Calling an undo unsupported Api does not clear the Undo stack.

[James-Gauld-92]

Provide required information needed to triage your issue

When purposfully calling an Api that is marked as unsupported by Undo in order to clear the undo stack, the undo stack is not cleared and further actions that are supported are added to the stack like normal.

Your Environment

• Platform [PC desktop, Mac, iOS, Office on the web]: PC Desktop, Office on the Web
• Host [Excel, Word, PowerPoint, etc.]: Excel
• Office version number: 2511
• Operating System: Windows 11 (25H2)
• Browser (if using Office on the web): Chrome

Expected behavior

Calling an unsupported Api should clear the stack and prevent new actions from being recorded.

Current behavior

The undo stack remains as is, further actions are added on as they are performed.

Steps to reproduce

1. Clone https://github.com/James-Gauld-92/OfficeJs-Excel-Undo-UnsupportedApi-Example
2. Install dependencies and run npm run dev-server
3. Open Excel and sideload the manifest.
4. Click show task pane and then Insert Test Data PC Desktop
5. The current worksheet should be pushed to the end of the worksheets and the word TEST should be inserted to the current cell.
6. Clicking undo will remove the word TEST.
7. Open Excel on Web and sideload the manifest.
8. Click show task pane and then Insert Test Data Web.
9. The standardWidth of the current sheet should be altered and the word TEST should be inserted to the current cell.
10. Nothing will happen but the expected UndoNotSupported exception will be logged in the Javascript console

Provide additional details

1. Our interpretation of the green tip on this page, calling an unsupported api will clear the current undo stack. https://learn.microsoft.com/en-us/office/dev/add-ins/excel/excel-add-ins-undo-capabilities
2. It's not clear if this is for the duration of the Excel.Run(()=>{}) function, or during the Context.Sync() function.
3. This is related to another issue I've opened CustomXml Parts are not included in Undo/Redo #6415
4. I've not been able to get the UndoNotSupported error to appear on PC Desktop in any of my experiments, only in Office for Web.

Context

There is currently no way to stop a user from using Undo or returning to the previous behaviour present in Excel Api <=1.90.
With the Custom XML Issue linked above, we need to either include the Custom XML in the undo stack (Which can then be grouped with the mergeUndoHistory flag) or we need to prevent add-in actions from being added to the undo stack.
With the users currently able to partially undo the add-in's actions, the add-in state can be broken.

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[amagupta-collab]

@James-Gauld-92 Based on the code shared by you, in desktop, following api is being called to clear undo stack but I can see that this api is supported for undo and you can undo this operation. Hence the undo stack is not cleared

// Set the standardWidth property of the first worksheet to clear the Undo stack.
currentWorkbook.worksheets.getActiveWorksheet().position = worksheetCount - 1;

[James-Gauld-92]

@amagupta-collab That's strange, according to the documentation worksheet position isn't supported on desktop.
https://learn.microsoft.com/en-us/office/dev/add-ins/excel/excel-add-ins-undo-capabilities

I've updated the repository with the other couple of Apis I have tried, none of them work.

Workbook.protection.unprotect(); does throw the expected error, but that prevents the data being written to the cell, therefore nothing at all is added to the undo stack.

Can you provide an example of an API that isn't supported?

[amagupta-collab]

@James-Gauld-92 , Thanks for finding the gap in documentation, i have created internal ticket to address documentation.

Regarding clearing undo stack, Workbook.protection.unprotect() is a good candidate for same. Reason currently it is throwing error and not adding any content to cell is flag "mergeUndoGroup" is marked as true. This flag will try to merge cell update undo record and protection.unprotect into one undo record and since later one is unsupported , whole operation failed. I validated by making mergeUndoGroup as false, and the undo stack is being cleared.

[James-Gauld-92]

@amagupta-collab Thank you, I've retested it and I think I've got a viable workaround for now.
I think that documentation page could do with a really good rewrite.

Is there a way we can get informed as new APIs are added to Undo support? I can see this workaround breaking while we're waiting for the Custom Xml issue to be resolved.