Group disappears when dragging duplicate file onto it from another group

[stevencl]

Issue Type: Bug

Turn tabs off
Open a file
Split the editor so that there are two groups, each containing the same file
Now open another file in one of the groups.
You should have two groups. One group has two files (say fileA and fileB). The other group has one file (say fileA).
Select fileA in the group that contains two files.
Drag it over to the group that contains fileA only
Make sure that the selection rectangle covers the whole group before dropping.
When dropped, notice that the whole group disappears.

Found while testing: #52334

VS Code version: Code - Insiders 1.25.0-insider (368ab9c, 2018-06-26T05:18:23.085Z)
OS version: Windows_NT x64 10.0.16299

System Info

Item	Value
CPUs	Intel(R) Core(TM) i7-3687U CPU @ 2.10GHz (4 x 2594)
GPU Status	2d_canvas: enabled flash_3d: enabled flash_stage3d: enabled flash_stage3d_baseline: enabled gpu_compositing: enabled multiple_raster_threads: enabled_on native_gpu_memory_buffers: disabled_software rasterization: disabled_software video_decode: enabled video_encode: enabled vpx_decode: unavailable_software webgl: enabled webgl2: enabled
Memory (System)	7.89GB (0.35GB free)
Process Argv	C:\Program Files\Microsoft VS Code Insiders\Code - Insiders.exe
Screen Reader	no
VM	0%

Extensions (15)

Extension	Author (truncated)	Version
html-snippets	abu	0.2.1
jshint	dba	0.10.19
vscode-eslint	dba	1.4.12
tslint	eg2	1.0.33
vscode-great-icons	emm	2.1.35
vscode-gutter-preview	kis	0.12.2
vscode-azureappservice	ms-	0.8.1
vscode-cosmosdb	ms-	0.7.2
azure-account	ms-	0.4.1
csharp	ms-	1.15.2
vs-keybindings	ms-	0.2.0
team	ms-	1.136.0
debugger-for-chrome	msj	4.7.0
addDocComments	ste	0.0.8
cordova-tools	vsm	1.4.0

[bpasero]

@stevencl there is a setting to control this behaviour: "workbench.editor.closeEmptyGroups": false will change it to the behaviour you expected.

I thought this would be a good default because it matches exactly with how we behave today without grid. I would like to keep our UI as simple as possible and not add empty groups unless the user opted in. Would you agree?

[stevencl]

Oh, sorry, I got confused. I didn't notice fully what had happened. I think with tabs off it was a little more confusing for me. I just didn't look at the open editors list to confirm what had happened. Sorry!

[bpasero]

@stevencl no problemo