IModelDecorationOptions IsWholeLine extends range in unexpected ways

Reproducible in vscode.dev or in VS Code Desktop?

• Not reproducible in vscode.dev or VS Code Desktop

Reproducible in the monaco editor playground?

• Not reproducible in the monaco editor playground

Monaco Editor Playground Link

https://microsoft.github.io/monaco-editor/playground.html?source=v0.52.2#example-interacting-with-the-editor-line-and-inline-decorations

Monaco Editor Playground Code

Nothing special, just using the decorations example

Reproduction Steps

1. Notice the line decoration spans lines 3-5 and has isWholeLine = true
2. Select and delete lines 3-5
3. Notice that line 2 now has the line decoration
4. Ctrl+z until lines 3-5 are restored
5. Notice that the decoration now spans lines 2-5

Actual (Problematic) Behavior

Decorating a line that was never marked to be decorated is unexpected. The decoration was for line 3-5, so having line 2 decorated once 3-5 are deleted decorates something that was never the original intention. Ditto to line 2 still being decorated after the undo.

Expected Behavior

If a decorated line is deleted I would expect the decoration to be deleted as well, not move to a previously undecorated line. Granted, I could be missing some other context, but from evaluating Monaco as a potential replacement in our app, this is something that stood out as unexpected and would make it challenging to use full line decorations (something that we currently do a lot)

Additional Context

No response

Start with the linked Monaco Editor Playground example, focusing on the IModelDecorationOptions isWholeLine behavior and the line-decoration reproduction steps. Verify deletion and undo across lines 2-5, then trace the relevant decoration behavior and tests. Done means deleted decorated lines no longer cause the decoration to appear on a previously undecorated line.