Fixed Multicursor backspacing

[benthayer]

References

fixes #7205

Other references:
jupyter/notebook#4880
jupyter/notebook#4796

Code changes

Iterates through selections, and handle backspacing appropriately. There are three cases:

1. Selection
   • Delete everything in selection
2. Leading spaces
   • Delete to previous indentation
3. Other
   • Delete previous character

3. Can be broken down into the cases of the beginning of the line too, but they behave as you would expect

This solution is similar but not exactly the same as for the same problem in jupyter notebook jupyter/notebook#4880

User-facing changes

Basically, backspacing when using multicursor works as expected now whereas before it didn't handle tabs correctly.

Backwards-incompatible changes

None

[jupyterlab-dev-mode]

Thanks for making a pull request to JupyterLab!

To try out this branch on binder, follow this link:

[blink1073]

Thanks @bthayer2365! I don't have a working laptop at the moment to test but this logic looks great to me!

[benthayer]

Great, looking forward to you testing it!

[blink1073]

Very nice! This is identical to the behavior I see in VS Code. I think these build errors were temporary, kicking the builds.

[benthayer]

Linux integrity errors:

ERROR: /home/vsts/work/1/s/packages/codemirror/src/editor.ts:1364:5 - Forbidden 'var' keyword, use 'let' or 'const' instead
ERROR: /home/vsts/work/1/s/packages/codemirror/src/editor.ts:1365:5 - Forbidden 'var' keyword, use 'let' or 'const' instead
ERROR: /home/vsts/work/1/s/packages/codemirror/src/editor.ts:1366:10 - Forbidden 'var' keyword, use 'let' or 'const' instead
ERROR: /home/vsts/work/1/s/packages/codemirror/src/editor.ts:1368:7 - Forbidden 'var' keyword, use 'let' or 'const' instead
ERROR: /home/vsts/work/1/s/packages/codemirror/src/editor.ts:1369:7 - Forbidden 'var' keyword, use 'let' or 'const' instead
ERROR: /home/vsts/work/1/s/packages/codemirror/src/editor.ts:1370:7 - Forbidden 'var' keyword, use 'let' or 'const' instead
ERROR: /home/vsts/work/1/s/packages/codemirror/src/editor.ts:1374:9 - Forbidden 'var' keyword, use 'let' or 'const' instead
ERROR: /home/vsts/work/1/s/packages/codemirror/src/editor.ts:1377:11 - Forbidden 'var' keyword, use 'let' or 'const' instead
ERROR: /home/vsts/work/1/s/packages/codemirror/src/editor.ts:1378:11 - Forbidden 'var' keyword, use 'let' or 'const' instead
ERROR: /home/vsts/work/1/s/packages/codemirror/src/editor.ts:1382:23 - == should be ===
ERROR: /home/vsts/work/1/s/packages/codemirror/src/editor.ts:1383:27 - != should be !==
ERROR: /home/vsts/work/1/s/packages/codemirror/src/editor.ts:1384:15 - Forbidden 'var' keyword, use 'let' or 'const' instead
ERROR: /home/vsts/work/1/s/packages/codemirror/src/editor.ts:1384:19 - Duplicate variable: 'from'
ERROR: /home/vsts/work/1/s/packages/codemirror/src/editor.ts:1391:13 - Forbidden 'var' keyword, use 'let' or 'const' instead
ERROR: /home/vsts/work/1/s/packages/codemirror/src/editor.ts:1391:17 - Duplicate variable: 'from'

I fixed all the var/let issues. Changing var to let for from should remove the duplicate variable error. Also fixed == and != errors.

Windows JS error:

2019-10-24T04:11:02.3193805Z @jupyterlab/test-codemirror: Failed to collect coverage from D:\a\1\s\packages\codemirror\src\editor.ts
2019-10-24T04:11:02.3195636Z @jupyterlab/test-codemirror: ERROR: ..\..\packages\codemirror\src\editor.ts: Emit skipped
2019-10-24T04:11:02.3196024Z @jupyterlab/test-codemirror: STACK: TypeError: ..\..\packages\codemirror\src\editor.ts: Emit skipped

I don't know how to interpret these. Maybe changing things from var to let will clear that up, but if not, could you let me know what to do?

The Linux Docs error doesn't seem to be my fault, so I'm leaving it as is.

[blink1073]

The error you saw is being tracked in #6415. Yes, the docs failure is temporary until we release 1.2. Thanks again, and congratulations on your first contribution to JupyterLab!

[jasongrout]

@blink1073 - should this be backported to 1.2?

[blink1073]

@meeseeksdev backport to 1.x