Undo Internals

Undo Internals

Despite the "rollback" name, the shipped Sucrose.Undo.exe is effectively Sucrose's uninstaller / full-removal tool. It is the process Windows runs when you remove Sucrose from Apps & Features, and it is responsible for terminating every Sucrose process, deleting the install and (optionally) the user-data folders, removing shortcuts and the registry uninstall key, restoring hidden desktop icons, and finally deleting itself with a self-cleaning batch file. This page documents that removal flow for developers and administrators. For the user-facing steps, see Uninstalling Sucrose.

Contents

• Role and entry point
• The Yes / No / Cancel dialog
• Removal sequence
• The self-deleting batch
• Registry and the uninstall entry
• Exception handling
• See also

Role and entry point

Sucrose.Undo.exe is a WPF process registered as the uninstaller for Sucrose. Unlike most Sucrose apps, it does not single-instance-gate through Instance.Basic, and it does not route its own crashes through the Watchdog (see Exception handling).

Its behavior depends on whether it is launched with arguments:

• No arguments — plays SystemSounds.Asterisk and shows a localized confirmation dialog (the interactive uninstall).
• With the silent argument — runs the removal without prompting. The registry uninstall entry stores a QuietUninstallString that passes -s for unattended removal (used by choco uninstall, scoop uninstall, winget, etc.).

The Yes / No / Cancel dialog

When launched interactively, Undo shows a localized Yes / No / Cancel dialog (resource keys Undo.QuestionTitle, Undo.QuestionMessage, Undo.QuestionDescription). The choice controls whether user data is kept:

Choice	Removes app?	Removes user data?
Yes	Yes	Yes — also deletes UninstallDataPath = %AppData%\Sucrose
No	Yes	No — keeps %AppData%\Sucrose
Cancel	No (abort)	—

Removal sequence

On Yes or No, Undo performs the following (Cancel aborts before any of it):

1. Terminate all Sucrose processes — kills every process whose name contains Sucrose, in 3 passes spaced 1 second apart (Delay = 1000), so freshly-spawned helpers (Commandog, etc.) are also caught.
2. Restore the desktop — restores desktop-icon visibility and calls RefreshDesktop() (Sucrose can hide desktop icons while a wallpaper runs).
3. Delete the install folder — removes UninstallPath = %LocalAppData%\Sucrose, preserving the currently running Undo and Runtime folders (those are removed later by the batch file).
4. Optionally delete user data — on Yes, also deletes UninstallDataPath = %AppData%\Sucrose.
5. Remove shortcuts — deletes the Desktop and Start-Menu <AppLongName>.lnk shortcuts.
6. Remove the registry uninstall key — deletes the HKCU\Software\Microsoft\Windows\CurrentVersion\Uninstall\Sucrose subkey (see below).
7. Self-delete — generates and runs a batch file in %TEMP% that finishes the job after Undo exits.

The self-deleting batch

The install folder cannot fully delete the running Undo.exe and the private Sucrose.Runtime while they are in use, so Undo writes a one-shot batch file to the temp folder and launches it:

%TEMP%\del_<guid>.bat

The batch:

taskkill /F /IM Sucrose.Undo.exe
timeout /t 3
rd /s /q "<install path>"
rd /s /q "<runtime path>"
rd /s /q "<uninstall path>"
del "%~f0"

In words: taskkill the Undo process itself, wait 3 seconds for handles to release, recursively delete the remaining install / runtime / uninstall paths, then delete the batch file. This is how the last on-disk traces are removed after the WPF process is already gone.

flowchart TD
    Start["Sucrose.Undo.exe"] --> Dlg{"Yes / No / Cancel"}
    Dlg -->|Cancel| Abort["abort, no changes"]
    Dlg -->|Yes or No| Kill["kill all Sucrose processes<br/>3 passes, 1s apart"]
    Kill --> Desk["restore desktop icons<br/>+ RefreshDesktop()"]
    Desk --> DelInstall["delete %LocalAppData%/Sucrose<br/>keep Undo + Runtime folders"]
    DelInstall --> Data{"choice == Yes?"}
    Data -->|yes| DelData["also delete %AppData%/Sucrose"]
    Data -->|no| KeepData["keep user data"]
    DelData --> Short["remove Desktop + Start-Menu shortcuts"]
    KeepData --> Short
    Short --> Reg["delete HKCU Uninstall key (Sucrose)"]
    Reg --> Bat["spawn %TEMP%/del_&lt;guid&gt;.bat"]
    Bat --> Self["batch: taskkill Undo,<br/>delete install/runtime/uninstall, self-delete"]

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Registry and the uninstall entry

Sucrose installs per-user (no admin), so its uninstall entry lives under the current-user hive:

HKCU\Software\Microsoft\Windows\CurrentVersion\Uninstall\Sucrose

This is the entry that makes Sucrose appear in Apps & Features; its QuietUninstallString uses the -s switch for silent removal. Undo deletes this key as part of the removal sequence. The key is created by the installer, not by Undo — see Bundle / Installer Internals.

Exception handling

Undo handles its own unhandled exceptions with a plain WPF MessageBox — it deliberately does not route through the Crash Reporting Watchdog pipeline. This is intentional: by the time Undo runs, it may already have terminated the Watchdog and Commandog processes that the crash pipeline depends on, so a self-contained dialog is the only reliable feedback.

See also

• Uninstalling Sucrose — the user-facing removal guide, including package-manager uninstall.
• Bundle / Installer Internals — how the installer creates the registry uninstall entry that Undo removes.
• Data Locations — the install (%LocalAppData%\Sucrose) and data (%AppData%\Sucrose) folders that Undo deletes.
• Crash Reporting — why Undo opts out of the shared crash pipeline.
• Architecture Overview — Undo's place in the process roster.