NSIS uninstaller $INSTDIR resolves to Program Files (x86) on 64-bit after upgrade

[JamieRuderman]

Bug Description

After upgrading a 64-bit NSIS app (installed in C:\Program Files\App), the uninstaller's $INSTDIR resolves to C:\Program Files (x86)\App instead of the correct 64-bit path. This causes the uninstall to silently fail — the app directory is not removed.

Fresh install → uninstall works correctly. Only the upgrade → uninstall path is broken.

Steps to Reproduce

1. Install a 64-bit electron-builder NSIS app (installs to C:\Program Files\App)
2. Upgrade to a newer version (upgrade succeeds, correct path)
3. Uninstall the app
4. App directory remains at C:\Program Files\App — uninstaller targeted C:\Program Files (x86)\App

Evidence

Uninstall log showing $INSTDIR wrong after upgrade:

# During UPDATE — old uninstaller runs with correct path:
Start CustomRemoveFiles 3.41.0
Command: "C:\Program Files\Remote.It\resources\remoteit" agent uninstall
Result Code: 0
RMDir C:\Program Files\Remote.It

# Later UNINSTALL — $INSTDIR is wrong:
Start CustomRemoveFiles 3.45.2
Command: "C:\Program Files (x86)\Remote.It\resources\remoteit" agent uninstall
Result Code: error
RMDir C:\Program Files (x86)\Remote.It    ← wrong path, app left behind

The registry has the correct value in the 64-bit view:

HKEY_LOCAL_MACHINE\SOFTWARE\{app-guid}
    InstallLocation    REG_SZ    C:\Program Files\Remote.It

No entry exists under WOW6432Node (32-bit view).

Analysis

un.onInit in uninstaller.nsh calls check64BitAndSetRegView → initMultiUser → setInstallModePerAllUsers, which should read InstallLocation from the 64-bit registry and set $INSTDIR correctly. Despite the registry containing the correct value under the 64-bit view, $INSTDIR defaults to $PROGRAMFILES (the 32-bit path) in the upgrade→uninstall flow.

Notably, during BUILD_UNINSTALLER in installer.nsi, the .onInit function skips check64BitAndSetRegView entirely:

Function .onInit
  !ifmacrodef preInit
    !insertmacro preInit
  !endif

  !ifdef BUILD_UNINSTALLER
    WriteUninstaller "${UNINSTALLER_OUT_FILE}"
    !insertmacro quitSuccess          ; ← exits here
  !else
    !insertmacro check64BitAndSetRegView  ; ← never reached for uninstaller build
    !insertmacro initMultiUser
  !endif
FunctionEnd

This may contribute to the uninstaller binary's default $INSTDIR being set to the 32-bit path.

Workaround

We worked around this by explicitly reading the registry at the start of our customRemoveFiles macro:

SetRegView 64
ReadRegStr $0 HKLM "${INSTALL_REGISTRY_KEY}" InstallLocation
${ifNot} $0 == ""
    StrCpy $INSTDIR $0
${endIf}

Log confirming the workaround corrects the path:

INSTDIR before fix: C:\Program Files (x86)\Remote.It
INSTDIR after fix: C:\Program Files\Remote.It

Environment

• electron-builder: 26.8.1
• OS: Windows 11 x64
• NSIS config: oneClick: false, perMachine: true, allowToChangeInstallationDirectory: true
• Architecture: x64 app (APP_64 defined)

Expected Behavior

$INSTDIR in the uninstaller should resolve to the actual install location (C:\Program Files\App) regardless of whether the app was freshly installed or upgraded.