From fe58b67e24d007cb7dcd7005073a37bfba21737d Mon Sep 17 00:00:00 2001
From: Patrick Gansterer <paroga@paroga.com>
Date: Sat, 11 Jun 2011 12:14:56 +0200
Subject: [PATCH] Added CPACK_NSIS_ENABLE_UNINSTALL_BEFORE_INSTALL

If CPACK_NSIS_ENABLE_UNINSTALL_BEFORE_INSTALL is set to ON the NSIS installer will look for a previous installed version and ask the user about uninstall.
---
 Modules/CPack.cmake      |  4 ++++
 Modules/CPackNSIS.cmake  |  8 ++++++++
 Modules/NSIS.template.in | 22 ++++++++++++++++++++++
 3 files changed, 34 insertions(+)

diff --git a/Modules/CPack.cmake b/Modules/CPack.cmake
index 571770e98..707a99131 100644
--- a/Modules/CPack.cmake
+++ b/Modules/CPack.cmake
@@ -341,6 +341,10 @@ cpack_set_if_not_set(CPACK_RESOURCE_FILE_WELCOME
 
 cpack_set_if_not_set(CPACK_MODULE_PATH "${CMAKE_MODULE_PATH}")
 
+IF(CPACK_NSIS_ENABLE_UNINSTALL_BEFORE_INSTALL)
+  SET(CPACK_NSIS_ENABLE_UNINSTALL_BEFORE_INSTALL ON)
+ENDIF(CPACK_NSIS_ENABLE_UNINSTALL_BEFORE_INSTALL)
+
 IF(CPACK_NSIS_MODIFY_PATH)
   SET(CPACK_NSIS_MODIFY_PATH ON)
 ENDIF(CPACK_NSIS_MODIFY_PATH)
diff --git a/Modules/CPackNSIS.cmake b/Modules/CPackNSIS.cmake
index 5e2ba17f8..e34f782c7 100644
--- a/Modules/CPackNSIS.cmake
+++ b/Modules/CPackNSIS.cmake
@@ -46,6 +46,14 @@
 ##end
 #
 ##variable
+#   CPACK_NSIS_ENABLE_UNINSTALL_BEFORE_INSTALL - Ask about uninstalling
+#   previous versions first.
+#   If this is set to "ON", then an installer will look for previous
+#   installed versions and if one is found, ask the user whether to
+#   uninstall it before proceeding with the install.
+##end
+#
+##variable
 #   CPACK_NSIS_MODIFY_PATH - Modify PATH toggle.
 #   If this is set to "ON", then an extra page
 #   will appear in the installer that will allow the user to choose
diff --git a/Modules/NSIS.template.in b/Modules/NSIS.template.in
index 819cc5cc0..d4f596433 100644
--- a/Modules/NSIS.template.in
+++ b/Modules/NSIS.template.in
@@ -899,6 +899,28 @@ SectionEnd
 ; "Program Files" for AllUsers, "My Documents" for JustMe...
 
 Function .onInit
+  StrCmp "@CPACK_NSIS_ENABLE_UNINSTALL_BEFORE_INSTALL@" "ON" 0 inst
+
+  ReadRegStr $0 HKLM "Software\Microsoft\Windows\CurrentVersion\Uninstall\@CPACK_PACKAGE_NAME@" "UninstallString"
+  StrCmp $0 "" inst
+
+  MessageBox MB_YESNOCANCEL|MB_ICONEXCLAMATION \
+  "@CPACK_NSIS_PACKAGE_NAME@ is already installed. $\n$\nDo you want to uninstall the old version before installing the new one?" \
+  IDYES uninst IDNO inst
+  Abort
+
+;Run the uninstaller
+uninst:
+  ClearErrors
+  ExecWait '$0 _?=$INSTDIR' ;Do not copy the uninstaller to a temp file
+
+  IfErrors uninst_failed inst
+uninst_failed:
+  MessageBox MB_OK|MB_ICONSTOP "Uninstall failed."
+  Abort
+
+
+inst:
   ; Reads components status for registry
   !insertmacro SectionList "InitSection"