generate uninst when generating windows installer

.github/workflows/build.yml

@@ -128,7 +128,9 @@ jobs:
       uses: actions/upload-artifact@v4
       with:
         name: geode-installer-win
-        path: './installer/windows/geode-installer-win.exe'
+        path: |
+          ./installer/windows/geode-installer-win.exe
+          ./installer/windows/GeodeUninstaller.exe
 
     - name: Complete Build Debug Info
       uses: ./.github/actions/build-debug-info-post
@@ -335,7 +337,9 @@ jobs:
       - name: Zip Windows Artifacts
         uses: vimtor/action-zip@v1.2
         with:
-          files: geode-win/XInput1_4.dll geode-win/Geode.dll geode-win/GeodeUpdater.exe geode-win/Geode.lib geode-win/Geode.pdb
+          files: >-
+            geode-win/XInput1_4.dll geode-win/Geode.dll geode-win/Geode.lib geode-win/Geode.pdb
+            geode-win/GeodeUpdater.exe geode-installer-win/GeodeUninstaller.exe
           dest: geode-${{ steps.ref.outputs.hash }}-win.zip
 
       - name: Zip Android32 Artifacts

installer/windows/installer.nsi

@@ -491,6 +491,23 @@ Section "steam_appid.txt"
 SectionEnd
 
 Function .onInit
+    # huge thanks to Anders for the reference !!
+    # https://forums.winamp.com/forum/developer-center/nsis-discussion/4633037-creating-an-uninstaller-in-compile-time?p=4633073#post4633073
+!ifdef GENERATE_UNINSTALLER
+    WriteUninstaller "${__FILEDIR__}\GeodeUninstaller.exe"
+    SetErrorLevel 0
+    Quit
+!else
+    ; get a temporary file path
+    !tempfile TMPINST
+    !delfile "${TMPINST}"
+
+    ; create and run the installer that just uses WriteUninstaller
+    !makensis '-DGENERATE_UNINSTALLER "${__FILE__}" "-XOutFile `${TMPINST}.exe`"'
+    !system '"${TMPINST}.exe" /S'
+    !delfile "${TMPINST}.exe"
+!endif
+
     !insertmacro MUI_LANGDLL_DISPLAY
 
     IntOp $0 ${SF_SELECTED} | ${SF_RO}