Always run the uninstaller as the correct user

When a standard user uses an admin account for elevation to change an
existing single-user installation to all-users, the uninstaller is now
run for the correct (standard) user (instead of the admin).

misc/nsis/install.nsh

@@ -148,6 +148,48 @@ var KeepReg
 !macroend
 
 ; Functions
+Function CheckInstallation 
+  ; if there's an installed version, uninstall it first (I chose not to start the uninstaller silently, so that user sees what failed)
+  ; if both per-user and per-machine versions are installed, unistall the one that matches $MultiUser.InstallMode
+  StrCpy $0 ""
+  ${if} $HasCurrentModeInstallation = 1
+    StrCpy $0 "$MultiUser.InstallMode"
+  ${else}
+    !if ${MULTIUSER_INSTALLMODE_ALLOW_BOTH_INSTALLATIONS} = 0
+      ${if} $HasPerMachineInstallation = 1
+        StrCpy $0 "AllUsers" ; if there's no per-user installation, but there's per-machine installation, uninstall it
+      ${elseif} $HasPerUserInstallation = 1
+        StrCpy $0 "CurrentUser" ; if there's no per-machine installation, but there's per-user installation, uninstall it
+      ${endif}
+    !endif
+  ${endif}
+
+  ${if} "$0" != ""
+    ${if} $0 == "AllUsers"
+      StrCpy $1 "$PerMachineUninstallString"
+      StrCpy $3 "$PerMachineInstallationFolder"
+    ${else}
+      StrCpy $1 "$PerUserUninstallString"
+      StrCpy $3 "$PerUserInstallationFolder"
+    ${endif}
+    ${if} ${silent}
+      StrCpy $2 "/S"
+    ${else}
+      StrCpy $2 ""
+    ${endif}
+    ${if} $KeepReg = 1
+      StrCpy $4 "/upgrade"
+    ${endif}
+  ${endif}
+FunctionEnd
+
+Function RunUninstaller
+  StrCpy $0 0
+  ; $1 is quoted in registry; the _? param stops the uninstaller from copying
+  ; itself to the temporary directory, which is the only way for ExecWait to work
+  ExecWait '$1 /SS $2 _?=$3' $0 ; $1 is quoted in registry; the _? param stops the uninstaller from copying itself to the temporary directory, which is the only way for ExecWait to work
+FunctionEnd
+
 Function GetDefaultBrowser
   ReadRegStr $0 HKCU "SOFTWARE\Microsoft\Windows\Shell\Associations\UrlAssociations\http\UserChoice" "ProgId"
   ReadRegStr $1 HKCU "SOFTWARE\Microsoft\Windows\Shell\Associations\UrlAssociations\https\UserChoice" "ProgId"
@@ -180,54 +222,17 @@ InstType "Minimal"
 Section "Core Files (required)" SectionCoreFiles
   SectionIn 1 2 3 RO
 
-  ; if there's an installed version, uninstall it first (I chose not to start
-  ; the uninstaller silently, so that user sees what failed)
-  ; if both per-user and per-machine versions are installed, unistall the one
-  ; that matches $MultiUser.InstallMode
-  StrCpy $0 ""
-  ${if} $HasCurrentModeInstallation = 1
-    StrCpy $0 "$MultiUser.InstallMode"
-  ${else}
-    StrCpy $KeepReg 0
-    !if ${MULTIUSER_INSTALLMODE_ALLOW_BOTH_INSTALLATIONS} = 0
-      ${if} $HasPerMachineInstallation = 1
-        ; if there's no per-user installation, but there's per-machine installation, uninstall it
-        StrCpy $0 "AllUsers"
-      ${elseif} $HasPerUserInstallation = 1
-        ; if there's no per-machine installation, but there's per-user installation, uninstall it
-        StrCpy $0 "CurrentUser"
-      ${endif}
-    !endif
-  ${endif}
-
+  !insertmacro UAC_AsUser_Call Function CheckInstallation ${UAC_SYNCREGISTERS}
   ${if} "$0" != ""
-    ${if} $0 == "AllUsers"
-      StrCpy $1 "$PerMachineUninstallString"
-      StrCpy $3 "$PerMachineInstallationFolder"
-    ${else}
-      StrCpy $1 "$PerUserUninstallString"
-      StrCpy $3 "$PerUserInstallationFolder"
-    ${endif}
-    ${if} ${silent}
-      StrCpy $2 "/S"
-    ${else}
-      StrCpy $2 ""
-    ${endif}
-
-    ${if} $KeepReg = 1
-      StrCpy $4 "/upgrade"
-    ${endif}
-
     ; Make sure the uninstaller is there before attempting to run it
     ${if} ${FileExists} "$3\${UNINSTALL_FILENAME}"
-
       HideWindow
       ClearErrors
-      StrCpy $0 0
-      ; $1 is quoted in registry; the _? param stops the uninstaller from copying
-      ; itself to the temporary directory, which is the only way for ExecWait to work
-      ExecWait '$1 $4 /SS $2 _?=$3' $0
-
+      ${if} $0 == "AllUsers"
+        Call RunUninstaller
+      ${else}
+        !insertmacro UAC_AsUser_Call Function RunUninstaller ${UAC_SYNCREGISTERS}
+      ${endif}
       ${if} ${errors} ; stay in installer
         SetErrorLevel 2 ; Installation aborted by script
         BringToFront
@@ -248,9 +253,10 @@ Section "Core Files (required)" SectionCoreFiles
         ${EndSwitch}
       ${endif}
 
-      ; the uninstaller doesn't delete itself when not copied to the temp directory
-      !insertmacro DeleteRetryAbort "$3\${UNINSTALL_FILENAME}"
-      RMDir "$3"
+      ${if} $IsAdmin = 1
+        !insertmacro DeleteRetryAbort "$3\${UNINSTALL_FILENAME}"
+        RMDir "$3"
+      ${endif}
     ${endif}
   ${endif}