detect system installation on user installation

fixes #52965

build/gulpfile.vscode.win32.js

@@ -81,7 +81,8 @@ function buildWin32Setup(arch, target) {
 			AppMutex: product.win32MutexName,
 			Arch: arch,
 			AppId: arch === 'ia32' ? ia32AppId : x64AppId,
-			IncompatibleAppId: arch === 'ia32' ? x64AppId : ia32AppId,
+			IncompatibleTargetAppId: arch === 'ia32' ? product.win32AppId : product.win32x64AppId,
+			IncompatibleArchAppId: arch === 'ia32' ? x64AppId : ia32AppId,
 			AppUserId: product.win32AppUserModelId,
 			ArchitecturesAllowed: arch === 'ia32' ? '' : 'x64',
 			ArchitecturesInstallIn64BitMode: arch === 'ia32' ? '' : 'x64',

build/win32/code.iss

@@ -957,14 +957,26 @@ Root: {#EnvironmentRootKey}; Subkey: "{#EnvironmentKey}"; ValueType: expandsz; V
 // Don't allow installing conflicting architectures
 function InitializeSetup(): Boolean;
 var
+  RegRootKey: String;
   RegKey: String;
   ThisArch: String;
   AltArch: String;
 begin
   Result := True;
 
-  if IsWin64 then begin
-    RegKey := 'SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\' + copy('{#IncompatibleAppId}', 2, 38) + '_is1';
+#if "user" == InstallTarget
+  if '{#Arch}' = 'ia32' then RegRootKey := 'HKLM32' else RegRootKey := 'HKLM64';
+  RegKey := 'SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\' + copy('{#IncompatibleTargetAppId}', 2, 38) + '_is1';
+
+  if RegKeyExists(RegRootKey, RegKey) then begin
+    if MsgBox('{#NameShort} is already installed on this system for all users. Are you sure you want to install it for this user?', mbConfirmation, MB_YESNO) = IDNO then begin
+      Result := false;
+    end;
+  end;
+#endif
+
+  if Result and IsWin64 then begin
+    RegKey := 'SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\' + copy('{#IncompatibleArchAppId}', 2, 38) + '_is1';
 
     if '{#Arch}' = 'ia32' then begin
       Result := not RegKeyExists({#Uninstall64RootKey}, RegKey);