will merge.