Add a detection on non empty folder before installing the application.

cmake/install/windows/NSIS.template.in

@@ -504,8 +504,46 @@ Function ConditionalAddToRegisty
   ConditionalAddToRegisty_EmptyString:
 FunctionEnd
 
+
+Function isEmptyDir
+  # Stack ->                    # Stack: <directory>
+  Exch $0                       # Stack: $0
+  Push $1                       # Stack: $1, $0
+  FindFirst $0 $1 "$0\*.*"
+  strcmp $1 "." 0 _notempty
+    FindNext $0 $1
+    strcmp $1 ".." 0 _notempty
+      ClearErrors
+      FindNext $0 $1
+      IfErrors 0 _notempty
+        FindClose $0
+        Pop $1                  # Stack: $0
+        StrCpy $0 1
+        Exch $0                 # Stack: 1 (true)
+        goto _end
+     _notempty:
+       FindClose $0
+       ClearErrors
+       Pop $1                   # Stack: $0
+       StrCpy $0 0
+       Exch $0                  # Stack: 0 (false)
+  _end:
+FunctionEnd
+
+Function InstDirValidation
+	IfFileExists $INSTDIR\* 0 isEmpty
+	Push "$INSTDIR"
+	Call isEmptyDir
+	Pop $0
+	StrCmp $0 0 0 isEmpty
+		MessageBox MB_OK "$INSTDIR is not empty. Please delete it and retry."
+		Abort
+	isEmpty:
+FunctionEnd
+
 ;--------------------------------
 
+
 !ifdef CPACK_USES_DOWNLOAD
 Function DownloadFile
     IfFileExists $INSTDIR\* +2
@@ -555,6 +593,8 @@ FunctionEnd
   !endif
 
   Page custom InstallOptionsPage
+
+  !define MUI_PAGE_CUSTOMFUNCTION_LEAVE InstDirValidation
   !insertmacro MUI_PAGE_DIRECTORY
 
   ;Start Menu Folder Page Configuration
@@ -911,9 +951,6 @@ SectionEnd
 ; "Program Files" for AllUsers, "My Documents" for JustMe...
 
 
-
-
-
 Function .onInit
   ClearErrors
   ExecWait '"cmd" /C ""%SystemRoot%\System32\tasklist" /NH /FI "IMAGENAME eq @CPACK_NSIS_MUI_FINISHPAGE_RUN@" | "%SystemRoot%\System32\find" /I /C "@CPACK_NSIS_MUI_FINISHPAGE_RUN@""' $0