Error and sticky scroll screen cheese when deleting cell

[jrieken]

Testing #210961

• open slow.ipynb.txt
• show outline and have sticky scroll enabled
• scroll the cell with "# Header 1111111111111111111111989898" into view
• delete the cell
• 🐛 the sticky scroll breaks, the error below is printed

 ERR Cannot read properties of null (reading 'getFoldingState'): TypeError: Cannot read properties of null (reading 'getFoldingState')
    at get foldingState [as foldingState] (vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:2487:155257)
    at O.l (vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:2487:75392)
    at O.renderElement (vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:2487:74786)
    at A.renderElement (vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:626:37111)
    at Y.renderElement (vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:240:2234)
    at m.Z (vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:197:15986)
    at m.U (vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:197:12734)
    at m.splice (vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:197:11218)
    at vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:4:8845
    at Array.forEach (<anonymous>)
    at t.splice (vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:4:8832)
    at vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:240:8012
    at L.bufferEvents (vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:89:3585)
    at X.splice (vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:240:7988)
    at X.splice (vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:626:63403)
    at b.t (vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:193:26459)
    at b.splice (vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:193:24711)
    at T.l (vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:193:32890)
    at T.setChildren (vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:193:32434)
    at ie.m (vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:627:5861)
    at ie.updateChildren (vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:627:5515)
    at d.V [as value] (vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:2157:38798)
    at n.y (vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:89:659)
    at n.z (vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:89:729)
    at n.fire (vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:89:945)
    at d.value (vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:2487:77812)
    at n.y (vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:89:659)
    at n.z (vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:89:729)
    at n.fire (vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:89:945)
    at u.r (vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:1655:135297)
    at vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:1655:132158
    at vscode-file://vscode-app/Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:152:15443

[DonJayamanne]

@jrieken I'm unable to repro this.
Please can you share a screen recording of the steps.
Perhaps recoding from opehning the notebook to selecting and deleting.
Thanks.

[jrieken]

Looking at the stacktrace tells me this is coming here ⬇️ which means the model had been disposed already

vscode/src/vs/workbench/contrib/notebook/browser/viewModel/markupCellViewModel.ts

Line 75 in 6d23b7f

return this.foldingDelegate.getFoldingState(this.foldingDelegate.getCellIndex(this));

[jrieken]

@DonJayamanne following the steps above (empty profile) always reproduce the error (console) for me. The screen cheese shows in sticky scroll and/or other paces of the outline tree